Induction of luteolysis in mares by ultrasound-guided intraluteal treatment with PGF2alpha

Abstract

To evaluate the technique of ultrasound-guided luteal injection in mares, PGF2alpha was administered under ultrasound guidance to horse mares (n = 7 to 9 per group) on Day 9 postovulation via either a systemic (im; zero, 0.01, 0.1, or 5 mg/dose) route or a local intraluteal (il; zero, 0.01 or 0.1 mg/dose) route. The luteolytic efficacy of each treatment was determined based on post-treatment decreases in progesterone concentration, interval to uterine edema (IE) and interovulatory interval (IOI). Local administration of PGF2alpha directly into the CL consistently induced luteolysis, at doses up to 50-fold lower than the lowest effective systemic dose. Significant decreases in IOI and IE occurred in mares treated with 5 mg PGF2alpha im or 0.1 mg PGF2alpha il, but did not occur in mares treated with 0.1 or 0.01 mg PGF2alpha im, 0.01 mg PGF il, vehicle il or vehicle im. Progesterone concentrations were reduced to less than 10% of pretreatment values by two days post treatment in mares treated with 5 mg PGF2alpha im or 0.1 mg PGF2alpha il. PGF2alpha doses of 0.1 mg im and 0.01 mg il were associated with smaller but significant progesterone decreases (to 66% and 46% of pre-treatment values, respectively) by two days post treatment. Progesterone values after administration of il vehicle did not differ from pre-treatment values by two days post treatment, but were significantly lower (53% of pre-treatment values) by four days post treatment. Intramuscular treatment with vehicle or 0.01 mg of PGF2alpha did not significantly reduce progesterone concentrations below pretreatment values. Overall, the minimum effective luteolytic dose of PGF2alpha given intraluteally was between 0.01 and 0.1 mg. Based on the results of this study, ultrasound-guided il injection appears to be a repeatable method for studying the direct effect of other chemicals on luteal function. However, the current procedure carries some risk, since three il injections were associated with ovarian abscesses.