A single injection of a long-acting oxytocin analog (carbetocin) at estrus onset synchronizes ovulations and enhances ovulation rate in ewes

Intromission during mating induces oxytocin release, likely shortening behavioral estrus and enhancing luteal function in ewes. Oxytocin's short half-life and limited transfer into the brain, however, restrict its exogenous use. Carbetocin, a long-acting oxytocin analog with peripheral effects, may be a practical pharmacological alternative. The aim was to determine whether systemic administration of Carbetocin could induce changes in sexual receptivity, follicular development, timing of ovulation during the estrous period, and luteal function similar to those observed after multiple matings. Timing of behavioral estrus was synchronized among 20 multiparous Merilin ewes. Upon detection of estrus, ewes were randomly assigned to a control (CON, n = 10) or Carbetocin-treated (CAR, n = 10) group. Ewes in the CAR group were administered a single intravenous dose of Carbetocin (0.2 mg/100 kg) at estrous onset. Follicular and luteal dynamics were monitored by ultrasonography, and sexual receptivity was assessed based on the ewe’ immobility when mounted of a ram. Luteal images were analyzed using ImageJ™ software to quantify both total and perfused corpus luteum areas. Carbetocin treatment increased the ovulation rate (1.9 ± 0.2 and 1.4 ± 0.2; P = 0.04) and reduced the dispersion in interval between the end of estrus and time of ovulation (SD: 3.86 and 8.01, respectively, P = 0.04). In conclusion, Carbetocin administration at the onset of estrus enhanced synchrony in time of ovulation among ewes, and increased ovulation rate but compared with ewes where there were multiple matings, did not shorten duration of estrus.