Vercruysse J, Hilderson H, Claerebout E
University of Gent, Faculty of Veterinary Medicine, Department of Parasitology, Belgium.
Vet Parasitol. 1995 May;58(1-2):35-48. doi: 10.1016/0304-4017(94)00714-n.
The influence of chemoprophylaxis on the immune response to gastrointestinal nematodes was evaluated in three groups of ten first-season grazing calves. Group C functioned as untreated controls, whereas Group L received two treatments, one at turn-out and one 8 weeks later, with doramectin (200 micrograms kg-1) and Group H three treatments, 3, 8, and 13 weeks post turn-out, with ivermectin (200 micrograms kg-1). At housing, five calves of each group were randomly selected for necropsied for worm counts. The remaining calves were challenged with 50,000 Ostertagi and 100,000 Cooperia oncophora and necropsied 4 weeks later. During the grazing season, Group C suffered from an outbreak of parasitic gastroenteritis which necessitated two anthelmintic treatments. In both treated groups no clinical symptoms were observed and growth rates were normal. Pepsinogen levels and antibody concentrations indicated a moderate and low gastrointestinal nematode infection in Group L and Group H, respectively. The Ostertagia and Cooperia worm populations present in the calves necropsied at housing were reduced in both treated groups in comparison with Group C. In the challenged calves, egg output was significantly higher in Group H than in Group L and Group C. Ostertagia and Cooperia worm burdens after challenge were high in Group H, moderate to low in Group L and low in Group C. This study indicates that highly suppressive prophylactic programmes, such as the ivermectin 3, 8 and 13 weeks schedule, can impair immune development against gastrointestinal nematodes during the first grazing season.
在三组每组十头的第一季放牧犊牛中评估了化学预防对胃肠道线虫免疫反应的影响。C组作为未治疗的对照组，而L组接受两次治疗，一次在放牧开始时，一次在8周后，使用多拉菌素（200微克/千克），H组在放牧开始后3周、8周和13周接受三次治疗，使用伊维菌素（200微克/千克）。在圈舍时，每组随机选择五头犊牛进行尸检以计数蠕虫。其余犊牛用50,000条奥斯特他线虫和100,000条柯柏线虫进行攻击，4周后进行尸检。在放牧季节，C组爆发了寄生性胃肠炎，需要进行两次驱虫治疗。在两个治疗组中均未观察到临床症状，生长率正常。胃蛋白酶原水平和抗体浓度分别表明L组和H组存在中度和低度胃肠道线虫感染。与C组相比，两个治疗组中在圈舍时进行尸检的犊牛体内的奥斯特他线虫和柯柏线虫数量均减少。在受到攻击的犊牛中，H组的虫卵产量显著高于L组和C组。攻击后H组的奥斯特他线虫和柯柏线虫负荷高，L组为中度至低度，C组为低度。本研究表明，高度抑制性的预防方案，如伊维菌素在3周、8周和13周的给药方案，可能会损害第一季放牧期间犊牛对胃肠道线虫的免疫发育。
