Genetic Analysis On Prolificacy In Inner Mongolia Cashmere Goat

By analyzing the pedigree records of Inner Mongolia cashmere goat ranch, we found , from 1990 to 2008, that average litter size of Inner Mongolia cashmere goat rose from 1.08 to 1.55. At the same time, the proportion of single birth fell to 46.36 percent from 92.28 percent during the 19 years. However, the fundamental proportion of multiple births (more than or equal to three lambs) has no any change. In order to explore the causes leading to this phenomenon, many studies have been carried out. These studies distinguish between environmental factors and genetic factors affecting litter size. First of all, using linear model, threshold model and generalized linear model, we identified the proportion of genetic factors and environmental factors affecting litter size. In other words, we want to know the extent to which genetic factors and non-genetic factors decide multiple births of Inner Mongolian cashmere goat. Second, the segregation analysis was applied to determine inheritance mode of litter size in Inner Mongolian cashmere goat. Finally, the genetic markers related with high fecundity gene in high fecundity families and low fecundity families had been studied by 33 microsatellite markers in Inner Mongolian cashmere goat. Furthermore, we found microsatellite loci correlated with multiple births in Inner Mongolia cashmere goats. The results suggested as following:1. By using Family finder 1.0 software, we found that there was a significant difference in litter size between high fecundity families and low fecundity families in population of Inner Mongolia cashmere goats.2. The segregation analysis method was used to prove that genetic potential of litter size in Inner Mongolia Cashmere goats is mainly controlled by a pair of major genes, which have dominant and recessive relationships. At the same time, the estimated results of parameters also show that FPMM is more suitable than MLM to analysis heredity rule of the litter size in Inner Mongolia Cashmere goats.3. The Gibbs sampling method was used to compare the variance components of litter size in Inner Mongolian Cashmere Goats under two differences models (the threshold model and linear model). The correlation coefficient of predictive and phenotype values were calculated. The results showed that accuracy of the forecast of linear model (ρ=0.093) slightly higher than the threshold model's (ρ=0.062) in the estimate variance components of litter size in Inner Mongolia Cashmere goats.4. The calculation shows that the first threshold value Th1 of litter size is 0.678σand the second threshold value Th2 of litter size is 2.472σin Inner Mongolia Cashmere Goats. There are 7 high reproduction rate families and 20 low reproduction rate families in the population of Inner Mongolia Cashmere goats. Average litter size in the high reproduction rate families is 20 percent higher than in the low reproduction rate families, but it is not still larger than first threshold value Th1. At the same time, correlation coefficient of the litter size are computed in the 21 major kinships.5. Different methods to detect main gene produce different results. We have a preliminary conclusion that MB056 locus (linkage to BMPRIB) may be associated with litter size in Inner Mongolia Cashmere goats. And 140bp fragment of MB009 (linkage to FSHβ) locus and 150bp fragment of FCB304 (linkage to BMP15) locus are specific nucleotide fragments of multiple births in Inner Mongolia Cashmere goats.