Reproductive performance of sows is an important
factor in the economics of pig production. Therefore,
many studies were carried out to identify the effect
of polymorphisms of some genes, e.g. estrogen receptor
(ESR) gene, leptin (LEP) gene and prolactin receptor
(PRLR) gene or retinol-binding protein 4 (RBP4) gene, onreproductive traits (Rothschild et al., 1996; Vincent et al.,
1998; Chen et al., 2004; Kmie´c and Terman, 2004; Korwin-
Kossakowska et al., 2005).