The Donkey Sanctuary Devon has, like many equine units, faced problems with anthelmintic resistance within the cyathostomin parasite population. Cyathostomins are ubiquitous, and although they are to some extent tolerated by their hosts they are also linked to potentially serious disease processes, making their management an important part of equine husbandry. Over use of the available anthelmintics has been blamed for the current situation, with cases of drug resistance reported across all the classes of anthelmintic currently licensed for use in equidae. Alternative methods of controlling cyathostomins include pasture hygiene by removal of faeces, which theoretically reduces re-infection by removing the immature larval stages from the grazing area, and targeted selective treatment (TST), which works by treating those animals shedding the highest number of eggs and leaving other animals untreated. The aim of this thesis is to evaluate these methods of parasite control at The Donkey Sanctuary Devon over an entire grazing season.
The most widely used method of monitoring parasitism is the Faecal Worm Egg Count
(FWEC), which is known to be highly variable and can be difficult to analyse appropriately
using traditional statistical methods. Therefore, computationally intensive Bayesian Markov chain Monte Carlo (MCMC) methods were employed, to ensure that the conclusions made are robust. A faecal egg count reduction test (FECRT) was also used to evaluate anthelmintic drug efficacy at the end of the study. There was a study population of 667 donkeys, divided into 15 groups under four different management strategies across four farms of The Donkey Sanctuary Devon. Ninety pasture larval counts and nearly 3000 FWEC were conducted from May 2010 to November 2010, followed by a FECRT on a proportion of the study population.
The principal conclusion was that twice-weekly removal of faeces from pasture, combined
with a relatively high TST threshold of 2000 EPG, provides control of cyathostominosis in
the donkey population studied. Manual removal of faeces (rather than using an automated
sweeper) was also found to significantly reduce the requirement for anthelmintic doses when using a treatment threshold of 2000 EPG. Where faeces removal from pasture is not practical, lower TST thresholds provide greater control of cyathostomin transmission than higher thresholds, at the cost of more frequent dosing. The groups with higher dosing rates showed reduced drug efficacy at the end of the grazing season, highlighting the necessity to reduce reliance on anthelmintic use.