The intramammary inflammatory response of genetically resistant Merino ewes infected with Haemonchus contortus.

The mammary glands of 103 pasture-reared non-lactating, non-pregnant Merino ewes were infused via the teat canal with antigens prepared from the nematode Haemonchus contortus, and the inflammatory response to infusion assessed by washing the gland of its contents after 24 h and 14 days. The ewes were of two genotypes: one with proven high levels of resistance to infection with the nematode H. contortus, the other random-bred animals with relative susceptibility to infection. On day 0 of a H. contortus infection, one gland of the subgroups of both genotypes was infused with the antigen preparation. At the same time, the other gland of the random-bred ewes was infused with sterile physiological saline. A third group of infected random-bred ewes was infused with only sterile physiological saline. Similar infusions were performed on other subgroups on days 12, 21 and 35 of infection, which was then terminated with anthelmintic. A fourth group of uninfected random-bred control ewes was given both infusions 35 days after the other groups were infected. Sheep of the resistant genotype had lower worm egg counts and smaller reductions in blood packed cell volumes from day 21 of infection. Infusion of antigen had no effect on the course of infection and no effect on the response of the other gland, which had been infused with saline alone. The dominant leukocyte response from the antigen-infused gland was eosinophilia. On all days of infusion, and after both 24 h and 14 days, eosinophil counts from the resistant genotype were higher than those from their random-bred counterparts. The sheep mammary gland provides a source of eosinophils whose number is related to host genotype and stage of infection and may provide a model for the investigation of cellular responses in mucosal immunity to nematode infections.