Role of exogenous oxytocin in eliciting milk ejection in dairy cows.

The efficacy of small doses of exogenous oxytocin in eliciting milk ejection was measured in eight lactating Holstein cows. Treatments comprised intravenous administration of .02, .05, .10, and .30 IU of oxytocin. The smallest dose of oxytocin that induced milk ejection in all cows was .10 IU. Administration of .10 and .30 IU produced greater peak rates of milk flow and shorter milking times. Ranges for these two variables were 2.9 to 3.9 kg/min and 4.8 to 5.6 min. Variations in mild yield (8.2 to 9.1 kg/milking) were not significant, but more fat was harvested after administration of the two higher doses. Differences in peak concentrations of serum oxytocin were 17.7 to 21.2 microunits/ml. Differences in latent time before peak concentration was reached were 1.3 to 4.0 min.