Estimation Of Genetic Parameters And Breeding Values For Milk Production And Body Measurement Traits In Saanen Dairy Goats

The research object of this study is Saanen dairy goat.The data set consisted of 3566Saanen dairy goats from the Guanzhong region of Shaanxi Province from 2015 to 2022,with single measurement data of body weight and measurement;In the dairy goat farm A,there were 289357 milk production records from 1414 lactations from 2006 to 2021,and 7335milk composition records from 2010 to 2021;In the dairy goat farm B,there were 23832milk production records from 2015 to 2019.There was no goat overlap in the pedigree of milk and body measurement trait data.Using the nonlinear regression function of SPSS statistical software,and Wood,Nelder,Wilmink,and AS models(Ali Schaeffer model)to fit the lactation curve of each parity in milk production dataset,the optimal model was selected based on the size of R~2,and the 300 d milk production correction coefficients for different lactation days and parity were calculated.And the milk yield trait was uniformly corrected to300 d using the correction coefficients.The significance of non genetic factors was tested using the general linear model of SPSS software for weight,body measurement traits,milk production and composition traits.The influence of different levels of significant factors was explored through least squares analysis of variance.Finally,DMU software was used to estimate genetic parameters and breeding values for weight,body measurement traits,and milk production and composition traits.The results of this study are as follows:1.Except for the insignificant effects of months of age and birth season on weight,other non genetic factors had a highly significant impact on body measurement traits(P<0.01).Under the gender effect,the weight and body measurement traits of male goats were significantly higher than those of female goats(P<0.01).Under the months of age effect,the body measurement traits tended to increase with months of age.The estimated heritability of body weight,body height,body length,chest circumference and tube circumference were 0.585(0.109)、0.678(0.059)、0.664(0.061)、0.478(0.092)and0.327(0.091),respectively,which were all high heritability traits.The breeding values of sire and dam goats were calculated to obtain the top ten rankings of single breeding values for body measurement traits.2.The ranking of the four models fitting lactation curves was AS>Wilmink>Wood>Nelder,with the AS model having a fitting degree greater than 0.99 for all parities.Calculated the parameters of the lactation curves and ploted the lactation curves based on the optimal model,and calculated the correction coefficients for the 300 d milk production for each parity and each parity of 5-300 days.3.The year of birth had a significant impact on 8 milk production traits(P<0.01),and the lactation stage had a significant impact on 7 milk composition traits(P<0.01).The birth season,lambing season,and parity had different degrees of influence on milk yield,milk fat rate,milk protein rate,total solids,non fat milk solids,lactose rate,freezing point,and titratable acidity.Under the lambing season effect,dairy goats lambing in winter had a higher milk production than the goats lambing in spring.Under the parity effect,the milk production increased with the increase of parity.The milk production of third and fourth-seventh parity was significantly higher than that of first and second parity(P<0.01),and the total solids and titratable acidity of first parity were significantly higher than those of other parities(P<0.01).Under the lactation stage effect,the milk fat rate,total solids,and lactose rate in the early lactation stage were significantly higher than other stages(P<0.01).The estimated heritability of milk yield,milk fat rate,milk protein rate,total solids,non fat milk solids,lactose rate,freezing point and titrated acidity were 0.216(0.057)、0.093(0.018)、0.118(0.019)、0.110(0.018)、0.272(0.029)、0.455(0.027)、0.768(0.018)and 0.662(0.024),respectively.The lactose rate,freezing point and titrated acidity were high heritability traits.Milk yield,milk protein rate,total solids and non fat milk solids were medium heritability traits,while the milk fat rate was low heritability traits.The genetic and phenotypic correlations of milk production traits ranged from-0.878 to 0.983 and from-0.859 to 0.916,respectively.The breeding values of sire and dam goats were calculated to obtain the top ten rankings of single breeding values for milk production traits.In summary,when estimating genetic parameters,non genetic factors should be fully considered to ensure the accuracy of the results.The exploration of lactation curve patterns and the estimation of genetic parameters and breeding values for weight and body measurement traits,milk production traits can provide theoretical reference and practical guidance for production management,breeding core group formation,selection and mating of dairy goats.