Selection for prolificacy is of major economic interest in most husbandry situations. However, there is an optimum litter size for each environment which maximizes the return profit per ewe. Uniform optimum litter sizes result in the highest profit, and when mean prolificacy of a breed is close to this optimum, then uniformity of litter sizes is a new additional objective. Genetic models involving genes controlling the mean as well as its environmental variability have been developed and used with data on the Lacaune breed. A genetic component for uniformity of litter size has been found, showing that selection for decreasing variability of prolificacy would be possible.