Manipulation of ruminal fermentation to alter milk fatty acid composition in dairy cows

Abstract

The objective of this study was to determine the effects of method of barley grain processing (dry-rolled vs. pelleted barley) and source of oilseed (ground canola vs. ground flaxseed), arranged as a 2 x 2 factorial, on feed intake, ruminal fermentation, nutrient flow to the duodenum, and milk production and composition in dairy cows. Eight Holstein cows (655 ± 69 kg; 83 ± 16 DIM) were used in a replicated 4 x 4 Latin square with 28-d periods. Cows in one square were fitted with ruminal and duodenal cannulae. Cows fed dry-rolled barley consumed 1.8 to 3.5 kg/d more (P = 0.02) DM than those fed pelleted barley; however, source of supplemental dietary fat had no effect on DM intake. Ruminal pH was lower (P = 0.045) in cows fed pelleted barley compared to those fed dry-rolled barley. Ruminal concentration of acetate was greater (P = 0.001), whereas ruminal concentration of propionate tended to be lower (P = 0.11), in cows fed dry-rolled barley compared to those fed pelleted barley; consequently, the acetate:propionate ratio was higher (P = 0.01) in cows fed dry-rolled barley compared to those fed pelleted barley. Ruminal concentration of total VFA was unaffected (P > 0.05) by diet. Source of dietary fat had no effect on ruminal digestion of OM, NDF, ADF or starch; however, ruminal starch digestion was slightly higher in cows fed pelleted barley compared to those fed dry-rolled barley (90.8 vs. 89.5%). Total dietary fatty acid intake was higher (P < 0.05) in cows consuming dry-rolled barley compared to those fed pelleted barley. Duodenal flow of C18:0 was lower, whereas that of C18:2n6c was higher (P < 0.05) in cows fed pelleted barley compared to those fed dry-rolled barley. Feeding flaxseed increased duodenal flows of C18:3n3, cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid compared to feeding canola. Milk yield was unaffected (P > 0.05) by diet; however, milk fat content was higher (P = 0.004) in cows fed dry-rolled barley compared to those fed pelleted barley. Milk fat content of C18:3 was higher (P = 0.005) in cows fed canola compared to those fed flax. Milk fat content of C18:3 and cis-9, trans-11 C18:2 were higher in cows fed pelleted barley compared to those fed dry-rolled barley with flax as the source of oilseed, but not with canola (interaction, P < 0.01). Milk fat content of saturated fatty acids decreased (P < 0.001) and that of polyunsaturated fatty acids increased (P = 0.003) in cows fed pelleted barley compared to those fed dry-rolled barley. In summary, milk fatty acid profiles were altered by method of grain processing and source of oilseed.