J Dairy Sci. 2023 Sep 8:S0022-0302(23)00641-0. doi: 10.3168/jds.2023-23874. Online ahead of print.
We determined the effects of altering the ratio of palmitic (C16:0) and stearic (C18:0) acids in supplemental fatty acid (FA) blends on production responses of mid-lactation dairy cows. Twenty-four multiparous Holstein cows (mean ± standard deviation; 47.1 ± 5.8 kg of milk yield, 109 ± 23 DIM) were randomly assigned to treatment sequences in a replicated 4 × 4 Latin square design with 21-d periods. Treatments were a non-FA supplemented control diet (CON), and 3 diets incorporating 1.5% dry matter (DM) FA supplement blends containing 30% C16:0 + 50% C18:0 (L-PA), 50% C16:0 + 30% C18:0 (M-PA), and 80% C16:0 + 10% C18:0 (H-PA). Additionally, the FA blends were balanced to contain 10% oleic acid (cis-9 C18:1). The FA blends replaced soyhulls in the CON diet. Diets were formulated to contain (% DM) 31.0% neutral detergent fiber, 27.0% starch, and 16.9% crude protein. The statistical model included the random effect of cow within square and the fixed effects of period, treatment, and their interaction. Pre-planned contrasts included CON vs. overall effect of FA supplementation (FAT) and the linear and quadratic effects of increasing C16:0 in FA blends. Overall FAT had no effect on dry matter intake but increasing C16:0 linearly increased dry matter intake. Compared with CON, overall FAT increased yields of milk, 3.5% fat corrected milk, energy corrected milk, and milk fat, but did not affect milk protein yield. Increasing C16:0 linearly increased milk fat yield and tended to linearly increase the yields of 3.5% fat corrected milk and energy corrected milk. FAT decreased the yield of de novo milk FA, but increased yields of mixed and preformed milk FA compared with CON. Increasing C16:0 in FA treatments did not affect the yield of de novo milk FA, linearly increased the yield of mixed and decreased the yield of preformed milk FA. In summary, feeding FA supplements containing C16:0 and C18:0 increased milk production responses with no effect on DMI compared with a non-FA supplemented control diet. Mid-lactation cows producing ∼40-50 kg/d of milk yield responded best to increasing supplemental C16:0 in FA supplements, demonstrating that FA supplements higher in C16:0, and limiting C18:0, improves production responses.