Abstract #M265

# M265
Effect of feeding two fat sources varying in palmitic and stearic acid content in mid-lactation dairy cows.
P. Piantoni*1, Y. Sun1, A. A. A. Jacobs1, G. F. Schroeder1, 1Cargill Animal Nutrition Innovation Center, Elk River, MN.

Twenty-four cows were used in a 3 × 3 Latin square design experiment with 21-d periods to evaluate production responses to 2 highly saturated fatty acid (FA) supplements enriched in either stearic or palmitic acid. Cows (122 ± 39 DIM; 43.5 ± 9 kg/d milk yield) were randomly assigned to squares and treatment sequences within square. Treatments were: control (CTR; base diet with no supplemental FA; 53% forage, 1:1 corn silage to alfalfa ratio), an enriched palmitic acid supplement (PALM; > 80% C16:0), and an enriched stearic acid supplement (STEAR; 65–75% C18:0, 20–25% C16:0). Both free FA supplements were added to the base diet at 2.0% of the diet DM. Milk yield and DMI from d 14 to 20 and milk composition from d 20 of each period were used for the analysis. Contrasts compared CTR vs. PALM and STEAR, and PALM vs. STEAR. FA supplementation decreased dry matter intake (DMI) by 1.3 kg/d (22.0 vs. 23.3 kg/d; P = 0.03), but did not affect net energy intake compared with CTR. Treatments did not affect fat or protein concentrations in milk or yields of milk, 3.5% fat-corrected milk, and milk components. FA supplementation increased components efficiency (yields of milk fat and protein/DMI; 11.3 vs. 10.7%; P = 0.04) and feed efficiency (milk yield/DMI) compared with CTR (1.77 vs. 1.66, P = 0.01). Treatments did not affect body weight or body condition score. Production responses to PALM were not different from those of STEAR. Overall, FA supplementation decreased concentration of FA from de novo synthesis in milk compared with CTR (24.6 vs. 26.9%; P < 0.01), and the effect tended to be more pronounced for PALM than STEAR (24.1 vs. 25.1%; P = 0.07). FA supplementation increased mixed-source (P < 0.01) but not pre-formed FA in milk compared with CTR. PALM increased concentration of mixed-source FA in milk compared with STEAR (35.3 vs. 30.6%; P < 0.01), while STEAR increased that of pre-formed FA compared with PALM (41.2 vs. 37.1%; P < 0.01). In conclusion, FA supplements decreased DMI, did not affect milk yield or concentrations of milk fat or protein, and increased feed efficiency compared with a control diet with no supplemental FA.

Key Words: fatty acids, palmitic acid, stearic acid