Control of strongylosis in horses by alternate grazing of horses and sheep and some other aspects of the epidemiology of Strongylidae infections.

Alternate grazing of horses and sheep as a control measure for gastrointestinal helminthiasis was studied in three grazing experiments in 1981, 1982 and 1983. Each year a group of three mare yearling Shetland ponies, which were kept on a small pasture from spring to autumn, were compared with a similar group which grazed a similar or the same pasture until July and were subsequently removed to a similar pasture which had been grazed by sheep from April to July. In addition both groups were treated with an anthelmintic when the latter group was removed to the sheep pasture. Pasture larval counts and worm counts and, in 1982 and 1983, faecal egg counts, clinical condition, total protein, albumin and beta-globulin levels demonstrated that the groups removed to sheep pasture acquired considerably lower burdens of nematodes of the subfamilies Cyathostominae and Strongylinae, but considerably higher burdens of Trichostrongylus axei than the groups which were not moved. These T. axei infections resulted in higher serum pepsinogen levels in the former groups compared to the latter in 1981 and 1982. At necropsy an important part of the T. axei burdens and, in 1982 and 1983, the Cyathostominae burdens consisted of inhibited early third stage larvae. A total of 20 species of the subfamily Cyathostominae and 7 species of the Strongylinae were found. Generally the composition of species was in agreement with other observations in western Europe, the most common species being: Cylicostephanus longibursatus, Cylicostephanus minutus, Cylicostephanus calicatus, Cylicostephanus goldi, Cylicostephanus poculatus, Cyathostomum labratum, Cyathostomum coronatum, Cyathostomum catinatum, Cylicocyclus leptostomus, Cylicocyclus nassatus, Cylicocyclus insigne, Strongylus edentatus and Strongylus vulgaris.