Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: Production responses, nutrient...

The objective of our study was to evaluate the effects of long-term palmitic acid (C16:0) supplementation and parity on production, nutrient digestibility, and energy partitioning of mid-lactation dairy cows. Forty mid-lactation Holstein cows (18 primiparous and 22 multiparous) were used in a block design. Cows were assigned to receive either a control diet containing no supplemental fat (CON) or a C16:0-enriched supplemented diet (PA; 1.5% diet dry matter) fed for 10 wk. Compared with CON, PA increased dry matter intake, milk yield, cumulative milk yield, milk fat content, milk fat yield, 16-carbon milk fatty acid (FA) yield, 3.5% fat-corrected milk yield, and energy-corrected milk yield. Additionally, PA increased body weight change, but did not affect body condition score change compared with CON. A tendency for a treatment by parity interaction was observed for milk yield due to PA increasing milk yield in multiparous but not in primiparous cows. In addition, we observed interactions between treatment and parity for fat-corrected milk, energy-corrected milk, and milk fat yield due to PA increasing these variables to a greater extent in multiparous compared with primiparous cows. Interestingly, we observed an interaction between treatment and parity for body weight change, due to PA increasing body weight change in primiparous but not in multiparous cows. The PA treatment increased dry matter and neutral detergent fiber digestibilities compared with CON. Although PA did not affect 18-carbon FA digestibility, compared with CON, PA decreased 16-carbon and total FA digestibilities and increased total FA intake by 470 g/d and absorbed total FA by 316 g/d. We also observed an interaction between treatment and parity for total absorbed FA due to PA increasing it to a greater extent in multiparous than in primiparous cows. Compared with CON, PA increased apparent energy intake and milk energy output. We observed an interaction between treatment and parity for milk energy output due to PA increasing milk energy output to a greater extent in multiparous than primiparous cows. Additionally, an interaction between treatment and parity was observed for energy output in body reserves due to PA increasing energy output in body reserves in primiparous but not in multiparous cows. In conclusion, production responses of dairy cows to PA were consistent throughout the 10-wk treatment period. In addition, PA supplementation interacted with parity, with production responses increased to a greater extent in multiparous than primiparous cows and energy partitioned to body reserves only increased in primiparous cows.