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Crushed sunflower, flax, or canola seeds in lactating dairy cow diets: Effects on methane production, rumen fermentation, and milk production

      Abstract

      The objective of this study was to investigate the potential of reducing enteric methane production from dairy cows by incorporating into the diet various sources of long-chain FA varying in their degree of saturation and ruminal availability. The experiment was conducted as a crossover design with 16 lactating dairy cows maintained in 2 groups and fed 4 dietary treatments in four 28-d periods. Eight ruminally cannulated primiparous cows (96 ± 18 d in milk) were assigned to group 1 and 8 multiparous cows (130 ± 31 d in milk) were assigned to group 2. The dietary treatments were: 1) a commercial source of calcium salts of long-chain fatty acids (CTL), 2) crushed sunflower seeds (SS), 3) crushed flaxseed (FS), and 4) crushed canola seed (CS). The oilseeds added 3.1 to 4.2% fat to the diet (DM basis). All 3 oilseed treatments decreased methane production (g/d) by an average of 13%. When corrected for differences in dry matter intake (DMI), compared with CTL, methane production (g/kg of DM intake) was decreased by feeding FS (−18%) or CS (−16%) and was only numerically decreased (−10%) by feeding SS. However, compared with the CTL, feeding SS or FS lowered digestible DMI by 16 and 9%, respectively, because of lowered digestibility. Thus, only CS lowered methane per unit of digestible DM intake. Feeding SS and CS decreased rumen protozoal counts, but there were no treatment effects on mean ruminal pH or total volatile fatty acid concentration. Milk efficiency (3.5% fat corrected milk/DMI), milk yield, and component yield and concentrations were not affected by oilseed treatments. The study shows that adding sources of long-chain fatty acids to the diet in the form of processed oilseeds can be an effective means of reducing methane emissions. However, for some oilseeds such as SS or FS, the reduction in methane can be at the expense of diet digestibility. The use of crushed CS offers a means of mitigating methane without negatively affecting diet digestibility, and hence, milk production.

      Key words

      Introduction

      Methane produced by ruminants contributes to enhanced greenhouse gas effect and global warming (

      International Panel on Climate Change (IPCC). 2006. Revised IPCC Guidelines for National Greenhouse Gas Inventories. Workbook (Vol. 2), Module 4, Agriculture. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol4.htm Accessed Nov. 12, 2008.

      ). Consequently, strategies to mitigate enteric CH4 emissions are currently being explored by several research groups worldwide, as recently reviewed by
      • Beauchemin K.A.
      • Kreuzer M.
      • O’Mara F.
      • McAllister T.A.
      Nutritional management for enteric methane abatement: Aa review.
      and
      • McAllister T.A.
      • Newbold C.J.
      Redirecting rumen fermentation to reduce methanogenesis.
      . Enteric CH4 produced during fermentation in the rumen represents an energy loss to the animal; about 2 to 12% of gross energy intake (GEI) is converted to CH4, depending on the level of feed intake and the composition of the diet (
      • Johnson K.A.
      • Johnson D.E.
      Methane emissions from cattle.
      ).
      Supplementation of diets with lipids that are not protected from ruminal digestion is one strategy recognized to lower enteric CH4 emissions (
      • Boadi D.
      • Benchaar C.
      • Chiquette J.
      • Massé D.
      Mitigation strategies to reduce enteric methane emissions from dairy cows: Update review.
      ;
      • Monteny G.-J.
      • Bannink A.
      • Chadwick D.
      Greenhouse gas abatement strategies for animal husbandry.
      ). Added fats decrease CH4 emissions by lowering the quantity of OM fermented in the rumen, the activity of ruminal methanogens, and protozoal numbers, and for lipids rich in unsaturated fatty acids (FA), through biohydrogenation of FA (
      • Johnson K.A.
      • Johnson D.E.
      Methane emissions from cattle.
      ). However, there appears to be considerable variation in the effects of supplemental fats on CH4 production and only a limited number of studies have been conducted using dairy cows (as summarized by
      • Giger-Reverdin S.
      • Morand-Fehr P.
      • Tran G.
      Literature survey of the influence of dietary fat composition on methane production in dairy cattle.
      and
      • Eugène M.
      • Massé D.
      • Chiquette J.
      • Benchaar C.
      Metaanalysis on the effects of lipid supplementation on methane production in lactating dairy cows.
      ). Reductions in CH4 (g/kg of DMI) have been substantial in some cases: 26% reduction for extruded flaxseed (FS;
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      ; 5.7% fat added to the dietary DM), 49% reduction for FS oil (
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      ; 5.7% added fat), and a 27% reduction for a mixture of sunflower and fish oil (
      • Woodward S.L.
      • Waghorn G.C.
      • Thomson N.A.
      Supplementing dairy cows with oils to improve performance and reduce methane—Does it work?.
      ; 3.8% added fat). However, other dairy studies have shown no effects (
      • Johnson K.A.
      • Kincaid R.L.
      • Westberg H.H.
      • Gaskins C.T.
      • Lamb B.K.
      • Cronrath J.D.
      The effect of oilseeds in diets of lactating cows on milk production and methane emissions.
      ; 5.6% added fat from canola seeds and whole cottonseed;
      • Woodward S.L.
      • Waghorn G.C.
      • Thomson N.A.
      Supplementing dairy cows with oils to improve performance and reduce methane—Does it work?.
      ; 2% added fat from a mixture of FS oil and fish oil).
      The CH4-suppressing effects of supplemental fats may depend upon several factors, including the amount added and the resulting total concentration of fat in the diet, the FA profile of the fat source, the form in which the fat is administered (i.e., either as refined oil or as full-fat oilseeds), and the composition of the diet (high forage vs. high grain). In some cases, added fats lower the intake of ruminally fermented OM by decreasing DMI, diet digestibility, or both (
      NRC
      Nutrient Requirements of Dairy Cattle.
      ) accounting for some of the CH4 suppression. For example, in the study by
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      the reduction in CH4 caused by feeding extruded FS or FS oil was accompanied by a 14% reduction in total tract NDF digestibility, and feeding extruded FS reduced DMI by 16% and feeding FS oil reduced DMI by 26%. Reduction in CH4 production accompanied by lowered digestible DMI may result in lower milk production.
      The potential for implementing lipid feeding on commercial dairy farms as a CH4 mitigation strategy is high, because lipid sources are already often added to the diet to increase its energy density (
      NRC
      Nutrient Requirements of Dairy Cattle.
      ). Furthermore, feeding fats high in polyunsaturated FA can alter the FA composition of milk (
      • Bu D.P.
      • Wang J.Q.
      • Dhiman T.R.
      • Liu S.J.
      Effectiveness of oils rich in linoleic and linolenic acids to enhance conjugated linoleic acid in milk from dairy cows.
      ) in a manner beneficial to human health, including increased proportions of monounsaturated FA and polyunsaturated FA and increased concentrations of the conjugated linoleic acid isomer cis-9, trans-11 (
      • Hu F.B.
      • Willett W.C.
      Optimal diets for prevention of coronary heart disease.
      ). However, dairy producers are unlikely to feed supplemental fats to mitigate CH4 until a variety of fat sources are shown to be effective CH4 suppressants in a range of situations, and until effects on milk yield and composition are well established. Hence, the objective of this study was to investigate the effect of supplementing a dairy cow diet with sources of long-chain FA varying in their degree of saturation and ruminal availability [including sunflower seeds (SS), FS, and canola seed (CS)] on enteric CH4 emissions and milk production of lactating dairy cows.

      Materials and Methods

      The experiment was conducted at Agriculture and Agri-Food Canada's Research Centre in Lethbridge, Alberta, Canada. The cows were cared for in accordance with the guidelines of the
      Canadian Council on Animal Care
      .

      Animals, Experimental Design, and Diets

      The experiment was conducted as a crossover design with 16 lactating dairy cows maintained in 2 groups and fed 4 dietary treatments in four 28-d periods. Eight primiparous cows (570 ± 38.4 kg of BW; 96 ± 18 DIM) that were previously ruminally cannulated (Bar Diamond, Parma, ID) were assigned to group 1 and 8 intact multiparous cows (643 ± 52 kg of BW; 130 ± 31 DIM) were assigned to group 2. Rumen fermentation variables were measured only in group 1 cows. The groups were staggered by 2 wk to simplify measurements.
      The dietary treatments were: 1) calcium salts of long-chain FA (Enertia, ADM Alliance Nutrition, Quincy, IL; control, CTL), 2) SS, 3) FS, and 4) CS. The oilseeds were added to the diet to provide a theoretical level of 3.3% added fat (DM basis), based on an initial analysis of a sample of each fat source. The oilseeds were crushed using a roller mill with the roller setting adjusted to ensure the hulls were cracked. The calcium salts of long-chain FA was used as the control because it was assumed to be rumen-inert and would, therefore, have no effect on rumen fermentation or CH4 production.
      The diets were formulated using the Cornell-Penn-Miner System (CPMDairy, Version 3.0.4a; Cornell University, Ithaca, NY; University of Pennsylvania, Kennett Square, PA; and William H. Miner Agricultural Research Institute, Chazy, NY) to provide adequate ME and MP for a 650-kg cow producing 35 kg of milk/d containing 3.5% fat and 3.2% protein. All diets contained steam-rolled barley, a pelleted supplement, and barley silage as the forage source (Table 1). The diets were gradually (25% on d 1, 50% on d 2, 75% on d 3) introduced to cows at the start of each period.
      Table 1Ingredient composition of the diets (DM basis)
      Ingredients, %ControlSunflowerFlaxCanola
      Barley silage45.045.045.045.0
      Barley grain, steam-rolled32.5032.5032.6232.62
      Sunflower seeds, crushed010.5500
      Flaxseed, crushed009.320
      Canola seed, crushed0009.32
      Pelleted supplement
       Beet pulp4.65000
       Barley grain, ground3.231.243.223.22
       Ca salts of long-chain fatty acids
      Enertia, ADM Alliance Nutrition (Quincy, IL).
      3.95000
       Canola meal, high RUP
      Alberta Gold, Cambra Foods Ltd. (Lethbridge, AB, Canada).
      3.022.882.522.52
       Soybean meal, high RUP
      Soy Pass, Borregaard LignoTech (Rothschild, WI).
      3.092.602.562.56
       Corn gluten meal3.002.602.522.52
       Dicalcium phosphorus0.160.0900
       Urea0.560.560.210.21
       Calcium carbonate01.141.191.19
       Na bicarbonate0.420.420.420.42
       NaCl0.250.250.250.25
       Vitamin-mineral mix
      Added to supply per kilogram of dietary DM: 150mg of S, 120mg of K, 70mg of Mg, 30mg of Mn, 30mg of Zn, 8.5mg of Cu, 0.12mg of Co, 0.2mg of Se, 8,400 IU of vitamin A, 840 IU of vitamin D, and 8 IU of vitamin E.
      0.170.170.170.17
      1 Enertia, ADM Alliance Nutrition (Quincy, IL).
      2 Alberta Gold, Cambra Foods Ltd. (Lethbridge, AB, Canada).
      3 Soy Pass, Borregaard LignoTech (Rothschild, WI).
      4 Added to supply per kilogram of dietary DM: 150 mg of S, 120 mg of K, 70 mg of Mg, 30 mg of Mn, 30 mg of Zn, 8.5 mg of Cu, 0.12 mg of Co, 0.2 mg of Se, 8,400 IU of vitamin A, 840 IU of vitamin D, and 8 IU of vitamin E.

      Feeding and Management

      The cows had continuous access to water and each TMR was provided for ad libitum intake with at least 10% of daily feed refusal (as-fed basis). Cows were individually fed 3 times daily at 0600, 1200, and 1730 h with approximately 10, 50, and 40% of the total daily feed allocation provided at each feeding, respectively. The forage and concentrates were sampled weekly to determine DM content and the diets were adjusted to account for changes in DM content. Feed offered and refused were measured and recorded daily, and DM content of the TMR and the orts for individual cows was determined weekly to calculate DMI. These samples were then dried at 55°C, ground to pass a 1-mm screen (standard model 4; Arthur H. Thomas Co., Philadelphia, PA), and stored for subsequent analyses.
      The cows were housed in individual tie stalls fitted with rubber mattresses, bedded with wood shavings, and milked twice daily at 0630 and 1630 h. They were turned outside to a drylot for exercise for at least 1 h daily. Cows were weighed at the start of the experiment and at the end of each period at 1130 h. Milk production was recorded daily throughout the experiment. Milk was sampled during the a.m. and p.m. milking on 3 consecutive days (d 18–20) in each period. Milk samples were preserved with potassium dichromate, stored at 4°C, and then sent to CanWest DHI (Central Milk Testing Laboratory, Edmonton, Alberta, Canada) for analyses of fat, CP, and lactose (
      AOAC
      Official Methods of Analysis.
      ) using infrared spectroscopy (MilkoScan 605; Foss Electric, Hillerød, Denmark). Milk composition was corrected for differences in milk volume between a.m. and p.m. milkings.

      Digestibility

      Fecal samples (100 g of wet weight) were obtained twice daily from the rectum of each of the 16 cows on the last 5 d of the period. The samples were pooled for each cow within period and dried at 55°C for 48 h in a forced-draft oven, ground through a 1-mm screen, and analyzed for DM and OM. Samples of the TMR and orts (pooled by cow) were also taken on the same days, dried, and analyzed for DM and OM. Apparent total tract digestibility of DM and OM was determined using indigestible NDF as an internal marker (
      • Cochran R.C.
      • Adams D.C.
      • Wallace J.D.
      • Galyean M.L.
      Predicting digestibility of different diets with internal markers: Evaluation of four potential markers.
      ). Indigestible NDF content of the TMR, orts, and feces was determined as the NDF residue after 120-h incubation in buffered rumen fluid (DAISYII Incubator, Ankom Technology, Macedon, NY).

      Methane Production

      At the start of the last week of each period, each group of 8 cows (the 2 groups were staggered) was moved to 4 environmental chambers (2 animals/chamber) for measurement of enteric CH4. The cows had been conditioned to the chambers before beginning the experiment. The 2 cows fed the same diet were housed together within a chamber and this pairing was maintained throughout the experiment. Within the chambers, the cows were housed in 2 individual stanchions equipped with feeders. Methane was measured for 3 consecutive days beginning 12 h after the cows were put into the chambers.
      A small positive pressure (<2 Pa) inside the chamber prevented leakage into the chambers, and the air volume within the chamber was exchanged every 5 min. Flow rates of air in the intake and exhaust ducts were recorded and CH4 concentrations in these ducts were monitored as described by
      • Beauchemin K.A.
      • McGinn S.M.
      • Petit H.V.
      Methane abatement strategies for cattle: Lipid supplementation of diets.
      . The difference between the incoming and outgoing mass of CH4 was used to calculate the amount of CH4 generated in each chamber by the 2 cows. The chamber doors were opened twice daily for about 30 min to allow for feeding, cleaning, and milking. When the doors were opened, the corresponding CH4 emissions were omitted. Once the door was closed, the conditions within the chamber stabilized within 5 min. These daily interruptions were accounted for by calculating a mean CH4 emission for the day based on 10-min averages recorded only when the door was closed and the conditions within the chamber stabilized. The chambers were calibrated at the start of each period by releasing a known quantity of CH4 gas, and procedures were adjusted accordingly to obtain 100% recovery.

      Ruminal Fermentation and Protozoa

      Ruminal contents were sampled from group 1 cows on d 19 and 21 of each period. Samples were taken at 0 and 4 h after the morning feeding to measure ruminal fermentation characteristics (pH, NH3-N, and VFA) and protozoal counts (4-h sample only). Approximately 0.5 L of ruminal contents was obtained from multiple sites within the rumen and strained through a PECAP polyester screen (pore size 355 μm; B & S H Thompson, Ville Mont-Royal, Quebec, Canada). The ruminal pH of the filtered ruminal fluid was measured within 5 min using a pH meter (Accumet model 25, Denver Instrument Company, Arvada, CO). Five milliliters of the filtered ruminal fluid was added to 1 mL of 1% sulfuric acid and samples were retained for NH3-N determination. Another 5 mL of the filtered ruminal fluid was added to 1 mL of 25% meta-phosphoric acid and samples were retained for VFA determination. These samples were stored at −20°C until analyzed. In addition, 5 mL of strained ruminal fluid was preserved with 5 mL of methyl green-formalin-saline solution (1:1, vol/vol) and stored in darkness at room temperature for protozoa enumeration.

      Chemical Analyses

      All chemical analyses were performed on each sample in duplicate, and where the coefficient of variation was >5%, the analysis was repeated. Analytical DM was determined by drying the oven-dried samples at 135°C for 2 h, followed by hot weighing (
      AOAC
      Official Methods of Analysis.
      ; method 930.05). The OM content was calculated as the difference between 100 and the percentage ash (
      AOAC
      Official Methods of Analysis.
      ; method 942). Gross energy was determined using an adiabatic calorimeter (model 1241, Parr, Moline, IL). The NDF was determined as described by
      • 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.
      using heat-stable α-amylase (Termamyl 120L, Novo Nordisk Biochem, Franklinton, NC) and sodium sulfite, and ADF was determined according to
      AOAC
      Official Methods of Analysis.
      ; method 973.18). For the measurement of CP (N × 6.25), samples were ground using a ball mill (Mixer Mill MM2000, Retsch, Haan, Germany) to a fine powder and total N was quantified by flash combustion and thermal conductivity detection (Carlo Erba Instruments, Milan, Italy). Lipids were extracted from fat sources and diets using a Soxtec system HT6 apparatus (Tecator, Fisher Scientific, Montreal, QC, Canada) according to
      AOAC
      Official Methods of Analysis.
      , method no. 7.060). Concentration of lipid was determined by combustion of the extracted OM at 550°C overnight in a muffle furnace (
      AOAC
      Official Methods of Analysis.
      ).
      Ruminal VFA were quantified using a gas chromatograph (model 5890, Hewlett-Packard Lab, Palo Alto, CA) with a capillary column (30  m × 0.32 mm i.d., 1-μm phase thickness, Zebron ZB-FAAP, Phenomenex, Torrance, CA), and flame ionization detection. The oven temperature was 170°C held for 4 min, which was then increased by 5°C/min to 185°C, and then by 3°C/min to 220°C, and held at this temperature for 1 min. The injector temperature was 225°C, the detector temperature was 250°C, and the carrier gas was helium. Concentration of NH3-N in the ruminal contents was determined as described by
      • Rhine E.D.
      • Sims G.K.
      • Mulvaney R.L.
      • Pratt E.J.
      Improving the Berthelot reaction for determining ammonium in soil extracts and water.
      . Ruminal protozoa were counted using a Fuchs-Rosenthal counting chamber (Hausser Scientific Partnership, Horsham, PA) as described by
      • Ogimoto K.
      • Imai S.
      Atlas of Rumen Microbiology.
      . Duplicate preparations of each sample were counted, and if either value differed from the average by more than 10%, the counts were repeated.

      Calculations and Statistical Analysis

      Data for intake, milk production, and CH4 for each cow were summarized by day. Data for rumen fermentation were summarized by hour within sampling day, and digestibility and BW data were summarized by period. Data for protozoa were log10 transformed before analysis, with the inverse log10 least squares means reported. Digestible DMI was calculated for each cow using mean DMI and the corresponding digestibility coefficient for each period.
      Analysis of variance was conducted using the Mixed procedure of SAS (
      SAS Institute
      System for Windows Release 9. 1.
      ). Cow served as the experimental unit for all data except CH4 production, for which chamber was the experimental unit. The model for the intake and milk variables included the fixed effects of group, treatment, day, and their interactions, with cow within group and period within group designated as random effects. The effect of day was included as a repeated measure. The data for BW were analyzed using the same model, but without the effect of day. Rumen fermentation data were analyzed using a model that included the fixed effects of treatment, day, hour, and all interactions, and the random effects of cow and period. Day and hour were included as repeated measures. The CH4 data were analyzed using a model that included the fixed effects group, treatment, day, and their interaction, with chamber within group and period within group designated as random variables. The effect of day was included as a repeated measurement. For the repeated measures, various covariance structures were tried, with the final choice depending on low values for the Akaike's information criteria. Degrees of freedom were estimated with the Kenward-Roger specification in the model. Treatment effects were declared significant at P < 0.05, and means were compared using contrasts. Least squares means are reported throughout.

      Results

      The diets were formulated to provide 3.3% added fat based on a preliminary analysis of the fat sources. However, the actual fat content of the samples collected during the experiment indicated that the Ca salts of long-chain FA contained slightly less fat than expected while the oilseeds were higher in fat content than expected. Consequently, the amount of added fat averaged 3.7% of dietary DM, ranging from 3.1% for CTL to 4.2% for SS (Table 2). Total fat content of the diets averaged 6.5% (5.1 to 7.3%) of DM.
      Table 2Chemical composition of the diets and ingredients (DM basis)
      Ingredient
      Analysis performed on one composite sample for the study.
      Diet
      Analysis performed on 4 period samples.
      Ingredients
      FA = fatty acid; GE = gross energy.
      Ca salts of longchain FASunflower seedsFlaxseedCanola seedsControlSunflowerFlaxseedCanola
      OM, %78.396.596.595.393.3 ± 0.0593.7 ± 0.5593.7 ± 0.3293.4 ± 0.12
      GE, Mcal/kg8.226.716.526.634.45 ± 0.0344.52 ± 0.0384.57 ± 0.0454.54 ± 0.066
      CP, %017.226.430.716.8 ± 1.2116.4 ± 1.3616.4 ± 0.5216.9 ± 0.67
      NDF, %24.125.114.128.8 ± 1.7530.6 ± 0.6728.8 ± 0.5729.9 ± 0.68
      ADF, %19.311.312.018.3 ± 1.0619.6 ± 0.6018.4 ± 0.8119.6 ± 0.94
      NFC,
      NFC = 100 − CP − NDF − ether extract − ash.
      %
      22.08.514.842.739.441.639.9
      NEL,
      The NEL (Mcal/kg) was calculated based on energy output divided by DMI, with energy output determined using the NRC (2001) equations that account for maintenance, milk production, and BW changes.
      Mcal/kg (calculated)
      Crude fat, %78.341.839.639.75.0 ± 0.477.3 ± 0.516.9 ± 0.276.7 ± 0.71
      Added fat, % (calculated)3.14.23.73.9
      FA, g/100 g of FA
       C14:01.40.10.10.11.7 ± 0.130.5 ± 0.070.4 ± 0.030.5 ± 0.04
       C16:048.57.05.94.442.9 ± 4.2211.5 ± 0.6910.9 ± 0.4610.4 ± 0.76
       C18:04.04.13.91.83.2 ± 0.313.4 ± 0.283.2 ± 0.091.7 ± 0.04
       C18:1 n-9 cis35.817.916.756.525.8 ± 1.7317.4 ± 0.3816.8 ± 0.6543.5 ± 0.71
       C18:1 n-7 cis1.00.740.84.01.1 ± 0.071.0 ± 0.0911.1 ± 0.013.5 ± 0.04
       C18:2 n-6 cis9.070.119.922.122.7 ± 2.6763.6 ± 0.9829.6 ± 1.0931.6 ± 0.60
       C18:3 n-30.30.152.811.12.6 ± 0.232.6 ± 0.1238.0 ± 1.478.7 ± 0.73
      1 Analysis performed on one composite sample for the study.
      2 Analysis performed on 4 period samples.
      3 FA = fatty acid; GE = gross energy.
      4 NFC = 100 − CP − NDF − ether extract − ash.
      5 The NEL (Mcal/kg) was calculated based on energy output divided by DMI, with energy output determined using the
      NRC
      Nutrient Requirements of Dairy Cattle.
      equations that account for maintenance, milk production, and BW changes.
      Of the various oilseeds fed, only CS resulted in similar intakes of digestible DM compared with the CTL (Table 3). Although feeding SS or CS increased DMI compared with the CTL, feeding SS or FS decreased DM digestibility by 20% and 10%, respectively. The net effect was that digestible DMI was 16% lower for SS and 9% lower for FS than for CTL, whereas it was similar for CS and CTL.
      Table 3Effect of fat source on body weight, intake, and digestibility of lactating dairy cows (n = 16)
      Dietary treatment
      Crushed oilseeds were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL).
      ItemControlSunflowerFlaxCanola SE
      Mean BW, kg61662361961919.4
      BW change, g/d195bc−6.51c270
      Within a row, means that do not have a common superscript differ, P<0.05.
      Within a row, means that do not have a common superscript differ, P<0.05.
      510
      Within a row, means that do not have a common superscript differ, P<0.05.
      168.4
      DMI, kg/d18.7c19.5
      Within a row, means that do not have a common superscript differ, P<0.05.
      Within a row, means that do not have a common superscript differ, P<0.05.
      19.0
      Within a row, means that do not have a common superscript differ, P<0.05.
      Within a row, means that do not have a common superscript differ, P<0.05.
      20.1
      Within a row, means that do not have a common superscript differ, P<0.05.
      0.61
      DM digestibility, %61.3
      Within a row, means that do not have a common superscript differ, P<0.05.
      49.2
      Within a row, means that do not have a common superscript differ, P<0.05.
      55.2
      Within a row, means that do not have a common superscript differ, P<0.05.
      61.6
      Within a row, means that do not have a common superscript differ, P<0.05.
      1.75
      OM digestibility, %63.5
      Within a row, means that do not have a common superscript differ, P<0.05.
      52.0c58.1
      Within a row, means that do not have a common superscript differ, P<0.05.
      64.3
      Within a row, means that do not have a common superscript differ, P<0.05.
      1.67
      Digestible DMI, kg/d11.6
      Within a row, means that do not have a common superscript differ, P<0.05.
      9.8
      Within a row, means that do not have a common superscript differ, P<0.05.
      10.5
      Within a row, means that do not have a common superscript differ, P<0.05.
      12.5
      Within a row, means that do not have a common superscript differ, P<0.05.
      0.47
      a–c Within a row, means that do not have a common superscript differ, P < 0.05.
      1 Crushed oilseeds were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL).
      All 3 oilseed treatments lowered CH4 production (g/d); a 10% decrease occurred for SS and CS and an 18% decrease occurred for FS (Table 4). When corrected for differences in DMI, compared with CTL, CH4 production decreased by feeding FS (−18%) or CS (−16%) and tended to decrease (−10%; P = 0.098) by feeding SS. Methane production expressed as a percentage of GEI was not changed by the addition of SS in the diet, but was 20% lower for FS and 17.5% lower for CS, compared with CTL. However, only CS actually lowered CH4 production when expressed on the basis of digestible DMI, with FS only tending (P = 0.104) to lower CH4 per kilogram of digestible DMI.
      Table 4Effects of fat source on methane emissions from lactating dairy cows (n = 8 pairs of cows)
      Methane emissions and corresponding DMI determined for 3 d during which the animals were in the chambers.
      Dietary treatment
      Crushed oilseeds were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL).
      ItemControlSunflowerFlaxseedCanolaSEM
      DMI, kg/d18.1
      Within a row, means that do not have a common superscript differ, P<0.05.
      18.2
      Within a row, means that do not have a common superscript differ, P<0.05.
      18.0
      Within a row, means that do not have a common superscript differ, P<0.05.
      19.4
      Within a row, means that do not have a common superscript differ, P<0.05.
      0.54
      Methane g/(animal·d)293
      Within a row, means that do not have a common superscript differ, P<0.05.
      264
      Within a row, means that do not have a common superscript differ, P<0.05.
      241
      Within a row, means that do not have a common superscript differ, P<0.05.
      265
      Within a row, means that do not have a common superscript differ, P<0.05.
      19.3
       g/kg of DMI
      Sunflower seed vs. control, P=0.098.
      16.3
      Within a row, means that do not have a common superscript differ, P<0.05.
      14.6
      Within a row, means that do not have a common superscript differ, P<0.05.
      Within a row, means that do not have a common superscript differ, P<0.05.
      13.4
      Within a row, means that do not have a common superscript differ, P<0.05.
      13.7
      Within a row, means that do not have a common superscript differ, P<0.05.
      0.94
       % of GE intake4.9
      Within a row, means that do not have a common superscript differ, P<0.05.
      4.3
      Within a row, means that do not have a common superscript differ, P<0.05.
      Within a row, means that do not have a common superscript differ, P<0.05.
      3.9
      Within a row, means that do not have a common superscript differ, P<0.05.
      4.0
      Within a row, means that do not have a common superscript differ, P<0.05.
      0.30
       g/kg of digestible DMI
      Flaxseed vs. control, P=0.104.
      26.6
      Within a row, means that do not have a common superscript differ, P<0.05.
      29.7
      Within a row, means that do not have a common superscript differ, P<0.05.
      24.2bc22.3
      Within a row, means that do not have a common superscript differ, P<0.05.
      1.79
       g/kg of FCM12.4
      Within a row, means that do not have a common superscript differ, P<0.05.
      11.7
      Within a row, means that do not have a common superscript differ, P<0.05.
      10.5
      Within a row, means that do not have a common superscript differ, P<0.05.
      11.4
      Within a row, means that do not have a common superscript differ, P<0.05.
      1.21
      a–c Within a row, means that do not have a common superscript differ, P < 0.05.
      1 Methane emissions and corresponding DMI determined for 3 d during which the animals were in the chambers.
      2 Crushed oilseeds were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL).
      3 Sunflower seed vs. control, P = 0.098.
      4 Flaxseed vs. control, P = 0.104.
      Means for the rumen fermentation variables are given by hour and treatment because the effects of hour were statistically significant for most of the variables (Table 5). However, there were no hour × treatment interactions for any of the fermentation variables. Feeding SS and CS decreased rumen total protozoal counts, whereas feeding FS only numerically (P = 0.12) decreased counts compared with CTL. For all diets, about 99% of the protozoa were entodiniomorphs. There were no effects of treatment on mean ruminal pH or total VFA concentration and the only individual VFA concentration affected was butyrate, which was lowered for all 3 oilseed treatments. Rumen NH3-N concentration was higher for SS compared with the other treatments, with no differences between CTL, FS, and CS.
      Table 5Effect of fat source on ruminal fermentation characteristics of lactating dairy cows (n = 16)
      Hour
      Hour after feeding.
      Dietary treatment
      Crushed oilseeds were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL).
      Item04SEControlSunflowerFlaxCanolaSE
      Total protozoa, × 105/mL
      Protozoa were only counted in samples taken at 4h after feeding.
      8.28
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      5.16b6.35
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      5.23b0.081
      Mean ruminal pH6.32
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      5.75b0.0636.085.986.036.040.069
      Total VFA, mM mol/100 mol102
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      120b2.81131101091103.2
       Acetate (A)60.7
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      60.2b1.4960.160.161.759.91.64
       Propionate (P)25.2
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      26.7b1.5025.126.725.226.71.72
       Butyrate (B)9.3
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      9.0b0.2710.3
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      8.67b8.70b8.89b0.377
       Valerate1.61
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      1.48b0.0911.571.661.421.530.107
       Isobutyrate1.07
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      0.88b0.0290.941.000.971.000.045
       Isovalerate1.85
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      1.55b0.0551.581.621.831.770.103
       A:P2.55
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      2.44b0.2132.632.392.592.380.246
       (A + B):P2.94
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      2.81b0.2493.092.732.962.730.286
      NH3-N, mg/dL23.7
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      13.1
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      1.3315.7
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      22.9
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      17.6
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      17.5
      Within a row and heading, means that do not have a common superscript differ, P<0.05. No hour × treatment interactions were found for any of the variables listed.
      1.67
      a,b Within a row and heading, means that do not have a common superscript differ, P < 0.05. No hour × treatment interactions were found for any of the variables listed.
      1 Hour after feeding.
      2 Crushed oilseeds were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL).
      3 Protozoa were only counted in samples taken at 4 h after feeding.
      Milk yield, component yield, and milk component concentrations were not affected by oilseed treatments (Table 6). Similarly, milk efficiency (kg of 3.5% FCM/kg of DMI) was not affected by treatment.
      Table 6Effect of fat source on milk production of lactating dairy cows (n = 16)
      Dietary treatment
      Fat sources were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL). There were no differences among means within each row, P<0.05.
      ItemControlSunflower seedsFlaxseedCanola seedsSE
      Yield, kg/d
       Milk26.626.726.827.01.67
       3.5% FCM24.223.323.523.71.38
       Fat0.840.790.810.820.055
       Protein0.870.860.860.880.051
       Lactose1.231.221.211.240.084
      Components, %
       Fat3.243.093.223.160.192
       Protein3.253.293.353.310.069
       Lactose4.554.614.624.580.057
      Milk efficiency, kg of 3.5% FCM/kg of DMI1.351.271.301.260.101
      1 Fat sources were added to the diet to provide 3.7% added fat. For the control diet, Ca salts of long-chain fatty acids were added (Enertia, ADM Alliance Nutrition, Quincy, IL). There were no differences among means within each row, P < 0.05.

      Discussion

      Inventories of enteric CH4 emissions from the livestock sectors are calculated in many countries using the Intergovernmental Panel on Climate Change Tier 2 methodology (

      International Panel on Climate Change (IPCC). 2006. Revised IPCC Guidelines for National Greenhouse Gas Inventories. Workbook (Vol. 2), Module 4, Agriculture. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol4.htm Accessed Nov. 12, 2008.

      ), which calculates CH4 emissions as a percentage of GEI. A default CH4 conversion rate of 6.5 ± 1% is used for dairy cattle. However, CH4 conversion rates for dairy cows fed in North America may be lower than this default value (e.g., 4.7% of GEI;
      • Johnson K.A.
      • Kincaid R.L.
      • Westberg H.H.
      • Gaskins C.T.
      • Lamb B.K.
      • Cronrath J.D.
      The effect of oilseeds in diets of lactating cows on milk production and methane emissions.
      ). Recently,
      • Kebreab E.
      • Johnson K.A.
      • Archibeque S.L.
      • Pape D.
      • Wirth T.
      Model for estimating enteric methane emissions from United States dairy and feedlot cattle.
      used diet-specific mechanistic models to predict CH4 conversion rates for dairy cows fed diets typical of those used in various regions of the United States. They reported an average CH4 conversion rate of 5.63% of GEI, ranging from 3.78 to 7.43%. The mean values for our study (3.87–4.87%) are well within this range.
      Our study examined the potential of reducing enteric CH4 emissions from lactating dairy cows by adding oilseed to the diet that supplied long-chain FA varying in their degree of saturation and ruminal availability. A commercial source of calcium salts of long-chain FA, assumed to be rumen inert, was used in the control diet so that treatment effects were not caused by an increase in the fat content of the diet. It was assumed that the commercial fat source had no effect on methanogenesis relative to a diet without supplemental fat, which may not have been entirely the case.
      • Dohme F.
      • Machmüller A.
      • Wasserfallen A.
      • Kreuzer M.
      Comparative efficiency of various fats rich in medium chain fatty acids to suppress ruminal methanogenesis as measured with RUSITEC.
      used a rumen simulation technique and showed that compared with no added fat, adding 8.1% of the dietary DM as calcium salts of long-chain FA lowered CH4 emissions by 5.4%, because of a decrease in OM fermented in the rumen. Although the diet was supplemented with a lower concentration of fat in our study, it is possible that the CH4-suppressing effects of the oilseeds would have been greater had a control diet without added fat been used.
      All 3 oilseeds were processed before feeding to maximize rumen availability. Sunflower seeds, FS, and CS were chosen because they are readily available to dairy producers in western Canada and they range in FA profiles. The CS were high in C18:1 (60% of total FA), the SS were high in C18:2 (70%), and the FS were high in C18:3 (53%; Table 2). In contrast, the rumen inert fat was high in C16:0 (48.5%) and C18:1 (36%). The fat sources were added to the diet to supply 3.3% fat. This level of added fat was chosen to maximize CH4 abatement, while minimizing potentially detrimental effects on feed digestibility or intake (
      NRC
      Nutrient Requirements of Dairy Cattle.
      ). However, the actual amount of fat (3.7%) added to the diets was higher than expected, because the Ca salts of long-chain FA contained slightly less fat, and the oilseeds contained slightly more fat, than was expected. Nevertheless, the level of fat in the CTL, FS, and CS diets were within the
      NRC
      Nutrient Requirements of Dairy Cattle.
      recommendation for dairy diets, that is, an upper limit of 3 to 4% added fat and 6 to 7% total fat in the dietary DM. The SS diet slightly exceeded this recommendation at 4.2% added fat and 7.3% total fat.
      Compared with the CTL diet, feeding oilseeds reduced enteric CH4 emissions (g/d) by an average of 13%, with no differences among oilseeds. Because CH4 production is proportional to DMI (
      • Giger-Reverdin S.
      • Morand-Fehr P.
      • Tran G.
      Literature survey of the influence of dietary fat composition on methane production in dairy cattle.
      ;
      • Grainger C.
      • Clarke T.
      • McGinn S.M.
      • Auldist M.J.
      • Beauchemin K.A.
      • Hannah M.C.
      • Waghorn G.C.
      • Clark H.
      • Eckard R.J.
      Methane emissions from dairy cows measured using the sulfur hexafluoride (SF6) tracer and chamber techniques.
      ), emissions are often expressed on the basis of intake. Accounting for differences in intake revealed that SS were less effective suppressants of CH4 production than the other oilseeds; SS tended to reduce (P = 0.098) CH4 (g/kg of DMI) by 10% compared with the CTL, whereas FS and CS reduced CH4 (g/kg of DMI) by 16 to 18%.
      Our study shows that all 3 oilseeds reduced CH4 production when added to a diet to supply a similar concentration of added fat; however SS were less effective than FS and CS. The reduced effectiveness of SS for reducing CH4 production was unexpected. It has been suggested that the effectiveness of FA sources in lowering CH4 (g/kg of DMI) is inversely proportional to degree of saturation of the FA (
      • Giger-Reverdin S.
      • Morand-Fehr P.
      • Tran G.
      Literature survey of the influence of dietary fat composition on methane production in dairy cattle.
      ). If so, CS, not SS, should have been least effective. In a previous study with beef cattle, SS, sunflower oil, and tallow were equally effective in reducing CH4 (g/kg of DMI;
      • Beauchemin K.A.
      • McGinn S.M.
      • Petit H.V.
      Methane abatement strategies for cattle: Lipid supplementation of diets.
      ), indicating that the FA profile of fats may have little effect on CH4 emissions, whereas form of the fat and its rumen availability are likely highly important (
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      ).
      • Johnson K.A.
      • Johnson D.E.
      Methane emissions from cattle.
      suggested that although biohydrogenation of FA in the rumen competes with methanogenesis for hydrogen, differences in intake of saturated and unsaturated FA by the cows fed supplemental fats would likely be too small to detect differences in CH4 production caused by biohydrogenation of FA. In agreement with
      • Johnson K.A.
      • Johnson D.E.
      Methane emissions from cattle.
      ,
      • Woodward S.L.
      • Waghorn G.C.
      • Thomson N.A.
      Supplementing dairy cows with oils to improve performance and reduce methane—Does it work?.
      did a stoichiometric calculation showing that the biohydrogenation of flaxseed oil would only reduce enteric CH4 by about 13 g/d (or about 5% of the CH4 emissions).
      In reviewing the literature where sources of long-chain FA have been used for CH4 abatement, it is clear the responses have been variable. When dairy cows that were fed a restricted level of DMI were offered an additional 2.7 kg of whole cottonseed/d (adding 3.3% fat to the dietary DM), CH4 emissions (g/kg of DMI) were reduced by 26% (
      • Grainger C.
      • Clarke T.
      • Beauchemin K.A.
      • McGinn S.M.
      • Eckard R.J.
      Supplementation with whole cottonseed reduces methane emissions and increases milk production of dairy cows offered a forage and cereal grain diet.
      ).
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      fed various forms of FS (5.7% added fat) to dairy cow diets and reported a 10% reduction in CH4 (g/kg of DMI) for unprocessed seeds, a 26% reduction for extruded seeds, and a 49% reduction for crude oil.
      • Woodward S.L.
      • Waghorn G.C.
      • Thomson N.A.
      Supplementing dairy cows with oils to improve performance and reduce methane—Does it work?.
      fed 3.75% of DMI as a mixture of sunflower and fish oil and observed a 27% reduction in CH4 (g/kg of DMI) with no effects on DMI or milk yield.
      • McGinn S.M.
      • Beauchemin K.A.
      • Coates T.
      • Colombatto D.
      Methane emissions from beef cattle: Effects of monensin, sunflower oil, enzymes, yeast, and furmaric acid.
      added 5% sunflower oil to a forage-based diet fed to beef cattle and reduced CH4 (g/kg of DMI) by 17%.
      • Beauchemin K.A.
      • McGinn S.M.
      • Petit H.V.
      Methane abatement strategies for cattle: Lipid supplementation of diets.
      added tallow, sunflower oil, and whole sunflower seeds (3.4% added fat) to a forage-based diet fed to beef cattle and observed a 15% reduction in CH4 (g/kg of DMI) and a reduction in CH4/digestible DMI ranging from 9.9 (tallow) to 18.8% (SS).
      However, other studies have shown no effects of added fat on CH4 production.
      • Johnson K.A.
      • Kincaid R.L.
      • Westberg H.H.
      • Gaskins C.T.
      • Lamb B.K.
      • Cronrath J.D.
      The effect of oilseeds in diets of lactating cows on milk production and methane emissions.
      added up to 5.6% fat from a mixture of CS and whole cottonseed to the diet of dairy cows and observed no reduction in CH4 when measured every 3 mo over an entire lactation.
      • Woodward S.L.
      • Waghorn G.C.
      • Thomson N.A.
      Supplementing dairy cows with oils to improve performance and reduce methane—Does it work?.
      fed dairy cows on pasture a mixture of flaxseed oil and fish oil (added at 2% of DMI), and observed no effect on CH4 when measured after 3 mo of feeding. The reason for the lack of CH4 response to supplemental fats in some studies is not clear, but it is possible that there is an adaptation of the rumen methanogens over time. It is not clear whether the effects of added fat on CH4 suppression are maintained over the long term, as many of the studies have been short term.
      The reductions in CH4 (g/kg of DMI) per unit of added fat observed in our study (2.5% for SS, 4.9% for FS, and 4.1% for CS) are lower than the results of a meta-analysis conducted by
      • Beauchemin K.A.
      • Kreuzer M.
      • O’Mara F.
      • McAllister T.A.
      Nutritional management for enteric methane abatement: Aa review.
      , in which CH4 was reduced in ruminants by 5.6% with each percentage unit addition of supplemental fat. That study included a broad range of experimental conditions including different fat sources, levels of added fat, animal species, level of intake, and diet composition. However, almost all of the studies compared the effects of the added fat sources to a control diet without added fat rather than a control diet with added inert fat, as was used in the present study. Furthermore, only 4 of the 17 studies used dairy cows (
      • Johnson K.A.
      • Kincaid R.L.
      • Westberg H.H.
      • Gaskins C.T.
      • Lamb B.K.
      • Cronrath J.D.
      The effect of oilseeds in diets of lactating cows on milk production and methane emissions.
      ; 2 studies from
      • Woodward S.L.
      • Waghorn G.C.
      • Thomson N.A.
      Supplementing dairy cows with oils to improve performance and reduce methane—Does it work?.
      ;
      • Grainger C.
      • Clarke T.
      • Beauchemin K.A.
      • McGinn S.M.
      • Eckard R.J.
      Supplementation with whole cottonseed reduces methane emissions and increases milk production of dairy cows offered a forage and cereal grain diet.
      ) and highly effective medium-chain fatty acid sources such as coconut oil (
      • Machmüller A.
      • Kreuzer M.
      Methane suppression by coconut oil and associated effects on nutrient and energy balance in sheep.
      ) and pure myristic acid (
      • Machmüller A.
      • Soliva C.R.
      • Kreuzer M.
      Methanesuppressing effect of myristic acid in sheep as affected by dietary calcium and forage proportion.
      ) were included in the data set. In an analysis of data from 7 dairy cow studies,
      • Giger-Reverdin S.
      • Morand-Fehr P.
      • Tran G.
      Literature survey of the influence of dietary fat composition on methane production in dairy cattle.
      reported that CH4 (g/kg of DMI) was reduced by 2.3% with each 1% addition of fat. In another analysis of dairy cow data,
      • Eugène M.
      • Massé D.
      • Chiquette J.
      • Benchaar C.
      Metaanalysis on the effects of lipid supplementation on methane production in lactating dairy cows.
      reported a 2.3% decrease in CH4 (g/d) per 1% addition of fat, but no decrease in CH4 when expressed on the basis of intake (g/kg of DMI) indicating that the CH4 suppression in those studies was caused by lower intakes of cows fed diets with added fat.
      Examination of the literature clearly indicates that supplemental fats can reduce CH4 emissions, but in many cases the CH4 suppressing effects are caused by a decrease in DMI (
      • Eugène M.
      • Massé D.
      • Chiquette J.
      • Benchaar C.
      Metaanalysis on the effects of lipid supplementation on methane production in lactating dairy cows.
      ), a decrease in ration digestibility (
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      ), or both (
      • Hess B.W.
      • Moss G.E.
      • Rule D.C.
      A decade of developments in the area of fat supplementation research with beef cattle and sheep.
      ;
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      ). In our study, emissions were expressed on the basis of digestible DMI (g/kg of digestible DMI) to account for this possibility. The analysis revealed that the effect of SS on lowering emissions was entirely caused by a reduction in digestible DMI; for FS, CH4 suppression was partially caused by a decrease in digestible DMI. In contrast, none of the CH4 suppression observed with CS was attributed to effects on digestibility or intake. The extent of the decrease in diet digestibility with added SS was somewhat unexpected. Previously we fed (8.9% of DMI) SS to beef cattle receiving a forage based diet and observed slightly reduced DM digestibility, but CH4 per unit of digestible DMI was still less than the control (
      • Beauchemin K.A.
      • McGinn S.M.
      • Petit H.V.
      Methane abatement strategies for cattle: Lipid supplementation of diets.
      ). Furthermore,
      • Finn A.M.
      • Clark A.K.
      • Drackley J.K.
      • Schingoethe D.J.
      • Sahlu T.
      Whole rolled sunflower seeds with or without additional limestone in lactating dairy cattle rations.
      reported no effects on digestibility when dairy cows were fed rolled SS (9.7% of DMI).
      Feeding FS also reduced DM digestibility, but the reduction in CH4 production was not solely caused by reduced digestibility. A similar effect for FS was reported by
      • Martin C.
      • Rouel J.
      • Jouany J.P.
      • Doreau M.
      • Chilliard Y.
      Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil.
      ; feeding extruded FS decreased DM digestibility, but CH4 per unit of digestible OM was still reduced by 22%. In our study, CS had the advantage of lowering CH4 production (g/d, g/kg of DMI) without lowering DMI or digestibility.
      Lower protozoal counts when feeding oilseeds have been reported previously when feeding unsaturated FA (
      • Ivan M.
      • Mir P.S.
      • Mir Z.
      • Entz T.
      • He M.L.
      • McAllister T.A.
      Effects of dietary sunflower seeds on rumen protozoa and growth of lambs.
      ). Rumen methanogens exist on the surface of ciliate protozoa and account for between 9 and 37% of enteric CH4 production (
      • McAllister T.A.
      • Newbold C.J.
      Redirecting rumen fermentation to reduce methanogenesis.
      ). Complete elimination of ciliate protozoa from the rumen reduces methane emission by 30 to 45% (
      • Jouany J.P.
      • Zainab B.
      • Senaud J.
      • Groliere C.A.
      • Grain J.
      • Trivend P.
      Role of the rumen ciliate protozoa Polyplastron multivesiculatum. Entodinium spp. and Isotricha prostoma in the digestion of a mixed diet in sheep.
      ;
      • Itabashi H.
      • Kobayashi T.
      • Matsumoto M.
      The effects of rumen ciliate protozoa on energy metabolism and some constituents in rumen fluid and blood plasma of goats.
      ;
      • Ushida K.
      • Miyazaki A.
      • Kawashima R.
      Effect of defaunation on ruminal gas and VFA production in vitro.
      ). If the effect is assumed to be linear, the 37 to 38% reduction in protozoal numbers that occurred for CS and SS would be expected to account for an 11 to 17% reduction in methane, or almost the entire observed reduction in methane. While these calculations likely overestimate the effect of reduced protozoal numbers, it can be concluded that the observed reduction in protozoal numbers likely accounted for a substantial portion of the methane reduction that occurred, particularly for the CS treatment where reduced digestibility was not a factor.
      Ruminal NH3-N concentrations were expected to decrease with the reduction in protozoal numbers caused by oilseed supplementation, but that did not occur. Eliminating protozoa causes greater uptake of NH3-N caused by less intraruminal recycling of N and increased microbial protein synthesis (
      • Oldick B.S.
      • Firkins J.L.
      Effects of degree of fat saturation on fiber digestion and microbial protein synthesis when diets are fed twelve times daily.
      ). The lack of reduction in rumen NH3-N despite lower protozoal numbers that occurred in this study may have reflected the different protein sources used in the various diets to ensure similar RUP (35–38%) and RDP levels. It is also possible that the higher rumen NH3-N concentration of the SS diet was caused by a lower ruminal digestible OM and associated lower bacterial uptake of NH3-N caused by lower microbial protein synthesis.
      Yield of milk and its components were not affected by feeding oilseeds, probably because the cows were in midlactation and all diets were formulated to exceed energy and protein requirements of the cows. Future studies are needed to examine the potential effect of feeding oilseeds to reduce CH4 production on cow productivity. In our study, the calculated NEL values (Table 2) were lower for the SS diet, mainly because of slightly lower milk energy output and the lack of BW gain of these cows compared with cows fed the other diets. The lower calculated NEL value corresponded to the lower digestibility of this diet.

      Conclusions

      Adding crushed oilseeds to the diet of lactating dairy cows (supplying 3.7% added fat) reduced daily CH4 production (g/d) by 13% compared with a control diet containing calcium salts of palm FA, with no differences among the types of oilseeds. However, the reduction in CH4 for SS and FS was either entirely (SS) or partially (FS) caused by a reduction in digestible DMI. In contrast, CS lowered CH4 without reducing digestible energy intake of the cows. Although milk production and milk efficiency were not affected by oilseed addition in this study, reduced digestible energy intake such as that which occurred when feeding FS and SS would be expected to lower milk production of high-producing dairy cows.
      The study shows that adding oilseeds to the diet can be an effective means of reducing CH4 emissions. However, for some oilseeds the reduction in CH4 can be at the expense of diet digestibility with possible negative effects on milk production of high-producing dairy cows. Thus, the effects on milk production need to be evaluated in a wider context using cows in early lactation. Use of crushed CS offers a means of mitigating CH4 without negatively affecting diet digestibility and hence milk production, but this finding needs to be confirmed in subsequent studies. Although the results from this study supply evidence that CH4 emissions from the dairy sector can be reduced by adding oilseeds to the diet, the acceptance of adding FS and SS to diets by producers may not be as high as that for CS given the possible negative effect of FS and SS on milk production.

      Acknowledgments

      We thank K. Andrews, T. Coates, B. Farr, and D. Vedres (all of Agriculture and Agri-Food Canada) for their invaluable technical assistance in conducting the experiment; T. Entz (Agriculture and Agri-Food Canada) for advice with the statistical analysis; the Lethbridge Research Centre farm staff for caring for the cows; and J.-S. Eun (currently at Utah State University) for a preliminary analysis of the data.

      Supplementary data

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