Studies on the Worm Populations in the Alimentary Tract of Breeding Ewes

Abstract

Groups of breeding ewes were slaughtered at intervals before and after lambing in March. A post-parturient rise in egg count was observed in which Ostertagia spp. were dominant but in which other species took part, in particular Haemonchus contortus, Nematodirus battus and Chabertia ovina. The important contribution made by dormant larvae of Ostertagia spp. was confirmed but it was also found that reinfection greatly increased the number of worms present while the earliest part of the rise, often beginning prior to parturition, was probably due to the increased fecundity of adult worms already present. Adults of H. contortus present in ewes after lambing were derived from the maturation of dormant larvae and it is probable that the same applied to C. ovina. The close association of the postparturient rise with lactation rather than with pregnancy or parturition was shown and two possible explanations for this were discussed.