IMMUNE DEFENCES OF THE BOVINE MAMMARY GLAND

Toufic  O. NACHAR

Mastitis remains a serious economic and welfare problem despite the implementation of control measures, and there remains the need for alternative immunoprophylactic methods of control. The aim of this study was to determine the fate of antigens infused into the mammary gland and relates that to the subsequent immune response, so as to provide an indication of the mechanisms responsible for the generation of the immune response in the udder.

Initial studies were performed in a mouse model. Groups of lactating mice were inoculated intra-mammarily with various doses of ovalbumin. This resulted in the appearance of IgG in serum, and IgA and IgG in milk. In serum no IgA antibodies were detected. But IgG in milk increased significantly throughout lactation. IgA antibody appeared in milk from the highest dose group, and the number of responders for IgG increased in milk, but not in blood.

A parallel study in the cow looked at the uptake and fate of killed S.uberis and ovalbumin in the udder, and its subsequent effect on the immune response : a) pregnant heifers were locally infused, and tissue samples were collected from the gland and local lymph nodes, at intervals after infusion. The epithelium of the udder was involved in uptake of bacteria and ovalbumin, though this was limited in the case of the bacteria. Both ovalbumin and bacteria were present in the tissues as early as 1 and 3 hours after infusion, respectively. However, there was no evidence of phagocytosis in the connective tissue. Large numbers of bacteria remained in the lumen of ducts and alveoli. Ovalbumin appeared in blood 5-10 minutes after infusion, and in non-infused quarters. b) pregnant cows were intra-mammarily infused with ovalbumin and S.uberis. This resulted in IgG_l and IgG₂ antibody to ovalbumin in serum, and IgG_l and IgA antibody in serum and IgA antibody in milk, after infusion with S.uberis. IgA in milk was significantly higher in the infused quarters compared with the controls up to 2 months after calving. The IgA response in serum was of short duration in the majority of animals. All animals had pre-existing antibodies.