Oxytocin on Ovarian Function in Cycling and Hysterectomized Heifers

Abstract

Interestrous periods of 8 to 9 days were observed in heifers following 7 daily subcutaneous injections of oxytocin beginning at estrus. Oxytocin treatment in partially hysterectomized heifers and in heifers with the uterus opened in situ was equally effective in reducing the interestrous period. The corpus luteum was maintained and no estrus occurred in heifers given oxytocin for 7 days beginning on day 1 and hysterectomized on day 2. Carbon-marked corpora lutea, obtained after hysterectomy and injections of oxytocin, contained progesterone in concentrations equal to that of the mid-luteal phase of the estrous cycle, whereas the concentrations of Δ4 pregnen-20 β-ol-3-one (20 β-ol) were twice that found during the mid-luteal phase of the estrous cycle. Hysterectomized heifers returned to estruswithin a few days after enucleation of the corpus luteum. The corpus luteum of this estrous period was maintained until slaughter at 60 days. Uterine distention by plastic and metal cylinders in heifers resulted in an inconsistent reduction of the estrous cycle.