Feed restriction has no effect on milk lipolysis, although it results in a marked reduction in milk lipoprotein lipase activity in dairy goats

Climate change pressures livestock feeding systems by reducing the availability and nutritional quality of forages and pasture. Previous studies have shown that dietary restriction impacts milk lipolysis (i.e. the hydrolysis of milk fat by lipoprotein lipase (LPL)) in cows and ewes. However, data regarding the effects of feed restriction on milk lipolysis in goats are scarce. Therefore, the present study aims to investigate the impact of feed restriction on goat milk composition, with a specific focus on lipolysis, LPL activity and milk fat characteristics. For that purpose, two groups of 12 dairy goats (121 ± 7 days in milk) balanced with regard to the αs1-casein (CSN1S1) genotype (7 A/A goats, corresponding to strong CSN1S1 genotypes and 5 O/O goats, corresponding to null CSN1S1 genotypes) received either a control diet (100 % of the dry matter intake (DMI) ad libitum: non-restricted; NR) or the experimental diet (65 % of the DMI ad libitum: restricted; R) according to a 2 × 2 cross-over design. Dietary restriction did not significantly affect either lipolysis levels in milk or milk fat globule size, whereas a sharp decrease was observed in milk LPL activity within the short-term restriction window tested. A genotype effect was evidenced for milk lipolysis (copper soap method), milk fat content and milk fat yield. No genotype × diet effect was observed with regard to lipolysis or LPL activity under feed restriction. This work provides a solid framework for follow-up lipidomic and proteomic studies to gain a comprehensive understanding of the regulation of the lipolytic system in goats.