Knowledge of factors influencing the levels of 4-alkyl branched-chain fatty acid (vBCFA), and consequently the "sheepy flavor" intensity of New Zealand sheep milk, is currently limited. In this study, we investigated the effects of 2 contrasting farming systems (fully housed/mid-lactation or pasture-grazed/late lactation) on the levels of vBCFA in sheep milk on a commercial farm in the North Island of New Zealand. Fully housed/mid-lactation ewes were housed 24 h/d and fed a total mixed ration. Pasture-grazed/late-lactation ewes were grazed 24 h/d and offered approximately 40% supplements because of poor pasture growth resulting from dry and hot climatic conditions. Any effects of genetics, age, lactation stage, feed composition, lambing date, or the environment in the housing barn or outdoors were confounded. The results obtained in this study were descriptive rather than definitive, because of the limitations of the experimental design. Levels of 4-methyloctanoic acid and 4-methylnonanoic acid in milk from fully housed/mid-lactation ewes increased during the trial period, but remained low in milk from pasture-grazed/late-lactation ewes. Levels of 4-ethyloctanoic acid in milk from the 2 groups of ewes were comparable throughout the trial. Increases in levels of 4-methyloctanoic acid and 4-methylnonanoic acid in sheep milk were associated with lactation stage and the proportion of lucerne silage fed to ewes. The level of free-form 4-ethyloctanoic acid was positively correlated with the proportion of soy meal in the diet and negatively correlated with the proportion of barley. Milk from fully housed/mid-lactation ewes had a higher flavor values than milk from pasture-grazed/late-lactation ewes because of its higher total amounts of vBCFA.

中文翻译：

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影响新西兰两种对比农业系统中羊奶中挥发性4-烷基支链脂肪酸水平的因素。

当前，影响4-烷基支链脂肪酸（vBCFA）水平的因素的认识，以及因此影响新西兰绵羊乳的“羊皮风味”强度的因素，目前是有限的。在这项研究中，我们调查了新西兰北岛一家商业农场的两种对比耕作系统（完全饲养/泌乳期或牧场放牧/晚期哺乳期）对羊奶中vBCFA含量的影响。完全圈养/哺乳期的母羊圈养24 h / d，并饲喂总混合日粮。牧场放牧/哺乳期的母羊每24小时放牧一次，并提供约40％的补品，因为干旱和炎热的气候条件会导致牧草生长不良。遗传，年龄，泌乳阶段，饲料组成，产羔日期或家禽舍或室外环境的任何影响均会混淆。由于实验设计的局限性，本研究中获得的结果只是描述性的，而不是确定性的。在试验期间，完全饲养/泌乳中期的母羊的牛奶中4-甲基辛酸和4-甲基壬酸的含量增加，但是在牧场/哺乳期乳母羊的牛奶中，4-甲基辛酸和4-甲基壬酸的含量仍然较低。在整个试验过程中，两组母羊的牛奶中的4-乙基辛酸水平相当。绵羊乳中4-甲基辛酸和4-甲基壬酸水平的升高与泌乳阶段以及饲喂母羊的琉森青贮饲料的比例有关。游离形式的4-乙基辛酸的水平与日粮中豆粕的比例呈正相关，与大麦的比例呈负相关。