Epidemiological studies on horses infected with nematodes of the family Trichonematidae (Witenberg, 1925)

Observations are reported on seasonal changes in the age structure of populations of nematodes of the family Trichonematidae recovered at regular intervals from the lumens of the large intestines of horses slaughtered in S.W. England. The results show that changes in the size of parasitic populations of Trichonema nassatum follow seasonal variations in the rate of infection, more individuals maturing during summer/autumn than during winter/spring because of proportional differences in the numbers of infective larvae ingested from the pasture. In contrast, larvae of T. longibursatum, T. catinatum and T. goldi ingested by grazing horses during summer accumulate in the gut wall rather than promptly returning to the lumen and developing to maturity. Their development is apparently inhibited until the following spring when 4th-stage larvae emerge en masse and quickly reach the adult stage. The relationship between fluctuations in the size of the adult populations of the 4 species studied and the characteristic seasonal variations in horse faecal egg counts is discussed.