Milk fat secretion in lactating dairy cattle is influenced by soybean particle size and fatty acid profile

Abstract Text: It is well established in the literature that when feeding free vegetable oils, oleic acid has a smaller negative effect on milk fat secretion than does linoleic acid. The objectives of these experiments were to analyze the effects of oleic and linoleic acid fed as part of full fat soybeans and to analyze the interaction between soybean particle size and fatty acid (FA) profile. Trial 1 used 63 cows (28 primiparous, 35 multiparous; 111±20 days in milk (DIM)). Cows were housed in a common pen with 32 electronic feed gates and fed conventional or high oleic (Plenish) whole raw beans for 3 weeks following a covariate adjustment period. The second trial used 20 cows (10 primiparous, 10 multiparous; 88±10 DIM) in a tie stall barn; using two complementary 5x5 Latin Squares per parity. Raw Plenish or conventional beans, either ground (GP, GC) or whole (WP, WC), formed 4 iso-fat diets in a 2x2 factorial, plus a fifth treatment was a low fat diet without soybeans. Diets were 55% forage, iso-nitrogenous and contained 2.9-3.9% added ether extract from soybeans (15.5-18.7% soybeans, DM basis). In trial 1, there was a parity by diet interaction (P<0.10); there were no diet effects with primiparous cows (P>0.10), but for multiparous cows, feeding Plenish beans increased milk fat yield (P<0.05). In trial 2 when there was a significant interaction (P<0.10) between bean type and particle size we tested GP vs. GC and WP vs. WC. If the interaction was not significant (P>0.10), the main effects of bean type and particle size were tested. There was a significant interaction between bean type and particle size for both milk fat yield and concentration (P<0.05). GP resulted in greater milk fat yield and concentration than GC (P<0.05) whereas there was no difference between WP and WC (P>0.10). Diet affected milk yield with the Plenish diets resulting in lower milk yield (P<0.05). In both trials the increase in milk fat yield was due to an increase in 18 carbon milk FA (P<0.05) and there was not a difference in short chain FA yield (P>0.10). Plenish high oleic soybeans result in moderately increased milk fat compared with conventional soybeans and this difference is greater when soybeans are fed ground rather than whole.

Keywords: linoleic, oleic, soybeans