Prolactin (PRL) is one of polypeptide hormones secreted by the anterior pituitary gland in vertebrates. It has been proved that PRL plays an important role in the onset of poultry incubation and brooding behavior (Sharp et al., 1988; Shimada et al., 1991; Jiang et al., 2005). A rise of prolactin level in plasma may induce incubation behavior and then terminate laying (Sockmanet al., 2000), resulting in decreased egg production (Reddy et al., 2002). In some of avian species such as ducks and geese, a sharp rise in plasma PRL level occurs during the formation of the final 10-20% of the clutch, which females markedly increase their nest-box occupancy (Hall, 1987; 1991; Fang et al., 2005). Elevated levels of PRL decrease the egg sequence lengths (clutch length) by increasing the inter sequence pauses between the sequences of egg laying. This is particularly pronounced in native birds (Reddy et al., 2002; 2006).

PRL is also involved in the crop-sac development ofcolumbiforms, induction and maintenance of broody behavior, regulation of gonadal function and immune responses in a variety of species (Kansaku et al., 2008). Therefore, PRL exhibits similar changing profiles in the reproductive cycle and exerts biological functions in the similar pattern in different domestic avian species. To elucidate the genetics of PRL, genomic structure of PRL in avian have been investigated extensively (Kansaku et al., 2008). An abundance of SNP has been reported in the 5’-flanking region of chicken PRL (Liang et al., 2006) and the 24-bp insert-deletion was significantlyassociated with broody behavior and egg production (Jiang et al., 2005; Cui et al., 2006), indicating its usefulness as a molecular marker for egg production. Cloning of PRL cDNA in avian species was conducted in the chicken (Watahik et al., 1989), turkey (Wong et al., 1991) and domestic duck (Kansaku et al., 2008). The Japanese quail prolactin gene is 10 KB in size and is composed of 5 exons and 4 introns, encoding 229 amino acids. The Japanese quail PRL has an overall similarity with a comparable region of chicken (96.5%), turkey (93%), duck (93.4%), goose (93.4%), ostrich (91.3%) and budgerigar (92.6%) PRL (Kansaku et al,. 2008). The aim of the present study was to identify prolactin polymorphism and its possible association with reproductive traits in Japanese quail.