In sheep have identified ten alleles are associated with increased ovulation rate and prolificacy. The use of these or other possible mutations may be an important tool to increase the genetic progress of the prolificacy. In this paper we show evidence of the possible existence of a major gene affecting prolificacy in sheep. We analyzed the phenotypic characteristics of four Spanish sheep breeds by implementing a fivestep protocol: genetics evaluation of animals, analysis of the distribution of prolificacy, analysis of prolificacy within family groups, estimation of repeatability in animals suggestive and statistical analysis. Males were potential carriers of a major gene in Manchega breed. These results are a first approximation to the detection and identification of a major gene that could be affecting the prolificacy of this breed