Gibbs H C
Am J Vet Res. 1979 Feb;40(2):227-31.
A study was done in Maine to determine the relative importance of winter survival of nematode larvae in pasture and infected carrier animals as sources of infection for susceptible calves. Under the conditions of the experiment, it appeared that winter survivals in pasture of the infective stages of the genera Ostertagia, Cooperia, Nematodirus, and Trichostrongylus were of greater importance than carrier animals as sources of infection for susceptible calves. While animals in plots infected the previous summer and simultaneously allowed to graze alongside infected carrier animals did show more worms than those grazed only in infected plots, these differences were not statistically significant. Both groups had significantly (P greater than 0.01) more worms than did calves grazed only with carrier animals for the period of the experiment (8 weeks). It was also observed that carrier calves with low fecal egg counts (less than 200 eggs/g of feces) introduced in early spring to uncontaminated pasture could produce enough parasitic contamination by early fall to cause fulminating infections in susceptible calves grazing the pasture at the same time. Infected animals that survived clinical disease during their 1st summer developed a strong immunity which limited their acquisition of further infections when they were exposed to severe pasture contamination the following year.
在缅因州进行了一项研究，以确定牧场中线虫幼虫的冬季存活情况以及受感染的带虫动物作为易感犊牛感染源的相对重要性。在实验条件下，似乎奥斯特他线虫属、古柏线虫属、细颈线虫属和毛圆线虫属感染阶段在牧场中的冬季存活情况，作为易感犊牛的感染源比带虫动物更为重要。虽然前一年夏天感染地块中的动物，同时与受感染的带虫动物一起放牧，确实比仅在感染地块放牧的动物体内有更多的蠕虫，但这些差异没有统计学意义。在实验期间（8周），两组动物体内的蠕虫数量均显著（P大于0.01）多于仅与带虫动物一起放牧的犊牛。还观察到，早春引入未受污染牧场的粪便虫卵计数低（少于200个虫卵/克粪便）的带虫犊牛，到初秋时可能产生足够的寄生虫污染，从而导致同时在该牧场放牧的易感犊牛发生暴发性感染。在第一个夏天患临床疾病后存活下来的受感染动物产生了强大的免疫力，当它们次年接触严重污染的牧场时，这种免疫力限制了它们再次感染。
