“…The duration of oestrus synchronization protocols with progestin-releasing intrauterine devices has dissimilar effects on the success of superovulatory treatments in different breeds of sheep (Figueira, Alves, Maia, Souza-Fabjan, Batista, Morais, et al, 2020;Menchaca et al, 2009;Oliveira et al, 2014Oliveira et al, , 2020. While the period of progesterone or progestin exposure in Merino (5-14 days, Menchaca et al, 2010) and Santa Inês ewes (6.5 vs 14.5 days, Oliveira et al, 2020) had a limited effect on in vivo embryo production, the 9-day treatment with medroxyprogesterone acetate was associated with better outcomes compared with the short-term (6 days) protocol in Lacaune ewes (Figueira, Alves, Maia, Souza-Fabjan, Batista, Morais, et al, 2020). Results of a preliminary study comparing embryo yields in superovulated and oestrussynchronized, non-superovulated Morada Nova ewes subjected to progesterone-based oestrus synchronization protocols of varying durations (6, 9 or 12 days) showed that the 9-and 12-day protocols resulted in better embryo recovery rates than the 6-day regimen (Arrais et al, 2021), but a confirmatory trial is still needed.…”