Role of Exogenous Oxytocin in Eliciting Milk Ejection in Dairy Cows

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Abstract
The efficacy of small doses of exogenous oxytocin in eliciting milk ejection was measured in 8 lactating Holstein cows. Treatments comprised i.v. administration of 0.02, 0.05. 0.10 and 0.30 IU of oxytocin. The smallest dose of oxytocin that induced milk ejection in all cows was 0.10 IU. Administration of 0.10 and 0.30 IU produced greater peak rates of milk flow and shorter milking times. Ranges for these 2 variables were 2.9-3.9 kg/min and 4.8-5.6 min. Variations in milk yield (8.2-9.1 kg/milking) were not significant, but more fat was harvested after administration of the 2 higher doses. Differences in peak concentrations of serum oxytocin were 17.7-21.2 .mu.U/ml. Differences in latent time before peak concentration was reached were 1.3-4.0 min.