Baker N F, Farver T B
Department of Veterinary Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis 95616.
Am J Vet Res. 1990 Oct;51(10):1663-7.
On the basis of the hypothesis that the peak numbers of infective nematode third-stage larvae (L3) on herbage in winter months results from fall contamination of pastures, 2 methods to reduce fall contamination were tested. In trial 1, morantal sustained-release boluses were administered to 15 fall-calving cows on Sept 7, 1982. Fifteen untreated cows (controls) were placed on separate pastures. Numbers of L3 on herbage during the winter and spring were assessed by use of worm-free tracer calves. In trial 2, 19 cattle due to calve in the fall were administered 200 micrograms of invermectin/kg of body weight, SC, on Sept 2, 1983. Also, 17 cattle similarly were given a placebo injection and served as control animals. Treated cattle were placed on the pasture used by control cattle in trial 1 and control cattle on the pasture used by treated cattle in trial 1. Worm-free tracer calves were again used to assess numbers of L3 on herbage. In trial 1, tracer calves grazing the control animal pasture from January 14 to 28 acquired 37 times as many nematodes as did those grazing the treated animal pasture. In trial 2, the greatest difference observed was a 10-fold increase of nematodes in calves grazing control animal pastures, compared with worm numbers in tracer calves grazing the treated animal pasture.
基于冬季牧草上感染性线虫第三期幼虫（L3）的峰值数量是由秋季牧场污染所致这一假设，对两种减少秋季污染的方法进行了测试。在试验1中，1982年9月7日给15头秋季产犊的母牛投喂了莫兰特缓释丸剂。15头未处理的母牛（对照组）被安置在单独的牧场上。通过使用无蠕虫的示踪小牛来评估冬季和春季牧草上L3的数量。在试验2中，1983年9月2日给19头秋季产犊的牛皮下注射了每千克体重200微克的伊维菌素。另外，17头牛同样接受了安慰剂注射并作为对照动物。将试验1中接受处理的牛安置在对照组牛使用过的牧场上，而对照组牛则安置在试验1中接受处理的牛使用过的牧场上。再次使用无蠕虫的示踪小牛来评估牧草上L3的数量。在试验1中，1月14日至28日在对照组动物牧场放牧的示踪小牛感染的线虫数量是在接受处理的动物牧场放牧的示踪小牛的37倍。在试验2中，观察到的最大差异是，在对照组动物牧场放牧的小牛体内的线虫数量比在接受处理的动物牧场放牧的示踪小牛体内的线虫数量增加了10倍。
