ABSTRACTThe present study evaluated the effects of maternal undernutrition induced by a lower natural pasture allowance during gestation on the histological characteristics of fetal, neonatal and adult Semitendinosus ovine muscle. Two experiments were carried out.In experiment 1, ewes were assigned to two nutritional treatments from 23 days before conception until day 123 of gestation: High pasture allowance (HPA) ewes grazed on natural grasslands at 10-12 kg dry matter (DM)/100 kg of live weight (LW)/day, while low pasture allowance (LPA) ewes grazed at 5-8 kg DM /100 kg of LW/day. In experiment 2, ewes were assigned to two natural pasture allowances between days 30 and 143 of gestation: HPA ewes grazed on 14-20 kg of DM/100kg of LW/day; while LPA ewes grazed on 6?10 kg of DM/100 kg of LW/day.In experiment 1, samples were taken from 70-day old fetuses and newborn lambs to evaluate muscle histology, while in experiment 2 samples were taken from 200-day old heavy-lambs which were equally ad libitum fed from lambing until slaughtering. Maternal undernutrition reduced the number of secondary fibers and the number of nuclei/ fasciculi in fetal muscles. Maternal undernutrition reduced the mean fiber diameter and the number of nuclei per fiber and increased the proportion of non-muscle tissue in newborn lambs. Furthermore, maternal undernutrition reduced the weight and increased the proportion of oxidative fibers in the Semitendinosus of heavy-lambs. Our results suggest that a lower maternal pasture allowance during gestation affects myogenesis with possible future effects over meatproducing performance.