The effect of nonstructural carbohydrate and addition of full fat extrudedsoybeans on the concentration of conjugated linoleic acid in the milk fat of dairy cows

Conjugated linoleic acid (CLA), a naturally occurring anticarcinogen found in dairy products, is a byproduct of incomplete ruminal biohydrogenation of unsaturated fatty acids. Our objective was to determine the effect of nons tructural carbohydrate sources, addition of full fat extruded soybeans as a source of unsaturated fatty acids, and possible interactions on the milk f at content of CLA. Cows (n = 20) were assigned to a 4 x 4 Latin square invo lving two sources of nonstructural carbohydrate, high starch (corn) or high pectin (citrus pulp), with or without addition of extruded soybeans. Milk yield was not affected by nonstructural carbohydrate source, but milk produ ction was increased by 7.8 to 10.5% with dietary additions of extruded soyb eans. Mills fat content did not differ between treatments, but fatty acid c omposition was affected. Cows fed extruded soybean diets had reduced concen trations of C-8 to C-16 fatty acids and increased concentrations of octadec enoic acids. Diets with extruded soybeans also resulted in more than a doub ling in milk fat concentration and yield of CLA. Nonstructural carbohydrate source had only minor effects on CLA, and there was no interaction with ex truded soybeans. Milk fat content of trans-C-18:1 and CLA were closely rela ted (r(2) = 0.77). However, variation among cows was about threefold for ea ch of the diets and rank order of individual cows differed among diets. Ove rall, we demonstrated that diet modification can be used to alter CLA conte nt of milk fat, but there was substantial individual cow variation for all diets.