Impact of milking interval on milk spontaneous lipolysis in dairy cow

International audienceMilk 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 flavour and partial glycerides that impairs milk functional properties such as foaming and creaming abilities. Milk lipolysis is a complex phenomenon that depends on both animal parameters and breeding factors. Regarding milking rhythms, milk spontaneous lipolysis (SL) is higher in milk from evening milking. This may be related to the length of milking intervals or to nychtemera. The objective of the experiment was thus to study the impact of milking intervals on milk SL in a 2 milkings per day system: 10-14 (6.30 a.m. and 4.30 p.m.); 14-10 (6:30 a.m. and 8:30 p.m.); 12-12 (6:30 a.m. and 6:30 p.m.). To achieve this goal, 21 multiparous dairy cows in mid-lactation were used in a 3×3 Latin square design over 3 periods. The experiment lasted 5 weeks (3 experimental periods of 1 week alternating with a classic 10-14 milking week). The time interval between milkings influenced milk SL. Indeed, we observed more SL in the evening milk for 10-14 (+0.20 mEq/100 g fat) and in the morning milk for 14-10 (+0.22 mEq/100 g fat). No significant difference was seen for 12-12 even if SL was numerically higher in evening milk (+0.10 mEg/100 g fat). Higher SL was associated with lower milk production and higher fat content. Milk protein, total phosphorus and citrate contents increased with the duration of mammary gland storage of milk (from 10 to 14 hours). There was no effect of milking intervals on milk fat globule diameter. The Na/K ratio indicating an opening of tight junctions in the mammary gland only increased in evening milking with 12-12 and 14-10 intervals. In conclusion, the effect of milking intervals on SL seems to be more important than the effect of nychtemera, which was partly confirmed for 12-12. The underlying mechanisms will be further explored in the framework of the LIPOMEC project funded by French National Research Agency (ANR-19-CE21-0010), in which this study was conducted