Responses to infection with Haemonchus contortus and Trichostrongylus colubriformis in ewes of different reproductive status

Abstract

Groups of ewes which were either lactating, pregnant, non-lactating (lambs removed at birth) or unmated were subjected to twice weekly infection with constant numbers of H. contortus and T. colubriformis infective larvae for 8 weeks. From the size, structure and fecundity of their worm burdens, lactating ewes, and those in late pregnancy did not differ from each other and showed evidence of diminished immunological responses to infection compared with unmated ewes. The worm burdens of non-lactating ewes, slaughtered less than 30 days after parturition, resembled those of lactating and pregnant animals, but substantially fewer T. colubriformis were found in two ewes which had been deprived of their lambs for 33 and 40 days respectively. Increased numbers of mast cells, eosinophils and globule leucocytes were found in the gut mucosa of animals showing parasitological evidence of an immune response, and in particular, very few globule leucocytes were present in lactating and pregnant animals. Within animals over all groups there was a pronounced negative correlation between numbers of T. colubriformis and numbers of globule leucocytes in the small intestine.