Selection Of Higher Intramuscular Fat Content Yorkshire Population With Marker Assisted Selection Method

Intramuscular fat content, as a very importance trait affecting pig meat quality, is attracting increasingly more attention by researchers. Because of the low heritability of IMF and difficulty of IMF evaluation, traits evaluated in vivo are difficult, cost expensively and lost values after slaughter, so it is ineffective for IMF content improvement through conventional breeding selection. With the development of molecular biology techniques, lots of genetic markers have been used in breeding practice as MAS (marker-assisted selection), which greatly enhanced the accuracy and efficiency of selection. In this study, mainly in order to select high IMF Large White breeding population, three candidate functional genes (Halothane gene, H-FABP gene, Leptin gene) associated with IMF were tested and used in MAS for pig breeding. In additional, slaughtering test, correlation analysis between genotype and traits and breeding simulation was also studied. The main results are as follows:1. Five genotypes of the three candidate functional genes were tested in 482 Yorkshire breeding herd from Hubei Tianzhong Pig Breeding Company. The results showed that the frequency of favorable allele HalN (halothane-negative homozygous) was 78.84%. For the PCR-RFLP sites of H-FABP gene, the frequencies of favorable allele H, d and a were 71.37%,34.34% and 20.54%, respectively, but no aa genotype was detected. The frequency of favorable allele T of Leptin gene was 85.27%.2. The carcass trait and meat quality data of 25 Large White pigs of comparing population analysis showed that IMF content mean value was 2.27%, but the coefficient of variation was high as 28%; the corrected average backfat thickness was 23.82mm, and loin eye area was 43.71cm2. The correlation coefficient between IMF and the moisture was negative, while the correlation coefficients between IMF and the backfat of three position, average backfat and pre-slaughter live weight were positive, and approached significance (P<0.05 or P<0.01). The association analysis between the markers of three genes and traits showed only muscle color was significantly related with the Hinfl-RFLP in 5'upstream region of H-FABP gene (P<0.05). No significant difference was found between different combinations of the AA/aa-DD/dd-HH/hh. However the IMF of two slaughter individuals with the genotype AA-dd-HH was higher than the average IMF mean.3. According to strategy of generation selection and the detected genotype results of candidate functional genes, all individuals carrying halothane-sensitive allele were eliminated to build halothane-negative population. In terms of no aa in H-FABP gene and the frequency of allele T of Leptin gene was very high in the tested population and the selection of this favorable allele can be carried out in the later generation,2 boars with genotype of HalNN-H-FABPAA-dd-HH-LeptinTT and 43 sows of HalNN-H-FABPA--dd-HH-LeptinTT were selected for generating the next generation.4. The variation trend of single favorable allele in offspring was simulated in pig breeding system. The results showed that the selection of boars for genotypes pyramiding was much more important in pig line breeding and it can make more heredity progress with marker assisted selection.