A total of 21 spp. of Cyathostominae was found in the lumen of the large intestine of 86 mature horses of various ages and breeds killed in SW England during 1972-1974. Cylicostephanus longibursatus, C. goldi, C. calicatus, Cyathostomum catinatum, C. coronatum and Cylicocyclus nassatus were found in > 80% of the horses, while Cylicocyclus insigne, Cyathostomum labratum, C. labiatum, Cylicostephanus asymetricus, Gyalocephalus capitatus, Cylicodontophorus euproctus, Cylicostephanus poculatus, Cylicodontophorus bicoronatus, Poteriostomum ratzii, Cylicocyclus ultrajectinus, C. brevicapsulatus and C. elongatus were detected in < 30%. Cylicostephanus minutus, Cylicocyclus leptostomus and Cyathostomum pateratum were found in 40-70%. Quantitative studies on 55 horses showed the adult cyathostome burdens to rise to a sharp peak (average 400,000/horse) in April-June and a lower one in Nov.-Dec. Parallel fluctuations occurred in the lumen populations of 4th-stage larvae. The most numerous cyathostomes were generally those species with the highest prevelence. The 5 most plentiful (C. nassatus, Cyathostomum catinatum, Cylicostephanus longibursatus, C. minutus and C. goldi) comprised > 90% of the total number of adult cyathostomes recovered. The 3 regions of the large intestine had adult cyathostome faunas of different composition. That of the dorsal colon was dominated by C. longibursatus and C. goldi, the ventral colon by Cylicocyclus nassatus and Cyathostomum catinatum, while the sparsely inhabited cecum accommodated several equally numerous species. Each species showed a characteristic site distribution, 11 occurring predominantly in the ventral colon, 8 in the dorsal colon and 2 in the cecum. Seasonal changes in the site distributions of C. catinatum and Cylicocyclus nassatus and in the size of the cyathostome burdens are discussed in relation to the epidemiology of cyathostome infections.
