Stressful maternal events during pregnancy can modulate the development of fetal tissues, with potential long-term effects on the offspring, perhaps due to the involvement of the hypothalamic-pituitary-adrenal (HPA) axis and increased cortisol production. Thermal stress during various stages of pregnancy can alter fetal development with potential long-term damaging effects on fertility in replacement heifers. Most reports about thermal stress are focused on high temperatures in dairy cattle (heat stress), with few reports on beef cattle. Moreover, there is a scarcity of studies on the consequences of low temperatures in either dairy or beef cattle. Irrespective of the cause of stress, deviation from ‘normal’ physiological conditions during early stages of development has the potential to modulate offspring survival and growth, with direct impacts on long-term productive and reproductive consequences. In this project we aim to explore the effects of maternal thermal stress (heat and cold) on neonatal survival.