Parasite control methods used by horse owners: factors predisposing to thedevelopment of anthelmintic resistance in nematodes

One hundred and fifty horse owners, primarily private owners and riding sch ools, replied to a questionnaire concerning the practices they used to cont rol parasites. Twenty-seven had experienced a parasite problem. Faecal samp les from 188 horses selected at random showed that worm control practices w ere generally successful; however, many owners were not following recommend ations for slowing the development of resistant parasites. In 1996, 86 per cent of the owners were using either three or two classes of anthelmintic a year, and they used a median of six doses with a range from one to 11. App roximately half the owners, more commonly owners of up to five horses, pick ed up their horses' faeces at least once a week, but these owners also used more doses of anthelmintic a year than owners who did not pick up faeces. One-third of the owners manually removed Gasterophilus species eggs from th e horses' hairs, but 94 per cent of them also used ivermectin. Many owners treated specifically for Anoplocephala species, cyathostome larvae and Gast erophilus species, and these owners were the most likely to use three class es of anthelmintic a year. One-hundred-and-seven owners replied to a second questionnaire asking for information about the factors that influenced the ir anthelmintic control practices. Many owners, particularly private owners , were not influenced by the cost of the anthelmintic. For the timing and f requency of treatment and the choice of drug, owners were most influenced b y advertisements, magazine articles and veterinary surgeons. In two magazin es aimed at horse owners, the brands of drugs most frequently advertised we re the brands most commonly used by the owners, and articles in the magazin es recommended the use of three classes of drug per year. These results are discussed in relation to their influence on the development of anthelminti c-resistant nematodes.