Candy Paul M, Waghorn Tania S, Miller Chris M, Ganesh Siva, Leathwick Dave M
AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston North, 4442, New Zealand.
AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston North, 4442, New Zealand.
Vet Parasitol. 2018 Feb 15;251:56-62. doi: 10.1016/j.vetpar.2017.12.023. Epub 2018 Jan 2.
A replicated field trial was conducted to measure the effect on liveweight gain of failing to adequately control anthelmintic resistant populations of Cooperia oncophora and to determine whether populations, and hence production losses, increased with time. Eight mobs of 10 Friesian-Hereford calves were run on independent farmlets from January to December, over each of two years. All mobs were routinely treated with a pour-on formulation of eprinomectin every six weeks, which controlled parasites other than Cooperia. Four mobs also received six weekly treatments with an oral levamisole plus albendazole combination anthelmintic to control Cooperia. Liveweights, condition scores, faecal egg counts and larval numbers on pasture were measured throughout. In the first year animals treated with eprinomectin alone were 12.9 kg lighter in November than those treated with eprinomectin plus albendazole and levamisole, however, in the second year there was no difference between the treatment groups. The data, therefore, support the view that while C. oncophora is less pathogenic than other cattle parasite species it can still cause production losses when present in sufficient numbers. In the first year of the study, parasite load, as measured by faecal nematode egg count and larval numbers on herbage, tended to be higher and calf growth rates lower than in the second year. In both years, counts of infective larvae on herbage declined over winter-spring to be at low levels before mid-summer. This suggests that the carry-over of infection from one crop of calves to the next was relatively small and hence that the level of challenge to the young calves at the start of each year was largely due to the effectiveness of the quarantine treatments administered when the animals arrived on the trial site. Low survival of larvae on pasture between grazing seasons, resulting in small larval populations on pasture when drenching programmes start each summer, might help to explain the widespread development of anthelmintic resistance in this parasite under New Zealand grazing systems.
进行了一项重复的田间试验，以衡量未能充分控制抗驱虫药的柯氏类圆线虫种群对活体重增加的影响，并确定种群数量以及由此导致的生产损失是否随时间增加。在两年中的每一年，从1月到12月，在独立的小农场中饲养了8群，每群10头弗里生-赫里福德犊牛。所有牛群每六周定期用泼浇剂型的埃普利诺菌素进行处理，该药物可控制除柯氏类圆线虫以外的寄生虫。四群牛还接受了每周一次的口服左旋咪唑加阿苯达唑复方驱虫药处理，以控制柯氏类圆线虫。在整个试验过程中，测量了活体重、体况评分、粪便虫卵计数和牧场上的幼虫数量。在第一年，仅用埃普利诺菌素处理的动物在11月时比用埃普利诺菌素加阿苯达唑和左旋咪唑处理的动物轻12.9千克，然而，在第二年，各处理组之间没有差异。因此，数据支持以下观点：虽然柯氏类圆线虫的致病性低于其他牛寄生虫物种，但当数量足够多时，它仍会导致生产损失。在研究的第一年，通过粪便线虫虫卵计数和牧草上的幼虫数量衡量的寄生虫负荷往往高于第二年，犊牛生长率则低于第二年。在这两年中，牧草上感染性幼虫的数量在冬春季节下降，在仲夏前处于低水平。这表明从一批犊牛到下一批犊牛的感染传播相对较小，因此每年年初对幼犊造成的挑战水平很大程度上取决于动物到达试验场地时实施的检疫处理的效果。放牧季节之间牧场上幼虫的低存活率，导致每年夏天开始进行驱虫程序时牧场上的幼虫数量较少这一点，可能有助于解释在新西兰放牧系统下这种寄生虫中抗驱虫药现象的广泛出现。
