Seasonal changes in the prevalence of gastrointestinal nematodes in sheep in Nova Scotia, Canada

Abstract

Currently, there is a major lack of documentation regarding the seasonal changes in the prevalence of gastrointestinal nematodes (GINs) in sheep in Nova Scotia. Therefore, the objective of this study was to document the seasonal changes in the prevalence of GINs found in sheep in Nova Scotia so that farmers and researchers understand the trends in monthly and yearly infection. The primary focus was placed on the correlation between GIN levels and climate. It was predicted that the prevalence of GINs would increase in the early spring due to periparturient egg rise and cessation of winter larval hypobiosis, decrease during the late spring/early summer, remain low during a hot dry summer, increase in conjunction with the late summer/autumn rainfall and accumulated build-up of infective larvae (L3) and GIN ova on pasture, and decrease again as the GINs go into hypobiosis in the late autumn. For this study, particular attention was placed on the ova produced by Haemonchus spp., Telodorsagia (Ostertagia) spp., Trichostrongylus spp., Cooperia spp., Bunostomum spp., Nematodirus spp., and Trichuris spp. Faecal samples from a closed flock were taken in 2012 and 2013 that represented a typical flock encountered in Nova Scotia. Faecal egg counts (FEC) were used to monitor GIN prevalence, and were determined using the McMaster Technique. Larval cultures were used to identify certain GIN species. It was determined that the prediction was supported. However, prevalence increased from 2012 to 2013, which was not expected. This was likely caused by proliferative GINs dominating other GIN species, ova build up on pasture from month to month and year to year, or increasing anthelmintic resistance in GINs.