Ascaridia galli in laying hens: Adaptation of a targeted treatment strategy with attention to anthelmintic resistance

Sammanfattning: Ascaridia galli is a round-worm of wild and domesticated fowl in the Ascaridiidae family within phylum Nematoda. The direct life cycle includes free-living parasite eggs in the environment and larvae and adults worms in the small intestine of the host. Infection is associated with reduced health and production losses in laying hens. Since the EU ban on conventional battery cages in 2012, the occurrence of A. galli has increased markedly in many European countries. Treatment with anthelmintic drugs along with biosecurity measures and cleaning and disinfection of barns between flocks are central to control programmes. Treatment usually starts when parasite eggs are detected in faecal samples or when farmers observe worm expulsion or health impairment. At this late stage, the infection level and barn contamination with parasite eggs are often already high. This thesis therefore set out with the aim to gain more knowledge on optimal anthelmintic treatment strategies against A. galli by A) providing knowledge on the infection dynamics of A. galli in relation to deworming, B) validating a deworming strategy based on targeted treatment and C) apply tests for the detection and monitoring of AR . We showed that FLBZ was highly effective against all A. galli stages under field condition on two farms. However, the hens became re-infected within a week post treatment. We concluded that the way anthelmintics are used on farms needs to be refined. Comparison of the TT strategy and single treatment strategy (CT) with untreated control groups (UT) showed that barn contamination with parasite eggs, individual faecal egg counts (FEC) and worm burdens were lower in flocks where the TT strategy was applied. No significant difference was observed between the CT and UT flocks with regard to worm burden and FEC. We concluded that a single treatment late during the production cycle is suboptimal and cannot prevent the build-up of infection and barn contamination. We recommended that the TT strategy should be considered a better alternative to a single treatment late during production. Investigation into mutations of the β-tubulin isotype 1 gene at codon 167, 189 and 200 showed no evidence of AR. Moreover, the results of the faecal egg count reduction test and the larval development test did not point at existence of AR on the investigated farm.