Genetic parameters and genetic trends of conformation and management traits in Dairy Gir cattle

ABSTRACT The objective of this study was to estimate genetic parameters and genetic trends of different conformation and management traits regularly measured within the context of the National Dairy Gir Breeding Program (PNMGL). The estimation of genetic and residual variances for each trait was performed using average information restricted maximum likelihood (AI-REML) procedure in AIREMLF90 program software. The population was divided into three subpopulations constituted by measured females (with phenotype records), all females, and males. Linear regressions were applied for each trait, considering two periods of birth (1st period: 1938-1996; 2nd period: 1997-2012). The estimated heritability of conformation and management traits varied from 0.01 to 0.53, denoting a perspective of genetic improvement through selection and corrective matings for purebred Dairy Gir populations. The average genetic changes in conformation and management traits were, in general, variable and inexpressive, showing that the selection of Dairy Gir may have had been directed essentially to increase milk yield. The analysis of the two periods of birth indicated that some linear traits present progress (although inexpressive) in the 2nd period (more recent period).

摘要 本研究旨在估算国家吉尔奶牛育种计划（National Dairy Gir Breeding Program，简称PNMGL）框架下常规测定的各类体型性状与管理性状的遗传参数及遗传趋势。本研究采用AIREMLF90软件中的平均信息约束极大似然（average information restricted maximum likelihood, AI-REML）方法，对各性状的遗传方差与残差方差进行估算。研究群体被划分为三个亚群：具有表型记录的测定母牛、全部母牛以及公畜。针对各性状，结合两个产犊时期（第一时期：1938-1996年；第二时期：1997-2012年）开展线性回归分析。本研究估算得到的体型与管理性状遗传力介于0.01至0.53之间，表明针对纯种吉尔奶牛群体，可通过选择与矫正交配实现遗传改良。总体而言，体型与管理性状的平均遗传变化幅度不一且效果不显著，提示吉尔奶牛的选育方向可能主要聚焦于提升产奶量。对两个产犊时期的分析结果显示，部分线性性状在第二时期（即较近期）呈现出一定的遗传进展，尽管该进展幅度仍较小。