Direct and maternal annual genetic changes for selected traits at weaning and yearling in beef cattle

ABSTRACT. Heritability and direct and maternal genetic changes were estimated in Nellore cattle for the following traits: birth to weaning weight gain (BWG), weaning to yearling weight gain (YWG), weaning conformation (WC), weaning precocity (WP), weaning muscling (WM), yearling conformation (YC), yearling precocity (YP), yearling muscling (YM) and yearling scrotal circumference (SC). Direct and maternal heritability for weaning traits were 0.21±0.03 and 0.13±0.01 (BWG); 0.19±0.03 and 0.07±0.01 (WC); 0.22±0.03 and 0.07±0.01 (WP); 0.20±0.03 and 0.07±0.01 (WM), respectively. For yearling traits, direct heritability were 0.19±0.04 (YWG); 0.32±0.05 (YC); 0.37±0.05 (YP); 0.38±0.05 (YM) and 0.41±0.04 (SC). Positive and significant direct genetic changes (p < 0.05) were found for all traits, except for WC (p = 0.09), equal to 0.138 kg year-1 (BWG), 0.003 units year-1 (WC), 0.011 units year-1 (WP), 0.009 units year-1 (WM), 0.132 kg year-1 (YWG), 0.003 units year-1 (YC), 0.011 units year-1 (YP), 0.011 units year-1 (YM) and 0.020 cm year-1 (SC), indicating favorable genetic gains in the period. For weaning traits, we obtained negative and non-significant (p > 0.05) maternal genetic trends, with values of -0.084 kg year-1 (BWG), -0.004 units year-1 (WC), -0.004 units year-1 (WP) and -0.004 units year-1 (WM). Thus, greater emphasis should be given for maternal genetic merit of weaning traits in this population, if improvements in maternal ability were desirable.

摘要。本研究以内洛尔牛（Nellore cattle）为研究对象，对其9项性状的遗传力、直接遗传进展与母体遗传进展进行了估算，涉及性状包括：出生至断奶增重（birth to weaning weight gain, BWG）、断奶至周岁增重（weaning to yearling weight gain, YWG）、断奶时体况评分（weaning conformation, WC）、断奶时早熟性（weaning precocity, WP）、断奶时肌肉发育度（weaning muscling, WM）、周岁体况评分（yearling conformation, YC）、周岁早熟性（yearling precocity, YP）、周岁肌肉发育度（yearling muscling, YM）以及周岁阴囊围（yearling scrotal circumference, SC）。
断奶相关性状的直接遗传力与母体遗传力分别为：BWG：0.21±0.03和0.13±0.01；WC：0.19±0.03和0.07±0.01；WP：0.22±0.03和0.07±0.01；WM：0.20±0.03和0.07±0.01。
周岁相关性状的直接遗传力分别为：YWG：0.19±0.04；YC：0.32±0.05；YP：0.37±0.05；YM：0.38±0.05；SC：0.41±0.04。
除WC（p=0.09）外，其余所有性状均呈现正向且显著的直接遗传进展（p<0.05），年度遗传进展分别为：BWG 0.138 kg·年⁻¹、WC 0.003 单位·年⁻¹、WP 0.011 单位·年⁻¹、WM 0.009 单位·年⁻¹、YWG 0.132 kg·年⁻¹、YC 0.003 单位·年⁻¹、YP 0.011 单位·年⁻¹、YM 0.011 单位·年⁻¹、SC 0.020 cm·年⁻¹，表明该研究周期内各项性状均获得了有利的遗传改良。
对于断奶相关性状，其母体遗传趋势为负向且不显著（p>0.05），年度变化值分别为：BWG -0.084 kg·年⁻¹、WC -0.004 单位·年⁻¹、WP -0.004 单位·年⁻¹、WM -0.004 单位·年⁻¹。因此，若期望改良该群体的母体性能，则应更加重视断奶相关性状的母体遗传选育价值。