This project aims to increase ewe weaning rates and lifetime productivity by providing sheep producers with a more accurate method of identifying more fertile and fecund ewe lambs before first mating. The proposed marker is anti-müllerian hormone (AMH), which is produced solely by the ovary and can be measured accurately in peripheral blood. Preliminary evidence from Spanish / Italian sheep breeds showed that ewe lambs with high compared with low blood levels of AMH prior to 4 months of age were 12 weeks younger at first lambing, had higher pregnancy rates to first mating (65 versus 33%), and produced 40% more lambs per year and per lifetime. There is also a strong correlation between AMH levels and the number of embryos produced by Merino ewe lambs within juvenile in vitro embryo transfer (JIVET) programs.