Altering the ratio of dietary palmitic and oleic acids affects nutrient digestibility, metabolism, and energy balance during the immediate postpartum in dairy cows.

This article is the second from an experiment that determined the effects of altering the dietary ratio of palmitic (C16:0) and oleic (cis-9 C18:1) acids on digestibility, production, and metabolic responses of dairy cows during the immediate postpartum. This article elaborates on the effect of these diets on nutrient digestibility, energy balance, and metabolism. Fifty-six multiparous cows were used in a randomized complete block design and randomly assigned to 1 of 4 treatments fed from 1 to 24 d in milk. The treatments were: (1) control (CON) diet not supplemented with fatty acids (FA); (2) diet supplemented with a FA blend containing 80% C16:0 and 10% cis-9 C18:1 (80:10); (3) diet supplemented with a FA blend containing 70% C16:0 and 20% cis-9 C18:1 (70:20); and (4) diet supplemented with a FA blend containing 60% C16:0 and 30% cis-9 C18:1 (60:30). The FA supplement blends were added at 1.5% of diet dry matter by replacing soyhulls in the CON diet. Three preplanned contrasts were used to compare treatment differences: (1) CON versus FA-supplemented diets, (80:10 + 70:20 + 60:30)/3; (2) the linear effect of cis-9 C18:1 inclusion in diets; and (3) the quadratic effect of cis-9 C18:1 inclusion in diets. The FA-supplemented diets increased digestibility of dry matter, neutral detergent fiber, 18-carbon FA, and total FA compared with CON. We observed a tendency for an interaction between treatment and time for the digestibility of 18-carbon and total FA because the difference in digestibility between CON and 60:30 treatments tended to increase over time. Increasing dietary cis-9 C18:1 increased linearly the digestibility of dry matter, neutral detergent fiber, 16-carbon, 18-carbon, and total FA. Interestingly, total absorbed FA was positively related to milk, milk fat yield, energy-corrected milk, plasma insulin, and albumin, and negatively related to plasma nonesterified FA (NEFA) and body weight loss. The FA-supplemented diets increased intake of digestible energy, metabolizable energy, and net energy for lactation compared with CON. Compared with CON, FA-supplemented diets increased milk energy output and tended to increase negative energy balance. Increasing dietary cis-9 C18:1 increased intake of digestible energy, metabolizable energy, and net energy for lactation. Although increasing dietary cis-9 C18:1 did not affect milk energy output and energy for maintenance, increasing dietary cis-9 C18:1 improved energy balance. Compared with CON, FA-supplemented diets increased plasma insulin, but we did not observe differences between CON and FA-supplemented diets for NEFA and albumin. Increasing cis-9 C18:1 in FA treatments linearly decreased plasma NEFA and tended to linearly increase insulin and β-hydroxybutyrate. During the carryover period, no treatment differences in blood metabolites were observed. Our results indicate that feeding FA supplements containing C16:0 and cis-9 C18:1 during the immediate postpartum period increased nutrient digestibility, energy intake, and milk energy output compared with a non-fat-supplemented control diet. Increasing dietary cis-9 C18:1 increased energy intake, reduced markers of body fat mobilization, and improved energy balance during the immediate postpartum.