Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Animal and Nutritional Sciences

Committee Chair

E. Keith Inskeed.


Effects of oxytocin on the ovine corpus luteum have been controversial for a number of years. The present study investigated the effects of atosiban, a combined oxytocin and vasopressin 1A antagonist, administered systemically to ewes on post estrus day 8 to 10. Atosiban was given in four bolus intravenous injections at 0, 60, 120 and 180 minutes with blood sampling every 15 minutes from -60 through 480 minutes. Concentrations of serum progesterone ng/ml were measured via radioimmunoassay. A log10 transformation of progesterone values was conducted to account for the heterogeneity of variance of the values. During the treatment interval (0 to 240 minutes), log10 concentrations of progesterone were lower in ewes treated with 20 mg (0.99) than in the 5 or 10 mg treated groups (1.00; P < 0.05). Control ewes (P < 0.0001) differed from ewes treated with atosiban (5, 10 or 20 mg). During times greater than 240 minutes (hours 4 to 24), log10 concentrations of progesterone decreased in control ewes (1.04) and were lower in the ewes treated with 5, 10 or 20 mg (1.01) of atosiban (P < 0.005). There was also a significant difference (P < 0.05) when comparing the 20 mg group (1.01) to the ewes treated with 5 and 10 mg of atosiban (1.02). Over the entire sampling period, mean log10 progesterone concentrations were lower (P < 0.001) in ewes treated with atosiban (1.00) compared to the control group (1.05). Among doses of atosiban, log10 concentrations of progesterone were lower (P < 0.0001) in ewes treated with 20 mg (0.99) atosiban than in ewes treated with 5 mg or 10 mg (1.01) atosiban. The overall effect of systemic treatment with atosiban in this study was to decrease mean log10 concentrations of progesterone relative to control ewes, which is in agreement with earlier findings using intraluteal infusion. The most effective dose of atosiban was 20 mg. In conclusion, systemic treatment with atosiban decreased concentrations of progesterone during the treatment phase of the experiment. Atosiban delivered in 20 mg maintained the lowest values in contrast to the control ewes and ewes treated with 5 or 10 mg of atosiban throughout the duration of the experiment.