Study On Principle And Method For Early Selection Of Fleece Traits In Inner Mongolia Cashmere Goats

Inner Mongolia Cashmere goats(IMCG) is a dual purpose local breed, producing cashmere and meat, which are famous all over the world by the charateristic of high quality cashmere. As such, the target traits for IMCG are fleece traits. Considering characters of complex and repeatable performance measurement, the implementation of early selection is difficult. Therefore, it is necessary that the principle and menthod of early selection for fleece traits in goats will be studied. This will be helpful to increase the accuracy of selection, implement early selection and shorten generation interval, as well as speed up genetic progress. The fleece traits of IMCG, including staple length(SL), staple finess(SF),fiber length(FL) and fiber diameter(FD), were analyzed in this study. The data were collected from 2008 to 2012. The purpose of this study was to find if early selection of fleece traits in IMCG is possible or not, through constructing reasonable animal models. The main contents of this study were as follow:(1) Based on the yearling and repeat records (from one to seven years old) of fleece traits in IMCG, non-genetic factors were determined by a general linear model procedure using SAS software.The results showed that the fixed effects included year of production,herd, ages of animals and sex. In addition, random effects that affected each fleece trait were identified by combining yearling records with pedigree information. By ignoring or including maternal additive genetic effects and maternal permanent environment effects, and considering whether direct additive genetic and maternal additive genetic effects were correlated or not, six different single-trait animal models were obtained. The likelihood ratio test indicated that the most appropriate model for each fleece trait included only the individual direct additive genetic effect.(2) Comparing the estimates of genetic parameters between non-repeatability and repeatability animal model for fleece traits, it was found that the results from both of methods were similar. The heritabilties in non-repeatability and repeatability animal model were 0.28(0.30),0.27(0.27),0.17(0.18) and 0.34(0.32) for SL, SD, FL and FD, respectively. This comparation indicated that genetic evaluation by using yearling fleece traits have a significant statistic power and accuracy.(3) The heritabilities of all fleece traits, excluding FL, are moderate to high, which indicated that the genetic progress will be obtained by genetic breeding. Additionally, genetic correlation for SL/SF was strong and negative. Nonetheless, the positive genetic correlation for FL/FD was observed. Therefore, fiber length will become short when the animals with superior cashmere were selected, all of which may result in decrease of cashmere yield. The negative genetic correlation between SL and FD indicated that quality of cashmere in individuals with longer staple are better.(4) The change trends of each fleece trait with age groups indicated that effect of age on phenotypic and heritability of SL and FL were consistent, and phenotypic variation reflected genetic trends of SL and FL to a certain extent. However, the change trends of genetic and phenotypic in SF and FD were discordant, which suggested that environmental factors had a significant effect on both of the fleece traits.(5) Fleece traits of IMCG aged from one to five years old were modeled using repeatability and several multivariate models that varied in covariance structure, which was used to determine whether the genetic expression of fleece traits were unified at different ages. The results for model selection indicated that SL and FL could be sperated three traits, namely, yearlings,2 year olds, and older goats. Nevertheless, the genetic characteristics of SF and FD should be considered as 2 traits, yearlings and adults. The accuracy of genetic evaluation would be assuared only by records of animals before the age of 3 for SL/FL and 2 for SF/FD.(6)The relationships between cashmere yield(CY)and other economic traits, including fiber length(FL), fiber diameter(FD) and live body weight(LBW), were discussed under four fleece grades through constructing Linear Mixed animal model. The magnitudes of relationships between CY and FL, FD and LBW among fleece grades had significant difference. FL had significant effect on CY at any fleece grade. FD was not related to CW at coarse cashmere.LBW had no significant effect on CW at superfine and coarse cashmere. The three economic traits had positive effects on CY by regression analysis, however, negative relationship between FD and CY at coarse cashmere population was observed.