Abstract：
Spontaneous lipolysis results in the breakdown of milk fat by the lipoprotein lipase (EC: 3.1.1.34), an enzyme present in milk. Free fatty acids (FFAs) and by-products released in milk during lipolysis can alter both the organoleptic value of milk (off-flavors 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\" control diet (100% of ad libitum DM intake) or a \"restricted\" (RESTR) diet (65% of ad libitum DM intake) according to a 2 × 2 crossover design. Milk gross composition together with lipolysis analyses were performed. Blood samples were also screened for metabolites or hormone 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 (NEFAs), 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 BW 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 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.
摘要：
自发脂解导致脂蛋白脂肪酶分解乳脂（EC：3.1.1.34），牛奶中的一种酶。脂解过程中牛奶中释放的游离脂肪酸（FFA）和副产品会改变牛奶的感官价值（异味释放）和乳制品的技术特性（乳化能力降低）。当前的气候变化对放牧动物的饲养产生了重大影响，对草的可用性和质量产生负面影响。我们和其他人已经证明，饮食限制会增加奶牛物种的乳脂分解。然而,在母羊物种中，没有关于饲料限制对牛奶脂解的影响的数据。因此，本文旨在研究限制采食对奶牛脂肪分解值的影响。两组24只多胎Lacaune母羊在哺乳期中期接受“非限制性”控制饮食（100％的随意DM摄入量）或“限制性”（RESTR）饮食（65％的随意DM摄入量）根据2×2交叉设计。进行了牛奶总组成和脂解分析。还筛选血液样品的代谢物或激素浓度。RESTR处理导致产奶量降低（与对照处理相比为-21％），并改变了以血浆非酯化脂肪酸（NEFA）增加为特征的乳母的代谢。这代表了脂肪组织动员和其他组织使用NEFA之间的平衡（+153%），胆固醇(+17%)和β-羟丁酸(+4%)水平。因此,观察到奶牛的BW降低(-7%)。饲料限制还导致通过铜皂法测量的牛奶FFA估计的牛奶脂解减少（-63％和-62％，分别,用于早晚挤奶)或根据乳制品工业局的参考方法(-51和-57%，分别,早上和晚上挤奶)。限制采食条件下牛奶自发脂解的减少与母羊脂蛋白脂肪酶活性的降低无关。这些结果将通过牛奶样品中的蛋白质组学和脂质组学研究来完成，以更好地了解母羊物种中特别是关于牛奶中脂肪分解的机制。
