Two identical experimental protocols were followed at 200 and 3,600 m above sea level (a.s.l.) determining the changes of the milk fatty acid (FA) profile of Brown Swiss (BS) and indigenous Peruvian Criollo cows (CR) as a response to diets which were designed to cover the variation in feed quality caused by season. At each site (altitude), six BS and six CR cows, adapted to >3,500 m a.s.l., were fed three dietary treatments (DS, dry-season forage; RS rainy-season forage; OC, diet optimised to meet the cow's requirements) in a 2 × 2 × 3-factorial arrangement. Intakes of FA and milk yield increased from diet DS (low quality diet) to RS and OC (high quality diet) for both cow types. Milk fat proportions of conjugated linoleic acid (CLA), C18:3 c9,c12,c15, total n-3 and polyunsaturated FA (PUFA) were highest (p < 0.05) with diet OC and higher in the lowlands than in the highlands. Low intakes of diet DS obviously resulted in a ruminal energy deficiency and body lipid mobilisation. The ruminal energy deficiency with diet DS was especially pronounced in BS, apparently reducing biohydrogenation rate and leading to lower proportions of C18:0 and higher proportions of C18:3 c9,c12,c15 in milk fat (p < 0.05). Especially C18:3 c9,c12,c15 intake did not concur with its proportion in milk fat, suggesting a strong dependence on energy status. Milk yield and FA excretion with milk were higher for BS than for CR (p < 0.05) with all three diets although milk fat content was lower (p < 0.05) for BS than CR. Milk fat of BS was richer in CLA and PUFA than milk fat of CR (p < 0.05). The desaturase indices for 18 FA were also higher for BS than CR (p < 0.05), suggesting a slightly higher Δ9-desaturase activity for BS, especially with diet DS. Milk fat content was generally higher at the high altitude than at the lowland site (p < 0.05), whereas the FA profile was unexpectedly similar across sites. Various interactions were found among diet type, cow type and altitude (site) indicating that a combination of these factors contributes to the characteristic FA profile of the respective milk.

中文翻译：

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秘鲁 Criollo 和 Brown Swiss 奶牛的牛奶脂肪酸谱对低海拔和高海拔不同饮食质量的反应

在海拔 200 米和 3,600 米 (asl) 处遵循两个相同的实验方案，确定瑞士布朗 (BS) 和秘鲁本土 Criollo 奶牛 (CR) 的牛奶脂肪酸 (FA) 谱的变化，作为对饮食的反应旨在涵盖因季节引起的饲料质量变化。在每个地点（海拔），六头 BS 奶牛和六头 CR 奶牛，适应 > 3,500 m asl，饲喂三种日粮处理（DS，旱季草料；RS 雨季草料；OC，优化日粮以满足奶牛的需求）以 2 × 2 × 3 阶乘排列。两种奶牛的 FA 摄入量和产奶量从日粮 DS（低质量日粮）增加到 RS 和 OC（优质日粮）。共轭亚油酸 (CLA)、C18:3 c9、c12、c15、总 n-3 和多不饱和脂肪酸 (PUFA) 的乳脂比例最高（p < 0。05) 饮食 OC，低地高于高地。日粮 DS 摄入量低显然会导致瘤胃能量缺乏和身体脂质动员。DS日粮的瘤胃能量缺乏在BS中尤为明显，明显降低了生物氢化率，导致乳脂中C18:0的比例较低，C18:3 c9、c12、c15的比例较高（p < 0.05）。特别是 C18:3 c9,c12,c15 摄入量与其在乳脂中的比例不一致，表明对能量状态有很强的依赖性。尽管 BS 的乳脂含量低于 CR（p < 0.05），但 BS 的产奶量和牛奶中的 FA 排泄量均高于 CR（p < 0.05），但所有三种日粮均高于 CR。BS 的乳脂比 CR 的乳脂富含 CLA 和 PUFA（p < 0.05）。BS 的 18 FA 去饱和酶指数也高于 CR（p < 0.05），表明 BS 的 Δ9-去饱和酶活性略高，尤其是饮食 DS。高海拔地区的乳脂含量通常高于低地地区（p < 0.05），而不同地区的 FA 分布却出人意料地相似。在饮食类型、奶牛类型和海拔（地点）之间发现了各种相互作用，表明这些因素的组合有助于各自牛奶的特征 FA 特征。