Animal Nutrition and Health, Scottish Agricultural College, West Mains Road, Edinburgh, UK.
Prev Vet Med. 2009 Oct 1;91(2-4):95-106. doi: 10.1016/j.prevetmed.2009.05.026. Epub 2009 Jun 27.
In grazing systems, heterogeneous distributions of forage resources and faeces result in localised accumulations of nutrients and parasites (both macroparasites and microparasites), creating trade-offs between the costs of exposure to infestation or infection and the benefits of nutrient intake. Each contact between livestock and faeces in the environment is a potential parasite/pathogen transmission event. Thus, herbivores must make foraging decisions in complex environments which will affect their intake of both nutrients and parasites. However, the pattern of forage and faecal resources in agricultural environments will also be affected by the grazing management system in place. The aim of this study was to investigate the effect of grazing management on the risk of infection/infestation to livestock. We used a spatially explicit individual based stochastic foraging model to simulate livestock contact (both grazing and investigative) with faeces in the environment. The model was parameterised to simulate cattle grazing under three types of grazing management: set stock (i.e. where sward growth and cattle intake are in equilibrium in a single field); a two pasture rotation grazing system with increasing number of rotations; and a rotational grazing system with two rotations and increasing subdivisions of the pasture. Overall the amount of cattle contact with faecal-contaminated patches was similar in both set stocking and rotational grazing scenarios, suggesting no difference in the risk of infection or infestation between the different systems. However, the timing and absolute amounts of peak contact varied greatly indicating that different grazing management systems expose livestock to risks of different types of parasites at different times of the grazing season. Intensive rotational systems with small pasture blocks (especially the first grazing period) maximised livestock contact with fresh faeces, and thus exposure to microparasites (e.g. bacterial pathogens). Livestock re-entering pasture blocks in rotational systems and set stocked livestock had the highest contact with old faeces and thus have a greater risk of macroparasite transmission (gastrointestinal nematodes). This study highlights how livestock management affects the highly dynamic interaction between livestock and distributions of parasites in the environment and thus the levels of livestock exposure to parasites and pathogens via the faecal-oral route.
在放牧系统中，饲料资源和粪便的不均匀分布导致养分和寄生虫（包括大型寄生虫和小型寄生虫）在局部积聚，从而在暴露于感染或感染的成本与营养摄入的益处之间产生权衡。家畜与环境中的粪便每一次接触都是寄生虫/病原体传播的潜在事件。因此，食草动物必须在复杂的环境中做出觅食决策，这将影响它们对营养物质和寄生虫的摄入。然而，农业环境中的饲料和粪便资源模式也将受到放牧管理系统的影响。本研究旨在探讨放牧管理对家畜感染/感染风险的影响。我们使用空间显式个体基于随机觅食模型来模拟家畜与环境中的粪便接触（包括放牧和调查性接触）。该模型被参数化以模拟三种放牧管理下的牛放牧：固定存栏（即在单个牧场中，牧草生长和牛的摄入量达到平衡）；具有增加轮次的两牧场轮牧系统；以及具有两个轮次和增加牧场细分的轮牧系统。总体而言，牛与粪便污染斑块的接触量在固定存栏和轮牧情景中相似，表明不同系统之间的感染或感染风险没有差异。然而，接触高峰期的时间和绝对数量差异很大，表明不同的放牧管理系统在放牧季节的不同时间使家畜面临不同类型寄生虫的风险。具有小牧场块的密集轮牧系统（尤其是第一个放牧期）最大限度地增加了家畜与新鲜粪便的接触，从而暴露于小型寄生虫（例如细菌病原体）。轮牧系统和固定存栏家畜重新进入牧场块时，与旧粪便接触最多，因此更有可能传播大型寄生虫（胃肠道线虫）。本研究强调了家畜管理如何影响家畜与环境中寄生虫分布之间高度动态的相互作用，从而影响家畜通过粪-口途径接触寄生虫和病原体的程度。
