Age and previous lactations as factors in the amount of bovine colostral immunoglobulins.

Blood and colostrum samples were obtained from 87 dairy cows in five lactation groups and analyzed for immunoglobulins G1, G2, M, and A. The five groups ranged from cows in first lactation, about 30 mo of age, to cows in fifth or more lactation, about 84 mo of age. Compared to older groups, blood serum of cows in first lactation contained less G1. Cows in first lactation also produced less total colostrum containing less total G1, G2, and M. Immunoglobulin G1 comprised over two-thirds of the immunoglobulins in the colostrum of all groups. Older cows had more immunoglobulin G1 in their colostrum with a tendency toward a higher ratio of G1 to G2. Amount of immunoglobulin A was constant through all lactations. After a rise in the second lactation, total amount of immunoglobulins G2 and M tended to level off. Total immunoglobulin G1 tended to reach a maximum in the third or fourth lactation, almost doubling in amount compared to the first lactation. Age and number of lactations are factors correlated with amounts of these immunoglobulins in colostrum.