Generally pig breeding efficiency is defined as the number of piglets weaned per sow per year, so in every pig breeding programmes, great emphasis is placed on improving reproductive traits in sow lines and generally, the evaluation of litter size is carried out in most selection planes. Usually, the reproduction breeding goal is to increase the number of piglets born, but this trait, as reported by Hanenberg et al. (2001) gives an undesirable correlation with the number of stillborn piglets. Litter size is the result of a large number of traits as number of total piglets born, number of born alive, stillbirth, weaned survival; as reported by Tummaruk et al. (2000) the variation in these parameters is influenced by genetic value of the sow and by environmental factors, such as management and season. Regarding the genetic influence on the litter size, we know that the breed can influence the number of born, but its interaction with stillbirth is not significant, although Leenhouwers et al. (1999) found an higher stillbirth incidence in purebred than in crossbred litters........