Abstract: In the present research, the genetic polymorphisms of intron 9 and exon 10 of prolactin receptor (PRLR) gene of eight breeds or strains sheep, which including Small Tail Han, Poll Dorset, Suffolk, Germany Mutton Merino and Chinese Merino (Xinjiang type) (including Prolific strain, Meat strain and Large Frame strain), were detected by polymerase chain reaction- single strand conformation polymorphism（PCR-SSCP） and the relationship between genotypes and average litter size were analyzed. The results as follows：①There was a C→T transition at 259 in intron 9 of sheep PRLR gene. In Small Tail Han, the average litter size of BB genotype was 0.81 and 0.87 more than that of AA and AB genotypes respectively (P<0.05). ②There was a G→A transition at 304 in exon 10 of PRLR gene and this mutation cause an amino acid residue change of Glu→Lys at No. 387 of PRLR. Further research showed that average litter size of Chinese Merino (Xinjiang type) Prolific strain ewes with AB genotype was 0.58 and 0.80 more than that of ewes with AA and BB genotypes respectively (P<0.05). ③Moreover, three mutations (571G→A，585C→G and 606C→T) were identified in exon 10 of PRLR gene. The former two mutations resulted in two amino acid residues change of Ala→Thr and Ser→Arg at No. 476 and 480 of PRLR. In Small Tail Han, the average litter size of AB genotype of the 571G→A mutation increased 0.8 than that of AA genotype (P<0.05). These results preliminarily indicated that the prolactin receptor locus was either a major gene that influences the prolificacy in Small Tail Han sheep and Chinese Merino (Xinjiang type) prolific strain sheep or was in close linkage with such a gene.

Key words: sheep; prolificacy; prolactin receptor gene; genetic polymorphism