Comparative effects of fatty acid supplement form and profile on nutrient digestibility and milk production in dairy...

This study evaluated how the form and fatty acid (FA) profile of dietary fat supplements influence nutrient digestibility and milk yield in mid-lactation dairy cows. Twenty multiparous Holstein cows (mean ± SD; 44.3 ± 3.00 kg/d of milk; 99 ± 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 FA supplements at 2.0% DM of total FA of (1) blend of FA supplements to achieve a ratio of 70% palmitic (C16:0) + 20% oleic (cis-9 C18:1) using an FA prill and a Ca-salt of palm FA (PFAD) distillate (70FB), (2) a Ca-salt of fractionated FA containing 70% C16:0 + 20% cis-9 C18:1 (70CS), and (3) a Ca-salt of PFAD distillate containing 45% C16:0 + 35% cis-9 C18:1 (45CS). The 3 FA treatments replaced soyhulls in the CON diet. The statistical model included the random effect of cow within square and the fixed effects of treatment, period, and square. Preplanned contrasts included CON versus the average of the 3 FA treatments (FAS), the form of the FA supplement (70FB vs. 70CS), and the FA profile of the Ca-salt (70CS vs. 45CS). Compared with CON, FAS decreased DMI and NDF intake, increased intakes of 16-carbon, 18-carbon, and total FA, and increased digestibility of DM, NDF, 16-carbon, 18-carbon, and total FA. There was no difference in nutrient intake for the form of the supplement, but compared with 70CS, 70FB increased DM and 18-carbon digestibility and decreased NDF and 16-carbon digestibility, with no effect on total FA digestibility. When considering the FA profile of a Ca-salt, 70CS increased both DM and NDF intake but did not affect the digestibility of DM or NDF and decreased 16-carbon and total FA digestibility. Overall, FAS increased 3.5% FCM and milk fat yield but decreased milk protein yield. No differences were observed for production responses when comparing the form of the supplement. When comparing the FA profile of a Ca-salt, 70CS increased milk fat yield but decreased yields of milk and milk lactose. In conclusion, FAS primarily increased milk fat production by increasing FA digestibility and absorption. Digestibility varied slightly by supplement form, but production variables remained consistent regardless of form when FA profiles were similar. However, differences in FA profiles between traditional Ca-salt containing 45% C16:0 and 35% cis-9 C18:1 and 70% C16:0 and 20% cis-9 C18:1 influenced nutrient digestibility and production. These findings demonstrate that FA profile had a greater influence than supplement form on nutrient digestion and production outcomes.