Claerebout E, Dorny P, Vercruysse J, Agneessens J, Demeulenaere D
Department of Parasitology, Faculty of Veterinary Medicine, University of Gent, Merelbeke, Belgium.
Vet Parasitol. 1998 Apr 30;76(4):287-303. doi: 10.1016/s0304-4017(98)00101-0.
The objective of this study was to investigate the influence of different types of chemoprophylaxis in first season grazing calves on their resistance against a natural reinfection with Ostertagia ostertagi and Cooperia oncophora in the second grazing season. Thirty helminth-naive crossbred calves were randomly divided in three groups of 10 animals. The animals of group B received an ivermectin sustained release bolus on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg(-1) BW). Group C was the untreated control group ('immune' controls). Although exposure to gastrointestinal nematodes in the first grazing season was only limited, the chemoprophylactic treatments in groups B and D resulted in three distinctly different infection levels (group C > group D > group B). At the start of the second grazing season, six helminth-naive steers (group N, 'susceptible' controls) were turned out together with the second season animals. After 3 weeks of grazing, the 'susceptible' controls were slaughtered, together with four animals from each other group. Parasitological and immunological parameters indicated that resistance to reinfection with Ostertagia was reduced in the chemoprophylactic treated animals, and was negatively related to the degree of suppression of host-parasite contact in the first grazing season (group C > group D > group B > group N). None of the groups had developed a complete resistance against Cooperia yet. A negative relationship was observed between reduction of first grazing season exposure, and weight gains early in the second grazing season. The remaining animals stayed on pasture until the beginning of November. At the end of the second grazing season, levels of acquired resistance against Ostertagia infection were similar in all groups, and all animals had become immune against Cooperia. No effect of first year chemoprophylaxis on total weight gains could be demonstrated. Because of discrepancy between pasture larval counts and tracer worm counts, it was not possible to draw firm conclusions on the effect of chemoprophylaxis on pasture infestation levels in the second year.
本研究的目的是调查第一季放牧犊牛不同类型化学预防措施对其在第二季放牧季节抵抗奥斯特他线虫和牛古柏线虫自然再感染能力的影响。30头未感染蠕虫的杂交犊牛被随机分为三组，每组10头。B组动物在第0天接受了伊维菌素缓释丸剂。D组犊牛在第0天和第56天皮下注射多拉菌素（0.2mg/kg体重）。C组为未处理的对照组（“免疫”对照）。尽管第一季放牧季节对胃肠道线虫的接触仅有限，但B组和D组的化学预防处理导致了三种明显不同的感染水平（C组>D组>B组）。在第二季放牧季节开始时，6头未感染蠕虫的阉牛（N组，“易感”对照）与第二季动物一起放牧。放牧3周后，“易感”对照与每组另外4头动物一起被屠宰。寄生虫学和免疫学参数表明，化学预防处理的动物对奥斯特他线虫再感染的抵抗力降低，且与第一季放牧季节宿主-寄生虫接触的抑制程度呈负相关（C组>D组>B组>N组）。没有一组对古柏线虫产生完全抵抗力。观察到第一季放牧季节接触减少与第二季放牧早期体重增加之间存在负相关。其余动物一直留在牧场直到11月初。在第二季放牧季节结束时，所有组对奥斯特他线虫感染的获得性抵抗力水平相似，所有动物都对古柏线虫产生了免疫力。无法证明第一年化学预防对总体重增加有影响。由于牧场幼虫计数和示踪蠕虫计数之间存在差异，无法就化学预防对第二年牧场感染水平的影响得出确凿结论。
