The use of legumes under innovative grazing methods and strategic nutrients supplementation for cattle in tropical grazing systems

牧草是全世界反刍动物的主要饲料来源。然而，放牧动物的生产力通常受到低氮供应的限制，这阻碍了瘤胃中微生物蛋白质的合成。放牧系统下的N供应可以通过将豆科植物纳入草地，通过补充动物与集中的N源，或通过两种策略的组合来增加。豆科植物已成功地纳入温带放牧系统，但纳入热带系统则不太成功。这与豆类易受践踏以及这些物种优先放牧牲畜有关，这增加了豆类的压力。此外，牧场管理战略，这是从专属草地的基础上垂直落叶的植物，可能会导致极端的落叶豆类，进一步限制了豆类纳入热带放牧系统。在豆科植物被纳入放牧系统的情况下，动物营养状况的改善已经变得明显，但是，由于动物的优先放牧，已经观察到N浪费的证据，这与有效利用自然资源的目标相反。本研究的目的是：（1）评价一种基于豆科牧草混播草地水平利用的创新轮牧管理，在第一项研究中，将瘤牛分别在纯草地和豆科牧草混播草地上放牧，研究了氮素补充和牧草对放牧牛瘤胃动力学的影响。将根据未放牧牧场的水平比例的轮作方案与根据牧场高度的控制轮作方案进行比较。正构烷烃标记方法将用于估计总摄入量和每种消耗的比例。第二次试验用在单一牧草或豆科牧草牧场放牧的瘤牛，并补充有机或无机来源的N，将评估固体和液体瘤胃生物量的流出率。这将通过给公牛安装一个蠕动泵来完成，在放牧期间不断注入铬和镱-通过率的标志。微生物蛋白质合成和饮食选择将估计从嘌呤衍生物排泄，和正构烷烃的方法，分别。这项研究将产生一个更好的了解植物×动物的相互作用在放牧混合豆科牧草草地，它也将提供一个改进的牧场管理策略，成功地将豆科植物纳入热带放牧系统。此外，还将对豆科牧草混播草地上放牧时牛的瘤胃动态的生理反应产生重要的认识，因为补充N的特性对牛的瘤胃动态的影响。

Grasses are a main feed source for ruminants across the world. However, the productivity of grazing animals is commonly limited by a low supply of nitrogen (N), which hinders microbial protein synthesis in the rumen. The N supply under grazing systems can either be increased by incorporating legume species into the sward, by supplementing animals with concentrated N sources, or by a combination of both strategies. Legumes have been successfully incorporated into temperate grazing systems, but their incorporation into tropical systems has been less successful. This is related to the legumes’ susceptibility to trampling as well as to the preferential grazing of livestock for these species, which adds pressure to legumes. Additionally, pasture management strategies, which are adopted from exclusive grass swards based on the vertical defoliation of plants, can cause extreme defoliation of legumes, further limiting the incorporation of legumes into tropical grazing systems. In cases when legumes have been incorporated into the grazing system, an improvement in the nutritional status of animals has become clear, but, because of the preferential grazing by animals evidence of N wastage has been observed, a development opposite to the aim of efficiently using natural resources.Therefore, the aims of this research are i) to evaluate an innovative rotational grazing management based on the horizontal utilization of pastures in mixed legume-grass swards, and ii) to the study the interactions between N supplementation and the forages available in the pasture on the digesta kinetics of grazing cattle.For this, in a first study Zebu bulls will graze on experimental plots of only grasses or mixed legume-grass swards. A rotational scheme based on the horizontal proportion of un-grazed pasture will be compared with a control rotation scheme based on pasture height. The n-alkanes marker method will be used to estimate total intake and the proportion of each species consumed. A second trial with Zebu bulls grazing in sole grass or grass- legume tree pastures and supplemented with organic or inorganic sources of N will evaluate the fractional outflow rate of solid and liquid rumen digesta. This will be done by fitting the bulls with a peristaltic pump to constantly infuse Chromium and Ytterbium –markers for the passage rate - during grazing. Microbial protein synthesis and diet selection will be estimated from the purine derivatives excretion, and the n-alkanes methodology, respectively. The research will produce a better understanding of the plant × animal interactions during grazing of mixed legume-grass swards; it will also provide an improved pasture management strategy for a successful incorporation of legumes into tropical grazing systems. Moreover, important understanding will be generated on the physiological responses of the rumen dynamics of cattle, when grazing on mixed legume-grass swards, as affected by the characteristics of the supplemental N.