The challenge now is to convince stud owners/managers to deviate from their current practices to control strategies that are more likely to preserve anthelmintic efficacy. Veterinarians need to get more involved in implementing these control strategies, with better emphasis placed on the role of diagnostic tests in facilitating targeted treatments and in investigating anthelmintic sensitivity in the associated nematode populations.

Few studies have described the combined effect of age, gender, management and control programmes on helminth prevalence and egg shedding in grazing equines. Here, fecal samples collected from 1221 Thoroughbred horses, residing at 22 studs in the UK, were analysed. The distribution of strongyle eggs amongst individuals in relation to age, gender and management practices was investigated. Fecal worm egg counts (FWECs), described as the number of eggs per gramme (epg) of feces, were determined using a modification of the salt flotation method. The FWEC prevalence (mean%) of strongyles, Parascaris equorum, tapeworm spp. and Strongyloides westeri was 56, 9, 4 and 8%, respectively. Strongyle, P. equorum, tapeworm spp. and S. westeri infections were detected on 22 (100%), 11 (50%), 9 (41%) and 8 (36%) of studs, respectively. Within all age and gender categories, strongyle FWECs were highly over-dispersed (arithmetic mean = 95 epg, aggregation parameter k=0·111) amongst horses. Animal age, last anthelmintic type administered and management practices (for example, group rotation on grazing) most strongly influenced strongyle prevalence and level of egg shedding (P < 0·05). Overall, 11% of equines (range: 234-2565 epg) were responsible for excreting 80% of the strongyle eggs detected on FWEC analysis. The results confirm that the judicious application of targeted treatments has potential to control equine strongyle populations by protecting individual horses from high burdens, whilst promoting refugia for anthelmintic susceptible genotypes.

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The high frequency of MOX use represents a potential risk factor for macrocyclic lactone resistance. As veterinarians were the most influential factor in anthelmintic choice, awareness of macrocyclic lactone resistance and potential risk factors for its development and spread should be incorporated into client advice.

No abstract