in sheep, intrauterine growth restriction can be caused by heat stress in early to mid pregnancy. the effect is attributed to reduced placental development causing reduced fetal growth. hormonal effects appear implicated in the reduced placental development. although early reduction of placental development is not accompanied by concurrent reduction of fetal growth; it tends to limit fetal growth later in gestation. normally, ovine placental mass increases until about day 70 of gestation, but high demand on the placenta for fetal growth occurs later. (for example, research results suggest that a normal average singleton suffolk x targhee sheep fetus has a mass of about 0.15 kg at day 70, and growth rates of about 31 g/day at day 80, 129 g/day at day 120 and 199 g/day at day 140 of gestation, reaching a mass of about 6.21 kg at day 140, a few days before parturition.)