Gastrointestinal nematode species burdens and host mortality in a feral sheep population

Abstract

Every few years a large proportion of the feral sheep on Hirta, St Kilda die due to food shortage. The effects of malnutrition are exacerbated by gastrointestinal nematodes. As found in sheep flocks in mainland Britain,Teladorsagia circumcinctahas long been considered the predominant and most pathogenic nematode species in all age classes of Soay sheep. Previous research indicated that intensity of this species showed a negative association with host age and comprised 75% of the entire gastrointestinal burden. Here we present new data that showTrichostrongylus axeiandTrichostrongylus vitrinusto be the predominant worm pathogens in young Soay sheep. In the present study,Trichostrongylusspp. burdens declined with host age whereasT. circumcinctaactually increased in burden over the first few age classes. Also, male hosts had significantly higher burdens ofTrichostrongylusspp. than females, with this genus making up a higher proportion of the strongyle egg producing community in male hosts than female hosts. These new findings raise questions concerning our previous interpretation of the main nematode species contributing to strongyle egg count in the population, and the contrasting infection patterns of these nematode species in unmanaged St Kilda Soay sheep compared with domestic sheep in mainland Britain.