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Research Article| Volume 98, ISSUE 8, P5672-5687, August 2015

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Replacing dietary soybean meal with canola meal improves production and efficiency of lactating dairy cows1

  • Author Footnotes
    2 Retired; present address: Broderick Nutrition & Research LLC, 221Glen Hollow Road, Madison, WI 53705.
    Glen A. Broderick
    Correspondence
    Corresponding author:
    Footnotes
    2 Retired; present address: Broderick Nutrition & Research LLC, 221Glen Hollow Road, Madison, WI 53705.
    Affiliations
    Agricultural Research Service, USDA, US Dairy Forage Research Center, 1925 Linden Drive, Madison, WI 53706
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  • Antonio P. Faciola
    Affiliations
    Department of Agriculture, Nutrition, and Veterinary Sciences, 1664 North Virginia Street, University of Nevada, Reno 89557
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  • Louis E. Armentano
    Affiliations
    Department of Dairy Science, 1675 Observatory Drive, University of Wisconsin, Madison 53706
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  • Author Footnotes
    1 Mention of any trademark or proprietary product in this paper does not constitute a guarantee or warranty of the product by the USDA or the Agricultural Research Service and does not imply its approval to the exclusion of other products that also may be suitable.
    2 Retired; present address: Broderick Nutrition & Research LLC, 221Glen Hollow Road, Madison, WI 53705.
Open ArchivePublished:June 11, 2015DOI:https://doi.org/10.3168/jds.2015-9563
Replacing dietary soybean meal with canola meal improves production and efficiency of lactating dairy cows1
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      Abstract

      Previous research suggested that crude protein (CP) from canola meal (CM) was used more efficiently than CP from solvent soybean meal (SBM) by lactating dairy cows. We tested whether dietary CP content influenced relative effectiveness of equal supplemental CP from either CM or SBM. Fifty lactating Holstein cows were blocked by parity and days in milk into 10 squares (2 squares with ruminal cannulas) in a replicated 5 × 5 Latin square trial. Five squares were fed: (1) low (14.5–14.8%) CP with SBM, (2) low CP with CM, (3) low CP with SBM plus CM, (4) high (16.4–16.7%) CP with SBM, and (5) high CP with CM; the other 5 squares were fed the same diets except with rumen-protected Met plus Lys (RPML) added as Mepron (Degussa Corp., Kennesaw, GA) and AminoShure-L (Balchem Corp., New Hampton, NY), which were assumed to provide 8 g/d of absorbed dl-Met and 12 g/d of absorbed l-Lys. Diets contained [dry matter (DM) basis] 40% corn silage, 26% alfalfa silage, 14 to 23% corn grain, 2.4% mineral-vitamin premixes, and 29 to 33% neutral detergent fiber. Periods were 3 wk (total 15 wk), and data from the last week of each period were analyzed using the Mixed procedures of SAS (SAS Institute Inc., Cary, NC). The only effects of RPML were increased DM intake and milk urea N (MUN) and urinary N excretion and trends for decreased milk lactose and solids-not-fat concentrations and milk-N:N intake; no significant RPML × protein source interactions were detected. Higher dietary CP increased milk fat yield and tended to increase milk yield but also elevated MUN, urine volume, urinary N excretion, ruminal concentrations of ammonia and branched-chain volatile fatty acids (VFA), lowered milk lactose concentration and milk-N:N intake, and had no effect on milk true protein yield. Feeding CM instead of SBM increased feed intake, yields of milk, energy-corrected milk, and true protein, and milk-N:N intake, tended to increase fat and lactose yields, and reduced MUN, urine volume, and urinary N excretion. At low CP, MUN was lower and intake tended to be greater on SBM plus CM versus SBM alone, but MUN and N excretion were not reduced to the same degree as on CM alone. Interactions of parity × protein source and parity × CP concentration indicated that primiparous cows were more responsive than multiparous cows to improved supply of metabolizable protein. Replacing SBM with CM reduced ruminal ammonia and branched-chain VFA concentrations, indicating lower ruminal degradation of CM protein. Replacing SBM with CM improved milk and protein yield and N-utilization in lactating cows fed both low- and high-CP diets.

      Key words

      Introduction

      In recent years, increasing production of canola has given rise to greater availability of canola meal (CM) as a protein supplement for livestock feeding (
      • Harker K.N.
      • O’Donovan J.T.
      • Turkington T.K.
      • Blackshaw R.E.
      • Lupwayi N.Z.
      • Smith E.G.
      • Klein-Gebbinck H.
      • Dosdall L.M.
      • Hall L.M.
      • Willenborg C.J.
      • Kutcher H.R.
      • Malhi S.S.
      • Vera C.L.
      • Gan Y.
      • Lafond G.P.
      • May W.E.
      • Grant C.A.
      • McLaren D.L.
      High-yield no-till canola production on the Canadian prairies.
      Can. J. Plant Sci. 2012; 92: 221-233
      ). Greater access to CM has made it a viable alternative to soybean meal (SBM) for lactating dairy cows (
      • Hickling D.
      Maximized utilization of canola co-products in livestock industry.
      Proc. 29th Western Nutrition Conference, Edmonton, AB, Canada. University of Alberta, Edmonton, AB, Canada2008: 3-14
      ). We observed a numeric increase in milk and protein yields when CM replaced equal supplemental protein from solvent-extracted SBM in 16.5% CP diets fed to dairy cows (
      • Brito A.F.
      • Broderick G.A.
      Effects of feeding different protein supplements on milk production and nutrient utilization in dairy cows.
      J. Dairy Sci. 2007; 90: 1816-1827
      ). Recent meta-analyses of results published in peer-reviewed journals showed greater DMI and yield of milk and milk components when CM substituted for several commonly fed proteins (
      • Martineau R.
      • Ouellet D.R.
      • Lapierre H.
      Feeding canola meal to dairy cows: A meta-analysis on lactational responses.
      J. Dairy Sci. 2013; 96: 1701-1714
      ). These meta-analyses reported that replacing SBM with CM significantly increased milk protein yield (
      • Martineau R.
      • Ouellet D.R.
      • Lapierre H.
      Feeding canola meal to dairy cows: A meta-analysis on lactational responses.
      J. Dairy Sci. 2013; 96: 1701-1714
      ) and increased intake and yield of milk and milk components (
      • Huhtanen P.
      • Hetta M.
      • Swensson C.
      Evaluation of canola meal as a protein supplement for dairy cows: A review and a meta-analysis.
      Can. J. Anim. Sci. 2011; 91: 529-543
      ).
      The
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      model indicates ruminal degradation rates of 4.5%/h for SBM protein and 10.4%/h for CM protein, although larger insoluble fractions B and C in CM tend to equalize the predicted RUP and MP value of these proteins.
      • Brito A.F.
      • Broderick G.A.
      • Reynal S.M.
      Effects of different protein supplements on omasal nutrient flow and microbial protein synthesis in lactating dairy cows.
      J. Dairy Sci. 2007; 90: 1828-1841
      found that the proportion of RUP in CM was numerically greater than that in SBM.
      • Huhtanen P.
      • Hetta M.
      • Swensson C.
      Evaluation of canola meal as a protein supplement for dairy cows: A review and a meta-analysis.
      Can. J. Anim. Sci. 2011; 91: 529-543
      also concluded that CM contributed amounts of RUP and MP that were at least equal to those from SBM. Lactating dairy cows fed SBM-supplemented diets often respond to rumen-protected Met (e.g.,
      • Broderick G.A.
      • Stevenson M.J.
      • Patton R.A.
      Effect of dietary protein concentration and degradability on response to rumen-protected methionine in lactating dairy cows.
      J. Dairy Sci. 2009; 92: 2719-2728
      ), and the concentration of Met is greater in CM protein than in SBM (
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      ). This suggests that (1) lactating cows would be less responsive to rumen-protected Met when fed CM than SBM, and (2) the AA pattern in MP from a blend of CM plus SBM might be complementary. Furthermore, recent research has indicated that dietary CP content can be lowered substantially without reducing milk and protein yields in lactating cows (
      • Broderick G.A.
      Effects of varying dietary protein and energy levels on the production of lactating dairy cows.
      J. Dairy Sci. 2003; 86: 1370-1381
      ;
      • Kalscheur K.F.
      • Baldwin VI, R.L.
      • Glenn B.P.
      • Kohn R.A.
      Milk production of dairy cows fed differing concentrations of rumen-degraded protein.
      J. Dairy Sci. 2006; 89: 249-259
      ). If MP from CM contributes more absorbed Met than SBM, then CM might prove more effective in low-CP diets.
      Therefore, the objectives of this experiment were to (1) determine the relative effectiveness of CM and SBM as supplemental protein sources in both low- and high-CP diets; (2) compare effectiveness of feeding a blend of SBM plus CM versus SBM or CM alone; and (3) evaluate whether lactation performance on diets based on SBM or CM diets would be improved by supplementation with rumen-protected Met plus Lys. Moreover, the design of this study allowed evaluation of relative response to protein source and CP content of primiparous versus multiparous cows.

      Materials and Methods

      Experimental Design

      Thirty multiparous Holstein cows, including 10 fitted with permanent 10-cm ruminal cannulas (Bar Diamond Inc., Parma, ID), with mean (SD) 2.5 (0.6) parity, 81 (29) DIM, 47.8 (5.1) kg of milk/d, 620 (50) kg of BW, and SCC = 41 (62) × 103 cells/mL, plus 20 primiparous cows with mean (SD) 100 (39) DIM, 36.5 (4.4) kg milk/day, 543 (31) kg of BW, and SCC = 26 (20) × 103 cells/mL, were used in the trial. All cows were in good health and, on average, gaining BW at the start of the trial. Cows were grouped into ten 5 × 5 Latin squares to give 6 squares (2 squares ruminally cannulated) of multiparous cows and 4 squares of primiparous cows, all blocked into squares by DIM. Cows were randomly assigned to dietary treatment sequences within 5 pairs of 5 × 5 Latin squares (3 square-pairs of multiparous and 2 square-pairs of primiparous cows) that were balanced such that each square-pair had equal numbers of change-overs among the 5 basic diets. The 5 basic diets were fed as TMR composed of alfalfa silage, corn silage, and high-moisture shelled corn (ground to approximately 1.4-mm mean particle size;
      • Ekinci C.
      • Broderick G.A.
      Effect of processing high moisture corn on ruminal fermentation and milk production.
      J. Dairy Sci. 1997; 80: 3298-3307
      ), plus minerals and vitamins. Dietary protein supplements were solvent-extracted SBM, solvent-extracted CM, or both, fed in the following arrangement: (1) low CP (SBM), (2) low CP (CM), (3) low CP (blend of SBM plus CM), (4) high CP (SBM), and (5) high CP (CM). Rumen-protected Met plus Lys (RPML) was fed to 1 square in each square-pair, alternating the supplement such that RPML was fed to the square at later DIM for the first square-pair, and then to the square at earlier DIM for the second square-pair, and so on. Mean (SD) DIM for cows fed without and with RPML supplement were, respectively, 80 (28) and 96 (29) at the start of the trial. To improve distribution of RPML in the TMR, 2 premixes were prepared containing ground shelled corn plus molasses only or ground shelled corn, molasses, plus RPML added as Mepron (Evonik Corp., Kennesaw, GA) and AminoShure-L containing 38% l-Lys (Balchem Corp., New Hampton, NY). Depending on batch size, between 2.2 and 2.4 kg of either the control or RPML premix was added to the TMR batch fed to cows in the square in each square-pair receiving that specific treatment. The RPML supplement provided 15 g/d of chemical dl-Met and 19 g/d of chemical l-Lys; assuming, respectively, 72 and 64% bioavailability (
      • Lee C.
      • Hristov A.N.
      • Cassidy T.W.
      • Heyler K.S.
      • Lapierre H.
      • Varga G.A.
      • de Veth M.J.
      • Patton R.A.
      • Parys C.
      Rumen-protected lysine, methionine, and histidine increase milk protein yield in dairy cows fed a metabolizable protein-deficient diet.
      J. Dairy Sci. 2012; 95 (b): 6042-6056
      ), this corresponded to 8 g/d of absorbed Met and 12 g/d of absorbed Lys. Mean composition of the major feed ingredients fed during the trial is in Table 1. Compositions of the experimental diets actually fed during the trial (based on daily mean as-fed weights and weekly mean DM contents of each ingredient mixed into the TMR) are in Table 2.
      Table 1Composition of principal dietary ingredients
      CM=canola meal, HMSC=high-moisture shelled corn, SBM=solvent soybean meal.
      ComponentAlfalfa silageCorn silageHMSCSBMCM
      MeanSEMMeanSEMMeanSEMMeanSEMMeanSEM
      DM, %40.12.141.92.073.70.189.00.389.60.4
      CP, % of DM21.50.56.80.17.70.153.60.540.60.2
      OM, % of DM87.61.596.00.498.40.392.40.191.00.1
      NDF, % of DM39.51.041.73.35.40.37.00.329.90.3
      ADF, % of DM32.11.025.42.11.50.14.20.218.20.2
      NDIN, % of total N12.30.22.30.22.10.27.30.326.90.9
      ADIN, % of total N6.70.60.70.10.10.11.60.26.20.1
      B3,
      B3=NDIN – ADIN.
      % of total N      		5.70.71.60.12.00.25.80.220.70.8
      Ether extract, % of DM——————1.70.13.00.1
      NPN, % of total N49.54.769.18.0——————
      NH3, % of total N1.90.24.40.8——————
      Total AA-N,
      Computed assuming 40.3μmol of total free AA/mg of N in alfalfa and corn silages (Broderick, 1987).
      % of total N      		22.03.318.45.4——————
      pH4.480.044.260.55——————
      1 CM = canola meal, HMSC = high-moisture shelled corn, SBM = solvent soybean meal.
      2 B3 = NDIN – ADIN.
      3 Computed assuming 40.3 μmol of total free AA/mg of N in alfalfa and corn silages (
      • Broderick G.A.
      Determination of protein degradation rates using a rumen in vitro system containing inhibitors of microbial nitrogen metabolism.
      Br. J. Nutr. 1987; 58: 463-475
      ).
      Table 2Composition of diets (g/kg of DM, unless otherwise noted) containing either 15 or 17% CP with combinations of soybean meal (SBM) and canola meal (CM) and with or without rumen-protected Met and Lys (RPML; +, –)
      Item15% CP17% CP
      SBMCMSBM+CMSBMCM
      –+–+–+–+–+
      Ingredient
       Alfalfa silage26.226.226.226.226.226.226.226.226.126.1
       Corn silage40.040.040.040.040.140.140.140.039.939.9
       High-moisture shelled corn21.321.318.618.520.020.017.217.213.113.1
       Ground shelled corn1.381.111.381.111.381.111.381.111.381.11
       Solvent soybean meal8.78.7004.34.312.712.80.00.0
       Canola meal0011.411.55.65.60017.117.1
       Molasses0.030.030.030.030.030.030.030.030.030.03
       Mepron
      Rumen-protected Met product from Degussa Corp. (Kennesaw, GA).
      		00.0600.0600.0600.0600.06
       AminoShure-L
      Rumen-protected Lys product from Balchem Corp. (New Hampton, NY).
      		00.2100.2100.2100.2100.21
       Calcium sulfate1.361.361.361.361.361.361.361.361.361.36
       Monocalcium phosphate0.220.220.220.220.220.220.220.220.220.22
       Sodium chloride0.180.180.180.180.180.180.180.180.180.18
       Magnesium oxide/sulfate0.500.500.500.500.500.500.500.500.500.50
       Vitamins-trace minerals
      Provided (per kilogram of DM): 56mg of Zn, 46mg of Mn, 22mg of Fe, 12mg of Cu, 0.9mg of I, 0.4mg of Co, 0.3mg of Se, 6,440 IU of vitamin A, 2,000 IU of vitamin D, 16 IU of vitamin E, and 12mg of monensin.
      		0.130.130.130.130.130.130.130.130.130.13
      Composition
       CP14.714.814.514.614.614.716.616.716.416.5
       SBM CP, % of total CP3131001616414100
       CM CP, % of total CP0032321616004242
       Ash5.95.96.26.26.06.06.16.16.66.6
       NDF28.928.931.631.630.330.229.029.032.932.9
       ADF19.219.220.920.920.120.119.419.421.821.8
       NDIN, % of total N14.014.020.520.717.016.011.412.120.720.2
       ADIN, % of total N8.67.27.49.18.57.05.34.05.86.9
       B3,
      B3=NDIN – ADIN.
      % of total N      		5.46.813.211.68.58.96.18.114.913.2
       Ether extract2.52.82.82.92.63.22.52.42.72.9
       NFC
      NFC=100 − % NDF – [% CP × (100 − % NDIN)/100] ­− % fat − % ash.
      		50.149.747.847.749.048.347.747.844.844.5
       Starch28.830.827.328.729.128.428.425.823.122.0
       Calcium,
      Computed according to NRC (2001) model using mean observed DMI (25.2kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      % of DM      		0.890.890.940.940.910.910.900.900.980.98
       Phosphorus,
      Computed according to NRC (2001) model using mean observed DMI (25.2kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      % of DM      		0.360.360.420.420.390.390.380.380.470.47
       NEL,
      Computed according to NRC (2001) model using mean observed DMI (25.2kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      Mcal/kg of DM      		1.511.511.501.511.511.511.511.511.511.51
       NEL-allowable milk,
      Computed according to NRC (2001) model using mean observed DMI (25.2kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      kg/d      		38383838383838383838
       MP-allowable milk,
      Computed according to NRC (2001) model using mean observed DMI (25.2kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      kg/d      		30303030303032323333
       MP,
      Computed according to NRC (2001) model using mean observed DMI (25.2kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      g/d      		2,2162,2162,2492,2492,2242,2242,2992,2992,3672,367
       Lys:Met ratio in MP
      Computed according to NRC (2001) model using mean observed DMI (25.2kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      		3.73.33.33.03.53.23.83.43.43.1
      1 Rumen-protected Met product from Degussa Corp. (Kennesaw, GA).
      2 Rumen-protected Lys product from Balchem Corp. (New Hampton, NY).
      3 Provided (per kilogram of DM): 56 mg of Zn, 46 mg of Mn, 22 mg of Fe, 12 mg of Cu, 0.9 mg of I, 0.4 mg of Co, 0.3 mg of Se, 6,440 IU of vitamin A, 2,000 IU of vitamin D, 16 IU of vitamin E, and 12 mg of monensin.
      4 B3 = NDIN – ADIN.
      5 NFC = 100 − % NDF – [% CP × (100 − % NDIN)/100] ­− % fat − % ash.
      6 Computed according to
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      model using mean observed DMI (25.2 kg/d) and ingredient composition from Table 1 and NRC tables; Lys:Met ratios were estimated assuming 72% bioavailability of Met and 64% bioavailability of Lys in supplements of rumen-protected AA.
      All cows were injected every other week with bST (500 mg of Posilac; Elanco Animal Health, Greenfield, IN) beginning about 60 DIM; injections were synchronized such that animals received a full dose on d 1 of period 1 and continuing at 14-d intervals throughout the trial. Therefore, cows received bST twice during periods 1, 3, and 5 (on d 1 and 15) and once during periods 2 and 4 (on d 8). Because the design was a balanced 5 × 5 Latin square, an equal number of observations were made for each dietary treatment during periods in which bST was injected on both d 1 and d 15 and only once on d 8. This arrangement proved satisfactory in a previous trial (
      • Valadares Filho S.C.
      • Broderick G.A.
      • Valadares Filho R.F.D.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on nutrient utilization and milk production.
      J. Dairy Sci. 2000; 83: 106-114
      ). Cows were housed in tiestalls and had free access to water. The Animal Care and Use Committee of the College of Agricultural and Life Sciences of the University of Wisconsin-Madison approved all procedures involving animals.
      Each of the 5 experimental periods lasted 21 d and consisted of 14 d for adaptation after diet reversal and 7 d for collection of intake and production data. Diets were offered once daily at 1000 h; orts were collected and weights recorded at 0900 h. Feeding rate was adjusted daily to yield refusals equivalent to about 5 to 10% of intake. The mean refusal rate observed over the trial was 8.6% of feed DM offered. Weekly composites of alfalfa silage, corn silage, high-moisture shelled corn, and the 10 different TMR and orts were obtained from daily subsamples of about 0.5 kg of each material that were stored at −20°C. Weekly samples also were collected of SBM, CM, and control and RPML premixes and stored at room temperature. Dry matter was determined in weekly composites of corn silage, alfalfa silage, high-moisture shelled corn, and orts by drying at 60°C for 48 h and in weekly samples of SBM, CM, and RPML premixes by drying for 24 h at 105°C (method 967.03;
      AOAC
      Official Methods of Analysis. 15th. Assoc. Off. Anal. Chem., Arlington, VA1990
      ). These DM contents were used to adjust DM composition of TMR every week over the trial. Intake of DM was computed based on 60°C DM determinations of weekly composites of TMR and orts. Dried (60°C) samples of corn silage, alfalfa silage, and high-moisture shelled corn and undried samples of SBM, CM, and the 2 premixes from wk 3 of each period (5 samples of each ingredient over the trial) were ground to pass a 1-mm screen (Wiley mill; Arthur H. Thomas, Philadelphia, PA). These were analyzed for total N (Leco FP-2000 N Analyzer; Leco Instruments Inc., St. Joseph, MI), DM (method 967.03;
      AOAC
      Official Methods of Analysis. 15th. Assoc. Off. Anal. Chem., Arlington, VA1990
      ), ash and OM (
      AOAC
      Official Methods of Analysis. 13th. Assoc. Off. Anal. Chem., Washington, DC1980
      ), sequentially for NDF, ADF, and ADIN using heat-stable α-amylase and Na2SO3 (
      • Van Soest P.J.
      • Robertson J.B.
      • Lewis B.A.
      Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition.
      J. Dairy Sci. 1991; 74: 3583-3597
      ;
      • Hintz R.W.
      • Mertens D.R.
      • Albrecht K.A.
      Effects of sodium sulfite on recovery and composition of detergent fiber and lignin.
      J. AOAC Int. 1996; 79: 16-22
      ), and for NDIN omitting α-amylase and Na2SO3 during extraction (
      • Licitra G.
      • Hernandez T.M.
      • Van Soest P.J.
      Standardization of procedures for nitrogen fractionation of ruminant feeds.
      Anim. Feed Sci. Technol. 1996; 57: 347-358
      ). The 15 TMR samples and 5 samples each of SBM and CM from wk 3 of each period were analyzed for total lipid (ether extract) according to
      • International AOAC
      Official Methods of Analysis. 16th. AOAC International, Arlington, VA1997
      ; method 920.39; Dairyland Laboratories, Arcadia, WI). The 15 TMR samples were also analyzed for starch using a modification of the method of
      • Knudsen K.E.B.
      Carbohydrate and lignin contents of plant materials used in animal feeding.
      Anim. Feed Sci. Technol. 1997; 67: 319-338
      ; Dairyland laboratories, Arcadia, WI). Frozen composites of alfalfa and corn silages were thawed and analyzed for NPN (
      • Muck R.E.
      Dry matter level effects on alfalfa silage quality. 1. Nitrogen transformations.
      Trans. ASAE. 1987; 30: 7-14
      ; Leco FP-2000 N Analyzer).
      Cows were milked twice daily at 0500 and 1700 h, and milk yield was recorded at each milking in all experimental periods. Milk samples from a.m. and p.m. milkings were collected on d 17 to 18 of each period and analyzed for fat, true protein, lactose, SNF, and MUN by infrared analysis (AgSource, Verona, WI) with a Foss FT6000 (Foss North America Inc., Eden Prairie, MN) using
      AOAC
      Official Methods of Analysis. 15th. Assoc. Off. Anal. Chem., Arlington, VA1990
      method 972.16. Concentrations and yields of fat, true protein, lactose, and SNF, and MUN concentration were computed as weighted means based on a.m. and p.m. milk yields on each test day. Yields of ECM (
      • Krause K.M.
      • Combs D.K.
      Effects of forage particle size, forage source, and grain fermentability on performance and ruminal pH in midlactation cows.
      J. Dairy Sci. 2003; 86: 1382-1397
      ) were also computed. Efficiency of conversion of feed DM was calculated for each cow over the last week of each period by dividing mean yields of actual milk and ECM by mean DMI. Apparent N efficiency (assuming no retention or mobilization of body N) was also computed for each cow by dividing the period mean for milk N secretion (milk true protein/6.38) by mean N intake. For computation of BW change, BW was measured on 3 consecutive days at the beginning of the experiment and at the end of each period.
      Spot urine samples were collected on d 20 of each period at 6 h before and 6 h after feeding. Urine was immediately diluted by mixing 15 mL of each sample with 60 mL of 0.072 N H2SO4 and storing it at –20°C until analysis. Urine samples were thawed and analyzed for total N by elemental analysis (Leco FP-2000 N Analyzer), for urea using an automated colorimetric assay (
      • Broderick G.A.
      • Clayton M.K.
      A statistical evaluation of animal and nutritional factors influencing concentrations of milk urea nitrogen.
      J. Dairy Sci. 1997; 80: 2964-2971
      ) adapted to flow injection (Lachat Quik-Chem 8000 FIA, Lachat Instruments, Milwaukee, WI), and for creatinine (
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      ). Daily urine volume and excretion of urea N and total N were estimated from mean urinary concentrations in each period, assuming a creatinine excretion rate of 29 mg/kg of BW (
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      ).
      On d 20 to 21 of each period, about 100 mL of fluid digesta was collected from 4 locations under the ruminal mat in the ventral rumen at 0 (just before feeding), 1, 2, 4, 6, 8, 12, 18, and 24 h after feeding from the 10 lactating Holstein cows fitted with ruminal cannulas using the probe described by
      • Olmos Colmenero J.J.
      • Broderick G.A.
      Effect of amount and ruminal degradability of soybean meal protein on performance of lactating dairy cows.
      J. Dairy Sci. 2006; 89 (a): 1635-1643
      . At each sampling, mixed fluid digesta was strained through 2 layers of cheesecloth and pH measured immediately in strained fluid using a glass electrode. Two 10-mL aliquots of ruminal fluid were then preserved by addition of 0.2 mL of 50% H2SO4 and stored at −20°C. The remaining fluid and digesta were returned to the rumen. Just before analysis, samples were thawed and centrifuged (15,300 × g for 20 min at 4°C) and flow-injection analyses (Lachat QuikChem 8000) applied to supernatants to determine ammonia, using a phenol-hypochlorite method (Lachat Method 18-107-06-1-A), and total AA using a fluorimetric procedure based on the reaction with o-phthaldialdehyde (
      • Roth M.
      Fluorescence reaction of amino acids.
      Anal. Chem. 1971; 43: 880-882
      ). Leucine was the standard for this assay and total AA values are reported in Leu equivalents. Samples were thawed and centrifuged (28,000 × g for 30 min at 4°C) before VFA determination using a modification of the GLC method for free fatty acids described in Supelco Bulletin 855B (Supelco Inc., Supelco Park, Bellefonte, PA) with flame-ionization detection. Standards or supernatants (0.5 or 1 µL) were injected onto a ZB-FFAP capillary column (30 m × 0.53 mm × 1.0 μm; no. 7HK-G009-22; Phenomenex Inc., Torrance, CA) with helium carrier gas at 100 kPa and a flow rate of 20 mL/min. Column oven temperature was 100°C at injection; after 2 min, the temperature was increased to 130°C at 10°C/min. Injector and detector temperatures were 230°C and 250°C. This method did not resolve isovalerate and 2-methyl butyrate, which are reported as isovalerate plus 2-methylbutyrate.

      Statistical Analysis

      The basic design of the lactation trial was a 5 × 5 Latin square, replicated 10 times. Half of the squares were supplemented with RPML and half were not; thus, there were 10 different diets (Table 2). Results from the lactation trial were analyzed using the Mixed procedures of SAS (2003, SAS Institute Inc., Cary, NC) for replicated Latin squares applying 3 different statistical models. The following model (model 1) was used to compute least squares means for production and excretion in cows fed each of the 10 diets:
      Yijk=μ+Pi+Tj+P×Tij+Ck+Eijk,
      [1]


      where Yijk = dependent variable, µ = overall mean, Pi = effect of period i (i = 1 to 5), Tj = effect of dietary treatment j (j = 1 to 10), P × Tij = interaction of period i and treatment j, Ck = effect of cow k (k = 1 to 50), and Eijk = residual error. This model used 151 denominator degrees of freedom. All terms were considered fixed, except for except for Ck and Eijk, which were considered random. Results from this analysis are in Table 3.
      Table 3Least squares means for production and urinary excretion of lactating daiwry cows fed the 10 individual dietary treatments containing either 15 or 17% CP with different supplemental sources of CP and with or without rumen-protected Met and Lys (RPML; +, –)
      Sources of supplemental CP: CM=canola meal, SBM=solvent soybean meal, SBM+CM=blend with equal CP from solvent soybean meal and canola meal.
      ,
      Minus (−) indicates no RPML supplement; plus (+) indicates supplementation of 8g/d of absorbed Met and 12g/d of absorbed Lys (assuming 72% bioavailability of Met and 64% bioavailability of Lys from rumen-protected AA and 25.2kg/d of DMI).
      Trait15% CP17% CPSEM
      Standard error of the least squares means determined using statistical model 1.
      SBMCMSBM+CMSBMCM
      −+–+–+–+–+
      Production
       DMI, kg/d23.725.924.326.324.226.524.525.824.526.40.62
       BW gain, kg/d0.360.200.560.530.460.460.530.470.410.410.130
       Milk, kg/d38.440.639.341.139.141.339.440.540.541.71.32
       Milk:DMI1.621.571.621.571.621.561.601.571.651.580.037
       ECM, kg/d37.939.138.140.237.540.638.739.639.940.51.33
       ECM:DMI1.591.511.561.531.551.531.571.541.621.540.035
       Fat, %3.993.973.954.033.924.023.974.064.093.980.099
       Fat, kg/d1.531.591.541.641.521.651.571.631.641.660.062
       True protein, %3.063.023.063.042.983.083.053.033.103.000.054
       True protein, kg/d1.171.211.191.241.161.261.201.211.231.250.038
       Lactose, %4.984.824.924.864.834.914.894.814.894.730.058
       Lactose, kg/d1.911.951.911.991.882.021.931.941.951.990.067
       SNF, %8.948.728.868.788.698.878.848.728.888.590.101
       SNF, kg/d3.433.513.443.593.383.643.483.503.543.600.113
       SCC, ×10
      Standard error of the least squares means determined using statistical model 1.
      cells/mL      		276189307331247159291354447444135.7
       MUN, mg/dL9.99.98.49.19.29.912.713.611.812.20.26
       Milk-N:N intake, %32.830.932.931.732.131.828.827.630.028.40.64
      Urinary excretion
      Estimated from urinary excretion of creatinine according to Valadares et al. (1999).
       Urine volume, L/d23.927.724.323.826.225.829.230.928.129.71.35
       Urea-N, g/d105.2109.280.794.091.3111.6171.8179.0142.1166.66.67
       Total urinary-N, g/d184.2202.4164.0179.4187.1200.9265.9280.0233.3259.38.20
       Urea-N:total-N, %57.952.949.051.948.554.663.866.861.464.12.15
      1 Sources of supplemental CP: CM = canola meal, SBM = solvent soybean meal, SBM+CM = blend with equal CP from solvent soybean meal and canola meal.
      2 Minus (−) indicates no RPML supplement; plus (+) indicates supplementation of 8 g/d of absorbed Met and 12 g/d of absorbed Lys (assuming 72% bioavailability of Met and 64% bioavailability of Lys from rumen-protected AA and 25.2 kg/d of DMI).
      3 Standard error of the least squares means determined using statistical model 1.
      4 Estimated from urinary excretion of creatinine according to
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      .
      The following model (model 2) was used to fit production and excretion data to assess effects of RPML, protein source, CP concentration, parity, and their interactions:
      Yijklmn=μ+Pi+RPMLj+CPPSk+Parl+PSQParlm+RPML×CPPSjk+RPML×Parjl+CPPS×Parkl+Cnj+Eijklmn,
      [2]


      where Yijklmn = dependent variable, µ = overall mean, Pi = effect of period i (i = 1 to 5), RPMLj = effect of RPML supplement j (j = 1 to 2), CPPSk = effect of CP level-protein source k (k = 1 to 5), Parl = effect of parity l (primiparous or multiparous), PSQ(Par)lm = effect of square-pair m (m = 1 to 5) within parity l, RPML × CPPSjk = interaction of RPML supplement j and CP level-protein source k, RPML × Parjl = interaction of RPML supplement j and parity l, CPPS × Parkl = interaction of CP level-protein source k and parity l, Cn(j) = effect of cow n (n = 1 to 25) within RPML supplement j, and Eijklmn = residual error. All terms were considered fixed, except for Cn(j) and Eijklmn, which were considered random. This model used 183 denominator degrees of freedom. Contrasts were used to evaluate the effects of RPML, protein source, CP concentration, parity, and the interactions, without the SBM plus CM treatment; least squares means and SEM were estimated using LSM-estimate statements. Results from analysis of the effects of RPML, protein source, and dietary CP concentration and their interactions are in Table 4. Contrasts were used to evaluate the effects of SBM versus SBM plus CM, and CM versus SBM plus CM, only at low dietary CP; results from this analysis are in Table 5. Results from analysis of the effects of parity are in Table 6 and interactions of parity with protein source and with CP concentration are in Table 7.
      Table 4Effects of source of dietary protein, CP concentration, and supplemental rumen-protected Met plus Lys (RPML) on least squares means for production and urinary excretion in lactating dairy cows
      Sources of supplemental CP: CM=canola meal, SBM=solvent soybean meal; RPML=rumen-protected Met plus Lys.
      TraitProtein sourceFormulated [CP]SEM
      Standard error of the least squares means determined using statistical model 2; SEM for protein source and [CP] were identical.
      		RPML
      Minus (−) indicates no RPML supplement; plus (+) indicates supplementation with RPML.
      		SEM
      Standard error of the least squares means determined using statistical model 2; SEM for protein source and [CP] were identical.
      		Probability
      Probability of dietary treatment effects: Source=SBM versus CM; [CP]=15% versus 17% CP; RPML=no RPML versus plus RPML; Source × [CP]=interaction of protein source and CP concentration; Source × RPML=interaction of protein source and RPML supplement; [CP] × RPML=interaction of CP concentration and RPML supplement.
      SBMCM15%17%−+Source[CP]RPMLSource

      × [CP]      		Source

      × RPML      		[CP] ×

      RPML
      Production
       DMI, kg/d24.825.224.925.00.3924.125.90.530.050.470.010.910.510.17
       BW gain, kg/d0.380.470.410.450.0670.460.390.0670.320.670.430.070.610.73
       Milk, kg/d39.340.339.540.10.8438.940.71.16<0.010.070.260.330.870.21
       Milk:DMI1.591.601.591.600.0261.611.580.0350.110.140.440.170.430.88
       ECM, kg/d38.539.538.639.30.8238.239.71.110.040.110.340.390.740.36
       ECM:DMI1.551.571.551.570.0231.581.540.0300.210.160.270.140.960.98
       Fat, %3.994.023.994.020.0624.004.010.0810.490.500.950.510.580.59
       Fat, kg/d1.561.611.561.610.0391.551.630.0520.060.050.320.340.940.44
       True protein, %3.043.063.053.050.0333.083.030.0440.510.800.430.990.570.50
       True protein, kg/d1.191.221.191.220.0211.191.220.0290.020.140.340.470.580.30
       Lactose, %4.884.874.914.840.0324.934.830.0390.710.030.060.760.890.91
       Lactose, kg/d1.921.951.931.940.0431.901.960.0590.130.720.470.620.500.39
       SNF, %8.818.818.858.770.0568.908.720.0661.000.180.060.850.880.61
       SNF, kg/d3.453.533.473.510.0693.443.540.0930.070.390.420.540.510.30
       SCC, ×10
      Minus (−) indicates no RPML supplement; plus (+) indicates supplementation with RPML.
      cells/mL      		27738427438873.733632584.40.220.190.930.830.900.72
       MUN, mg/dL11.510.39.312.50.1710.711.20.22<0.01<0.010.110.630.560.40
       Milk-N:N intake, %30.030.832.128.80.3831.129.80.51<0.01<0.010.070.320.780.80
      Urinary excretion
      Estimated from urinary excretion of creatinine according to Valadares et al. (1999).
       Urine volume, L/d27.726.324.829.20.7526.127.90.910.07<0.010.150.700.210.81
       Urea-N, g/d138119961613.41221354.0<0.01<0.010.020.950.100.25
       Total-N, g/d2292061802544.42082265.6<0.01<0.010.020.670.470.67
       Urea-N:total-N, %60.456.752.764.41.0758.059.11.110.01<0.010.490.490.210.16
      1 Sources of supplemental CP: CM = canola meal, SBM = solvent soybean meal; RPML = rumen-protected Met plus Lys.
      2 Standard error of the least squares means determined using statistical model 2; SEM for protein source and [CP] were identical.
      3 Minus (−) indicates no RPML supplement; plus (+) indicates supplementation with RPML.
      4 Probability of dietary treatment effects: Source = SBM versus CM; [CP] = 15% versus 17% CP; RPML = no RPML versus plus RPML; Source × [CP] = interaction of protein source and CP concentration; Source × RPML = interaction of protein source and RPML supplement; [CP] × RPML = interaction of CP concentration and RPML supplement.
      5 Estimated from urinary excretion of creatinine according to
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      .
      Table 5Effects of source and concentration of dietary supplemental protein on least squares means for production and urinary excretion in lactating dairy cows
      Sources of supplemental protein: CM=canola meal, SBM=solvent soybean meal, SBM+CM=blend with equal CP from solvent soybean meal and canola meal.
      TraitProtein source (15% CP)SEM
      Standard error of the least squares means determined using statistical model 2.
      		Contrast
      Probability of contrasts: S vs. S+C=SBM versus SBM+CM; C versus S+C=CM vs. SBM+CM.
      SBMSBM+CMCMS vs. S+CC vs. S+C
      Production
       DMI, kg/d24.725.125.10.410.110.90
       BW gain, kg/d0.270.460.540.0960.170.53
       Milk, kg/d39.239.939.80.870.150.95
       Milk:DMI1.591.591.590.0270.840.97
       ECM, kg/d38.338.638.90.900.590.77
       ECM:DMI1.551.541.550.0250.560.68
       Fat, %3.993.963.990.0700.670.65
       Fat, kg/d1.551.571.580.0430.660.82
       True protein, %3.053.033.060.0380.700.40
       True protein, kg/d1.181.201.210.0240.480.69
       Lactose, %4.914.884.910.0400.410.44
       Lactose, kg/d1.921.931.940.0460.660.78
       SNF, %8.858.798.860.0700.480.40
       SNF, kg/d3.453.483.500.0750.590.74
       SCC, ×10
      Probability of contrasts: S vs. S+C=SBM versus SBM+CM; C versus S+C=CM vs. SBM+CM.
      cells/mL      		21119233796.50.880.24
       MUN, mg/dL9.99.58.70.190.03<0.01
       Milk-N:N intake, %31.831.932.30.430.780.26
      Urinary excretion
      Estimated from urinary excretion of creatinine according to Valadares et al. (1999).
       Urine volume, L/d25.725.824.00.920.890.09
       Urea-N, g/d10599864.30.290.02
       Total-N, g/d1911911705.20.99<0.01
       Urea-N:total-N, %55.151.350.41.480.070.64
      1 Sources of supplemental protein: CM = canola meal, SBM = solvent soybean meal, SBM+CM = blend with equal CP from solvent soybean meal and canola meal.
      2 Standard error of the least squares means determined using statistical model 2.
      3 Probability of contrasts: S vs. S+C = SBM versus SBM+CM; C versus S+C = CM vs. SBM+CM.
      4 Estimated from urinary excretion of creatinine according to
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      .
      Table 6Effect of parity on least squares means for production and urinary excretion in lactating dairy cows
      TraitPrimiparousSEM
      Standard error of the least squares means determined using statistical model 2.
      		MultiparousSEM
      Standard error of the least squares means determined using statistical model 2.
      		Probability
      Probability of parity effects.
      Production
       DMI, kg/d23.90.5826.00.470.01
       BW gain, kg/d0.400.0740.460.0600.53
       Milk, kg/d37.91.2741.71.040.03
       Milk:DMI1.590.0391.600.0320.81
       ECM, kg/d37.51.2240.40.990.06
       ECM:DMI1.570.0331.550.0270.70
       Fat, %4.020.0894.000.0730.86
       Fat, kg/d1.520.0571.650.0470.07
       True protein, %3.070.0483.030.0390.55
       True protein, kg/d1.160.0311.250.0260.03
       Lactose, %4.960.0434.800.035<0.01
       Lactose, kg/d1.880.0651.990.0530.18
       SNF, %8.920.0738.710.0590.02
       SNF, kg/d3.370.1023.600.0840.09
       SCC, ×10
      Estimated from urinary excretion of creatinine according to Valadares et al. (1999).
      cells/mL      		33492.532775.50.95
       MUN, mg/dL10.70.2411.10.200.16
       Milk-N:N intake, %30.60.5630.30.450.69
      Urinary excretion
      Estimated from urinary excretion of creatinine according to Valadares et al. (1999).
       Urine volume, L/d25.70.9928.40.810.04
       Urea-N, g/d1164.31413.5<0.01
       Total-N, g/d1986.12365.0<0.01
       Urea-N:total-N, %58.81.2258.30.990.74
      1 Standard error of the least squares means determined using statistical model 2.
      2 Probability of parity effects.
      3 Estimated from urinary excretion of creatinine according to
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      .
      Table 7Effects of parity, source of dietary protein and CP concentration on least squares means for production and urinary excretion in lactating dairy cows
      Sources of supplemental CP: CM=canola meal, SBM=solvent soybean meal.
      TraitProtein sourceSEM
      Standard error of the least squares means determined using statistical model 2; SEM for protein source and CP concentration within primiparous and multiparous cows were identical.
      		Protein sourceSEM
      Standard error of the least squares means determined using statistical model 2; SEM for protein source and CP concentration within primiparous and multiparous cows were identical.
      		Prob.
      Par × source=probability (Prob.) of interaction of parity and protein source; Par × [CP]=probability of interaction of parity and CP concentration.
      		Formulated [CP]Prob.
      Par × source=probability (Prob.) of interaction of parity and protein source; Par × [CP]=probability of interaction of parity and CP concentration.
      PrimiparousMultiparousPrimiparousMultiparous
      SBMCMSBMCMPar × source15%17%15%17%Par × [CP]
      Production
       DMI, kg/d23.724.10.6025.826.20.490.8824.223.725.626.4<0.01
       BW gain, kg/d0.330.460.1040.430.480.0850.670.380.410.430.480.92
       Milk, kg/d37.438.51.3041.342.01.060.5037.838.141.242.10.32
       Milk:DMI1.571.600.0401.601.600.0320.211.571.611.611.600.02
       ECM, kg/d36.638.41.2840.340.51.040.0937.337.739.841.00.42
       ECM:DMI1.541.600.0351.561.540.0290.031.551.591.551.550.16
       Fat, %3.964.070.0964.023.970.0780.084.024.013.964.030.39
       Fat, kg/d1.481.560.0601.651.660.0490.111.511.541.621.690.45
       True protein, %3.043.100.0523.053.020.0420.093.083.063.033.040.42
       True protein, kg/d1.131.190.0331.241.250.0270.131.151.171.231.260.51
       Lactose, %4.934.990.0504.844.750.0410.035.024.904.814.780.20
       Lactose, kg/d1.841.910.0671.991.990.0550.131.881.871.982.000.43
       SNF, %8.868.980.0868.778.640.0700.038.998.858.728.690.32
       SNF, kg/d3.313.440.1073.603.610.0870.113.373.383.573.630.49
       SCC, ×10
      Par × source=probability (Prob.) of interaction of parity and protein source; Par × [CP]=probability of interaction of parity and CP concentration.
      cells/mL      		274395114.328037493.30.882644052833700.76
       MUN, mg/dL11.210.20.2611.810.50.210.589.112.39.512.80.53
       Milk-N:N intake, %29.931.30.6030.130.40.490.0431.929.232.228.40.06
      Urinary excretion
      Estimated from urinary excretion of creatinine according to Valadares et al. (1999).
       Urine volume, L/d25.825.51.1529.627.10.940.1623.527.826.230.60.97
       Urea-N, g/d1211115.21541284.30.04861451051770.09
       Total-N, g/d2061916.82522215.60.051672301932790.01
       Urea-N:total-N, %60.557.21.6560.456.21.350.7751.865.953.762.90.10
      1 Sources of supplemental CP: CM = canola meal, SBM = solvent soybean meal.
      2 Standard error of the least squares means determined using statistical model 2; SEM for protein source and CP concentration within primiparous and multiparous cows were identical.
      3 Par × source = probability (Prob.) of interaction of parity and protein source; Par × [CP] = probability of interaction of parity and CP concentration.
      4 Estimated from urinary excretion of creatinine according to
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      .
      Time-weighted means were computed for all ruminal traits (pH and concentrations of ammonia, total free AA, and individual and total VFA) using the equation: Time-weighted mean = [2 × avg(0–2 h) + 2 × avg(2–4 h) + 2 × avg(4–6 h) + 2 × avg(6–8 h) + 4 × avg(8–12 h) + 6 × avg(12–18 h) + 6 × avg(18–24 h)]/24, where avg(0–2 h) .... avg(18–24 h) represents the mean value for each ruminal trait observed at 0 and 2 h … 18 and 24 h after feeding. Time-weighted means were fit to the following model (model 3):
      Yijkl=μ+Pi+Tj+Ckl+Eijkl,
      [3]


      where Yijkl = dependent variable, µ = overall mean, Pi = effect of period i (i = 1 to 5), Tj = effect of dietary treatment j (j = 1 to 10), Ck(l) = effect of cow k (k = 1 to 4) within square l (l = 1 to 2), and Eijkl = residual error. All terms were considered fixed, except for Ck(l) and Eijk, which were considered random. This model used 28 denominator degrees of freedom. Contrasts were used to evaluate the effects of RPML, protein source, and CP concentration, without the SBM plus CM treatment; least squares means and SEM were estimated using LSM-estimate statements. Contrasts were also used to evaluate the effects of SBM versus SBM plus CM, and CM versus SBM plus CM, only at low dietary CP. Results from this analysis are in Table 8. For all models, significance was declared at P ≤ 0.05 and trends were declared at 0.05 < P ≤ 0.10.
      Table 8Effects of source and concentration of dietary supplemental protein on ruminal pH and metabolite concentrations
      Sources of supplemental CP: CM=canola meal, SBM=solvent soybean meal, SBM+CM=blend with equal CP from solvent soybean meal and canola meal.
      Trait15% CP17% CPSEM
      Standard error of the least squares means determined using statistical model 3.
      		Prob.
      Probability (Prob.) of no rumen-protected Met plus Lys versus supplementation with rumen-protected Met plus Lys (RPML).
      		Contrasts
      Probability of contrasts for ruminal traits: [CP]=15% versus 17% CP (excluding the SBM+CM treatment); SBM vs. CM=SBM versus CM at both 15 and 17% CP (excluding the SBM+CM treatment); S vs. S+C=SBM versus SBM+CM at 15% CP; C vs. S+C=CM versus SBM+CM at 15% CP.
      SBMCMSBM+CMSBMCMRPML[CP]SBM vs.

      CM      		S vs.

      S+C      		C vs.

      S+C
      pH6.516.536.586.536.510.0520.970.960.930.090.23
      Ammonia-N, mg/dL4.344.144.857.226.250.3490.83<0.010.010.110.03
      Total AA, mM2.052.121.952.111.920.1480.740.430.490.440.18
      Total VFA, mM87.691.088.991.988.03.210.770.780.910.680.50
      Acetate, mM54.156.555.656.855.51.900.960.510.670.420.60
      Propionate, mM20.621.620.420.619.61.200.540.250.990.900.31
      Acetate:propionate ratio2.832.772.842.862.940.1150.340.150.980.990.47
      Butyrate, mM9.39.39.210.29.40.460.590.180.200.820.83
      Isobutyrate, mM0.830.760.850.990.840.0320.51<0.01<0.010.590.01
      Isovalerate + 2-methyl butyrate, mM1.581.471.591.801.430.1030.820.09<0.010.930.12
      BCVFA,
      Branched-chain VFA (isobutyrate plus isovalerate + 2-methyl butyrate).
      mM      		2.412.232.432.782.270.1310.970.01<0.010.830.06
      Valerate, mM1.231.311.271.431.300.0570.170.080.640.610.56
      1 Sources of supplemental CP: CM = canola meal, SBM = solvent soybean meal, SBM+CM = blend with equal CP from solvent soybean meal and canola meal.
      2 Standard error of the least squares means determined using statistical model 3.
      3 Probability (Prob.) of no rumen-protected Met plus Lys versus supplementation with rumen-protected Met plus Lys (RPML).
      4 Probability of contrasts for ruminal traits: [CP] = 15% versus 17% CP (excluding the SBM+CM treatment); SBM vs. CM = SBM versus CM at both 15 and 17% CP (excluding the SBM+CM treatment); S vs. S+C = SBM versus SBM+CM at 15% CP; C vs. S+C = CM versus SBM+CM at 15% CP.
      5 Branched-chain VFA (isobutyrate plus isovalerate + 2-methyl butyrate).

      Results and Discussion

      Feed Quality and Diet Composition

      Composition data on the major feed ingredients used in preparation of TMR fed in the trial are in Table 1. Contents of DM, CP, NDF, and ADF in alfalfa and corn silages and high moisture corn indicated that these feedstuffs were of typical composition (
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      ). The NPN in alfalfa silage represented 50% of total N; NPN normally accounts for 45 to 55% of total N in alfalfa silage (
      • Broderick G.A.
      Desirable characteristics of forage legumes for improving protein utilization in ruminants.
      J. Anim. Sci. 1995; 73 (b): 2760-2773
      ). Very low contents of ammonia-N in both alfalfa and corn silages indicated that these feeds were well preserved (
      • McDonald P.
      • Henderson A.R.
      • Heron S.J.E.
      The Biochemistry of Silage. Chalcombe Publications, Marlow, UK1991
      ).
      The chemical composition of both SBM and CM (Table 1) differed somewhat from
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      tabular values. Although CP, NDF, and ADF contents were similar, SBM fed in the current trial was substantially higher in NDIN and protein fraction B3, which were reported as, respectively, 1.3 and 0.6% of total N in Table 15–1 (
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      ). The principal differences from
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      values for CM were in CP, lipid, NDIN, and protein fraction B3, which were tabulated as, respectively, 37.8 and 5.3% of DM and 16.7 and 10.3% of total N (
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      ). The
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      refers to CM as “mechanically extracted”; mechanically extracted CM has lower CP and substantially higher fat contents than solvent-extracted CM (
      • Newkirk R.
      Canola Meal: Feed Industry Guide. 4th. Canadian International Grains Institute, Winnipeg, MB, Canada2009
      ). Solvent-extracted CM was fed in the current trial; solvent CM was reported to contain (DM basis) 40.9% CP and 4.0% crude fat (
      • Newkirk R.
      Canola Meal: Feed Industry Guide. 4th. Canadian International Grains Institute, Winnipeg, MB, Canada2009
      ). Higher NDIN contents explain the greater protein fraction B3 observed for both SBM and CM relative to
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      values. The NDIN values reported here derived from using a method in which both amylase and Na2SO3 are omitted from the neutral detergent extraction, which increases observed NDIN values (
      • Licitra G.
      • Hernandez T.M.
      • Van Soest P.J.
      Standardization of procedures for nitrogen fractionation of ruminant feeds.
      Anim. Feed Sci. Technol. 1996; 57: 347-358
      ).
      Composition of the 10 diets fed in this trial is given in Table 2. Diets ranged from (DM basis) 29 to 33% NDF, 1.50 to 1.51 estimated Mcal of NEL/kg (computed using
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      software), 22 to 31% starch, and 45 to 50% NFC (Table 2). As judged from milk fat content (3.92 to 4.09%; Table 3) and mean rumen pH (6.39 to 6.45; Table 8), the relatively high starch and NFC contents appeared to have no negative effects on ruminal environment or animal performance. Dietary CP was slightly lower than formulated, ranging from 14.5 to 14.8% (low protein) and from 16.4 to 16.7% (high protein); diets containing SBM had 0.2 percentage units more CP than those with CM (Table 2). Supplemental SBM and CM supplied between 31 and 32% (low protein) and 41 to 42% (high protein) of total dietary CP. Based on
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      computations at the overall mean DMI (25.2 kg/d), predicted MP-allowable milk was 30 kg/d (low protein) and 32 to 33 kg/d (high protein); MP-allowable milk was 5 to 8 kg/d less than NEL-allowable milk. The large magnitude of these differences may have occurred because the
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      model underestimates MP-allowable milk yield at low MP supply (
      • Lee C.
      • Hristov A.N.
      • Heyler K.S.
      • Cassidy T.W.
      • Lapierre H.
      • Varga G.A.
      • Parys C.
      Effects of metabolizable protein supply and amino acid supplementation on nitrogen utilization, milk production, and ammonia emissions from manure in dairy cows.
      J. Dairy Sci. 2012; 95 (a): 5253-5268
      ). However, these predictions suggest that milk and protein yield were limited by MP supply in the current trial. Estimates made with the
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      model also indicated that the CM diets supplied 14 to 39 g/d more RUP and 4 g/d more absorbable Met (low protein) and 73 g/d more RUP and 5 g/d more absorbable Met (high protein), and improved mean Lys:Met ratio (averaged across those 8 treatments) from 3.55 to 3.2.

      Production Responses

      Least squares means from the 10 individual treatments are reported in Table 3. Lactation performance was relatively high in this experiment, with DMI and yields of milk, fat, and protein averaging, respectively, 25.2, 40.2, 1.60, and 1.21 kg/d. However, our main objective was to compare production responses to SBM and CM at low and high dietary protein, to determine whether these were influenced by RPML supplementation and whether responses differed according to parity. Evaluation of the effects of blending CM and SBM CP was a secondary objective; thus, we omitted both SBM + CM treatments (with and without RPML) from the statistical analyses presented in Table 4. Although milk SCC were relatively high, SCC was not associated with any main effect or interaction, indicating that subclinical mastitis did not influence differences in production among treatments. Replacing SBM with CM increased (P ≤ 0.05) DMI (0.4 kg/d) and yields of milk (0.9 kg/d), ECM (0.4 kg/d), and true protein (0.03 kg/d), and resulted in trends for greater fat and SNF yields. Moreover, the CM diets improved (P ≤ 0.01) N-utilization as indicated by increased milk-N:N intake (from 30.0 to 30.8%) and reduced MUN and urinary excretion of urea-N, total-N, and urea-N:total-N. Urine volumes, which were estimated based on creatinine concentration and ranged from 24 to 31 L/d, were lower than that found by
      • Valadares R.F.D.
      • Broderick G.A.
      • Valadares Filho S.C.
      • Clayton M.K.
      Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives.
      J. Dairy Sci. 1999; 82: 2686-2696
      , who reported a mean volume of 40 L of urine/d using the method applied in the present study. Urine volume is influenced by mineral intake, particularly potassium consumption.
      • Eriksson T.
      • Rustas B.-O.
      Effects on milk urea concentration, urine output, and drinking water intake from incremental doses of potassium bicarbonate fed to mid-lactation dairy cows.
      J. Dairy Sci. 2014; 97: 4471-4484
      ) measured (by total collection) excretions of 14, 27, and 40 L of urine/d when dairy cows consumed 20.2 kg of DM/d of diets containing, respectively, potassium at 1.19, 2.31, and 3.22% of DM. Dietary potassium in the present trial, computed from
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      tables, ranged from 1.51 to 1.65% of DM. Urine volume tended to be reduced when CM replaced SBM in the diet (Table 4). In an earlier comparison of CM with SBM (
      • Brito A.F.
      • Broderick G.A.
      Effects of feeding different protein supplements on milk production and nutrient utilization in dairy cows.
      J. Dairy Sci. 2007; 90: 1816-1827
      ), we observed numeric improvements in these same traits but likely had insufficient power to detect statistical significance. In their meta-analysis,
      • Huhtanen P.
      • Hetta M.
      • Swensson C.
      Evaluation of canola meal as a protein supplement for dairy cows: A review and a meta-analysis.
      Can. J. Anim. Sci. 2011; 91: 529-543
      reported generally positive responses when CM replaced other dietary proteins but noted that these effects were smaller when CM replaced SBM. Those researchers attributed increased DMI on CM to a “pull effect,” whereby a better AA pattern in MP improved yield of milk and milk components, which in turn stimulated greater feed consumption to support the elevated yield. However,
      • Martineau R.
      • Ouellet D.R.
      • Lapierre H.
      Feeding canola meal to dairy cows: A meta-analysis on lactational responses.
      J. Dairy Sci. 2013; 96: 1701-1714
      , in their meta-analysis, observed improved protein yield but not improved yield of milk and ECM or milk-N:N intake, when CM was substituted for SBM.
      Greater dietary CP content was associated with increased (P = 0.05) fat yield with a trend for increased milk yield (Table 4). However, greater dietary CP also elevated MUN, urinary volume, and N excretion and depressed apparent N-efficiency.
      • Kalscheur K.F.
      • Vandersall J.H.
      • Erdman R.A.
      • Kohn R.A.
      • Russek-Cohen E.
      Effects of dietary crude protein concentration and degradability on milk production responses of early, mid, and late lactation dairy cows.
      J. Dairy Sci. 1999; 82: 545-554
      found that increasing dietary CP increased the yields of milk, fat, and protein from wk 4 through 14 of lactation, but not after wk 19 of lactation, in high-producing dairy cows. On average, cows were about 13 wk into lactation at the start of the current trial. Our findings generally differed from earlier observations of greater production of milk and milk components, on diets formulated from similar feedstuffs with SBM as supplemental protein, when CP was increased from 15.4 to 16.7% but not from 16.7 to 18.4% CP (
      • Broderick G.A.
      Effects of varying dietary protein and energy levels on the production of lactating dairy cows.
      J. Dairy Sci. 2003; 86: 1370-1381
      ), and from 15.7 to 16.7% but not from 16.7 to 17.7% CP (
      • Olmos Colmenero J.J.
      • Broderick G.A.
      Effect of dietary crude protein concentration on milk production and nitrogen utilization in lactating dairy cows.
      J. Dairy Sci. 2006; 89 (b): 1704-1712
      ). Several other studies have shown that reducing dietary CP substantially improved apparent N efficiency (
      • Wu Z.
      • Satter L.D.
      Milk production during the complete lactation of dairy cows fed diets containing different amounts of protein.
      J. Dairy Sci. 2000; 83: 1042-1051
      ;
      • Olmos Colmenero J.J.
      • Broderick G.A.
      Effect of amount and ruminal degradability of soybean meal protein on performance of lactating dairy cows.
      J. Dairy Sci. 2006; 89 (a): 1635-1643
      ), but maximal N efficiency in another trial came at the expense of depressed yields of milk and milk components (
      • Broderick G.A.
      • Stevenson M.J.
      • Patton R.A.
      • Lobos N.E.
      • Olmos Colmenero J.J.
      Effect of supplementing rumen-protected methionine on production and nitrogen excretion in lactating dairy cows.
      J. Dairy Sci. 2008; 91: 1092-1102
      ). An interesting observation was reduced milk lactose content (P = 0.03), but not yield, when dietary CP was increased.
      Although RPML supplementation increased DMI by 1.8 kg/d (P = 0.01), it had no significant effect on yields of milk, ECM, or milk components (Table 4). It is unclear why RPML stimulated such a large feed intake effect, and contradictory responses have been reported in the literature. A recent meta-analysis (
      • Zanton G.I.
      • Bowman G.R.
      • Vázquez-Añón M.
      • Rode L.M.
      Meta-analysis of lactation performance in dairy cows receiving supplemental dietary methionine sources or postruminal infusion of methionine.
      J. Dairy Sci. 2014; 97: 7085-7101
      ) indicated small DMI increases with abomasally infused dl-Met (0.12 kg/d) and with feeding 2-hydroxy-4-methylthio-butyrate (0.15 kg/d) and Smartamine-M (Adisseo Corp., Alpharetta, GA; 0.31 kg/d), but a negative effect (−0.25 kg/d) of feeding Mepron, which was also fed in present study.
      • Arriola Apelo S.I.
      • Bell A.L.
      • Estes K.
      • Ropelewski J.
      • de Veth M.J.
      • Hanigan M.D.
      Effects of reduced dietary protein and supplemental rumen-protected essential amino acids on the nitrogen efficiency of dairy cows.
      J. Dairy Sci. 2014; 97: 5688-5699
      found no effect on DMI when feeding rumen-protected Met, Lys, and Leu, either singly or in combination. Supplementing diets with small amounts of “low-solubles” fish meal, a protein source that is high in both RUP and Met, had differential effects depending on whether it was fed with diets based on alfalfa silage or alfalfa hay. Addition of fish meal to the higher CP alfalfa silage diet increased DMI by 1.2 kg/d but had no effect on the alfalfa hay diet, on which cows were already consuming 2.6 kg/d more DM and secreting 0.10 kg/d more milk protein (
      • Broderick G.A.
      Performance of lactating dairy cows fed either alfalfa silage or alfalfa hay as the sole forage.
      J. Dairy Sci. 1995; 78 (a): 320-329
      ). Supplemental RPML in the present study elevated (P ≤ 0.05) MUN and urinary urea-N and total-N excretion, and tended to reduce milk-N:N intake. This likely occurred because elevated N intake, due to the substantial increase in DMI, was not accompanied by significantly increased secretion of milk or protein. Thus, the extra CP consumed contributed to the urea pool and was excreted in the urine. Note that supplemental RPML supplied an additional 11 g/d to N intake; urinary urea-N increased by 13 g/d on the RPML treatment. As was detected with elevated CP, dietary RPML tended to reduce milk lactose content, which was related to a trend for reduced milk SNF content. Yields of lactose and SNF were not, however, altered. In an earlier trial (
      • Broderick G.A.
      Relative value of fish meal versus solvent soybean meal for lactating dairy cows fed alfalfa silage as sole forage.
      J. Dairy Sci. 1992; 75: 174-183
      ), reduced milk lactose concentration was observed when cows were supplemented with small amounts of low-solubles fish meal, the high-Met, high-RUP source mentioned above. Depressed milk lactose content may derive from increased supply of absorbable Met, acting through some unknown mechanism. However, lactose yield was not different and reduced lactose concentration was likely due to dilution from elevated milk yield.
      Aside from a trend for an interaction of protein source and dietary CP concentration on DMI and a trend for an interaction of protein source and RPML on urinary excretion of urea-N, no other interaction of protein source × CP or protein source × RPML (P ≥ 0.14) was detected in this study (Table 4). This indicated that replacing SBM with CM was just as effective at high CP as at low CP and that there were no differential effects of adding RPML, regardless of whether diets contained SBM or CM. Previously, we had observed production responses with addition of rumen-protected Met alone to diets supplemented with protein as SBM plus roasted soybeans or solvent plus expeller SBM: increased milk and protein yield and N-efficiency occurred when rumen-protected Met was fed as Mepron (
      • Broderick G.A.
      • Muck R.E.
      Effect of alfalfa silage storage structure and rumen-protected methionine on production in lactating dairy cows.
      J. Dairy Sci. 2009; 92: 1281-1289
      ;
      • Broderick G.A.
      • Stevenson M.J.
      • Patton R.A.
      Effect of dietary protein concentration and degradability on response to rumen-protected methionine in lactating dairy cows.
      J. Dairy Sci. 2009; 92: 2719-2728
      ), and increased milk protein content and fat yield occurred when rumen-protected Met was fed as Smartamine-M or Meta-Smart (Adisseo Corp.;
      • Chen Z.H.
      • Broderick G.A.
      • Luchini N.D.
      • Sloan B.K.
      • Devillard E.
      Effect of feeding different sources of rumen-protected methionine on milk production and N-utilization in lactating dairy cows.
      J. Dairy Sci. 2011; 94: 1978-1988
      ). A large body of literature documents that feeding rumen-protected Met increases milk concentrations of total protein (
      • Armentano L.E.
      • Bertics S.J.
      • Ducharme G.A.
      Response of lactating cows to methionine or methionine plus lysine added to high protein diets based on alfalfa and heated soybeans.
      J. Dairy Sci. 1997; 80: 1194-1199
      ;
      • Berthiaume R.
      • Thivierge M.C.
      • Patton R.A.
      • Dubreuil P.
      • Stevenson M.
      • McBride B.W.
      • Lapierre H.
      Effect of ruminally protected methionine on splanchnic metabolism of amino acids in lactating dairy cows.
      J. Dairy Sci. 2006; 89: 1621-1634
      ), true protein (
      • Berthiaume R.
      • Thivierge M.C.
      • Patton R.A.
      • Dubreuil P.
      • Stevenson M.
      • McBride B.W.
      • Lapierre H.
      Effect of ruminally protected methionine on splanchnic metabolism of amino acids in lactating dairy cows.
      J. Dairy Sci. 2006; 89: 1621-1634
      ), and casein (
      • Overton T.R.
      • Emmert L.S.
      • Clark J.H.
      Effects of source of carbohydrate and protein and rumen-protected methionine on performance of cows.
      J. Dairy Sci. 1998; 81: 221-228
      ). Moreover, rumen-protected Met supplementation has elevated yields of milk (
      • Schmidt J.
      • Sipocz P.
      • Cenkvari E.
      • Sipocz J.
      Use of protected methionine (Mepron M 85) in cattle.
      Acta Vet. Hung. 1999; 47: 409-418
      ), total protein (
      • Armentano L.E.
      • Bertics S.J.
      • Ducharme G.A.
      Response of lactating cows to methionine or methionine plus lysine added to high protein diets based on alfalfa and heated soybeans.
      J. Dairy Sci. 1997; 80: 1194-1199
      ), and true protein (
      • Rulquin H.
      • Delaby L.
      Effects of the energy balance of dairy cows on lactational responses to rumen-protected methionine.
      J. Dairy Sci. 1997; 80: 2513-2522
      ). The greater Met concentration in CM and the predicted greater supply of absorbable Met (Table 2) implied that cows would be less responsive to RPML on CM diets.
      • Lee C.
      • Hristov A.N.
      • Cassidy T.W.
      • Heyler K.S.
      • Lapierre H.
      • Varga G.A.
      • de Veth M.J.
      • Patton R.A.
      • Parys C.
      Rumen-protected lysine, methionine, and histidine increase milk protein yield in dairy cows fed a metabolizable protein-deficient diet.
      J. Dairy Sci. 2012; 95 (b): 6042-6056
      found that adding RPML as Mepron plus AminoShure-L to a 13.6% CP diet (with supplemental protein from roasted soybeans and CM) resulted in milk and protein yields that were equal to that on a 15.7% CP diet, in which the additional CP came from expeller SBM.
      • Polan C.E.
      • Cummins K.A.
      • Sniffen And C.J.
      • Muscato T.V.
      • Vicini J.L.
      • Crooker B.A.
      • Clark J.H.
      • Johnson D.G.
      • Otterby D.E.
      • Guillaume B.
      • Muller L.D.
      • Varga G.A.
      • Murray R.A.
      • Peirce-Sandner S.B.
      Responses of dairy cows to supplemental rumen-protected forms of methionine and lysine.
      J. Dairy Sci. 1991; 74: 2997-3013
      reported that rumen-protected Lys improved milk yield in cows fed diets containing corn gluten meal, a low Lys protein, as the principal CP supplement. It is noted that SBM, CM, and rumen microbial protein all have relatively high Lys concentrations (
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      ) and would be expected to contribute large amounts of absorbable Lys. However,
      • Socha M.T.
      • Putnam D.E.
      • Garthwaite B.D.
      • Whitehouse N.L.
      • Kierstead N.A.
      • Schwab C.G.
      • Ducharme G.A.
      • Robert J.C.
      Improving intestinal amino acid supply of pre- and postpartum dairy cows with rumen-protected methionine and lysine.
      J. Dairy Sci. 2005; 88: 1113-1126
      observed that rumen-protected Met (without Lys) and an RPML treatment both improved ECM:DMI and N-efficiency in early-lactation cows fed a soy-protein based diet containing 18.6% CP; these researchers also reported that their RPML treatment was substantially more effective than rumen-protected Met alone for increasing milk yield.
      We were interested in whether dilution of 50% of the dietary CM protein with SBM protein would give production responses similar to CM alone; this was done only at the low CP concentration. The only responses detected were lower (P = 0.03) MUN and a trend for lower proportion of urea-N in total urinary-N (Table 5). Although DMI was the same on CM alone as on SBM + CM, this numeric difference was not different from that on SBM alone (P = 0.11). Intake and production were similar (P ≥ 0.24) on the CM and SBM + CM treatments except that traits related to N-efficiency (MUN, urine volume, and urinary excretion of urea-N and total-N) were poorer on the SBM + CM diet. These results suggest that, although yield of milk and milk components would be comparable on CM and SBM + CM, this occurred without the improved protein utilization occurring on CM alone.
      As expected, multiparous cows had greater (P ≤ 0.03) DMI and yields of milk, true protein, lactose, and SNF, with trends for greater fat and ECM yield compared with primiparous cows (Table 6). Reduced (P ≤ 0.02) lactose and SNF contents in milk secreted by multiparous cows was also observed; reduced lactose accounted for most of the reduction in SNF concentration. Reduced lactose and SNF concentrations were only partly due to dilution because milk yield was 8.8% greater in multiparous cows, whereas lactose and SNF yields were, respectively, 5.9 and 6.8% greater in multiparous versus primiparous cows.
      • Miglior F.
      • Sewalem A.
      • Jamrozik J.
      • Bohmanova J.
      • Lefebvre D.M.
      • Moore R.K.
      Genetic analysis of milk urea nitrogen and lactose and their relationships with other production traits in Canadian Holstein cattle.
      J. Dairy Sci. 2007; 90: 2468-2479
      reported that milk lactose concentration declined from 4.71 to 4.53% between parity 1 and parity 3 in a survey of Canadian Holsteins. Urine volume (P = 0.04) and excretion of urea-N and total-N (P < 0.01) were also higher in multiparous cows. However, greater N excretion was probably driven by greater CP intake because MUN, milk-N:N intake, and urinary urea-N as a proportion of total-N were not different by parity (P ≤ 0.16), indicating similar efficiency of MP utilization between primiparous and multiparous cows.
      Interactions of parity with protein source and with CP concentration for production and urinary excretion traits are given in Table 7. No significant RPML × parity interactions were observed (P ≥ 0.18) and these have been omitted from Table 7. However, parity × protein source interactions were detected (P ≤ 0.04) for ECM:DMI, milk lactose, and SNF contents, and milk-N/N intake; trends also were detected for ECM yield and milk fat and true protein contents. The general pattern of these effects was that CM increased these traits in primiparous cows, whereas little change or even slight declines occurred in multiparous cows; components increased in concentration in milk from primiparous cows and tended to decrease in milk from multiparous cows. For example, ECM yield, milk fat content, true protein content, and milk-N:N intake increased from, respectively, 36.6 to 38.4 kg/d, 3.96 to 4.07%, 3.04 to 3.10%, and 29.9 to 31.3% when CM replaced SBM in diets fed to primiparous cows; however, ECM yield, milk fat content, true protein content, and milk-N:N intake changed from, respectively, 40.3 to 40.5 kg/d, 4.02 to 3.97%, 3.05 to 3.02%, and 30.1 to 30.4% when CM replaced SBM in diets fed to multiparous cows. This suggested that production and N-efficiency in primiparous cows were somewhat more responsive to improved amount and quality of MP supply. Nevertheless, replacement of SBM with CM resulted in greater reduction (P ≤ 0.05) in urinary excretion of urea-N and total-N in multiparous than in primiparous cows. Evaluating the interactions of parity with dietary CP concentration revealed that increased dietary CP content reduced DMI in primiparous cows but elevated DMI in multiparous cows (P < 0.01; Table 7); however, the opposite trend was observed for milk:DMI (P = 0.02). Interactions for total urinary N excretion (P = 0.01) and trends for milk-N:N intake, urinary urea-N, and urea-N:total-N, reflected greater effects on all 4 traits in multiparous than primiparous cows. Results in the present trial appear to contradict the assumption that primiparous dairy cows are less responsive than multiparous cows to increasing nutrient supply. Additional requirements for growth as well as lactation (
      NRC
      Nutrient Requirements of Dairy Cattle. 7th rev. Natl. Acad. Sci., Washington, DC2001
      ) may make primiparous animals more responsive to improved amount and EAA pattern of MP. There are few literature reports of parity × nutrient interactions related to N efficiency.
      • Drackley J.K.
      • Cicela T.M.
      • LaCount D.W.
      Responses of primiparous and multiparous Holstein cows to additional energy from fat or concentrate during summer.
      J. Dairy Sci. 2003; 86: 1306-1314
      observed no parity × diet interactions when varying dietary NEL content from 1.53 to 1.62 Mcal/kg of DM by adding starch or fat.
      • Flis S.A.
      • Wattiaux M.A.
      Effects of parity and supply of rumen-degraded and undegraded protein on production and nitrogen balance in Holsteins.
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      ) detected parity × RUP interactions for metabolism of absorbed N: although similar proportions of N intake were secreted as milk N in both parities, urinary N excretion was greater in primiparous cows whereas apparent tissue retention was greater in multiparous cows, a result at variance with our findings. Although they observed parity effects on milk and component yield when increasing dietary CP from 14 to 16%,
      • Hymøller L.
      • Alstrup L.
      • Larsen M.K.
      • Lund P.
      • Weisbjerg M.R.
      High-quality forage can replace concentrate when cows enter the deposition phase without negative consequences for milk production.
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      reported no parity × diet interactions.

      Ruminal Metabolites

      Ruminal pH and metabolites are given in Table 8. Ruminal pH and concentrations of total VFA, the major VFA (acetate, propionate, and butyrate), and acetate:propionate ratio were not affected by diet in this trial (P ≥ 0.15). The RPML supplement also did not alter traits related to protein breakdown in the rumen. As expected, increasing dietary CP concentration increased (P ≤ 0.01) ruminal concentrations of ammonia, isobutyrate, and total branched-chain VFA (BCVFA), and gave rise to a trend for increased isovalerate concentration. These compounds all derive from AA catabolism by ruminal microbes. The BCVFA are formed from microbial deamination and decarboxylation of branched-chain AA, and reduced BCVFA levels reflect reduced ruminal protein degradation (
      • Van Soest P.J.
      Nutritional Ecology of the Ruminant. 2nd. O&B Books Inc., Corvallis, OR1994
      ). Moreover, we detected a trend for increased valerate concentration on 17% versus 15% dietary CP.
      • El-Shazly K.
      Degradation of protein in the rumen of the sheep. 2. The action of rumen micro-organisms on amino-acids.
      Biochem. J. 1952; 51: 647-653
      reported that n-valeric acid was formed from ruminal catabolism of the protein AA Arg, Pro, and Lys, likely explaining the elevated ruminal valerate. Ruminal concentrations of total free AA were not influenced by diet (P ≥ 0.18) and notably were not elevated with the greater dietary protein diet. The o-phthaldialdehyde fluorescence assay used in this trial detects free AA only but is insensitive to oligopeptides, which are the major metabolites formed in protein degradation (
      • Colombini S.
      • Broderick G.A.
      • Clayton M.K.
      Effect of quantifying peptide release on ruminal protein degradation determined using the inhibitor in vitro system.
      J. Dairy Sci. 2011; 94: 1967-1977
      ). Earlier, we observed no relationship between protein degradation rate, measured in the in vivo rumen, and total AA concentrations measured using o-phthaldialdehyde fluorescence (
      • Reynal S.M.
      • Broderick G.A.
      Effects of feeding dairy cows protein supplements of varying ruminal degradability.
      J. Dairy Sci. 2003; 86: 835-843
      ). We conclude that ruminal total free AA concentrations alone are an unreliable index of ruminal protein degradation. Replacing SBM with CM in the diet clearly reduced (P ≤ 0.01) concentrations in the rumen of ammonia and individual and total BCVFA. Relative to the CM diet, isobutyrate and ammonia were also elevated (P ≤ 0.03), with a trend for elevated BCVFA, on the SBM + CM diet, indicating that ruminal metabolites related to protein degradation on this diet were more similar to the SBM diet than to the CM diet. These results strongly suggest lower ruminal degradation of, and greater RUP contribution from, CM than SBM.

      Conclusions

      Replacing equal SBM CP with CP from CM in diets formulated from corn silage, alfalfa silage, and high-moisture corn and averaging 14.7 or 16.5% CP increased intake and yields of milk and true protein, improved milk-N:N intake, and depressed MUN, urine volume, and urinary N excretion. Responses to CM feeding were greater in primiparous than in multiparous cows. Higher dietary CP gave rise to small increases in fat yield but substantially elevated MUN and urinary N excretion. We detected no protein source × CP concentration interaction, indicating that replacing SBM with CM was effective at both low and high dietary CP. Reduced ruminal concentrations of ammonia and BCVFA indicated lower degradation of CM protein. Rumen-protected Met plus Lys increased intake without affecting production in this trial. Blending equal CP from SBM and CM at low CP decreased MUN and urinary N excretion compared with SBM alone but was not as effective as CM alone in improving N-utilization. Replacing SBM with CM increased production of milk and milk protein, reduced urinary N-excretion, and improved N-efficiency in lactating dairy cows fed both low and high dietary CP.

      Acknowledgments

      The authors thank Rick Walgenbach and his farm crew (US Dairy Forage Research Center, Madison, WI) for harvesting and storing the feeds used in this trial and Nancy Betzold and her barn crew at the US Dairy Forage Research Center Farm (Prairie du Sac, WI) for feeding and animal care; Wendy Radloff and Mary Becker of the US Dairy Forage Research Center (Madison, WI) for assisting in sampling and laboratory analyses; Peter Crump of the University of Wisconsin-Madison for assisting with statistical analyses; and the Canola Council of Canada (Winnipeg, MB, Canada) for partial funding of this project.

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      Article info

      Publication history

      Published online: June 11, 2015
      Accepted: April 22, 2015
      Received: March 12, 2015

      Identification

      DOI: https://doi.org/10.3168/jds.2015-9563

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      © 2015 American Dairy Science Association. Published by Elsevier Inc.

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