The epidemiology of equine strongylidosis on Prince Edward Island

Detailed knowledge of the seasonal patterns of transmission of gastro-intestinal parasites of livestock is important for the design of effective and efficient control programmes. Climatic factors have a major impact on these patterns, hence it is necessary to investigate specific patterns for each unique climatic region. The purpose of this study was to monitor the level of strongyle infection and pasture contamination in pastured horses in Prince Edward Island; investigate the patterns of pasture infectivity during the grazing season; and determine the rates of development, migration and longevity of the free-living stages of horse strongyles on pasture plots at different times of the year.

Three horse herds were monitored for 13 months (April 1993-April 1994) using monthly faecal egg counts. Herds 1 and 2 were standbred brood mare herds; Herd 3 was a mixed breed herd consisting entirely of adult horses. Positive faecal samples were cultured and third stage larvae (L3) recovered and identified. Peak egg counts occurred between August and September in all groups. Minor peaks were observed between January and April. Cultures revealed that the majority of the eggs contributing to the peaks in Herds 1 & 2 were cyathostomes while in Herd 3 all were cyathostomes. These results were consistent with the necropsy findings from 3 tracer/cull horses from 2 of the herds, in which Strongylus vulgaris (Herd 1), Triodontaphorus spp. (Herd 1) and various species of cyathostomes (Herds 1 and 3) were recovered. (Abstract shortened by UMI.).