Feed restriction affects milk performances and decreases milk lipolysis in dairy ewes

Abstract

Spontaneous lipolysis results in the breakdown of milk fat by the lipoprotein lipase (LPL; EC: 3.1.1.34), an enzyme present in milk. Free fatty acids (FFA) and by-products released in milk during lipolysis can alter both the organoleptic value of milk (off-flavours release) and technological properties of dairy products (decrease in creaming capabilities). Current climate change is having significant impacts on the feeding of grazing animals, with negative consequences on the availability and quality of grass. We and others have demonstrated that dietary restriction increases milk lipolysis in the cow species. However, no data about the impact of feed restriction on milk lipolysis is available in the ewe species. Thus, this paper aims to investigate the effect of feed restriction on milk characteristics with regard to lipolysis values in dairy ewes. Two groups of 24 multiparous Lacaune ewes in mid-lactation received a “non-restricted” (NON RESTR) control diet (100 % of ad libitum DM intake) or a “restricted” (RESTR) diet (65 % of ad libitum DM intake) according to a 2 X 2 crossover design. Milk gross composition together with lipolysis analyses were performed. Blood samples were also screened for metabolites or hormones concentrations. The RESTR treatment induced a decrease in milk production (- 21 % compared with control treatment) and a modification of the metabolism of dairy ewes characterized by an increase in plasma non-esterified fatty acids (NEFA), which represents the balance between adipose tissue mobilization and the use of NEFA by other tissues (+ 153 %), cholesterol (+ 17 %) and β-hydroxybutyrate (+ 4 %) levels. As a result, a decrease in body weight of dairy ewes was observed (-7 %). Feed restriction also resulted in a decrease in milk lipolysis estimated by the milk FFA measured by the copper-soap method (- 63 % and - 62 %, respectively for morning and evening milking) or by the reference Bureau of Dairy Industry (BDI) method (- 51 % and – 57 %, respectively for morning and evening milking). The decrease in milk spontaneous lipolysis under feed restriction was not associated with a decrease in lipoprotein lipase activity in ewes. These results will be completed with proteomic and lipidomic studies in milk samples to better understand mechanisms initiated in the ewe species specifically with regard to lipolysis in milk.