Mare and stallion effects on blastocyst production in a commercial equine ovum pick-up–intracytoplasmic sperm injection program

Abstract

This study retrospectively examined the degree to which success within a commercial ovum pick-up (OPU)–intracytoplasmic sperm injection (ICSI) program varied between individual mares and stallions. Over 2 years, 552 OPU sessions were performed on 323 privately owned warmblood mares. For mares that yielded at least one blastocyst during the first OPU-ICSI cycle, there was a 77% likelihood of success during subsequent attempts; conversely, when the first cycle yielded no blastocyst, the likelihood of failure (no embryo) in subsequent cycles was 62%. In mares subjected to four or more OPU sessions, the mean percentage of blastocysts per injected oocyte was 20.5% (range 1.4–46.7%), whereas the mean number of blastocysts per OPU-ICSI session was 1.67 (0.2–4.2). Age did not differ significantly between mares that yielded good or poor results. The number of recovered oocytes per OPU was positively associated with the likelihood of success (P<0.001). Although there were considerable between-stallion differences, most stallions (14/16) clustered between 15.6% and 26.8% blastocysts per injected oocyte, and the number of blastocysts per OPU (mean 1.4; range 0.2–2.2) was less variable than among mares. In conclusion, although both mare and stallion affect the success of OPU-ICSI, mare identity and the number of oocytes recovered appear to be the most reliable predictors of success.

Deslorelin Slow-Release Implants Delay Ovulation and Increase Plasma AMH Concentration and Small Antral Follicles in Haflinger Mares

“…In Zebu beef cows, treatment with deslorelin SRI resulted in effects on small follicles similar as in the mares of the present study for up to 180 days and allowed for the aspiration of a higher number of follicles via OPU [35]. In horses, the number of recovered oocytes after the OPU procedure is one of the most important factors for the successful application of ICSI [36]. Follicles similar to the size of the subpopulation increased in the present study promise the best recovery rates [15,37] because they allow for scraping of a greater proportion of the follicular wall, which is a prerequisite for oocyte recovery in horses [36].…”

“…In horses, the number of recovered oocytes after the OPU procedure is one of the most important factors for the successful application of ICSI [36]. Follicles similar to the size of the subpopulation increased in the present study promise the best recovery rates [15,37] because they allow for scraping of a greater proportion of the follicular wall, which is a prerequisite for oocyte recovery in horses [36]. Currently, protocols for the manipulation of the ovarian follicular population in horses are lacking.…”

Anti-Müllerian Hormone and OPU-ICSI Outcome in the Mare

“…This association was not significant in old mares, which may be due to the smaller sample size of this group (18/103). A decrease in the number of aspirated follicles and recovered oocytes in a commercial OPU-ICSI program was also established in mares with increasing age, although the blastocyst rate was not affected [6,26]. The effect of the maternal age on AMH concentration, follicle and oocyte number was not observed in our data.…”

“…Therefore, establishment of a predictive model for OPU-ICSI outcome in mares would represent a useful tool to support client counselling and management of expectations. The success of equine in vitro embryo production is significantly influenced by many factors such as the identity of the donor stallions and mares, the antral follicle count, the number of oocytes recovered, and notably the clinician and laboratory expertise [5,6]. The oocyte developmental capacity appears to be less affected by the sperm donor than by the oocyte donor, leading to the hypothesis that a factor intrinsic to the mares could be used as a marker for success [6].…”

“…The advantages include the necessity for only a small amount of scarce and expensive semen [2,5], the production of embryos at any moment of the year, without compromising sport engagements, and the Animals 2021, 11,2004 2 of 15 possibility to determine the gender of the embryo before cryopreservation and transfer [1]. Individuality of the mare and the number of retrieved oocytes come across as the two main parameters influencing a successful outcome of OPU-ICSI [5,6], though male factors have to be considered too [7].…”