Observations on development of natural infection and species composition of small strongyles in young equids in Kentucky.

Early development and maturation of species of small strongyles have not been studied extensively. Most information is on the first appearance of strongyle eggs in feces of foals. However, species cannot be determined in this manner because of similarity of the morphological features of the eggs. To determine more definitive knowledge on development and species composition of natural infections of small strongyles, eight equid foals were necropsied and examined at various ages (31 to 92 days of age). The entire contents of the large intestine were examined, and all worms (6,671) recovered were identified. This was done to recover small strongyle specimens in an effort to find the stage of development of the worms for different time periods. The primary interest was to obtain data on the potential prepatent period. A total of 17 species of small strongyles were recovered. The earliest gravid female was Cylicostephanus longibursatus in a 57-day-old foal; then Cylicostephanus goldi was positive at 64 days, Cyathostomum catinatum at 68 days, Coronocyclus coronatus and Cylicostephanus calicatus at 70 days, Coronocyclus labiatus, Cylicocyclus leptostomus, Cylicocyclus nassatus, Cylicostephanus hybridus, and Cylicostephanus minutus at 74 days, and Cylicostephanus bidentatus at 92 days. While it is not known exactly when the foals began eating pasture vegetation (typically they begin to graze a short time after birth) and first ate infective free-living third-stage larvae, the results give an indication of the natural prepatent period of several species of small strongyles. Additional data are presented on the number of worms per foal, distribution of the worms in the parts (cecum, ventral colon, and dorsal colon) of the large intestine, and proportion of species found.