The effect of glucocorticoid on immunoglobulin secretion into colostrum in cows.

The effect of corticosteroid-induced parturition on transfer of immunoglobulin into mammary secretion of cows has been studied. Seven non-lactating cows in late gestation were injected intramuscularly with a long-acting synthetic glucocorticoid and the concentrations of IgG-1 and IgG-2 were followed in blood serum and mammary secretion which were collected before and after parturition. Within 1 week of injection the udder became distended with secretion identical in appearance to mature milk. In contrast to the situation in normal cows approaching parturition, both the concentration of IgG-1 in secretion and the selective index of IgG-1 decreased after the glucocorticoid injection. A feature of the results were absence in treated cows of the characteristic decrease in serum concentration of IgG-1 just before parturition. It is concluded that glucocorticoid treatment of cows in late pregnancy results in a decreased availability of colostral immunoglobulin to the newborn calf.