Laboratory for Animal Nutrition and Animal Product Quality (Lanupro), Department of Animal Sciences and Aquatic Ecology, Ghent University, 9000 Gent, Belgium.
Instituto de Ganadería de Montaña (CSIC-University of León), Finca Marzanas s/n, 24346 Grulleros, León, Spain.
J Dairy Sci. 2020 Sep;103(9):7655-7681. doi: 10.3168/jds.2019-17662. Epub 2020 Jun 27.
To meet the energy requirements of high-yielding dairy cows, grains and fats have increasingly been incorporated in ruminant diets. Moreover, lipid supplements have been included in ruminant diets under experimental or practical conditions to increase the concentrations of bioactive n-3 fatty acids and conjugated linoleic acids in milk and meat. Nevertheless, those feeding practices have dramatically increased the incidence of milk fat depression in dairy cattle. Although induction of milk fat depression may be a management tool, most often, diet-induced milk fat depression is unintended and associated with a direct economic loss. In this review, we give an update on the role of fatty acids, particularly originating from rumen biohydrogenation, as well as of rumen microbes in diet-induced milk fat depression. Although this syndrome seems to be multi-etiological, the best-known causal factor remains the shift in rumen biohydrogenation pathway from the formation of mainly trans-11 intermediates toward greater accumulation of trans-10 intermediates, referred to as the trans-11 to trans-10 shift. The microbial etiology of this trans-11 to trans-10 shift is not well understood yet and it seems that unraveling the microbial mechanisms of diet-induced milk fat depression is challenging. Potential strategies to avoid diet-induced milk fat depression are supplementation with rumen stabilizers, selection toward more tolerant animals, tailored management of cows at risk, selection toward more efficient fiber-digesting cows, or feeding less concentrates and grains.
为了满足高产奶牛的能量需求，谷物和脂肪越来越多地被添加到反刍动物的日粮中。此外，在实验或实际条件下，脂质补充剂已被添加到反刍动物的日粮中，以增加牛奶和肉中生物活性 n-3 脂肪酸和共轭亚油酸的浓度。然而，这些饲养实践极大地增加了奶牛乳脂率下降的发生率。虽然诱导乳脂率下降可能是一种管理工具，但大多数情况下，日粮诱导的乳脂率下降是意外的，并与直接的经济损失有关。在这篇综述中，我们更新了脂肪酸（特别是来自瘤胃生物氢化的脂肪酸）以及瘤胃微生物在日粮诱导的乳脂率下降中的作用。尽管这种综合征似乎是多病因的，但最著名的因果因素仍然是瘤胃生物氢化途径从主要形成反式-11 中间产物向更多反式-10 中间产物的积累的转变，称为反式-11 向反式-10 的转变。这种反式-11 向反式-10 转变的微生物病因尚未得到很好的理解，似乎揭示日粮诱导的乳脂率下降的微生物机制具有挑战性。避免日粮诱导的乳脂率下降的潜在策略包括补充瘤胃稳定剂、选择更耐受的动物、对有风险的奶牛进行有针对性的管理、选择更高效的纤维消化奶牛，或减少精料和谷物的喂养。
