Milking frequency and dairy cow susceptibility to lipolysis interact to alter milk lipolysis and composition

Lipolysis is an ongoing issue for the French dairy industry that must be minimized. Milk lipolysis is defined as the hydrolysis of triglycerides, the major component of milk fat, resulting in the release of short-chain fatty acids responsible for rancid flavor and partial glycerides that impair functional properties such as foaming and creaming abilities. Milk lipolysis is a complex phenomenon that depends on both animal parameters and farming factors. Milk spontaneous lipolysis is higher in milk from automatic milking systems, which could be due to the number and intervals of milking, as lipolysis is lower in the case of a single daily milking. In addition, considerable interindividual variability in milk lipolysis has been observed, with some dairy cows being highly susceptible or nonsusceptible to lipolysis. The objective of this study was therefore to evaluate the impact on spontaneous milk lipolysis of different milking frequencies (i.e., 1 [morning or evening], 2, or 3 milkings per day) with evenly spaced milking intervals while accounting for individual susceptibility to lipolysis. To achieve this goal, 32 primiparous and multiparous dairy cows in mid-lactation were conducted using a continuous design with milking frequency as the main factor for a period of 3 wk. Four treatments were applied on 4 groups of cows: 1 milking per day at 6:00 a.m. (1M6am), 1 milking per day at 6:00 p.m. (1M6pm), 2 milkings per day at 6:00 a.m. and 6:00 p.m. (2M), and 3 milkings per day at 6:00 a.m., 2:00 p.m., and 10:00 p.m. (3M). In each group, there were 4 susceptible (SUS) dairy cows (lipolysis of SUS >0.70 mEq/100 g fat) and 4 nonsusceptible (NONSUS) dairy cows (lipolysis of NONSUS <0.70 mEq/100 g fat). As expected, 2M and 3M milkings increased milk yield by up to 30% compared with once-a-day milking. We confirmed that milk spontaneous lipolysis was influenced by increased milking frequency: compared with 2M, we observed more lipolysis with 3M and less with 1M. Regardless of the lipolysis susceptibility, the 1M6am and 1M6pm treatments caused a similar reduction in lipolysis. On the other hand, lipolysis was significantly higher in SUS cows with 2M and 3M treatments. In conclusion, although increased milking frequency results in greater milk yield, our results indicate that it can adversely impact milk quality with regard to free fatty acid concentrations. Conversely, although once-a-day morning or evening milking lead to decreased milk yield, they significantly reduced milk lipolysis regardless of a cow's susceptibility to lipolysis.