Use of IVF and ET in Mexican Criollo Sheep (Ovis aries): Immediate and Delayed Embryo Transfers

Abstract

There is little information in the scientific literature concerning sheep pregnancy and lambing success with regard to the timeframe from when in vitro produced embryos are transported to the designated location for embryo transfer (ET). The aim of this study was to transfer in vitro produced embryos under two different conditions that could typically occur using the aforementioned assisted reproductive techniques (ARTs). Abattoir ovaries were used to procure oocytes for in vitro embryo production and subsequent transfer to synchronized ewes. The study consisted of two experiments: Experiment 1 (Exp1)—embryos taken from the laboratory to a nearby surgical room for immediate ET, and Experiment 2 (Exp2)—ET after 5 hours (h) of transport to a rural farm. Lambing in relation to detected pregnancies, births compared to pregnancies, and the proportion of twin offspring were all higher in Exp2. Notably, in both Exp1 and Exp2, there was not a significant difference (P > 0.05) between the number of embryos transferred, i.e., 3 versus 4, respectively, and the number of ewes that underwent parturition in each group. Also, in both experiments there was not a significant difference (P > 0.05) in the number of ewes that underwent parturition based on the number (i.e., ≥1) of corpora lutea present. The results of the present study demonstrate the importance of evaluating different conditions when applying ARTs, as there are many variables that can influence the outcome. Importantly, Exp2 results show that ovine ET in places located far away from the embryo production site can be useful and successful provided that embryo transport, ET, and recipient conditions are adequate.