Effect of cloprostenol on luteolysis in jennies

An intensive farm system has progressively emerged with the rapid development of the donkey industry. One of the primary challenges impeding the development of the donkey industry and the preservation of endangered donkey species is the low reproductive efficiency of jennies (Feng Yang et.al. Equine Veterinary Journal 2021, 53: 1218-1226). In donkeys, luteolysis occurs between days 15 and 17 after ovulation (Carluccio A. et.al. Theriogenology, 2007, 68(6): 914-919). To shorten the estrus cycle, a new estrus cycle may start after luteolysis is induced by the PGF2α analog (Duccio P. et.al. Theriogenology, 2018, 121: 175-180). Treatment of mares and cattle with PGF2α analogs from the fifth day after ovulation induces luteolysis (Bergfelt DR. et.al. Theriogenology, 2006, 65(8): 1605-1619). However, information regarding luteolysis in jennies is limited. In this study, we aimed to investigate the effect of cloprostenol on luteolysis in jennies. The PGF2α analog used in the experiment was cloprostenol (0.2 mg/2 ml, Ningbo Second Hormone Factory, Zhejiang, China). To study the effects of different cloprostenol doses on the estrus cycle, jennies were treated with 0.2 mg (n=30), 0.4 mg (n=30), or 0.6 mg (n=30)cloprostenol (PGF2α), respectively. The time of luteolysis, ovulation interval, follicular size at ovulation, and ovulation rates were compared between the groups. The results showed that luteolysis rates in the jennies within 72 h of treatment were higher than 90% in the three treatment groups. The time required for luteolysis was not statistically different among the three groups. In addition, the estrus interval, ovulation interval, ovulation diameter, and ovulation rate did not differ among the three groups. To examine the timing effect of cloprostenol treatment on the estrus cycle, jennies were treated with 0.4 mg cloprostenol on the third (D 3, n=30), fifth (D 5, n=30), or seventh (D 7, n=30) day following ovulation, respectively. The results showed that the luteal phase of the D 3 treatment group was shorter than that of the D 5 and D 7 treatment groups, and in the D 5 treatment group was shorter than that of the D 7 group (P < 0.05). In can be concluded that treatment with 0.4 mg cloprostenol on the third day following ovulation shortens the length of the luteal phase and estrus cycle considerably.