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

This research article explores parasite control practices among horse owners and how these may contribute to the development of anthelmintic resistance in parasites. It was found that most owners were successful at controlling worms, but many were not following recommendations to slow down the development of resistance.

Survey of Horse Owner Practices

• The study began with a questionnaire distributed to 150 horse owners, including private owners and riding schools. Out of these, 27 had experienced problems with parasites.
• In addition to the survey, faecal samples from 188 randomly selected horses were examined to see the effectiveness of the worm control practices.

Anthelmintic Use Among Horse Owners

• The survey revealed that in 1996, most of the surveyed horse owners were using either two or three classes of anthelmintic drugs per year, with a median usage of six doses, ranging from one to 11.
• It was found that around half the horse owners, particularly those owning up to five horses, picked up their horses’ faeces at least weekly. However, these owners also used more anthelmintic doses annually than those who did not pick up faeces.

Specific Treatment Practices

• Specific practices included the manual removal of Gasterophilus species eggs from the horses’ hairs by one third of the owners. However, 94% of these horse owners also made use of ivermectin.
• The most frequent treatments were targeted at Anoplocephala species, cyathostome larvae and Gasterophilus species, and the owners practicing this were more likely to use all three types of anthelmintic in a year.

Factors Influencing Anthelmintic Control Practices

• Further inquiry into the factors affecting the horse owners’ parasite control practices revealed that for many, particularly private owners, cost of the drugs was not a deciding factor.
• The timing and frequency of treatment and the choice of drugs were influenced largely by advertisements, magazine articles and advice from veterinary surgeons.
• The study discovered a correlation between the drug brand names advertised in two horse owner-oriented magazines and the drugs most commonly used by the horse owners. It was also found that the magazines recommended the use of three classes of drugs per year.

Implications for Anthelmintic Resistance

• The information gathered from this study is analyzed in the context of its potential effects on the emergence of anthelmintic-resistant parasites.
• The practices of using multiple drug classes per year, not following dosing recommendations, targeting specific parasites and being influenced by non-scientific sources for information could potentially contribute to the development of drug resistance in parasites.