In addition to the >300 recognized physiological functions of PRL [20], significant attention has focused on the potential use of the PRLR gene as a marker for reproductive performance, a factor that carries economic significance in pig production [21]. Mapped to chromosome 16 [22], only a small 3′ portion of the pPRLR coding sequence and 3′ UTR has been sequenced to date (GenBank Accession U96306). Within this region, an AluI polymorphism results in A and B alleles with different frequency in several breeds [22] and [23]. Further studies have demonstrated that this polymorphism links with several reproductive phenotypes including ovulation rate, litter size, ovarian weight, estrus cycle length, uterine length and placental weight [23], [24] and [25].