Successful mule embryo transfer to a recipient mule during late diestrus

Abstract

Mating between a donkey (Equus asinus) and a mare (Equus caballus) results in a mule foal, which is an infertile hybrid due to the different number of chromosomes in the parent species. However, mules have been successfully used as recipients of donkey embryos, horse embryos and, recently, mule embryos. In non-cyclic recipient mules, progesterone supplementation is needed to sustain pregnancy, but some mules can develop pre-ovulatory follicles which ovulate and form active CLs that produce enough progesterone to sustain pregnancy. In spite of this, it is possible that the induction of additional CL formation to increase progesterone concentrations prior to embryo transfer could increase the chances of successful pregnancy. In this study an 8-day old mule embryo produced by the insemination of a mare with fresh donkey semen was transferred to a cyclic mule that had been induced to form a secondary CL by the injection of 1.8mg of deslorelin acetate on day 8 post-ovulation, when a spontaneously developed follicle reached 38 mm of diameter. Progesterone concentrations at that time confirmed that the primary CL was active. Secondary ovulation occurred 2 days later and a secondary CLformed during the following days, resulting in a significant increase in blood progesterone concentrations. The 8-day old embryo was transferred nine days after the secondary ovulation (19 days after the primary ovulation), when both the primary and secondary CL were fully active as indicated by sustained progesterone concentrations and by their diameters of 37 and 35.5 mm, respectively. Pregnancy diagnosis was made 4 days after transfer of the embryo, that is, 23 days after the primary ovulation and 13 days after the secondary ovulation. At that time, the 12-day old embryo was within a 15mm embryonic vesicle. On days 55 and 58 of pregnancy two new supplementary CL formed spontaneously, reaching diameters of 36 and 29mm. This report of a successful mule-in-mule pregnancy using as a recipient a mule with both a primary and an artificially induced secondary CL suggests the possibility of improving the chances of successful pregnancy in recipient mules by increasing endogenous progesterone production through induction of secondary ovulations prior to embryo transfer. Acknowledgements. This study was supported by grant PAPIIT IN 223920, DGAPA-UNAM.