Efficiency of equine oocyte recovery from post mortem ovaries or by ovum pick up

Abstract

Most oocytes used for cloned embryo production are obtained from abattoir ovaries even though in some countries, slaughtering horses is not allowed. The advantage of scraping post mortem ovaries is the high number of oocytes available in a short period of time to perform somatic cell nuclear transfer. However, mare age, reproductive and health status or ovary manipulation by abattoir staff are not controlled before slaughter and the effect on oocyte quality and early embryo development is uncertain. Ovum pick up (OPU) is an alternative technique to obtain oocytes ex vivo from controlled mares and embryos obtained from those oocytes potentially have better development. Cortez et al. (Journal of Equine Veterinary Science 113 2022; 14) reported higher cleavage and blastocyst rates in cloned embryos from OPU-derived rather than post mortem derived ovaries. The aim of this retrospective study was to determine and compare the oocyte recovery rates from abattoir-sourced ovaries or collected by OPU. Data was collected between September and November 2022 in Argentina. For statistical analysis, generalized linear models were used. A total of 3476 ovaries were collected from the abattoir and 16% (557/3476) were discarded since antral follicles were not visible. Using the scraping technique, 8392 oocytes were recovered in 24 sessions obtaining an averageof 350 oocytes per session. Mean (± SD) oocyte recovered per scraped ovary was 2.9±0.4 and for all collected ovaries per session was 2.4±0.3. On average the scraping time calculated per mare (pair of ovaries) for all collected ovaries per session was 1 min and 36 sec (59 sec-2 min). OPU was performed in 44 mixed breed healthy mares during the southern hemisphere breeding season in which a mean of 16.7 (7-29) follicles were aspirated per mare in an average of 27 min and 7 sec (6 min and 3 sec- 58 min). Oocyte recovery rate per aspirated follicle was 63.3% and a mean of 9.7 oocytes were retrieved per OPU. Mean oocyte retrieval per mare was higher using OPU than scraping (9.7 ± 4.8 vs. 5.8 ± 0.9; p<0.0001). Although oocyte recovery per follicle could not be compared in this study these results could be influenced by mares’ selection for OPU although there was not a minimum number of follicles set as a criteria to perform OPU. The data show that the OPU procedure is a suitable technique to obtain oocytes for equine cloning programs. In some circumstances, the procedures to obtain oocytes by OPU are more expensive than those recovered by scraping, however published data suggest that fewer oocytes recovered by OPU are needed to obtain a cloned embryo.