Increases in milk fat yield are maintained with prolonged palmitic acid supplementation in midlactation dairy cows

Supplementing palmitic acid (C16:0) increases yields of milk and milk fat in mid-lactation dairy cows. Because previous research has characterized the effects of short-term C16:0 feeding (~14 to 28 d) on production parameters, our objective was to determine whether prolonged C16:0 supplementation can maintain milk fat yield and FA incorporation into milk fat. Twenty multiparous Holstein cows were enrolled in a study consisting of a 5 d covariate, 49 d treatment, and 14 d post-treatment evaluation. Cows received a sorghum silage-based diet and were randomly assigned to treatments consisting of no added fat (control; soyhull pellets; n = 10; 138 ± 45 DIM) or C16:0 at 4% of ration DM (98% C16:0; PALM; n = 10; 136 ± 44 DIM). Milk yields were recorded and samples were composited at wk 0, 3, and 7 relative to the start of the treatment period, and 2 wk post-treatment. Data were analyzed as repeated measures using a mixed model with the fixed effects of treatment and time. Effects of PALM are presented as changes relative to control. We observed that PALM increased yields of milk and milk fat by wk 3 and 7 (P < 0.05), without changing milk fat concentration (P = 0.33). PALM increases in milk fat yield were preserved post-treatment (P < 0.05). PALM increased milk C16:0 yield by 52 and 46% by wk 3 and 7, respectively (P < 0.01). Similar observations were observed for yields of milk cis-9 C16:1. Although yields of de novo synthesized and preformed FA in milk remained unchanged, milk saturated FA yield increased in PALM by wk 3 and 7 (P < 0.01). Post-treatment, the yields of C16:0 (P = 0.19) and cis-9 C16:1 (P = 0.49) in PALM were comparable to control. Post-treatment, the sustained increase in milk fat yield with PALM was due to increased yields of de novo and preformed FA in milk (P < 0.01). Comparable to changes in milk FA yields, PALM increased milk C16:0 concentrations by 26 and 21% by wk 3 and 7, respectively (P < 0.01). Concentrations of milk de novo synthesized and unsaturated FA were lower in PALM-fed cows (P < 0.01). We did not observe any differences in the concentrations of milk FA post-treatment. We conclude that feeding mid-lactation dairy cows C16:0 for 7 wk maintained milk fat synthesis for the duration of supplementation because of sustained C16:0 and cis-9 C16:1 incorporation.