Fish Oil and Extruded Soybeans Fed in Combination Increase Conjugated Linoleic Acids in Milk of Dairy Cows More Than When Fed Separately

Abstract

Eight multiparous Holstein and four multiparous Brown Swiss (78 ± 43 DIM) cows were used in a 4 × 4 Latin square with 28-d periods to evaluate if feeding fish oil with a source of linoleic acid (extruded soybeans) would stimulate additional amounts of conjugated lino- leic acid in milk. Four treatments consisted of a control diet with a 50:50 ratio of forage to concentrate (DM basis), a control diet with 2% added fat from either menhaden fish oil or extruded soybeans, or a combina- tion of fish oil and extruded soybeans each adding 1% fat. DM intake (24.3, 21.6, 24.5, and 22.5 kg/d, for con- trol, fish oil, extruded soybeans, and combination diets, respectively), milk production (32.1, 29.1, 34.6, and 31.1 kg/d), and milk fat content (3.51, 2.79, 3.27, and 3.14%) were lower for cows that consumed either fish oil-con- taining diet, especially the 2% fish oil diet. The propor- tion of n-3 fatty acids in milk fat increased similarly among all three fat-supplemented diets. Concentra- tions of transvaccenic acid (1.00, 4.16, 2.17, and 3.51 g/100 g of fatty acids) and cis-9, trans-11 conjugated linoleic acid (0.60, 2.03, 1.16, and 1.82 g/100 g of fatty acids) in milk fat increased more with fish oil than with extruded soybeans. When fed the combination diet, these fatty acids were approximately 50% higher than expected for Holsteins, whereas concentrations were similar for Brown Swiss compared with feeding each fat source separately. These data indicated that fish oil modifies ruminal or systemic functions, stimulating increased conversion of linoleic acid into transvaccenic and conjugated linoleic acids.