Colostral immunoglobulin concentration in two fractions of first milking postpartum and five additional milkings.

Colostrum removed from mammary glands of parturient cows before letdown contained no greater concentration of immunoglobulins than colostrum collected after letdown and complete milking. Greater absorption of colostral immunoglobulins in calves suckling their dams initially postpartum over those hand fed by buckets or bottles is not from higher concentration of immunoglobulins in the gland and teat cistern. Colostral concentrations of three immunoglobulin classes (G, M, and A) obtained from one partial and six consecutive complete milkings at 12-h intervals postpartum decreased at different rates over time or number of milkings. Potential prophylactic value is discussed of continued lacteal secretion of immunoglobulins A and M available to the calf after intestinal closure to systemic absorption of colostral immunoglobulins.