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Evaluation of corn germ from ethanol production as an alternative fat source in dairy cow diets1

      Abstract

      Sixteen multiparous cows (12 Holstein and 4 Brown Swiss, 132 ± 20 d in milk) were used in a replicated 4 × 4 Latin square design with 4-wk periods to determine the effects of feeding corn germ on dairy cow performance. Diets were formulated with increasing concentrations of corn germ (Dakota Germ, Poet Nutrition, Sioux Falls, SD) at 0, 7, 14, and 21% of the diet dry matter (DM). All diets had a 55:45 forage to concentrate ratio, where forage was 55% corn silage and 45% alfalfa hay. Dietary fat increased from 4.8% in the control diet to 8.2% at the greatest inclusion level of corn germ. The addition of corn germ resulted in a quadratic response in DM intake with numerically greater intake at 14% of diet DM. Feeding corn germ at 7 and 14% of diet DM increased milk yield and energy-corrected milk as well as fat percentage and yield. Milk protein yield tended to decrease as the concentration of corn germ increased in the diet. Dietary treatments had no effect on feed efficiency, which averaged 1.40 kg of energy-corrected milk/kg of DMI. Increasing the dietary concentration of corn germ resulted in a linear increase in milk fat concentrations of monounsaturated and polyunsaturated fatty acids at the expense of saturated fatty acids. Milk fat concentration and yield of cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid were increased with increased dietary concentrations of corn germ. Although milk fat concentrations of both total trans-18:1 and cis-18:1 fatty acids increased linearly, a marked numeric increase in the concentration of trans-10 C18:1 was observed in milk from cows fed the 21% corn germ diet. A similar response was observed in plasma concentration of trans-10 C18:1. Feeding increasing concentrations of corn germ had no effect on plasma concentrations of glucose, triglyceride, or β-hydroxybutyrate; however, the concentration of nonesterified fatty acids increased linearly, with plasma cholesterol concentration demonstrating a similar trend. Germ removed from corn grain before ethanol production provides an alternative source of fat for energy in lactating dairy cows when fed at 7 and 14% of diet DM. Our results suggest that fat from corn germ may be relatively protected with no adverse effect on DM intake, milk production, and milk composition when fed up to 14% of diet DM.

      Key words

      Introduction

      Feeding fats to dairy cows is a common practice to increase the energy density of the diet. Vegetable oil, oilseeds, and soaps of long-chain fatty acids (LCFA) are common fat sources used in dairy cow diets (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). With the rapid expansion of the ethanol industry, alternative fat sources are becoming available in the form of corn coproducts such as corn germ (CG) and dry and wet distillers grains with solubles. Corn coproducts are major sources of linoleic acid. Feeding fat supplements rich in linoleic and linolenic acids has been shown to increase concentrations of polyunsaturated fatty acids (PUFA) in milk, especially the concentration of conjugated linoleic acid (CLA) and its precursor vaccenic acid (VA;
      • Dhiman T.R.
      • Satter L.D.
      • Pariza M.W.
      • Galli M.P.
      • Albright K.
      • Tolosa M.X.
      Conjugated linoleic acid (CLA) content of milk from cows offered diets rich in linoleic and linolenic acid.
      ;
      • Chouinard P.Y.
      • Corneau L.
      • Butler W.R.
      • Chilliard Y.
      • Drackley J.K.
      • Bauman D.E.
      Effect of dietary lipid source on conjugated linoleic acid concentrations in milk fat.
      ).
      Corn coproducts are attractive to dairy and beef cattle producers because of their high energy, protein, and fiber contents, and low starch content compared with corn. Corn germ is obtained during the corn wet milling or dry grind process (
      • Moreau R.A.
      • Johnston D.B.
      • Hicks K.B.
      The influence of moisture content and cooking on the screw pressing and prepressing of corn oil from corn germ.
      ). Corn germ produced during the wet milling process contains about 40 to 50% fat. The fat content of CG produced through the dry grinding process, however, is about 20 to 25% (
      • Moreau R.A.
      • Johnston D.B.
      • Hicks K.B.
      The influence of moisture content and cooking on the screw pressing and prepressing of corn oil from corn germ.
      ). Regardless of source, CG contains a greater concentration of fat compared with the original grain source.
      Feeding large amounts of dietary fat to ruminants can negatively affect DMI, milk production, and milk fat concentration (
      • Griinari J.M.
      • Dwyer D.A.
      • McGuire M.A.
      • Bauman D.E.
      • Palmquist D.L.
      • Nurmela K.V.
      Trans-octadecenoic acids and milk depression in lactating dairy cows.
      ;
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). Therefore, milk fat depression is a major concern when feeding large amounts of high-fat corn coproducts to dairy cows. Inclusion of 4% corn oil in a low forage diet resulted in a 30 and 35% decrease in milk fat percentage and yield, respectively (
      • Griinari J.M.
      • Dwyer D.A.
      • McGuire M.A.
      • Bauman D.E.
      • Palmquist D.L.
      • Nurmela K.V.
      Trans-octadecenoic acids and milk depression in lactating dairy cows.
      ). Milk fat percentage has been reported to decrease linearly when feeding increasing concentrations of dried distillers grains with solubles (
      • Leonardi C.
      • Bertics S.
      • Armentano L.E.
      Effect of increasing oil from distillers grains or corn oil on lactation performance.
      ). Several studies have been conducted to evaluate distillers grains coproducts as potential feeds for cattle; however, no research data have been reported either on the use of CG as an alternative fat source, or on the upper limit for inclusion in dairy cattle diets. The objective of this study was to evaluate CG as a potential source of fat for dairy cows and its effect on DMI, milk production and composition, and milk CLA concentration as affected by feeding increasing concentrations of CG.

      Materials and Methods

      Animals and Diets

      Sixteen multiparous cows (12 Holstein and 4 Brown Swiss, 132 ± 20 DIM) were used in a multiple 4 × 4 Latin square design with 4-wk experimental periods. The first 2 wk were used for diet adaptation and the last 2 wk for sampling and data collection. Cows were blocked according to DIM, and dietary treatments were randomly assigned to cows within each block. Cows’ BW and BCS were recorded at the beginning of the first period and during the last 3 d of each period. Diets were formulated with increasing concentrations of CG (Dakota Germ, Poet Nutrition, Sioux Falls, SD) at 0, 7, 14, and 21% of the diet DM (Table 1). All diets had a 55:45 forage to concentrate ratio, where forage consisted of 55% corn silage and 45% alfalfa hay. Dietary fat increased from 4.8% in the control diet to 8.2% at the greatest inclusion rate of CG (Table 2). Dietary treatments were formulated to meet or exceed NRC nutrient requirements (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ) for cows producing 45 kg of milk per day at 28.5 kg of daily DMI. Cows were housed in a free-stall barn and individually fed once daily (0800 h) for ad libitum intake using Calan Broadbent feeder doors (American Calan Inc., North-wood, NH). Amounts fed and refused were recorded daily and adjusted to allow for 5 to 10% refusals. Cows were milked 3 times daily at 0600, 1400, and 2100 h, and milk yield was recorded at each milking.
      Table 1Ingredient composition of diets containing increasing concentration of corn germ (CG)
      Ingredient, % of DMDietary treatment (% CG)
      071421
      Alfalfa hay25.025.025.025.0
      Corn silage30.030.030.030.0
      Ground corn28.522.917.211.6
      Soybean meal, 44%, solvent-extracted8.57.25.84.5
      Soybeans, extruded5.05.05.05.0
      Fish meal, menhaden1.01.01.01.0
      Corn germ0.07.014.021.0
      Vitamin/mineral premix
      Dairy Micro Premix (Land O’Lakes Inc., St. Paul, MN); contained 10% Mg, 4,783mg/kg Fe, 4,857mg/kg Cu, 122mg/kg Co, 17,793mg/kg Mn, 26,556mg/kg Zn, 408mg/kg I, 144mg/kg Se, 545,000IU/kg vitamin A, 109,000IU/kg vitamin D, and 2,181IU/kg vitamin E.
      0.250.250.250.25
      Limestone0.800.800.800.80
      Magnesium oxide0.100.100.100.10
      Salt0.450.450.450.45
      Sodium bicarbonate0.200.200.200.20
      Zinpro 4-Plex
      Zinpro Corp., Eden Prairie, MN.
      0.200.200.200.20
      1 Dairy Micro Premix (Land O’Lakes Inc., St. Paul, MN); contained 10% Mg, 4,783 mg/kg Fe, 4,857 mg/kg Cu, 122 mg/kg Co, 17,793 mg/kg Mn, 26,556 mg/kg Zn, 408 mg/kg I, 144 mg/kg Se, 545,000 IU/kg vitamin A, 109,000 IU/kg vitamin D, and 2,181 IU/kg vitamin E.
      2 Zinpro Corp., Eden Prairie, MN.
      Table 2Nutrient composition of diets (% of DM unless otherwise noted) containing increasing concentrations of corn germ (CG; n = 4)
      Number of samples used for each analysis; each sample was run in duplicate.
      ItemDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L=linear, Q=quadratic, and C=cubic.
      071421LQC
      DM, %55.555.656.357.00.340.0020.070.56
      CP, % of DM17.417.417.317.30.090.310.880.53
      NDF, % of DM28.328.829.830.70.29<0.0010.550.82
      Forage NDF, % of DM23.523.523.523.5
      ADF, % of DM17.116.917.017.00.160.990.240.31
      NFC,
      NFC=100 – (% NDF + % CP + % ether extract + % ash).
      % of DM
      42.641.339.337.30.52<0.0010.460.74
      Starch, % of DM24.023.321.619.30.70<0.0010.280.91
      Ether extract, % of DM4.85.97.18.20.05<0.0010.910.10
      Ca, % of DM0.730.740.720.700.030.420.350.93
      P, % of DM0.320.400.440.520.01<0.0010.900.96
      Mg, % of DM0.260.290.310.330.01<0.0010.320.19
      NEL,
      Calculated using NRC (2001).
      Mcal/kg
      1.561.601.641.68
      1 Number of samples used for each analysis; each sample was run in duplicate.
      2 Contrasts: L = linear, Q = quadratic, and C = cubic.
      3 NFC = 100 – (% NDF + % CP + % ether extract + % ash).
      4 Calculated using
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      .

      Sampling and Chemical Analysis

      Samples of alfalfa hay, corn silage, concentrates, and complete diet were collected weekly. Corn silage and diet samples were stored at −20°C until analysis. Alfalfa hay and concentrate samples were stored at room temperature. Feed samples were made into composites by period and dried at 55°C in a forced-air oven (style V-23, Despatch Oven Co., Minneapolis, MN) for 48 h and then ground through a 2-mm screen using a Wiley mill (model 3; Arthur H. Thomas Co., Philadelphia, PA). Samples were reground through a 1-mm screen (Brinkman ultracentrifuge mill, Brinkman Instruments Co., Westbury, NY). Subsamples of feed composites were dried at 105°C for 4 h to determine DM. Composites were analyzed for CP, ether extract (EE), and ash according to AOAC methods (

      AOAC. 2002. Official Methods of Analysis. 17th ed. AOAC, Gaithersberg, MD.

      ). Composites were analyzed for NDF with heat-stable α-amylase and sodium sulfite (
      • 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.
      ), ADF (
      • Robertson J.B.
      • Van Soest P.J.
      The detergent system of analysis and its application to human foods.
      ), and acid detergent lignin (
      • Lowry J.B.
      • Conlan L.L.
      • Schlink A.A.
      • McSweeney C.S.
      Acid detergent dispersible lignin in tropical grasses.
      ) sequentially using an Ankom200 fiber analyzer (Ankom Technology, Fairport, NY). Starch content was determined as described by
      • Bach Knudsen K.E.
      Carbohydrate and lignin contents of plant materials used in animal feeding.
      .
      Feed fatty acids were prepared as butyl esters according to the
      • Sukhija P.S.
      • Palmquist D.L.
      Rapid method for determination of total fatty acid content and composition of feedstuffs and feces.
      procedure with some modifications. Briefly, 100 to 150 mg of sample was placed into 16 × 100-mm Pyrex extraction tubes with Teflon-lined screw caps, followed by the addition of 750 μL of butanol and 25 μL of internal standard (12-nonadecenoic acid, Nu-Chek Prep Inc., Elysian, MN) and vortexed for 20 s. Samples were vortexed at low speed while slowly adding 150 μL of acetyl chloride; then, 750 μL of butanol was used to wash the wall of the extraction tube, the tube was gassed with N2, capped tightly, and heated on a dry heating block at 100°C for 90 min. After samples cooled to room temperature, 8 mL of 6% K2CO3 was added and the samples were vortexed for 30 s. One milliliter of hexane was added and samples were vortexed for another 30 s. Samples were then centrifuged for 25 min at 2,800 × g, and the bottom layer was aspirated and discarded. The remaining hexane layer containing butyl esters was washed 4 times with distilled deionized water and centrifuged for 25 min at 2,800 × g. The upper layer, containing hexane and butyl esters of fatty acids, was removed and placed in injection vials for GC analysis.
      Milk samples from each of the 3 daily milkings were collected for 3 consecutive days at the end of each period. Samples were mixed by gentle inversion and composited in volumes corresponding to the respective milking for each cow on the sampling day, and 2 milk aliquots were obtained for each day. One aliquot was sent to Heart of America DHI laboratory (Manhattan, KS) for compositional analysis, where fat, true protein, and lactose were determined using mid-infrared spectroscopy (Bentley 2000 Infrared Milk Analyzer, Bentley Instruments, Chaska, MN; method 972.16;

      AOAC. 2002. Official Methods of Analysis. 17th ed. AOAC, Gaithersberg, MD.

      ). Concentrations of MUN were determined using chemical methodology based on a modified Berthelot reaction (ChemSpec 150 Analyzer, Bentley Instruments), and somatic cells were counted using a flow cytometer laser (Somacount 500; Bentley Instruments; method 975.16;

      AOAC. 2002. Official Methods of Analysis. 17th ed. AOAC, Gaithersberg, MD.

      ). The second aliquot of milk was stored at −20°C until analysis for fatty acids. Milk fatty acids were prepared as butyl esters with a minor modification of the
      • Sukhija P.S.
      • Palmquist D.L.
      Rapid method for determination of total fatty acid content and composition of feedstuffs and feces.
      procedure. Briefly, milk samples (10 mL) were centrifuged at 2,800 × g for 30 min at room temperature. The top fat layer was removed, transferred into microcentrifuge tubes, and centrifuged at 2,800 × g for 30 min at room temperature. The fat (10 to 20 mg) was then placed into 13 × 100-mm Pyrex extraction tubes with Teflon-lined screw caps, followed by the addition of 750 μL of butanol and 25 μL of internal standard (12-tridecenoic acid, Nu-Chek Prep Inc.), and vortexed for 20 s. Samples were vortexed at low speed while slowly adding 75 μL of acetyl chloride; then, tubes were gassed with N2, capped tightly, and heated on a dry heating block at 100°C for 90 min. After samples cooled to room temperature, 5 mL of 6% K2CO3 was added and the samples vortexed for 30 s. Subsequently, 1 mL of hexane was added and samples were again vortexed for 30 s. Samples were then centrifuged for 25 min at 2,700 × g, and the bottom layer was aspirated and discarded. The remaining hexane layer containing butyl esters was washed 4 times with distilled deionized water and centrifuged for 25 min at 2,700 × g. The upper layer containing hexane and fatty acid esters were removed and placed in injection vials for GC analysis.
      Samples of blood from the coccygeal vein and the subcutaneous mammary vein were collected into evacuated tubes (Becton Dickinson and Co., Franklin Lakes, NJ) containing K-EDTA approximately 3 to 4 h after feeding on 3 consecutive days at the end of each period. Samples were immediately placed on ice and transported to the laboratory where they were centrifuged (2,700 × g). Plasma was collected and stored at −20°C until analysis. Coccygeal plasma samples were thawed and analyzed for glucose using glucose oxidase (Glucose kit, cat. no. G7521, Pointe Scientific, Canton, MI) according to
      • Trinder P.
      Determination of glucose in blood using glucose oxidase with an alternative oxygen acceptor.
      . The concentration of BHBA in plasma was determined (BHBA kit, cat. no. H7587-58, Pointe Scientific) following the methods of
      • Williamson D.H.
      • Mellanby J.
      • Krebs H.A.
      Enzymatic determination of D(-)β-hydroxybutyrate and acetoacetic acid in blood.
      . The NEFA concentration was determined following modifications of the procedure of
      • Johnson M.M.
      • Peters J.P.
      Technical note: An improved method to quantify nonesterified fatty acids in bovine plasma.
      (NEFA-C kit, Wako Chemicals, Richmond, VA). Plasma triglyceride concentration was determined (TG kit, cat. no. T7532, Pointe Scientific) according to the procedure of
      • Fossati P.
      • Lorenzo P.
      Serum triglycerides determined colorimetrically with an enzyme that produces hydrogen peroxide.
      . Total cholesterol was determined (Cholesterol kit, cat. no. C7510, Pointe Scientific) following the procedure of
      • Allain C.C.
      • Poon L.S.
      • Chan C.S.
      • Richmond W.
      • Fu P.C.
      Enzymatic determination of total serum cholesterol.
      .
      Plasma fatty acids were analyzed as butyl esters and prepared as described for milk samples, with some modifications. One milliliter of plasma was transferred into 13- × 100-mm extraction tubes with Teflon-lined screw caps, followed by the addition of 750 μL of butanol and 25 μL of internal standard (nonadecanoic acid, Nu-Chek Prep Inc.) and vortexed for 20 s. Samples were vortexed at low speed while slowly adding 500 μL of acetyl chloride; tubes were gassed with N2, capped tightly, and heated at 100°C for 90 min. After samples cooled to room temperature, 5 mL of 6% K2CO3 was added and the samples were vortexed for 30 s. Then, 1 mL of hexane was added and samples were vortexed for another 30 s. Samples were then centrifuged for 25 min at 2,700 × g, and the bottom layer was aspirated and discarded. The remaining layer was washed 4 times with distilled deionized water and centrifuged for 20 min at 2,700 × g. The upper layer was removed and placed in injection vials for GC analysis.
      All samples prepared as fatty acids esters were analyzed by GC in a chromatograph equipped with a flame-ionization detector and an autoinjector (Hewlett Packard model 6890, Hewlett Packard, Palo Alto, CA). Fatty acids were separated using a CP-Sil 88 fused silica capillary column (100 m × 0.25 mm, i.d. × 0.20 μm film thickness; Varian Inc., Lake Forest, CA). The split ratio at the injector port was set at 100:1 with He as a carrier at a column flow of 2 mL/min. The column temperature was held at 50°C for 1 min after the injection, then increased at 5°C/min to 145°C, held at 145°C for 30 min, increased to 190°C at 10°C/min, and held at 190°C for 30 min. Finally, the temperature was increased at 5°C/min to 210°C and held at this temperature for 40 min. The injection and detector temperatures were 230°C. Individual fatty acids were identified by order of elution and comparison to known commercially prepared reference standards (GLC-606 and GLC-566, Nu-Chek Prep Inc.).

      Energy Balance Calculations

      Energy values were calculated as follows: milk NEL (Mcal/d) = [milk yield (kg) × (0.0929 × % fat + 0.0563 × % true protein + 0.0395 × % lactose]; (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ; page 19, equation 2–15); the maintenance requirement was calculated as NEM (Mcal/d) = [0.08 × BW0.75]. The NEL (empty BW change) calculated according to (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ) from the following equations: total reserves energy (Mcal/kg) = [proportion empty body fat × 9.4 + proportion of empty body protein × 5.55] (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ; page 24, equation 2–23). The proportion of empty body fat was calculated as = 0.037683 × BCS(9) (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ; page 22, equation 2–20), and proportion of empty body protein = 0.200886 – 0.0066762 × BCS(9) (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ; page 22, equation 2–21), and the BCS(9) is = {[(dairy BCS – 1) × 2] + 1} (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ; page 22, equation 2–22). The NEL from body reserves were calculated by converting tissue energy per kilogram of empty BW (EBW) into tissue energy per kilogram of BW (EBW × 0.855) and then converting to dietary NEL using an efficiency of 0.82 for converting tissue energy from live weight loss to dietary NEL, and an efficiency of 1.12 for converting dietary NEL to tissue energy for live weight gain (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ; page 24). Total NEL (Mcal/d) = sum [NEL (milk) + NEM (maintenance) + NEL (EBW change)]. Estimated diet NEL =[total NEL (Mcal/d)/DMI (kg)].

      Statistical Analysis

      Data for DMI, diet composition, milk production and composition, energy values, blood metabolites, and fatty acid compositions of milk and plasma were analyzed as a replicated 4 × 4 Latin square using the MIXED procedure of SAS (version 9.1, SAS Institute, Cary, NC). Cow within breed was designated as a random effect in the model. The statistical model was Yijlk = μ + Ti + Pj + Ckl + Bl + eijkl, where μ = mean, Ti = treatment effect (i = 1, 2, 3, and 4), Pj = period effect (j = 1, 2, 3, or 4), Ckl = cow effect within breed, Bl = breed effect (l = Brown Swiss or Holstein), and eijkl = residual (error). Breed effects and interaction terms (treatment × breed, treatment × period, breed × period, and treatment × breed × period) were tested but were not included in the model unless found to be significant. Data for 1 cow were deleted from the first period because the cow had problems with adaptation to Calan doors. Three polynomial contrasts (linear, quadratic, and cubic) were used to test the effect of feeding increasing concentrations of corn germ to dairy cows. Significance was declared at P ≤ 0.05, and a tendency was reported if 0.05 < P ≤ 0.10. Declaring a linear, quadratic or a cubic response as a pattern that best fit the data was based on acceptance of the pattern with the smallest P-value if 2 of the 3 polynomial contrasts were significant (P < 0.05), unless the lack of fit test proved otherwise, which was conducted as described by
      • Kaps M.
      • Lamberson W.R.
      Biostatistics for Animal Science.
      . If P-values were similar for 2 of the 3 polynomial contrasts, the higher order polynomial contrast was chosen to better fit the model.

      Results

      CG and Dietary Treatments

      Nutrient composition of CG, alfalfa hay, and corn silage are presented in Table 3. Corn germ used in the current experiment was obtained from a dry milling processor, and it contained (DM basis) 15.8% CP, 22.8% NDF, 24.2% starch, and 19.9% EE. The phosphorus concentration in CG was 1.13%, which is 4.3 times greater than that of corn. The predicted value for NEL of the germ was estimated to be 2.4 Mcal/kg (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). Fatty acid composition of CG is presented in Table 4, and CG contained 17.9% total fatty acids (DM basis), with 53.2% linoleic acid (C18:2), 25.3% oleic acid (C18:1), and 11.4% palmitic acid (C16:0). The fat concentration in CG obtained from dry grind or dry milling processes is less than that obtained from wet milling, which is attributed to differences in separation efficiency between the processes. In dry milling, separation of corn components is not as complete as in wet milling; therefore, small amounts of pericarp and endosperm remain attached to the germ, which decreases its fat concentration (
      • Rausch K.D.
      • Belyea R.L.
      The future of coproducts from corn processing.
      ). The NDF content of the diets was increased as the concentration of CG incrementally increased across diets (Table 2). This is because the NDF content of CG is 3 and 1.6 times greater than that of corn and soybean meal, respectively. The starch and nonfibrous carbohydrate content of the diet were decreased as CG increased in the diets. Phosphorus concentration of CG is 3.7 times greater than that of corn; therefore, dietary P concentration was increased as the concentration of CG increased in the diet. Diet concentrations were in excess of the
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      recommendations for P concentration. The EE content of the diet increased from 4.8% DM in the control diet to 8.2% DM in the 21% CG diet. Consistent with the EE concentrations, the concentrations of total fatty acids linearly increased (P < 0.001) as CG increased from 0 to 21% of diet DM (Table 4). Increasing the concentration of CG in the diets linearly decreased (P < 0.001) the concentration of C16:0 and increased the concentrations of C18:2 n-6 and total C18:1 fatty acid (Table 4).
      Table 3Nutrient composition of corn germ, alfalfa hay and corn silage (n = 4)
      Number of samples used for each analysis; each sample was run as duplicate.
      ItemCGForage
      Alfalfa hayCorn silage
      DM, %95.0 (0.22)
      Standard deviation in parentheses.
      91.7 (1.09)27.2 (0.74)
      CP, % of DM15.8 (0.23)24.3 (0.64)8.4 (0.18)
      NDF, % of DM22.8 (0.59)36.9 (0.82)47.7 (2.17)
      ADF, % of DM6.0 (0.18)25.3 (0.88)26.8 (0.53)
      NFC,
      NFC=100 – (% NDF + % CP + % ether extract + % ash).
      % of DM
      36.0 (0.67)27.6 (0.81)35.7 (2.25)
      Starch,
      Single sample analysis.
      % of DM
      24.25.225.0
      Ether extract, % of DM19.9 (0.11)2.6 (0.13)3.7 (0.17)
      Ca,
      Single sample analysis.
      % of DM
      0.021.390.34
      P,
      Single sample analysis.
      % of DM
      1.130.300.13
      Mg,
      Single sample analysis.
      % of DM
      0.490.360.17
      NEL,
      Calculated using NRC (2001).
      Mcal/kg
      2.391.381.39
      1 Number of samples used for each analysis; each sample was run as duplicate.
      2 Standard deviation in parentheses.
      3 NFC = 100 – (% NDF + % CP + % ether extract + % ash).
      4 Single sample analysis.
      5 Calculated using
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      .
      Table 4Fatty acid composition of corn germ, forages, and dietary treatments (n = 4)
      Number of samples used for each analysis.
      ItemCGForageDietary treatment (% CG)
      Alfalfa hayCorn silage071421
      Total fatty acids, g/100 g of DM17.91.71.83.75.06.37.5
      Fatty acid, g/100 g of FA
       C14:00.57.59.51.00.80.70.6
       C14:1 trans-9ND
      ND=not detectable.
      0.40.60.20.20.10.1
       C14:1 cis-90.10.20.60.60.50.40.3
       C16:011.424.615.517.015.414.814.0
       C16:1 trans-90.21.01.10.40.30.30.2
       C16:1 cis-91.02.10.52.52.11.41.1
       C18:01.74.41.93.22.92.72.5
       C18:1 total25.313.515.222.123.324.124.6
       Nonconjugated C18:2
        Trans-9,trans-120.11.11.30.10.10.10.1
        Cis-9,cis-1253.216.526.638.741.744.346.9
        C18:3 n-60.42.52.61.41.41.10.9
        C18:3 n-32.914.58.07.77.15.44.5
        C20:00.41.40.50.60.50.50.5
       Other fatty acids
      Other fatty acids = sum of (C15:0, C15:1, C17:0, C17:1, C20:1, C20:2, C20:3, C20:4, C22:0, C22:1, C22:2, C22:5, C22:6).
      2.710.516.24.03.43.63.2
      1 Number of samples used for each analysis.
      2 ND = not detectable.
      3 Other fatty acids = sum of (C15:0, C15:1, C17:0, C17:1, C20:1, C20:2, C20:3, C20:4, C22:0, C22:1, C22:2, C22:5, C22:6).

      DMI, Milk Yield, and Milk Composition

      Inclusion of CG resulted in a quadratic pattern in daily DMI, which was maximized when cows were fed the 7 and 14% CG diets and then declined when CG was included at 21% of diet DM (Table 5). Feeding increasing concentrations of CG resulted in a linear increase in intake of EE, total fatty acids, and saturated and unsaturated fatty acids. Milk production and ECM were increased quadratically as the concentrations of CG increased in the diets. Cows fed the 7 and 14% CG diets had numerically greater milk yield and ECM values compared with those fed the 21% CG diet. Feed efficiency expressed as ECM/kg of DMI was not different among dietary treatments; however, there was a breed effect as Holstein cows expressed a tendency (P = 0.08) for greater feed efficiency compared with Brown Swiss (1.50 vs. 1.30 for Holstein and Brown Swiss, respectively). A quadratic relationship between concentrations of CG and milk fat percentage was found, with milk fat percentage being numerically lower for cows fed the 21% CG compared with the other dietary treatments. Milk fat yield also increased in a quadratic manner as concentrations of CG increased, with milk fat yield being greatest for cows fed the 14% CG diet. Feeding increasing concentrations of CG resulted in a linear decrease in milk protein percentage, and a tendency for milk protein yield to decrease linearly with increasing CG in the diets. Increasing CG in dairy cow diets had no adverse effect on lactose yield or MUN; however, a cubic effect was observed in milk lactose percentage in response to dietary treatments. The lactose response reflected a numerically inverse relationship to milk fat percentage although the milk fat response was not determined to have a cubic response to diet CG. Lactose concentrations were greater (4.83 vs. 4.59; P < 0.01) in milk from Holstein cows compared with milk from Brown Swiss. Milk from Brown Swiss cows had greater concentrations of MUN compared with milk from Holstein cows (14.47 vs. 11.83; P < 0.01). Although N in milk tended to decrease linearly as the concentration of CG increased in the diets, the efficiency of N utilization was not affected by dietary treatments; however, Holstein cows tended (P = 0.10) to have greater N efficiency when compared with Brown Swiss cows (0.27 vs. 0.24; respectively).
      Table 5Least squares means for intake, milk yield, and milk composition by dairy cows fed increasing concentrations of corn germ (CG)
      ItemDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L=linear, Q=quadratic, and C=cubic.
      071421LQC
      DMI, kg/d28.129.128.827.31.020.310.030.90
      Ether extract intake, kg/d1.31.72.02.30.07<0.0010.0021.00
      FA intake,
      FA=fatty acids; SFA=saturated FA=sum of the intake of (C14:0, C15:0, C16:0, C17:0, C18:0, C20:0 C22:0); UFA=unsaturated FA=sum of the intake of (C14:1, C15:1, C16:1, C17:1, C18:1, C18:2, C18:3, C20:1, C20:2, C20:3, C20:4, C22:1, C22:2, C22:5, C22:6).
      kg/d
      1.11.41.71.90.06<0.0010.020.71
      SFA intake,
      FA=fatty acids; SFA=saturated FA=sum of the intake of (C14:0, C15:0, C16:0, C17:0, C18:0, C20:0 C22:0); UFA=unsaturated FA=sum of the intake of (C14:1, C15:1, C16:1, C17:1, C18:1, C18:2, C18:3, C20:1, C20:2, C20:3, C20:4, C22:1, C22:2, C22:5, C22:6).
      g/d
      216.7261.4317.0326.610.34<0.0010.0030.03
      UFA intake,
      FA=fatty acids; SFA=saturated FA=sum of the intake of (C14:0, C15:0, C16:0, C17:0, C18:0, C20:0 C22:0); UFA=unsaturated FA=sum of the intake of (C14:1, C15:1, C16:1, C17:1, C18:1, C18:2, C18:3, C20:1, C20:2, C20:3, C20:4, C22:1, C22:2, C22:5, C22:6).
      g/d
      819.71123.41340.91524.444.70<0.0010.020.64
      Milk, kg/d37.338.038.236.31.420.250.030.55
      ECM,
      ECM=[(0.327 × milk yield (kg)) + (12.95 × fat yield (kg)) + (7.2 × protein yield (kg))]; Orth (1992).
      kg/d
      39.539.840.436.21.530.030.020.25
      FCM, kg/d35.836.337.032.51.450.030.010.21
      ECM/DMI1.431.381.451.330.080.370.560.28
      Fat, %3.723.723.783.300.130.020.040.24
      Fat, kg/d1.391.411.451.190.070.020.010.18
      Protein, %3.463.373.323.370.060.040.050.76
      Protein, kg/d1.291.281.271.220.050.070.550.76
      Lactose, %4.744.744.594.760.050.550.03<0.01
      Lactose, kg/d1.771.801.791.720.070.230.110.93
      SCS
      SCS=log2(SCC/100,000) + 3.
      3.533.963.884.060.400.140.590.46
      MUN, mg/dL13.4012.3713.2513.450.520.580.150.15
      N intake, g/d781.2805.3795.7756.929.000.230.040.95
      N milk, g/d202.5200.0199.0191.68.560.070.550.67
      N utilization,
      N utilization = [(milk protein yield/6.38)/(protein intake/6.25)].
      g/d
      0.260.250.250.260.010.710.240.73
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      2 FA = fatty acids; SFA = saturated FA = sum of the intake of (C14:0, C15:0, C16:0, C17:0, C18:0, C20:0 C22:0); UFA = unsaturated FA = sum of the intake of (C14:1, C15:1, C16:1, C17:1, C18:1, C18:2, C18:3, C20:1, C20:2, C20:3, C20:4, C22:1, C22:2, C22:5, C22:6).
      3 ECM = [(0.327 × milk yield (kg)) + (12.95 × fat yield (kg)) + (7.2 × protein yield (kg))];

      Orth, R. 1992. Sample Day and Lactation Report. DHIA 200 Fact Sheet A-2.

      .
      4 SCS = log2(SCC/100,000) + 3.
      5 N utilization = [(milk protein yield/6.38)/(protein intake/6.25)].
      All cows among dietary treatments had similar BW and BCS (Table 6). Feeding CG resulted in a quadratic relationship between CG concentration in the diet and milk energy, and cows fed 21% CG had numerically the least milk energy compared with those fed the other dietary treatments. Neither NEM nor EBW NEL was affected by dietary treatments. The estimated dietary NEL was linearly increased with increasing CG in the diets.
      Table 6Least squares means for BW, BCS, and energy values
      ItemDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L=linear, Q=quadratic, and C=cubic.
      071421LQC
      BW, kg69469570569918.50.560.700.52
      BW change, kg9.7−1.116.526.312.30.190.370.48
      BCS3.43.43.43.30.10.940.300.51
      BCS change−0.010.030.05−0.030.050.870.210.68
      Energy
       Milk NEL,
      NEL (milk) (Mcal/d)=milk yield (kg) × (0.0929 × fat% + 0.0563 × true protein% + 0.0395 × lactose%; NRC, 2001).
      Mcal/d
      27.527.728.025.11.10.020.030.28
       Maintenance NEM,
      NEM (maintenance) (Mcal/d)=0.08 × BW0.75.
      Mcal/d
      11.911.912.011.90.20.580.710.53
       NEL
      NEL (empty BW change) calculated according to NRC (2001).
      empty BW change, Mcal/d
      1.40.72.42.71.00.180.610.34
       Total NEL,
      Total NEL (Mcal/d)=sum [NEL (milk) + NEM (maintenance) + NEL (empty BW change)].
      Mcal/d
      43.942.346.142.21.50.770.25<0.01
       Estimated diet NEL,
      Estimated diet NEL=[Total NEL (Mcal/d)/DMI (kg)].
      Mcal/d
      1.511.521.631.670.070.020.770.47
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      2 NEL (milk) (Mcal/d) = milk yield (kg) × (0.0929 × fat% + 0.0563 × true protein% + 0.0395 × lactose%;
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ).
      3 NEM (maintenance) (Mcal/d) = 0.08 × BW0.75.
      4 NEL (empty BW change) calculated according to
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      .
      5 Total NEL (Mcal/d) = sum [NEL (milk) + NEM (maintenance) + NEL (empty BW change)].
      6 Estimated diet NEL = [Total NEL (Mcal/d)/DMI (kg)].

      Milk Fatty Acid Profiles

      The fatty acid composition of milk fat is presented in Tables 7, 8 and 9. The concentrations of C14:0 and C16:0 fatty acids were decreased linearly, whereas those of C18:0, total C18:1, and cis-9, cis-12 C18:2 fatty acids were increased linearly as CG concentration increased across dietary treatments (Table 7). The ratio of n-6 to n-3 fatty acids was linearly increased mainly because of the linear increase in the concentrations of C18:2 fatty acids and the linear decrease in the concentration of C18:3 (n-3). Grouping fatty acids based on their origin (Table 8) showed that feeding increasing concentrations of CG resulted in a linear decrease in the concentration of de novo synthesized fatty acids (<16 carbon), a linear increase in the concentration of preformed fatty acids (>16 carbon), and a linear decrease in those fatty acids derived from both sources (16-carbon). The yields of both de novo synthesized and the 16-carbon fatty acids were linearly decreased as the concentration of unsaturated fatty acid from CG increased in the diets (Table 9); however, the yield of preformed fatty acids was quadratically increased as the concentrations of CG increased in the diets. Feeding increasing concentrations of CG resulted in a linear decrease in the concentrations of saturated fatty acids (SFA) and a linear increase in milk fat concentration of both monounsaturated fatty acids (MUFA) and PUFA (Table 8). The concentrations of total trans-18:1 and total cis-18:1 isomers in milk were linearly increased as CG increased in the diets (Table 8). The addition of CG to diets resulted in pronounced changes in milk fat concentrations of specific trans and cis isomers of octadecanoic acid. Milk fat concentrations of trans-9 and trans-10 C18:1 fatty acids were increased linearly with increasing CG concentration in the diets. The concentration of trans-10 C18:1 isomer in milk fat from cows fed the 7, 14, and 21% CG diets was 25, 42, and 158% greater, respectively, than those fed the control diet. Feeding CG resulted in a linear increase in the concentrations of trans-11 C18:1, and the concentration in milk fat from cows fed the 21% CG diet was 49% greater than the control diet. When milk fatty acids were expressed on grams per day basis (Table 9), feeding increasing concentrations of CG resulted in a linear increase in the yield of trans-10 C18:1 isomer; however, a positive quadratic response in the yield of trans-11 C18:1 was found, with cows fed the 21% CG diet having a numerically lower yield than those fed the other dietary treatment.
      Table 7Fatty acid composition of milk from cows fed increasing concentrations of corn germ (CG)
      Fatty acid, g/100 gDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L=linear, Q=quadratic, and C=cubic.
      071421LQC
      C4:02.932.883.042.510.11<0.01<0.010.01
      C5:00.100.090.090.100.0050.470.140.68
      C6:01.841.751.761.350.07<0.01<0.010.02
      C7:00.0290.0280.0220.0180.003<0.010.460.48
      C8:01.491.381.341.000.06<0.01<0.010.02
      C9:00.060.060.050.070.020.730.400.54
      C10:03.553.152.902.180.15<0.010.070.12
      C11:00.350.320.270.210.01<0.010.060.99
      C11:1 cis-100.100.090.060.050.01<0.010.840.32
      C12:04.343.763.332.740.18<0.010.990.48
      C12:1 cis-110.140.120.090.080.01<0.010.330.40
      C13:00.140.130.090.090.01<0.010.530.11
      C14:011.7910.629.758.960.27<0.010.320.80
      C14:1 trans-90.200.180.160.140.01<0.010.800.48
      C14:1 cis-91.701.601.351.490.09<0.010.100.10
      C15:01.011.000.810.820.05<0.010.890.08
      C15:1 cis-140.250.200.210.170.01<0.010.610.03
      C16:028.7426.5824.0423.340.71<0.010.060.20
      C16:1 trans-90.140.150.150.170.01<0.010.720.25
      C16:1 cis-91.731.731.451.760.120.650.100.04
      C17:00.480.460.430.400.01<0.010.780.91
      C17:1 cis-100.110.110.090.100.010.150.440.02
      C18:07.548.299.7810.120.45<0.010.640.33
      C18:1 total23.6026.9029.8632.620.81<0.010.570.95
      C18:2 trans-9, trans-120.120.110.080.100.010.040.220.15
      C18:2 cis-9, cis-122.933.373.673.820.10<0.010.090.96
      C18:3 n-60.040.050.040.030.01<0.010.030.27
      C18:3 n-30.530.510.460.440.02<0.010.920.45
      C20:00.160.170.170.170.010.231.000.87
      C20:10.260.310.350.360.02<0.010.020.70
      C20:20.040.060.050.040.010.890.130.57
      C20:3 n-60.130.130.120.110.01<0.010.120.72
      C20:3 n-30.040.040.060.080.01<0.010.110.66
      C20:4 n-60.260.250.250.230.010.040.250.53
      C20:5 n-30.090.050.050.020.01<0.010.900.20
      Other FA
      Other FA=sum of (unidentified fatty acids, C19:0, C19:1).
      0.980.910.840.780.04<0.010.950.92
      Ratio of n-3:n-6 fatty acids5.246.527.418.100.24<0.010.180.84
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      2 Other FA = sum of (unidentified fatty acids, C19:0, C19:1).
      Table 8Isomers of C18:1 and conjugated linoleic acid (CLA) and unsaturation classes of fatty acids in milk of cows fed increasing concentrations of corn germ (CG)
      Fatty acid, g/100 gDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L=linear, Q=quadratic, and C=cubic.
      071421LQC
      Total trans2.162.643.243.960.15<0.010.270.96
       C18:1 trans-40.0020.0060.0170.0150.004<0.010.310.14
       C18:1 trans-60.080.130.130.150.01<0.010.200.22
       C18:1 trans-90.160.220.270.320.01<0.010.850.85
       C18:1 trans-100.590.740.841.520.11<0.010.010.19
       C18:1 trans-111.321.561.981.960.11<0.010.120.10
      Total cis21.4424.2526.6228.650.80<0.010.360.95
       C18:1 cis-60.170.220.270.320.01<0.010.480.89
       C18:1 cis-919.0021.3723.4225.380.77<0.010.610.90
       C18:1 cis-110.860.900.931.070.06<0.010.340.63
       C18:1 cis-120.470.620.740.670.03<0.01<0.010.12
       C18:1 cis-130.440.530.590.560.02<0.01<0.010.25
       C18:1 cis-150.310.380.390.440.02<0.010.520.17
       Other cis-C18:10.190.240.280.240.02<0.01<0.010.35
      Conjugated C18:2
      Trans-10, cis-120.100.120.130.200.01<0.010.080.42
      Cis-9, trans-110.720.860.971.130.05<0.010.830.61
       Other CLA isomers0.210.270.320.330.03<0.010.220.53
      De novo
      Fatty acids (FA) based on their origin; de novo = FA <C16 carbon, performed = FA >C16 carbon, and FA from both origin = C16 carbons.
      30.1127.4625.4022.100.69<0.010.220.53
      Preformed
      Fatty acids (FA) based on their origin; de novo = FA <C16 carbon, performed = FA >C16 carbon, and FA from both origin = C16 carbons.
      39.2144.0148.8652.641.10<0.010.440.71
      C16 carbon
      Fatty acids (FA) based on their origin; de novo = FA <C16 carbon, performed = FA >C16 carbon, and FA from both origin = C16 carbons.
      30.6828.5425.7325.360.77<0.010.040.11
      SCFA
      Fatty acids based on their chain length; SCFA = short-chain FA (C4 to C9), MCFA = medium-chain FA (C10 to C16), and LCFA = long-chain FA (FA≥C17).
      6.446.196.295.050.21<0.01<0.010.02
      MCFA
      Fatty acids based on their chain length; SCFA = short-chain FA (C4 to C9), MCFA = medium-chain FA (C10 to C16), and LCFA = long-chain FA (FA≥C17).
      55.0050.3945.3442.841.06<0.010.120.31
      LCFA
      Fatty acids based on their chain length; SCFA = short-chain FA (C4 to C9), MCFA = medium-chain FA (C10 to C16), and LCFA = long-chain FA (FA≥C17).
      38.5843.4448.3752.141.10<0.010.420.68
      SFA
      FA based on their degree of saturation; SFA = saturated FA, MUFA = monounsaturated FA, and PUFA = polyunsaturated FA.
      64.6960.8558.0554.260.93<0.010.970.46
      MUFA
      FA based on their degree of saturation; SFA = saturated FA, MUFA = monounsaturated FA, and PUFA = polyunsaturated FA.
      29.1832.2934.6137.470.83<0.010.980.48
      PUFA
      FA based on their degree of saturation; SFA = saturated FA, MUFA = monounsaturated FA, and PUFA = polyunsaturated FA.
      6.156.877.348.030.23<0.010.940.54
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      2 Fatty acids (FA) based on their origin; de novo = FA <C16 carbon, performed = FA >C16 carbon, and FA from both origin = C16 carbons.
      3 Fatty acids based on their chain length; SCFA = short-chain FA (C4 to C9), MCFA = medium-chain FA (C10 to C16), and LCFA = long-chain FA (FA ≥ C17).
      4 FA based on their degree of saturation; SFA = saturated FA, MUFA = monounsaturated FA, and PUFA = polyunsaturated FA.
      Table 9Daily production of C18:1 and conjugated linoleic acid (CLA) isomers in milk fat, and normalized ratios of fatty acids (FA) in milk from cows fed increasing concentrations of corn germ (CG)
      Fatty acid, g/dDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L = linear, Q = quadratic, and C = cubic.
      071421LQC
      Total trans29.236.945.946.72.5<0.010.090.30
       C18:1 trans-40.020.080.240.200.05<0.010.270.16
       C18:1 trans-61.21.82.01.80.1<0.01<0.010.72
       C18:1 trans-92.23.03.93.80.2<0.01<0.010.20
       C18:1 trans-107.910.312.116.81.1<0.010.180.40
       C18:1 trans-1117.821.827.824.21.9<0.010.030.14
      Total cis294.9340.4386.6343.019.7<0.01<0.010.16
       C18:1 cis-63.33.13.93.60.2<0.01<0.010.15
       C18:1 cis-9261.5299.5339.8303.617.2<0.01<0.010.16
       C18:1 cis-1111.712.613.612.71.00.260.250.62
       C18:1 cis-126.58.910.88.20.7<0.01<0.010.11
       C18:1 cis-136.17.58.86.90.50.07<0.010.12
       C18:1 cis-154.35.45.75.20.40.02<0.010.92
       Other cis C18:12.53.44.12.80.30.23<0.010.16
      Conjugated C18:2
      Trans-10, cis-121.41.61.92.30.2<0.010.660.82
      Cis-9, trans-119.812.113.713.71.0<0.010.170.74
       Other CLA isomers2.83.84.23.80.4<0.010.020.83
      De novo421.4386.0367.1262.820.2<0.010.020.14
      Preformed539.6617.8709.6632.134.9<0.01<0.010.15
      C16 carbons430.9403.4372.8299.922.5<0.010.150.58
      Short-chain FA89.887.290.061.65.3<0.01<0.010.07
      Medium-chain FA779.8719.0665.0512.836.5<0.010.080.37
      Long-chain FA522.4601.7694.8620.534.4<0.01<0.010.15
      Saturated FA905.1858.0842.9649.944.6<0.010.040.19
      Monounsaturated FA402.4453.5501.7448.923.90.02<0.010.21
      Polyunsaturated FA84.596.3105.496.15.50.030.020.44
      Desaturase index
      Normalized ratio = product/[substrate + product] (Sol Morales et al., 2000).
       C14:1/C14:00.130.130.120.140.010.030.130.05
       C16:1/C16:00.060.060.060.070.01<0.010.190.09
       C18:1/C18:00.720.720.710.720.010.690.830.32
       CLA/TVA
      CLA = cis-9, trans-11 CLA, and TVA (trans vaccenic acid) = trans-11 C18:1.
      0.360.360.340.370.010.900.090.06
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      2 Normalized ratio = product/[substrate + product] (
      • Sol Morales M.
      • Palmquist D.L.
      • Weiss W.P.
      Effects of fat source and copper on unsaturation of blood and milk triacylglycerol fatty acids in Holstein and Jersey cows.
      ).
      3 CLA = cis-9, trans-11 CLA, and TVA (trans vaccenic acid) = trans-11 C18:1.
      Corn germ fed at increasing concentrations of dietary DM resulted in a linear increase in concentrations of milk conjugated C18:2 isomers (Table 8). Milk fat concentrations of the predominant CLA isomer cis-9, trans-11 linearly increased from 0.72% in cows fed the control diet to 1.13% of total milk fatty acids for those fed the 21% CG diet. This difference accounted for a 57% increase in the concentration of milk fat cis-9, trans-11 CLA isomer; however, milk fat concentration of cis-9, trans-11 CLA from cows fed the 21% CG diet was only 16% greater than that obtained in milk fat from cows fed the 14% CG diet. Similarly, milk fat concentrations of trans-10, cis-12 CLA also linearly increased in response to dietary treatments. Milk fat from cows fed the 21% CG diet contained numerically the greatest concentrations of trans-10, cis-12 CLA, which was 100, 67, and 54% greater than those obtained from cows fed the 0, 7, and 14% CG diets, respectively. Milk fat yield of cis-9, trans-11 CLA was linearly increased in response to increasing CG in the diets (Table 9). Cows fed the 14 and 21% CG diet produced numerically similar milk fat content of cis-9, trans-11 CLA, which averaged 13.7 g/d (Table 9). Milk fat yield of trans-10, cis-12 CLA was also linearly increased from 1.4 g/d on the control diet to 2.3 g/d when cows were fed the 21% CG diet.

      Plasma Metabolites and Fatty Acids Composition

      Adding CG had no effect on glucose, triglyceride, and BHBA plasma concentrations; however, feeding increasing concentrations of CG resulted in a linear increase in the concentration of blood NEFA and tended to linearly increase the concentration of cholesterol (Table 10). Feeding increasing concentrations of CG caused an alteration in plasma fatty acids composition (Tables 11 and 12). Feeding CG at 0, 7, 14, and 21% of dietary DM resulted in a linear decrease in the concentrations of C14:1 isomers and a cubic effect on the concentrations of C16:0 (Table 11). Increasing CG in the diets resulted in a linear increase in plasma concentrations of C18:0, C18:1, and cis-9, cis-12 C18:2 fatty acids. Plasma concentrations of both trans-10 and trans-11 C18:1 were linearly increased (Table 12). The concentration of plasma trans-10, cis-12 CLA was linearly increased in response to increasing CG in the diets. There was a 93% increase in plasma concentration of trans-10, cis-12 CLA when cows were fed the 21% CG diet compared with those fed the 0% CG diet; however, feeding CG had no effect on plasma concentration of cis-9, trans-11 CLA isomer. The plasma concentration of SFA tended to quadratically increase, whereas the concentration of PUFA linearly increased as the concentration of supplemental fat from CG increased across treatments.
      Table 10Concentrations of glucose, NEFA, triglyceride, cholesterol, and BHBA in plasma of cows fed increasing concentrations of corn germ (CG)
      ComponentDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L = linear, Q = quadratic, and C = cubic.
      071421LQC
      Glucose, mg/dL70.469.768.067.31.20.171.000.80
      NEFA, μEq/L188.7221.3219.1242.017.20.040.770.42
      Triglyceride, mg/dL16.416.815.515.21.50.430.780.62
      Cholesterol, mg/dL169.7167.5196.4178.99.40.070.280.02
      BHBA, mg/dL7.47.77.37.10.40.390.180.94
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      Table 11Fatty acid composition of plasma from cows fed increasing concentrations of CG
      Fatty acid, μg/mLDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L = linear, Q = quadratic, and C = cubic.
      071421LQC
      C14:014.814.716.113.71.30.700.290.29
      C14:1 trans-92.22.02.01.80.1<0.010.870.37
      C14:1 cis-99.08.89.28.00.5<0.010.100.17
      C16:0250.4254.2290.6262.110.60.070.070.02
      C16:1 trans-96.15.86.56.40.60.400.860.37
      C16:1 cis-918.919.122.021.41.50.090.790.31
      C18:086.491.8108.397.84.9<0.010.050.04
      C18:1 total130.4133.8163.0152.86.3<0.010.210.01
      Nonconjugated C18:2
      Trans-9, trans-126.47.77.06.70.80.910.250.42
      Cis-9, cis-121,095.71,125.41,430.91,254.164.9<0.010.03<0.01
       C18:3 n-621.619.021.818.81.90.250.740.07
       C18:3 n-378.167.973.760.04.0<0.010.51<0.01
       C20:01.71.71.91.90.10.040.820.20
       C20:12.22.63.13.60.3<0.010.960.34
       C20:22.63.12.82.50.30.700.130.47
       C20:3 n-655.452.559.552.04.00.790.390.04
       C20:3 n-30.10.70.30.10.30.660.230.35
       C20:4 n-643.045.654.448.12.90.040.080.06
       C20:5 n-321.520.727.325.02.30.050.700.07
       C22:10.30.20.20.20.10.360.951.00
       C22:212.616.814.913.61.90.860.100.38
       C22:3 n-35.44.45.24.40.80.440.850.34
       C22:4 n-63.53.42.73.10.50.370.580.41
       C22:5 n-612.912.014.912.90.90.270.360.01
       C22:5 n-37.15.46.45.70.70.300.440.14
       C22:6 n-36.65.88.06.90.60.070.830.01
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      Table 12Plasma C18:1 and conjugated linoleic acid (CLA) isomers from cows fed increasing concentrations of corn germ (CG)
      Fatty acid (FA), μg/mLDietary treatment (% CG)SEMContrast (P-value)
      Contrasts: L = linear, Q = quadratic, and C = cubic.
      071421LQC
      C18:1 trans-40.10.10.10.20.10.190.240.91
      C18:1 trans-60.40.60.90.80.1<0.010.180.51
      C18:1 trans-90.10.20.40.60.20.160.620.82
      C18:1 trans-101.11.41.32.00.30.030.420.32
      C18:1 trans-116.58.29.38.80.8<0.010.030.63
      C18:1 cis-6ND
      ND = not detectable.
      NDNDND
      C18:1 cis-9101.0105.6125.9118.14.9<0.010.160.03
      C18:1 cis-1112.111.713.012.10.50.450.500.03
      C18:1 cis-124.25.16.25.40.3<0.01<0.010.04
      C18:1 cis-131.82.02.42.00.10.050.010.03
      C18:1 cis-150.50.60.70.60.10.270.040.08
      CLA isomers
      Trans-10, cis-121.41.72.22.70.3<0.010.580.22
      Cis-9, trans-111.31.21.61.30.20.540.480.11
       Other CLA isomers0.60.81.00.70.10.220.020.15
      Saturated FA444.0452.3500.1461.618.00.120.100.07
      Monounsaturated FA423.3435.3493.9454.629.00.130.270.18
      Polyunsaturated FA1,448.31,378.31,722.81,584.386.5<0.010.630.02
      1 Contrasts: L = linear, Q = quadratic, and C = cubic.
      2 ND = not detectable.

      Discussion

      Replacing corn grain and soybean meal with CG at 0, 7, 14, and 21% of dietary DM resulted in increased concentrations of dietary fat from CG, which was equal to 0, 1.4, 2.8, and 4.2% of additional fat, respectively. Dietary fat supplements are typically used in dairy cattle rations to increase the energy density of the diet and increase milk production (
      • Palmquist D.L.
      Use of fats in diets for lactating dairy cows.
      ;
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ;
      • Litherland N.B.
      • Thire S.
      • Beaulieu A.D.
      • Reynolds C.K.
      • Benson J.A.
      • Drackley J.K.
      Dry matter intake is decreased more by abomasal infusion of unsaturated free fatty acids than by unsaturated triglycerides.
      ). Despite the potential of improving the energetic value of dairy cattle rations, supplemental dietary fat may decrease DMI when total dietary level exceeds 7% DM (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). Supplementing diets with fat sources rich in unsaturated rather than saturated fatty acids is more likely to depress DMI (
      • Firkins J.L.
      • Eastridge M.L.
      Assessment of the effects of iodine value on fatty acid digestibility, feed intake, and milk production.
      ;
      • Allen M.S.
      Effects of diet on short-term regulation of feed intake by lactating dairy cattle.
      ). Feeding CG at 7 and 14% of dietary DM resulted in a 3.6 and 2.4% increase in DMI, respectively, whereas feeding CG at 21% of dietary DM resulted in 2.9% decrease in DMI compared with the control diet. This decrease in DMI could have been related, in part, to a negative effect of dietary fat on rumen fermentation (
      • Jenkins T.C.
      Lipid metabolism in the rumen.
      ). A negative relationship was observed between dietary fatty acid content and DMI (
      • Firkins J.L.
      • Eastridge M.L.
      Assessment of the effects of iodine value on fatty acid digestibility, feed intake, and milk production.
      ); however, this relationship was not significant until the concentration of dietary fatty acids was 3.5 percentage units greater than that of the basal diet. In the current study, the control diet contained 3.7% total fatty acids on a DM basis. The addition of CG at 7, 14, and 21% DM accounted for 1.3, 2.6, and 3.8 percentage units of additional total fatty acids in the diets, respectively. Similar responses in DMI have been observed in previous studies when dietary fat was fed to, or abomasally infused into, lactating dairy cows (
      • Drackley J.K.
      • Klusmeyer T.H.
      • Trusk A.M.
      • Clark J.H.
      Infusion of long-chain fatty acids varying in saturation and chain length into the abomasum of lactating dairy cows.
      ;
      • Relling A.E.
      • Reynolds C.K.
      Feeding rumen-inert fats differing in their degree of saturation decreases intake and increases plasma concentrations of gut peptides in lactating dairy cows.
      ).
      The response of milk production to dietary fat supplementation is dependent upon the composition of the basal diet, stage of lactation, energy balance, level and source of dietary fat, and DMI (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). Milk production often increases in response to additional energy provided by fat supplementation in lactating dairy cow diets (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). The quadratic response observed in milk production is a typical response to dietary fat supplementation.
      • Palmquist D.L.
      Use of fats in diets for lactating dairy cows.
      indicated that milk yield response to supplemental fat is curvilinear and decreases as the concentration of fat increases in the diet. The decrease in milk production when cows were fed 21% CG could be partially attributed to the decrease in DMI.
      • Jenkins T.C.
      • Jenny B.F.
      Nutrient digestion and lactation performance of dairy cows fed combinations of prilled fat and canola oil.
      indicated that when fat supplements fail to improve milk production, it can usually be related to negative effects of dietary fat on feed intake, rumen fermentation, or poor digestibility of fatty acids.
      In the present study, inclusion of CG at increasing concentrations of dietary DM resulted in a linear decrease in milk protein percentage, with a tendency for a linear decrease in milk protein yield. Previous studies have shown that milk protein percentage often decreases when supplemental fat is fed to lactating dairy cows (
      • DePeters E.J.
      • Cant J.P.
      Nutritional factors influencing the nitrogen composition of bovine milk: A review.
      ;
      • Wu Z.
      • Huber J.T.
      Relationship between dietary fat supplementation and milk protein concentration in lactating cows: A review.
      ), and the effect diminishes as the concentration of fat supplement increases in the diet (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). The linear decrease in milk protein percentage and the numeric decrease in yield, particularly when cows were fed the 21% CG diet, may be a function of decreased milk production rather than decreased milk protein production per se (
      • DePeters E.J.
      • Cant J.P.
      Nutritional factors influencing the nitrogen composition of bovine milk: A review.
      ;
      • Shingfield K.J.
      • Reynolds C.K.
      • Hervás G.
      • Griinari J.M.
      • Grandison A.S.
      • Beever D.E.
      Examination of the persistency of milk fatty acid composition responses to fish oil and sunflower oil in the diet of dairy cows.
      ).
      Milk fat depression is often associated with diets containing greater concentrations of PUFA. Generally, increasing the amount of free or unesterified unsaturated fatty acids is more likely to cause milk fat depression (
      National Research Council
      Nutrient Requirements of Dairy Cattle.
      ). In the present study, a decrease in milk fat percentage and yield was not observed until CG was included at 21% of dietary DM; however, cows fed the 7 and 14% CG diets had numerically similar concentrations of milk fat compared with those fed the control diet. Data from the literature indicate that protected or saturated fat supplements tend to maintain or increase milk fat percentage (
      • Palmquist D.L.
      • Jenkins T.C.
      Fat in lactation rations.
      ;
      • Delbecchi L.
      • Ahnadi C.E.
      • Kennelly J.J.
      • Lacasse P.
      Milk fatty acid composition and mammary lipid metabolism in Holstein cows fed protected or unprotected canola seeds.
      ).
      • Klopfenstein T.J.
      • Erickson G.E.
      • Bremer V.R.
      BOARD-INVITED REVIEW: Use of distillers by-products in the beef cattle feeding industry.
      indicated in their meta-analysis on studies conducted in feedlot steers, that the fat in distillers grains might be partially protected from ruminal biohydrogenation and can result in greater concentrations of unsaturated fatty acids leaving the rumen. In the present study, cows fed the 7 and 14% CG diets maintained milk production as well as milk fat percentage and yield, which might indicate that the fat in CG is relatively protected from rumen biohydrogenation. Maintaining milk fat percentage could result from an increased mammary gland uptake of LCFA that might exceed the depression in milk fat synthesis (
      • Palmquist D.L.
      • Jenkins T.C.
      Fat in lactation rations.
      ).
      The numeric decrease in milk fat content when cows were fed 21% CG could be attributed to an increased dietary supply of unsaturated fatty acids, particularly C18:2. Dietary unsaturated fatty acids are known to modify rumen lipid metabolism, leading to increased concentrations of unique biohydrogenation intermediates, which are very effective inhibitors of mammary gland de novo fatty acid synthesis (
      • Bauman D.E.
      • Griinari J.M.
      Nutritional regulation of milk fat synthesis.
      ). Trans-10 C18:1 and trans-10, cis-12 CLA are primary candidates to be associated with milk fat depression. Previous studies established that postruminal infusion of trans-10, cis-12 CLA can inhibit milk fat synthesis in dairy cows (
      • Baumgard L.H.
      • Sangster J.K.
      • Bauman D.E.
      Milk fat synthesis in dairy cows is progressively reduced by increasing supplemental amounts of trans-10, cis-12 conjugated linoleic acid (CLA).
      ;
      • Loor J.J.
      • Herbein J.H.
      Reduced fatty acid synthesis and desaturation due to exogenous trans10, cis12-CLA in cows fed oleic or linoleic oil.
      ). Recently,
      • Lock A.L.
      • Tyburczy C.
      • Dwyer D.A.
      • Harvatine K.J.
      • Destaillats F.
      • Mouloungui Z.
      • Candy L.
      • Bauman D.E.
      Trans-10 octadecenoic acid does not reduce milk fat synthesis in dairy cows.
      concluded that trans-10 C18:1 does not decrease milk fat synthesis when infused abomasally; however, infusion of trans-10, cis-12 CLA resulted in a 27% decrease in milk fat content.
      In the present study, feeding CG at 21% of dietary DM resulted in a 100% increase in the concentration of milk fat trans-10, cis-12 CLA compared with that observed in cows fed the control diet. A linear relationship was reported by
      • de Veth M.J.
      • Griinari J.M.
      • Pfeiffer A.M.
      • Bauman D.E.
      Effect of CLA on milk fat synthesis in dairy cows: Comparison of inhibition by methyl esters and free fatty acids, and relationships among studies.
      between the dose of trans-10, cis-12 CLA infused into the abomasum and the milk fat yield of trans-10, cis-12 CLA. Moreover, it has been demonstrated that, during diet-induced milk fat depression, the formation of trans-10, cis-12 CLA increases because of modifications in ruminal lipid metabolism (
      • Bauman D.E.
      • Griinari J.M.
      Nutritional regulation of milk fat synthesis.
      ;
      • Shingfield K.J.
      • Reynolds C.K.
      • Hervás G.
      • Griinari J.M.
      • Grandison A.S.
      • Beever D.E.
      Examination of the persistency of milk fatty acid composition responses to fish oil and sunflower oil in the diet of dairy cows.
      ). The linear increase in the concentration and yield of trans-10, cis-12 CLA observed in milk in the current study might indicate an increase in the concentration of trans-10, cis-12 CLA leaving the rumen. A similar linear response in plasma concentration of trans-10, cis-12 CLA was observed. Plasma from cows fed the 21% CG diet had a 98% increase in the concentration of trans-10, cis-12 CLA compared with those fed the control diet. The increase in plasma concentration of trans-10, cis-12 CLA also indicates an increase in the availability of trans-10, cis-12 CLA presented to the mammary gland to be incorporated in milk fat. In the current study, the decrease in milk fat percentage and yield could be related to the increased concentration of trans-10, cis-12 CLA; however, there are discrepancies in the relationship between milk fat concentration of trans-10, cis-12 CLA and the degree of milk fat depression as previously observed by
      • Loor J.J.
      • Ferlay A.
      • Ollier A.
      • Doreau M.
      • Chilliard Y.
      Conjugated linoleic acids (CLA), trans fatty acids, and lipid content in milk from Holstein cows fed a high- or low-fiber diet with two levels of linseed oil.
      and
      • Peterson D.G.
      • Matitashvili E.A.
      • Bauman D.E.
      Diet induced milk fat depression in dairy cows results in increased trans-10, cis-12 CLA in milk and coordinate suppression of mRNA abundance for mammary enzymes involved in milk fat synthesis.
      . These findings clearly suggest that other substances may be involved or that a critical concentration threshold was not exceeded.
      • de Veth M.J.
      • Griinari J.M.
      • Pfeiffer A.M.
      • Bauman D.E.
      Effect of CLA on milk fat synthesis in dairy cows: Comparison of inhibition by methyl esters and free fatty acids, and relationships among studies.
      indicated that a substantial decrease in milk fat yield occurs in response to small doses of trans-10, cis-12 CLA; however, increasing the infused amount of trans-10, cis-12 CLA beyond 6 g/d caused little or no further decrease in milk fat synthesis.
      In the present study, the concentration of trans-10 C18:1 increased linearly from 0.59% in milk from cows fed the control diet to 1.52% for those fed the 21% CG diet. Cows fed the 21% CG diet had the greatest concentration of trans-10 C18:1 in milk fat, which was 105 and 81% greater than that obtained from cows fed the 7 and 14% CG diets, respectively. Plasma concentration of trans-10 C18:1 increased linearly as the concentration of CG increased. This could explain the linear increase in the yield of milk fat trans-10 C18:1. Although milk fat concentration of trans-10 C18:1 has been shown to increase during diet-induced milk fat depression, no direct relationship has been established between the depression of milk fat synthesis and milk fat concentration of this fatty acid. An increase in the concentration of both trans-10, cis-12 CLA and trans-10 C18:1 indicates that ruminal lipid metabolism had been modified, which shifted the biohydrogenation pathway toward the formation of trans-10 C18:1 (the increase in the concentrations of these 2 fatty acids has been reported to cause milk fat depression;
      • Bauman D.E.
      • Griinari J.M.
      Nutritional regulation of milk fat synthesis.
      ).
      • Peterson D.G.
      • Matitashvili E.A.
      • Bauman D.E.
      Diet induced milk fat depression in dairy cows results in increased trans-10, cis-12 CLA in milk and coordinate suppression of mRNA abundance for mammary enzymes involved in milk fat synthesis.
      reported that the relationship between milk fat concentration of trans-10, cis-12 CLA and the decrease in milk fat yield during diet-induced milk fat depression was not necessarily the same relationship observed during abomasal infusion of relatively pure trans-10, cis-12 CLA. Therefore, the involvement of other biohydrogenation intermediates containing conjugated bonds in milk fat depression has been hypothesized (
      • Bauman D.E.
      • Griinari J.M.
      Nutritional regulation of milk fat synthesis.
      ;
      • Perfield II, J.W.
      • Saebo A.
      • Bauman D.E.
      Use of conjugated linoleic acid (CLA) enrichments to examine the effects of trans-8, cis-10 CLA and cis-11, trans-13 CLA on milk fat synthesis.
      ).
      • Shingfield K.J.
      • Reynolds C.K.
      • Hervás G.
      • Griinari J.M.
      • Grandison A.S.
      • Beever D.E.
      Examination of the persistency of milk fatty acid composition responses to fish oil and sunflower oil in the diet of dairy cows.
      showed that milk fat content was inversely correlated (r = −0.808) with milk fat concentration of trans-9, cis-11 CLA, and changes in this CLA isomer could account for approximately 80% of the variation in milk fat content when cows were fed a fish oil and sunflower oil diet.
      • Perfield II, J.W.
      • Lock A.L.
      • Griinari J.M.
      • Sæbø A.
      • Delmonte P.
      • Dwyer D.A.
      • Bauman D.E.
      Trans-9, cis-11 conjugated linoleic acid reduces milk fat synthesis in lactating dairy cows.
      demonstrated that trans-9, cis-11 CLA isomer can decrease milk fat content in abomasally infused cows. In the current study, the concentrations of the total unidentified CLA isomers linearly increased from 0.21% on the control diet to 0.33% on the 21% CG diet. A linear increase (P < 0.01) in the concentration of one of these unidentified CLA isomers was observed in the current study. Feeding increasing concentrations of CG at 0, 7, 14, and 21% resulted in a milk fat concentration of this unidentified CLA isomer of 0.04, 0.06, 0.07, and 0.09%, respectively. In the current study we could not identify this CLA isomer, but we speculated it could be the trans-9, cis-11 CLA.
      In the present study, the plasma concentration of trans-11 C18:1 was linearly increased by increasing CG in the diets. Cows fed the 14% CG diet had numerically the greatest plasma concentration of trans-11 C18:1. This fatty acid is the primary precursor for endogenously synthesized cis-9, trans-11 C18:2 CLA isomer (
      • Griinari J.M.
      • Dwyer D.A.
      • McGuire M.A.
      • Bauman D.E.
      • Palmquist D.L.
      • Nurmela K.V.
      Trans-octadecenoic acids and milk depression in lactating dairy cows.
      ). This increase in the plasma concentration of trans-11 C18:1 is indicative of an enhanced supply that will be available for endogenous synthesis of cis-9, trans-11 CLA in the mammary gland. A decline in trans-11 C18:1 in both plasma and milk was observed when cows were fed 21% CG, which was simultaneously associated with an increase of trans-10 C18:1 in the plasma and milk fat. This indicates a shift in the biohydrogenation process in the rumen, resulting in trans-10 C18:1 replacing trans-11 C18:1 as the predominant trans-C18:1 fatty acid. This shift in biohydrogenation pathways toward trans-10 C18:1 instead of trans-11 C18:1 in cows fed 21% CG could explain the numerically similar production of milk fat cis-9, trans-11 CLA when cows were fed the 14% CG diet.
      Changes in milk fatty acid composition observed in this study are consistent with known effects of unsaturated fat supplements on de novo fatty acids in the mammary gland (
      • Palmquist D.L.
      • Beaulieu A.D.
      • Barbano D.M.
      Feed and animal factors influencing milk fat composition.
      ). It is well established that feeding unsaturated oils is typically associated with a decrease in de novo synthesis of short-chain fatty acids (SCFA) and medium-chain fatty acids (MCFA;
      • Litherland N.B.
      • Thire S.
      • Beaulieu A.D.
      • Reynolds C.K.
      • Benson J.A.
      • Drackley J.K.
      Dry matter intake is decreased more by abomasal infusion of unsaturated free fatty acids than by unsaturated triglycerides.
      ;
      • Shingfield K.J.
      • Reynolds C.K.
      • Hervás G.
      • Griinari J.M.
      • Grandison A.S.
      • Beever D.E.
      Examination of the persistency of milk fatty acid composition responses to fish oil and sunflower oil in the diet of dairy cows.
      ;
      • Cruz-Hernandez C.
      • Kramer J.K.G.
      • Kennelly J.J.
      • Glimm D.R.
      • Sorensen B.M.
      • Okine E.K.
      • Goonewardene L.A.
      • Weselake R.J.
      Evaluating the conjugated linoleic acid and trans 18:1 isomers in milk fat of dairy cows fed increasing amounts of sunflower oil and a constant level of fish oil.
      ).
      • Ney D.M.
      Potential for enhancing the nutritional properties of milk fat.
      indicated that the decrease in MCFA is an improvement in the profile of milk fatty acids, because they have been reported to constitute the hypercholesterolemic portion of milk fat. Milk fat C16:0 is derived either from the diet or can be de novo synthesized in the mammary gland (
      • Grummer R.R.
      Etiology of lipid-related metabolic disorders in periparturient dairy cows.
      ). The decrease in milk fat concentration of C16:0 in cows fed the CG diets compared with the control diet indicates a decrease in de novo synthesis of C16:0 in the mammary gland.
      Concentrations of glucose in blood were not affected by feeding increasing concentrations of CG, which averaged 68.8 mg/dL.
      • Grummer R.R.
      • Carroll D.J.
      Effects of dietary fat on metabolic disorders and reproductive performance of dairy cattle.
      indicated that fat supplementation might spare glucose, but it will not necessarily increase blood glucose concentration; however, spared glucose could be utilized for lactose synthesis and milk production. Feeding supplemental dietary fat is typically associated with an increase in NEFA and cholesterol concentration in plasma of dairy cows (
      • Grummer R.R.
      • Carroll D.J.
      Effects of dietary fat on metabolic disorders and reproductive performance of dairy cattle.
      ;
      • Chilliard Y.
      Dietary fat and adipose tissue metabolism in ruminants, pigs, and rodents: A review.
      ;
      • Drackley J.K.
      Biology of dairy cows during the transition period: The final frontier.
      ). Increases in plasma NEFA could be attributed to mobilization of adipose tissue or to a decrease in NEFA clearance by the tissues, or both (
      • Grummer R.R.
      • Carroll D.J.
      Effects of dietary fat on metabolic disorders and reproductive performance of dairy cattle.
      ). An increase in plasma NEFA attributable to mobilization of adipose tissue is more likely to be associated with a negative energy balance; however, in the present study cows were in a neutral or positive energy balance and the plasma NEFA concentrations were linearly increased as the concentration of CG increased in the diets. Therefore, this increase in plasma NEFA is more likely to be a result of inefficient uptake of fatty acids by peripheral tissue as has been proposed by
      • Grummer R.R.
      Etiology of lipid-related metabolic disorders in periparturient dairy cows.
      .
      Plasma BHBA was not affected by feeding increasing concentrations of CG. Feeding supplemental fat in dairy cow diets has been reported to have minimal or no effect on plasma BHBA concentrations (
      • Grummer R.R.
      • Carroll D.J.
      Effects of dietary fat on metabolic disorders and reproductive performance of dairy cattle.
      ). The effect of added CG on plasma cholesterol concentration tended (P = 0.07) to be linear and agreed with previous studies that reported a positive relationship between serum cholesterol concentration and dietary fat (
      • Palmquist D.L.
      • Conrad H.R.
      High fat rations for dairy cows: Effects on feed intake, milk and fat production, and plasma metabolites.
      ;
      • Drackley J.K.
      • Klusmeyer T.H.
      • Trusk A.M.
      • Clark J.H.
      Infusion of long-chain fatty acids varying in saturation and chain length into the abomasum of lactating dairy cows.
      ). Previous findings by
      • Khorasani G.R.
      • de Boer G.
      • Robinson P.H.
      • Kennelly J.J.
      Effect of canola fat on ruminal and total tract digestion, plasma hormones, and metabolites in lactating dairy cows.
      and
      • Khorasani G.R.
      • Kennelly J.J.
      Effect of added dietary fat on performance, rumen characteristics, and plasma metabolites of midlactation dairy cows.
      demonstrated a quadratic response in cholesterol concentration when canola seed was fed at increasing concentrations of the diet DM.
      • Nestel P.J.
      • Poyser A.
      • Hood R.L.
      • Mills S.C.
      • Willis M.R.
      • Cook L.J.
      • Scott T.W.
      The effect of dietary fat supplements on cholesterol metabolism in ruminants.
      proposed that increasing dietary fat concentration may stimulate intestinal cholesterol synthesis to meet the demands for fat transport and absorption.

      Conclusions

      Results from the current study indicate the potential for CG to be included in dairy cow diets up to 14% of dietary DM with no adverse effect on DMI, milk yield, and milk composition. Cows fed 7 and 14% CG had numerically greater DMI and milk yield compared with those fed 21% CG. Feeding CG at 21% or greater concentration of dietary DM could negatively affect DMI, milk yield, and milk fat concentration. Inclusion of CG in dairy cow diets increased milk fat concentrations of MUFA and PUFA in milk fat and the concentration of cis-9, trans-11 CLA. Overall, CG provides an alternative source of fat for energy in lactating dairy cows when fed up to 14% of dietary DM.

      Acknowledgment

      The authors express their gratitude to the farm crew at the South Dakota State University Dairy Research and Training Facility and to Poet LLC (Sioux Falls, SD) for supplying corn germ. This research was partially supported by the United States Department of Energy.

      Supplementary data

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