Immunoglobulin G1 transfer into induced mammary secretions: the effect of dexamethasone

The purpose of this study was to correlate the time of administration of the synthetic glucocorticoid dexamethasone with IgG1 concentrations in hormonally induced mammary secretions of nonpregnant cattle. Nonpregnant, nonlactating Holsteins were randomly assigned to three experimental groups of 8 cows each, and all were given .05 mg/kg of estrogen and .125 mg/kg of progesterone by subcutaneous injection every 12 h for 7 d. In addition, cows in groups 1 and 2 received dexamethasone (20 mg/d) on d 8 to 10 and on d 11 to 13, respectively. Group 3 cows were not given dexamethasone. The IgG1 concentrations in the mammary secretions of all three treatment groups rose steadily during d 1 to 7. The IgG1 concentrations in mammary secretions of groups 1 and 2 decreased sharply within 3 d of the first dexamethasone injection. The IgG1 concentrations in mammary secretions of group 3 also tended to peak and then decrease, but the decreases were generally later than those of cows receiving dexamethasone. The results indicate that the IgG1 transfer that occurs during induction of lactation is affected by glucocorticoid administration in a pattern similar to that reported during colostrum formation in pregnant cows.