Effects of unilateral prepartum milking on concentrations of immunoglobulin G1 and prolactin in colostrum.

Concentration of IgG1 in colostrum of Holstein cows is often low at calving. Unilateral prepartum milking was applied twice daily beginning 10 d prepartum to seven dry cows to determine whether premature lactogenesis caused cessation of IgG1 transfer into secretion. All four quarters were milked twice daily for 3 d postpartum. Samples of blood sera and mammary secretion were collected at each milking and analyzed for IgG1, progesterone, and prolactin. Four cows that produced > 4 L/d of milk by 4 d prepartum were retrospectively designated as responders. Three cows produced less and were designated as nonresponders. Milk volume was greater for responders than nonresponders from 6 d prepartum through parturition. Concentrations of prolactin and IgG1 in secretion were lower for responders than nonresponders and for milked than unmilked sides by 6 d prepartum. For responders, cumulative secretions of IgG1, milk, and prolactin were higher for milked than unmilked sides. For non-responders, the trend was similar, but differences were not significant. Cumulative secretion of IgG1 was higher for nonresponders. Differences between sides indicate that local control is important to the regulation of colostrogenesis. Differences in IgG1 between response groups indicate that maintenance of transport and dilution are important determinants of IgG1 concentration in colostrum.