Forbes T D
Agric. Eng. Dept., University of Kentucky, Lexington 40546.
J Anim Sci. 1988 Sep;66(9):2369-79. doi: 10.2527/jas1988.6692369x.
Profitable livestock production from forages largely depends on efficiency of converting forages into products. Efficient grazing management systems require an understanding of the roles of system components. However, experimentation should be conducted with regard to the system as a whole rather than on the systems components in isolation. This may necessitate development of computer models. The short-term intake of forage by grazing animals is controlled both by the structure of the forage and by effects of the ingested forage on gut fill as moderated by the hunger-satiety complex. Intake can be defined as the product of bite size, rate of biting and grazing time. Measurement of these variables is facilitated by the use of esophageally fistulated animals and automatic recording devices. Bite size has the greatest influence on intake, with rate of biting and grazing time being compensatory variables. Sward structure influences bite size to varying degrees. In temperate grass swards, leaf surface height appears to be the dominant influence on bite size. But in tropical grass swards, leaf density and leaf:stem ratio have a greater influence on bite size than does leaf surface height. Alternative techniques to conventional grazing trials are described. Diversity of environments and forages in the U.S. requires further research into the development of grazing systems. In the future, small-scale trials and computer simulation techniques likely will be used to a greater extent.
利用牧草实现盈利的畜牧业生产很大程度上取决于将牧草转化为产品的效率。高效的放牧管理系统需要了解系统各组成部分的作用。然而，试验应该针对整个系统进行，而不是孤立地对系统组成部分进行。这可能需要开发计算机模型。放牧动物对牧草的短期采食量既受牧草结构的控制，也受摄入的牧草对肠道充盈度的影响，而这种影响由饥饿-饱腹感复合体调节。采食量可以定义为咬口大小、咬食速率和放牧时间的乘积。使用食管造瘘动物和自动记录设备有助于测量这些变量。咬口大小对采食量影响最大，咬食速率和放牧时间是补偿变量。草皮结构对咬口大小有不同程度的影响。在温带草地中，叶表面高度似乎是对咬口大小的主要影响因素。但在热带草地中，叶片密度和叶茎比相比叶表面高度对咬口大小的影响更大。描述了传统放牧试验的替代技术。美国环境和牧草的多样性需要对放牧系统的开发进行进一步研究。未来，小规模试验和计算机模拟技术可能会得到更广泛的应用。
