Selective anthelmintic therapy has been recommended as a sustainable strategy for cyathostomin control in horse populations for several decades. The traditional approach has been to determine strongyle fecal egg counts (FEC) for all horses, with treatment only recommended for those exceeding a predetermined threshold. The aims are to achieve a reduction of overall egg shedding, while leaving a proportion of the herd untreated, which lowers anthelmintic treatment intensity and reduces selection pressure for development of anthelmintic resistance. This study made use of the cyathostomin model to evaluate the influence of treatment strategies with between 1 and 8 yearly treatment occasions, where either 1) all horses were treated, 2) a predetermined proportion of the herd remained untreated, or 3) horses were treated if their FEC exceeded thresholds between 100 and 600 strongyle eggs per gram. Weather data representing four different climatic zones was used and three different herd age structures were compared; 1) all yearlings, 2) all mature horses 10-20 years old, and 3) a mixed age structure of 1-20 years of age. Results indicated a consistent effect of age structure, with anthelmintic resistance developing quickest in the yearling group and slowest among the mature horses. Development of anthelmintic resistance was affected by treatment intensity and selective therapy generally delayed resistance. Importantly, the results suggest that the effects of selective therapy on resistance development are likely to vary between climatic zones and herd age structures. Overall, a substantial delaying of resistance development requires that the average number of treatments administered annually across a herd of horses needs to be about two or less. However, results also indicate that an age-structured prioritisation of treatment to younger horses should still be effective. It appears that a 'one-size-fits-all' approach to the management of anthelmintic resistance in cyathostomins is unlikely to be optimal.

中文翻译：

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处理腹足动物寄生虫的驱虫抗药性：研究基于避难所的策略的益处。

数十年来，选择性驱虫治疗已被推荐为控制马人群中总鞘脂的可持续策略。传统方法是确定所有马匹的粪便粪便卵数（FEC），仅建议对超过预定阈值的马进行治疗。目的是要减少总体卵的脱落，同时使一部分猪群未经处理，从而降低驱虫治疗的强度并降低产生驱虫抗药性的选择压力。这项研究利用了氰菊酯模型评估了每年1至8次治疗情况下治疗策略的影响，其中1）所有马匹均得到治疗，2）预定比例的牧群未得到治疗，或3）如果马的FEC超过每克100至600个坚韧鸡蛋的阈值，则对马进行治疗。使用了代表四个不同气候区的天气数据，并比较了三个不同的畜群年龄结构；1）所有一岁鸽，2）所有10-20岁的成年马，以及3）1-20岁的混合年龄结构。结果表明，年龄结构的影响是一致的，一岁鸽组中驱虫抗药性发展最快，而成年马中最慢。驱虫抗药性的发展受到治疗强度的影响，选择性治疗通常会延迟抗药性。重要的是，这些结果表明选择性治疗对耐药性发展的影响可能在气候区和畜群年龄结构之间有所不同。总体，抵抗力发展的实质性延误要求每年对一群马进行的平均治疗次数约为2或更少。但是，结果还表明，对年龄较小的马匹进行年龄结构的优先治疗仍然应该有效。似乎“一刀切”的方法来处理细胞寄主蛋白中的驱虫药耐药性可能不是最佳方法。