Effect of dietary palmitic acid supplementation and milking frequency: 1. Milk production and composition in early-lactation dairy cows.

Dietary palmitic acid (PA) supplementation can be used to increase milk fat yield by dairy cows. Additionally, increasing milking frequency (MF) promotes milk production. Both practices are of interest to enhance milk performance, but their effects on milk properties are a concern from a milk processing perspective. Moreover, little is known regarding the possible interaction between those 2 practices on milk performance. This study aimed to evaluate whether milk responses of early-lactation dairy cows could benefit from the combined effects of PA supplementation and increased MF. Additionally, we determined the effects of the 2 practices on milk free fatty acids (FFA) content, milk protein fractions such as CN and whey proteins, and plasmin activity in milk. Eight early-lactation multiparous Holstein cows were randomly allocated to treatment sequences in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Levels of treatments were dietary PA (0% or 2% on a DM basis) and 2 or 3 milkings per day at equal intervals of time. Periods lasted 21 d with 16 d for treatment adaptation before data and sample collection. Except for lactose concentration, no significant interaction between MF and PA supplementation was observed. Dry matter intake was not affected by treatment. Increased MF and PA supplementation both increased milk, fat, and protein yields, as well as milk efficiency. Palmitic acid supplementation increased the yield of 16 C fatty acids (FA) in milk at the expense of shorter de novo FA. Calculated desaturase indexes increased with PA, indicating an increased Δ-desaturase activity or expression. In contrast, most desaturase indexes decreased with MF. Dry matter and NDF digestibilities were similar between treatments. However, PA decreased total and 16 C FA digestibilities. Transfer of 16 C FA into milk was increased with PA supplementation. Neither MF nor PA had an effect on FFA concentration in fresh milk. Milk concentrations of total N, true protein, CN, or whey proteins were similar between treatments. However, even if milk CP yield was increased by both PA and thrice-daily milking, CN yield was not affected by PA and only tended to be increased by thrice-daily milking. The effects of PA supplementation and MF on milk performance were additive. Under the conditions of this trial, increased MF and PA supplementation did not impair milk composition parameters of importance for milk processing.