Claerebout E, Hilderson H, Shaw D J, Vercruysse J
Department of Parasitology, Faculty of Veterinary Medicine, University of Gent, Merelbeke, Belgium.
Vet Parasitol. 1997 Mar;68(4):337-46. doi: 10.1016/s0304-4017(96)01086-2.
The aim of the present study was to determine if the presence of inhibited L4 Ostertagia ostertagi populations during the housing period influenced the level of acquired immunity in calves at the start of the second grazing season. Four groups (A-D) of first season grazing calves were turned out onto a heavily infected pasture for five months, while the fifth group (E) was kept as uninfected controls. At housing all group A calves were necropsied for worm counts. A mean total of 78915 Ostertagia worms were found, of which 85% were in the early L4 stage. The calves of group C were dewormed with ivermectin at housing, while groups B and D remained untreated. After the calves were housed, egg counts, pepsinogen and antibody levels all declined in groups B, C and D, but during the second half of the housing period pepsinogen and antibody levels increased again in groups B and D. The effect of housing on the resident worm population was evaluated by slaughtering all group B calves for worm counts at the end of the housing period. A mean burden of 57,950 Ostertagia was present, with 78% as early L4 larvae. The remaining three groups (C, D and E) were treated with oxfendazole and turned out on the same pasture as the previous year for a challenge period of four weeks. In the control calves (group E) the egg output rose steeply, while egg counts remained low in groups C and D. In addition the worm burdens of the previously infected groups C and D were significantly reduced (75-90%), and the percentage of inhibited L4 larvae was significantly increased compared to the control group E. No significant difference was observed between the calves that were treated at housing (group C) and the untreated animals of group D. It was concluded that the continued presence of an inhibited L4 population during housing was not essential for maintenance of immunity.
本研究的目的是确定在圈舍饲养期存在受抑制的L4期奥斯特他线虫种群是否会影响犊牛在第二个放牧季节开始时获得性免疫的水平。将四组（A - D）第一季放牧的犊牛放到重度感染的牧场放牧五个月，而第五组（E）作为未感染的对照。在圈舍饲养时，对所有A组犊牛进行剖检以计数蠕虫。平均共发现78915条奥斯特他线虫，其中85%处于早期L4阶段。C组犊牛在圈舍饲养时用伊维菌素驱虫，而B组和D组未进行处理。犊牛圈舍饲养后，B、C和D组的虫卵计数、胃蛋白酶原和抗体水平均下降，但在圈舍饲养期的后半段，B组和D组的胃蛋白酶原和抗体水平再次升高。在圈舍饲养期结束时，通过屠宰所有B组犊牛来计数蠕虫，以评估圈舍饲养对宿存蠕虫种群的影响。平均有57950条奥斯特他线虫，其中78%为早期L4幼虫。其余三组（C、D和E）用奥芬达唑进行处理，然后放到与前一年相同的牧场进行为期四周的激发期试验。在对照犊牛（E组）中，虫卵产量急剧上升，而C组和D组的虫卵计数保持较低水平。此外，之前感染过的C组和D组的蠕虫负荷显著降低（75 - 90%），与对照组E组相比，受抑制的L4幼虫百分比显著增加。在圈舍饲养时接受处理的犊牛（C组）和未处理的D组动物之间未观察到显著差异。得出的结论是，圈舍饲养期间受抑制的L4种群的持续存在对于维持免疫力并非必不可少。
