The relative contributions of 'T. colubriformis', 'T. vitrinus', 'T. axei' and 'T. rugatus' to sheep infected with 'Trichostrongylus' spp. on the northern tablelands of New South Wales

Abstract

This survey was designed to determine the spatial and temporal distribution and the relative contributions of 'Trichostrongylus colubriformis', 'Trichostrongylus vitrinus', 'Trichostrongylus axei' and 'Trichostrongylus rugatus' to sheep infected with 'Trichostrongylus spp.' on the northern tablelands of NSW. Thirty completed larval cultures were collected from a commercial parasitology laboratory servicing the northern tablelands of NSW between June and December 2007. Cultures were selected at random from farms within the study area whenever the combined results of faecal worm egg counting and coproculture indicated >200 'Trichostrongylus spp.' eggs per gram and >40% 'Trichostrongylus spp.' respectively. Selection of cultures was constrained to prevent multiple samples from a single grazing property. Larval cultures were stored at 4 °C and subsequently used to artificially infect GIN-free sheep which were sacrificed for the collection of gut contents at 3 weeks post-infection. Abomasal contents were examined for the presence of 'T. axei'. From the anterior small intestine 100 adult male 'Trichostrongylus spp.' per animal were identified to species ('T. colubriformis', 'T. vitrinus' or 'T. rugatus') according to spicule morphology. 'T. colubriformis' was the most prevalent 'Trichostrongylus' species (present in 100% of the samples) as anticipated in a summer rainfall region. 'T. vitrinus' was present in 20% of the samples whilst 'T. rugatus' was present in only 10% of the samples, yet when present comprised a much higher proportion of the total 'Trichostrongylus' population than has previously been reported. In an unexpected result, 'T. axei' was not identified in any of the samples collected. The epidemiological basis for these results and the implications for gastro-intestinal nematode control are discussed.