Regulation of bovine labor with a long-acting carba-analog of oxytocin: a preliminary report.

The long-acting oxytocin (OT) analog 1-desamino-1-monocarba-E12-Tyr(OMe)]-OT(dCOMOT) was given IV to 13 pregnant cows near to term, but not in actual labor. The animals were para 1 to 5. Of these cows, four were treated with 20 mg of dexamethoasone 48 hours before the peptide was injected; the remaining nine animals were given no other medication. The animals usually were given a single injection of 5 mg of dCOMOT into the jugular veiw (5 to 7 micrograms/kg of body weight). In those instances where delivery was not complete within six hours, a second injection of peptide was given. In all instances, the first injection initiated labor as judged by the behavior of both uterus and cow. In most instances, there was also intermittent spurting of colostrum from the udder over a six-hour period after injection. In the four cows treated first with dexamethasone, the mean duration of induced labor was 4.35 hours after dCOMOT injection. In the nine non-treated cows, the mean duration of induced labor was 14.25 hours. The difference between the two values was significant. For both groups separately, and all data together, there was a linear inverse relation between the size of the external ostium uteri at injection and the duration of labor after peptide injection. All calves were healthy with no signs of hypoxia and the dose rates used did not result in any instance of uterine tetany or tachyphylaxis.