A survey of the trichostrongylid nematode species present on UK sheep farms and associated anthelmintic control practices

A survey of sheep farms from across the UK was conducted to establish information on farming practices, the trichostrongylid nematode species present and anthelmintic usage. Questionnaires and faecal samples were returned from 118 farms. First stage larvae (L1) were cultured from faecal samples and used for PCR analysis to determine the presence/absence of selected trichostrongylid species. Teladorsagia circumcincta was the only species present on 100% of farms. Haemonchus contortus was found on ∼50% of farms and was widespread throughout the UK. The most common Trichostrongylus spp. was T. vitrinus, found on 95% of farms. Determining the anthelmintic dose rate based on the weight of the heaviest animal in the flock to avoid under dosing was carried out on 58% of farms and was associated with a significantly lower mean epg (p < 0.001) in lambs. However, the weight of animals was only estimated (as opposed to animals weighed) on 32% of farms. Macrocyclic lactones (ML) were the most commonly used anthelmintic class for ewes, whilst benzimidazoles (BZ) were the most widely used in lambs. Twenty-two of the surveyed farms had confirmed anthelmintic resistance, of these, 18 had BZ resistance, one had levamisole (LEV) resistance and 3 had resistance to both BZ and LEV. No farms in this survey reported resistance to ML. Location had a significant effect on the incidence of anthelmintic resistance on the farms in this survey (p = 0.002). There was evidence of a lower risk of anthelmintic resistance occurring on farms from Scotland compared to those in England (pf = 0.047) and Wales (pf = 0.012). Farm type, flock type and open or closed status did not have any significant effect on the incidence of anthelmintic resistance when all other factors were taken into consideration.