1University of Zurich, Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, Switzerland.
Animal. 2010 Jul;4(7):979-92. doi: 10.1017/S1751731110000388.
Comparative physiology applies methods established in domestic animal science to a wider variety of species. This can lead to improved insight into evolutionary adaptations of domestic animals, by putting domestic species into a broader context. Examples include the variety of responses to seasonally fluctuating environments, different adaptations to heat and drought, and in particular adaptations to herbivory and various herbivore niches. Herbivores generally face the challenge that a high food intake compromises digestive efficiency (by reducing ingesta retention time and time available for selective feeding and for food comminution), and a variety of digestive strategies have evolved in response. Ruminants are very successful herbivores. They benefit from potential advantages of a forestomach without being constrained in their food intake as much as other foregut fermenters, because of their peculiar reticuloruminal sorting mechanism that retains food requiring further digestion but clears the forestomach of already digested material; the same mechanism also optimises food comminution. Wild ruminants vary widely in the degree to which their rumen contents 'stratify', with little stratification in 'moose-type' ruminants (which are mostly restricted to a browse niche) and a high degree of stratification into gas, particle and fluid layers in 'cattle-type' ruminants (which are more flexible as intermediate feeders and grazers). Yet all ruminants uniformly achieve efficient selective particle retention, suggesting that functions other than particle retention played an important role in the evolution of stratification-enhancing adaptations. One interesting emerging hypothesis is that the high fluid turnover observed in 'cattle-type' ruminants - which is a prerequisite for stratification - is an adaptation that not only leads to a shift of the sorting mechanism from the reticulum to the whole reticulo-rumen, but also optimises the harvest of microbial protein from the forestomach. Although potential benefits of this adaptation have not been quantified, the evidence for convergent evolution toward stratification suggests that they must be substantial. In modern production systems, the main way in which humans influence the efficiency of energy uptake is by manipulating diet quality. Selective breeding for conversion efficiency has resulted in notable differences between wild and domestic animals. With increased knowledge on the relevance of individual factors, that is fluid throughput through the reticulo-rumen, more specific selection parameters for breeding could be defined to increase productivity of domestic ruminants by continuing certain evolutionary trajectories.
比较生理学将家畜科学中建立的方法应用于更广泛的物种。这可以通过将家畜置于更广泛的背景下，从而深入了解家畜的进化适应。例如，对季节性波动环境的各种反应、对热和干旱的不同适应，以及特别是对食草性和各种食草动物生态位的适应。食草动物通常面临着这样的挑战，即高食物摄入量会降低消化效率（通过减少食糜停留时间和可供选择性进食和食物粉碎的时间），并因此进化出了多种消化策略。反刍动物是非常成功的食草动物。它们受益于前胃的潜在优势，同时又不像其他前胃发酵动物那样受到食物摄入的限制，这是因为它们独特的网胃分拣机制保留了需要进一步消化的食物，但清除了已消化的前胃内容物；同一机制还优化了食物粉碎。野生反刍动物在其瘤胃内容物分层的程度上差异很大，在“驼鹿型”反刍动物（主要限于食叶生态位）中几乎没有分层，而在“牛型”反刍动物（作为中间食草动物和食草动物更为灵活）中则存在高度分层的气体、颗粒和流体层。然而，所有反刍动物都能均匀地实现有效的选择性颗粒保留，这表明除了颗粒保留之外，其他功能在促进分层的适应进化中发挥了重要作用。一个有趣的新兴假设是，在“牛型”反刍动物中观察到的高液体周转率——这是分层的前提——是一种适应，不仅导致分拣机制从网胃转移到整个网胃-瘤胃，而且还优化了从瘤胃中收获微生物蛋白。尽管这种适应的潜在好处尚未量化，但向分层进化的趋同进化证据表明，这些好处必须是实质性的。在现代生产系统中，人类影响能量吸收效率的主要方式是通过操纵饮食质量。为了提高转化率，对家畜进行了选择性繁殖，这导致了野生和家畜之间的显著差异。随着对个体因素（即通过网胃的液体通量）相关性的认识不断增加，可以定义更具体的繁殖选择参数，通过继续某些进化轨迹来提高家畜反刍动物的生产力。
