Abstract
In sheep, embryo loss reduces farm profitability and increases the environmental footprint per kg of sheep meat produced. Additionally, improving embryo survival in assisted reproductive technologies is critical for accelerating genetic gain. However, embryo loss remains hidden, and thus often unrecognized, and our ability to improve embryo survival is limited. To reduce embryo loss, we need to first understand when the loss is occurring during gestation and then delineate the mechanisms that result in failure of the embryo to survive. It is only through using this knowledge that we will be able to improve embryo survival and thereby improve farm profitability and environmental credentials. This review will focus on understanding the role that embryo survival may play in optimizing farm productivity and factors influencing embryo survival in sheep. We present insights gained from both in vivo and in vitro experiments, focusing on the role of steroids and the immune system. We highlight potential new approaches to improving farm productivity within a reduced environmental footprint and key areas of research where additional knowledge may lead to new interventions to improve embryo survival.
• Unrecognised embryo loss causes economic loss and increases environmental footprint.
• Majority of ovine pregnancy loss occurs prior to maternal recognition of pregnancy.
• Oocyte quality, oviduct and uterine environment are key to improving embryo survival.
• Steroids and immune factors are critical regulators of embryo development.
• Reproductive tract can be a favourable or hostile environment for embryo development.