Selection Of Cross Combination For Lamb Production In Natural Pasture And Polymorphisms Of OLA-DRB1 Gene Exon 2 In Tibetan Sheep

To select optimal cross combination of grazing lamb production, and find a more beneficial way for using Gansu Alpine Merino germplasm resource in the plateau habitats, take introduced breeds (Texel, White Suffolk, Australian Merino and Bond) as rams, Gansu Alpine Merino as ewes to carry out cross experiment and pilot studies. With artificial insemination, the mating season was in November, and lambing in April next year. The growth rate of the crossing lambs (birth weight, weaning weight, 6-month-old weight, 12-month-old weight) were observed, and slaughter trials were conducted when the lambs were weaning, 6-month-old and 12-month-old. And Logistic model and Gompertz model were used to analyse the suitable model for crossing lambs and parameters of body-weight gains of crossing lambs. The results showed that, the average birth weight, weaning weight and 6-month-old weight of Texel F1 were 5.53 kg, 27.86 kg and 31.24 kg respectively, higher than other cross combination (P<0.05). The growth of crossing lambs became slow from 6-month-old to 12-month-old. And the T10-90 value of Texel was smallest among 4 groups. The carcass weight of Texel F1 was 14.25 kg, which was higher than other crossing group when the lambs weaning (P<0.01). When the lambs were 6-month-old, the carcass weight of Texel F1 was 14.55 kg , which was also higher than other crossing group respectively (P<0.01). The carcass meat percentage of Texel F1 were higher than other crossing group (P<0.05) when the lambs were 6-month-old. The ratio of meat to bone was lower than other crossing group (P<0.05) when the lambs weaning and 6-month-old. By comprehensive consideration of Growth and slaughter performance, the Texel crossing model was the ideal combination for grazing lamb production. To understand the evolution and provide the basis for sheep disease resistance, polymorphism of DRB1 exon 2 gene in Tibetan sheep was analyzed. The PCR-SSCP, cloning and sequencing were used to analyse DRB1 gene variation in 600 Tibetan sheep of China. The number of alleles/ Single nucleotide polymorphisms (SNPs) sites/ variation type/ the genetic relationship and evolutionary significance of the alleles had been analyzed. Total of 31 alleles were identified, in which 15 alleles has not been reported before. And there were 70 SNPs sites in DRB1 gene haplotypes, the proportion was 29.5% to the whole exon2 sequence. The phylogenetic tree results showed that the 31 haplotypes of Tibetan sheep DRB1 exon 2 could divide into two clusters. It is showed that Tibetan sheep DRB1 gene is differentiated into three major categories alleles from three mutant alleles at first. All of this indicated that DRB1 exon 2 is highly polymorphic in sheep from Tibet. However, whether these variations detected in the ovine exon2 of the DRB1 gene is functional or not is still unclear which need further research.