Variations in the fecundity of strongylid worms of the horse

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Abstract
SUMMARY: A large proportion of Strongylus vulgaris, S. edentatus and Trichonema nassatum collected from the gut lumen of slaughtered horses during the winter did not contain eggs. The proportion of Trichonema catinatum without eggs declined to a low level during the winter and rose to relatively high levels during the summer, It has been concluded that worms without eggs are newly matured individuals and that seasonal variations in fecundity reflect similar fluctuations in the age distribution of the adult populations. These fluctuations are related to seasonal differences in the numbers of infective larvae ingested and to the length of parasitic development.Most Strongylus vulgaris, S. edentatus and Trichonema nassatum reach the adult stage during the winter and it has been suggested that an increase in worm numbers during this period is responsible for a rise in the faecal egg counts of horses in the spring. The observations on T. catinatum indicate that the level is maintained by the arrival of new individuals during the summer.I wish to thank Dr H. D. Crofton for his constant advice and encouragement during this work and Professor H. E. Hinton, F.R.S., for the provision of laboratory facilities. I am indebted to Mr L. J. Potter for allowing me to collect the parasites from his slaughterhouse at Bishop Sutton, near Bristol. This work was carried out during a research studentship funded by the Horse Race Betting Levy Board.