Milk Production, Production Systems Natural Resources Institute Finland (Luke), FI-31600 Jokioinen, Finland.
Food Processing and Quality, Production Systems Natural Resources Institute Finland (Luke), FI-31600 Jokioinen, Finland.
J Dairy Sci. 2019 Oct;102(10):8825-8838. doi: 10.3168/jds.2018-15833. Epub 2019 Aug 14.
We examined the effects of 2 grass silage-based diets differing in forage:concentrate (FC) ratio and those of a red clover silage-based diet on intake, milk production, ruminal fatty acid (FA) biohydrogenation, milk FA composition, and milk fat globule (MFG) size distribution. Ten multiparous Nordic Red cows received the following treatments: grass silage-based diets containing high (70:30, HG) or low (30:70, LG) FC ratio or a red clover silage-based diet with an FC ratio of 50:50 (RC) on a dry matter basis. Determinations of MFG were performed from fresh milk samples without addition of EDTA so the results of fat globules >1 µm in diameter are emphasized instead of the entire globule population. Lower FC ratio in grass silage-based diets increased milk production with no effect on daily fat yield, leading to 13% lower milk fat concentration. The effect of FC ratio on MFG size was moderate. It did not affect the volume-weighted diameter in grass silage-based diets, although LG lowered the volume-surface diameter of MFG in the size class >1 µm compared with HG. Compared with HG, feeding LG moderately decreased the biohydrogenation of 18:2n-6, leading to a higher level of polyunsaturated fatty acids in milk fat. Feeding RC lowered milk fat concentration and daily milk fat yield compared with grass silage-based diets. The volume-weighted diameter of MFG in the size class >1 µm was smaller in RC milk compared with grass silage-based diets. Feeding RC increased the flow of 18:3n-3 at the omasum by 2.4-fold and decreased the apparent ruminal 18:3n-3 biohydrogenation compared with grass silage-based diets despite similar intake of 18:3n-3. It also resulted in the lowest amount of saturated FA and the highest amounts of cis-9 18:1, 18:3n-3, and polyunsaturated FA in milk. In conclusion, LG decreased milk fat content and induced minor changes in MFG size distribution compared with HG, whereas RC lowered milk fat production, altered milk FA composition to nutritionally more beneficial direction, and led to smaller MFG compared with grass silage-based diets.
我们研究了两种基于青贮饲料的日粮（饲草：精料比不同）和一种基于红三叶草青贮饲料的日粮对奶牛采食量、产奶量、瘤胃脂肪酸（FA）生物氢化、乳 FA 组成和乳脂肪球（MFG）大小分布的影响。10 头经产北欧红牛接受了以下处理：基于青贮饲料的日粮，饲草：精料比分别为高（70:30，HG）或低（30:70，LG），或基于红三叶草青贮饲料的日粮，饲草：精料比为 50:50（RC）（均基于干物质）。从未经添加 EDTA 的新鲜牛奶样品中进行 MFG 的测定，因此强调大于 1 µm 直径的脂肪球的结果，而不是整个脂肪球群体。青贮饲料中较低的饲草：精料比增加了产奶量，而对每日脂肪产量没有影响，导致乳脂浓度降低 13%。饲草：精料比对 MFG 大小的影响中等。它没有影响基于青贮饲料的日粮中 MFG 的体积加权直径，尽管 LG 降低了大于 1 µm 大小级别的 MFG 的体积表面积直径。与 HG 相比，LG 适度降低了 18:2n-6 的生物氢化，导致乳脂中多不饱和脂肪酸水平升高。与基于青贮饲料的日粮相比，RC 降低了乳脂浓度和每日产奶量。与基于青贮饲料的日粮相比，RC 乳中大于 1 µm 大小级别的 MFG 的体积加权直径较小。与基于青贮饲料的日粮相比，RC 增加了瘤胃中 18:3n-3 的流量，使其增加了 2.4 倍，并降低了 18:3n-3 的表观瘤胃生物氢化，尽管 18:3n-3 的摄入量相似。它还导致乳中饱和 FA 的量最低，顺式 9 18:1、18:3n-3 和多不饱和 FA 的量最高。总之，与 HG 相比，LG 降低了乳脂含量并导致 MFG 大小分布发生较小变化，而与基于青贮饲料的日粮相比，RC 降低了乳脂产量，使乳 FA 组成朝着更有益的营养方向改变，并导致 MFG 小于基于青贮饲料的日粮。
