Luteal function in jennies following PGF2alpha treatment 3 days after ovulation

Native PGF2a and its analogs have been used in the horse mare to manipulate ovarian activity, primarily as luteolytic agents toinduce estrus. Despite numerous studies on the effects of these luteolysins in the mare, to date only a single investigation has beenconducted in the jenny. The aim of this study was to evaluate the response of the corpus luteum (CL) to a single dose of PGF2a given3 days (72 h) after ovulation and to establish the plasma progesterone (P4) profile from pre-treatment to post-treatment ovulation inthe Martina Franca donkey. Twenty-two jennies were ultrasonographically monitored and treated 72 h after the detection ofovulation with 0.075 mg i.m. of R-cloprostenol. From the day of ovulation until ovulation post-treatment, blood was collected dailyfor P4 determination by enhanced luminescence immunoassay. All the jennies except one, exhibited behavioral signs of PGF2ainducedestrus within 4 days of treatment lasting 5.4 1.16 days. Post-treatment ovulation was also hastened, reducing theinterovulatory interval (9.6 days). In response to treatment, plasma P4 concentrations fell to estrus levels and then remained constantuntil the next ovulation in all but the non-responding animal. Our findings indicate that PGF2a treatment on Day 3 post-ovulationcauses the functional regression of the CL in the jenny, reflected both by the rapid induction of estrus and ovulation and by an abruptdrop in circulating P4 concentrations.[...]