Sheep are seasonal, short-day polyestrus breeders (ie, estrus occurs in response to shortening day length).Most sheep are bred from late September to November, with October being the most popular time to put in the rams. While there are a few breeds of sheep can that breed anytime of the year. Lamb supply is seasonal in nature and is explained largely by the seasonal nature of sheep reproduction, yet demand for product is present year-round. In order to meet market demand, deficits in supply are met by imported product and by domestic lamb feeders who hold lambs to extend the season of supply. Another strategy to fill in gaps in supply and to avoid product quality concerns is through out-of-season lamb production. Out-of-season production allows lambs with the optimal degree of maturity to be harvested throughout the year. This strategy, when combined with a decrease in the production birth interval, is referred to as accelerated production. Accelerated production has the potential to increase production efficiency and simultaneously remove the constraint caused by seasonal supply.