INRA, UMR1213 Herbivores, F-63122 Saint-Genès-Champanelle, France.
J Dairy Sci. 2013 Feb;96(2):1232-6. doi: 10.3168/jds.2012-6046. Epub 2012 Dec 6.
In ruminants, the ability to maintain milk fat melting point within physiological values could play a role in the regulation of milk fat secretion when milk fatty acid (FA) composition varies, such as in response to feeding factors. However, the relationship between milk fat fluidity and changes in milk FA composition is difficult to study experimentally. A meta-analysis was therefore conducted to compare the magnitude of diet-induced variations in milk FA composition and the calculated melting point of milk FA (used as a proxy to estimate the variations in the melting point of milk fat) in 3 dairy ruminant species (cow, goat, and sheep). The coefficient of variation (CV), a scale-free measure of statistical dispersion, was used to compare the variability of criteria differing in their order of magnitude. The analysis of a database of milk FA profiles from cows, goats, and sheep fed different dietary treatments (unsupplemented diets and diets supplemented with lipids rich in oleic acid, linoleic acid, linolenic acid, or C20-22 polyunsaturated FA) revealed that the variability of the calculated melting point of milk FA was narrow (CV of 5%) compared with the variability of milk FA percentages (CV of 18 to 72%). The regulation of the melting point of milk fat is thus probably involved in the control of diet-induced variations in milk fat secretion. The calculated melting point of ewe milk FA was approximately 3°C lower than that of goats or cows across all types of diets, which might be linked to differences in milk fat content (higher in sheep) or the structure of milk triacylglycerides among these species. Lipid supplementation increased the calculated melting point of C18 FA in milk, whereas that of total FA was significantly reduced by supplements rich in oleic, linoleic, and linolenic acids but not C20-22 polyunsaturated FA. However, the slight effects of dietary treatments on the calculated melting point of milk FA did not differ between cows, goats, and ewes.
在反刍动物中，当乳脂肪酸（FA）组成发生变化（例如，响应喂养因素）时，维持乳脂熔点在生理值范围内的能力可能在调节乳脂分泌方面发挥作用。然而，乳脂流动性与乳 FA 组成变化之间的关系很难通过实验进行研究。因此，进行了一项荟萃分析，以比较 3 种乳用反刍动物（奶牛、山羊和绵羊）中饮食诱导的乳 FA 组成变化的幅度和计算的乳 FA 熔点（用作估计乳脂熔点变化的替代指标）。变异系数（CV）是一种无标度的统计离散度度量，用于比较数量级不同的标准的可变性。对不同日粮处理（未补充日粮和富含油酸、亚油酸、亚麻酸或 C20-22 多不饱和 FA 的日粮补充）的奶牛、山羊和绵羊乳 FA 谱数据库进行分析后发现，与乳 FA 百分比的变异性（18%至 72%）相比，计算的乳 FA 熔点的变异性较窄（CV 为 5%）。因此，乳脂熔点的调节可能参与了对饮食诱导的乳脂分泌变化的控制。在所有类型的日粮中，母羊乳 FA 的计算熔点比山羊或奶牛低约 3°C，这可能与乳脂含量的差异（绵羊中较高）或这些物种的乳三酰甘油结构有关。脂类补充剂增加了乳中 C18 FA 的计算熔点，而富含油酸、亚油酸和亚麻酸的补充剂显著降低了总 FA 的计算熔点，但 C20-22 多不饱和 FA 除外。然而，日粮处理对乳 FA 计算熔点的微弱影响在奶牛、山羊和母羊之间没有差异。
