Ejection of Milk in Relation to Levels of Oxytocin Injected Intramuscularly

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Abstract
As level of oxytocin injected increased, the time from injection to beginning o£ milk flow (latent period) decreased, and the du- ration of milk flow and milk :~ield in- creased. The data indicated a difference in response at the levels of oxytocin used. A linear response was observed with all levels of oxytocin up to 5 USPU, followed by a plateau between 5 and 12.5, with a greater response when 20 USPU were injected. Correlation coefficients were --0.57 for the latent period, 0.52 for duration of milk flow, and 0.36 for milk yields. All corre- lation coefficients were highly significant (P = < .01). The response of lactating cows to varying levels o£ oxytocin injected intravenously has been studied by a number of investigators (1, 2, 4, 5, 6, 8, 9). Many of their studies have dealt with the effect on residual milk ejection. I(oshi and Petersen (4) compared effects of intravaginal, intramuscular, and subcutaneous routes of injection of oxytocin with that of the intravenous route. They found that higher dosages and longer waiting periods were neces- sary before a response comparable to that of 10 U of oxytocin administered intravenously was obtained. Premachandra et al. (9) com- pared intravenous with subcutaneous injection of oxytocin ia effect on removal of residual milk. They observed that 20 U injected sub- cutaneously, and 10 U injected intravenously resulted in maximum yields of residual milk with latent periods of 1.5 to 2 rain and 15 to 25 sec, respectively. No reference was found in the literature to the effects of exogenous oxytocin on milk ejec- tion after cisternal milk removal from the cow. Jones (3) studied these effects on milk ejection by ewes with varying levels of oxytocin. The objective of this study was to determine the effects of the cow's milk ejection of varying levels of oxytocin injected intramuscularly as measured by time from injection to beginning