Effect of dietary lipid source on conjugated linoleic acid concentrations in milk fat

Conjugated linoleic acids (CLA) found in ruminant milk fat are a byproduct of incomplete biohydrogenation of lipids by ruminal bacteria. We examined t he effect of different dietary fat supplements and processing methods on CL A. In trial 1, dietary supplements of Ca salts of fatty acids from canola o il, soybean oil, and linseed oil increased CLA content of milk fat by three to fivefold over the control diet. Trials 2 and 3 examined the effect of p rocessing methods for heat treatment of full fat soybeans. In trial 2, extr usion, micronizing, and roasting resulted in two- to threefold greater conc entrations of CLA in milk fat than the control diet (raw ground soybeans). In trial 3, different temperatures of extrusion (120, 130, and 140 degreesC ) increased the CLA content of milk fat to a similar extent; CLA averaged 1 9.9 mg/g of fatty acids for the extrusion treatments compared with 4.2 mg/g of fatty acids for the control diet (raw ground soybeans). Fish oil (200 a nd 400 ml/d) was examined in trial 4 and both levels resulted in CLA concen trations in milk fat that were about threefold greater than the control die t. In trial 5, grain and silage from a high oil corn hybrid increased the C LA content of milk fat; however, responses were modest with the CLA concent ration (mg/g of fatty acids) averaging 4.6 and 2.8 for diets with high oil hybrid and normal hybrid, respectively. Similarly, dietary supplements of a nimal fat byproducts (tallow plus yellow grease; trial 6) resulted in modes t increases in the CLA content of milk fat. Overall, several dietary manipu lations involving lipid sources and processing methods were identified that allow for a marked increase in the conjugated linoleic acid content of mil k fat.