| Because of its very low heritability of litter size of pig, the improvement of the litter size is limited by the conventional breeding technology. It is very important to find the major genes and the genetic markers related to the litter size. All reproductive pathways of animal will be mediated by procreant hormones, including generation and maturation of procreant cells, ejaculation, ovulation, pregnancy, secretion of milk and so on. Hence genes, which coding procreant hormones or their receptors, are presumed to be ideal candidate genes for reproductive traits. In this experiment, 323 pigs including Laiwu Black, Lulai Black, Licha Black, Luyan White, New Yimeng Black, Yorkshire, Landrace and Duroc were selected to detect genetic variants of PRLR and RBP4 genes by PCR-RFLP. According to the genotypic frequency of these two genes, we calculated the allelic frequency in each pig breeds. And the genetic effects of the genes on litter size were also analyzed by the least square analysis. Gathering the litter size data of examined pigs, including the total number of born (TNB) and the number of born alive( NBA), we analyze the effects of them on prolificacy, The main results are asfollows:For PRLR gene, In Laiwu Black, Licha Black, Lulai Black, Landrace and Yorkshire, the preponderant alleles is B allele, the genotype frequency was AB>BB>AA. In New Yimeng Black, Luyan White and Duroc, the preponderant alleles was A allele, the frequency of AA genotype was significantly higher than the frequency of BB genotype(P<0.05),among this three pig breeds, the frequency of the allele A was highest in Duroc (0.8000). The results of Chi square showed that, all the eight pig breeds populations fitted the H-W equilibrium situation(P>0.05). In Shandong local breeds, the average TNB and NBA of AA was 1.03 and 0.89 more than that of BB, while 1.26 and 1.11 more than BB in the foreign pig breeds respectively, and the effect of the genotype on reproduction traits was significant (P<0.05).For RBP4, the frequency of AA genotype was higher than the other two genotype frequency in the three foreign pig breeds and two shandong local breeds(New Yimeng Black, Luyan White), and the preponderant allele was A, among these pig breeds, the frequency of the allele A was highest in Duroc (0.8462). While, in the other three Shandong local breeds, the genotype frequency was AB>BB>AA, and the preponderant allele was B. The results of Chi square showed that, all the eight pig breeds populations fitted the H-W equilibrium situation(P>0.05). In Shandong local breeds , the average TNB and NBA of AA was 0.59 and 0.51 more than that of BB, while 0.72 and 0.64 more than BB in the foreign pig breeds respectively(P<0.05).The Effects of PRLR and RBP4 of litter sizes in the first parity was higher than those in the later parities.For the first parity , AA genotypic sows of PRLR produced 1.25 TNB and1.13 NBA more than BB genotypic sows, AA genotypic sows of RBP4 produced 0.79 TNB and 0.72 NBA more than BB genotypic sows.While, for the later parities, AA genotypic sows of PRLR produced 0.87 TNB and 0.82 NBA more than BB genotypic sows, and AA genotypic sows of RBP4 produced 0.58 TNB and 0.42 NBA more than BB genotypic sows.the TNB and NBA of the combined genotype BBBB was 1.98 and1.80 more than those of AAAA in the first parity, while 1.39 and 1.19 more than in the later parities respectively (P<0.05). The effects of combined genotypes of PRLR and RBP4 have no obvious law. Its genetic effects on prolificacy are not simply the multiplications of every genotype. But its effect of combined genotypes was higher than the effect of individual genotype.In this research, the effects of PRLR and RBP4 on prolificacy was proved to be obvious, and they were abundant in polymorphism. From these results we can putatively drew the conclusion that these two genes could be used to select the high reproduction traits of pigs with molecular markers assisted selection programs, in order to improve the level of prolificacy. |
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