Uterotonic effect of prostaglandin F2 alpha and oxytocin on the postpartum cow.

Uterine motility was measured in 6 mixed-breed beef cows 48 to 72 hours after parturition, using an intrauterine balloon technique. Baseline uterine motility was measured for 30 minutes after a stabilization period. After 25 mg of prostaglandin F2 alpha (PGF2 alpha) was given IM, motility was recorded for 2 to 4 hours. After PGF2 alpha injection, 200 IU of oxytocin was given IM and motility was recorded for 2 to 4 hours. Twenty-four hours later, oxytocin treatment was administered, and 2 to 4 hours later, PGF2 alpha was given. The tension-time index was calculated. When PGF2 alpha was given initially, it did not affect (P greater than 0.05) uterine motility. However, oxytocin after PGF2 alpha increased uterine motility an average of about 225% of that of base line 20 minutes after injection. When oxytocin was given before PGF2 alpha treatment, the average increment of uterine motility was 875% above base line 20 minutes after oxytocin injection. The injection of PGF2 alpha did not affect uterine motility significantly (P greater than 0.05), whether given before or after oxytocin treatment. There was a linear decrease in the uterotonic effect of oxytocin between 10 minutes and 2 hours. When oxytocin was injected first, the correlation coefficient for the time-response relationship was -0.98. When oxytocin was injected after PGF2 alpha, the correlation coefficient was -0.84. Seemingly, PGF2 alpha should not be used as a uterotonic agent in the postpartum cow; however, oxytocin was an effective uterotonic agent.