Short communication: Lactational responses to palmitic acid supplementation when replacing soyhulls or dry ground corn.

The objective of this study was to evaluate the response of mid-lactation dairy cows to a palmitic acid (C16:0)-enriched fatty acid supplement when replacing soyhulls or dry ground corn in the diet. Twenty-four multiparous Holstein cows (182 ± 60 d in milk; mean ± SD) were blocked by preliminary 3.5% fat-corrected milk and randomly assigned to treatment sequence in a replicated 3 × 3 Latin square design with 21-d periods. Treatments consisted of a control diet containing no supplemental fat (CON), and 2 C16:0-enriched fatty acid-supplemented treatments (PA; BergaFat F100, Berg & Schmidt, Hanover, Germany) as a replacement for either soyhulls (PA-SH) or dry ground corn (PA-CG). The C16:0-enriched supplement was fed at 1.5% of diet dry matter. The PA treatments did not affect dry matter intake, but PA-SH increased dry matter intake by 1.4 kg/d compared with PA-CG. The PA treatments did not affect milk yield; however, PA-SH increased milk yield by 2.4 kg/d compared with PA-CG. The PA treatments tended to decrease milk protein content (3.12 vs. 3.15%). In contrast, PA-SH increased milk protein content (3.14 vs. 3.10%) and milk protein yield (1.27 vs. 1.19 kg/d) compared with PA-CG. The PA treatments increased milk fat concentration (3.68 vs. 3.55%) and milk fat yield (1.46 vs. 1.38 kg/d). The increase in milk fat yield with PA treatments was due to the increase in the yield of 16-carbon fatty acid in milk fat. Furthermore, PA-SH tended to increase yield of de novo fatty acids and yield of 16-carbon fatty acids compared with PA-CG. The PA treatments tended to increase feed efficiency (3.5% fat-corrected milk/dry matter intake) compared with CON (1.51 vs. 1.46). The PA-SH treatment tended to increase insulin concentration compared with PA-CG (1.58 vs. 1.49 μg/L) and PA treatments increased nonesterified fatty acids compared with CON (110 vs. 99 μEq/L). Overall, PA treatments improved feed efficiency and increased milk fat yield and the response to the C16:0-enriched fatty acid supplement was greater when it replaced soyhulls compared with when it replaced dry ground corn in the diet.