Genetic improvement of Nellore cattle in the semi-arid region of northeastern Brazil

ABSTRACT. The semi-arid region of Brazil represents approximately 57% of the northeastern territory. The main economic activity in this region is agriculture and livestock, in most cases, using traditional technologies. However, there is little published information currently available on cattle-raising in this part of Brazil. The objective of this study was to estimate genetic parameters and trends for productive and reproductive traits of Nellore cattle raised in semi-arid region of northeastern Brazil. Data were collected on weight-adjusted at 205 (W205), 365 (W365) and 550 (W550) days of life, age at first calving (AFC), calving interval (CI) and scrotal circumference (SC) at 550 days of life of cattle born between 1965 and 2011. Estimates of covariance and variance were obtained through univariate analysis using a Gibbs sampler. The estimated coefficients of heritability (mode) were 0.27 (W205), 0.36 (W365) and 0.39 (W550), 0.37 (SC), 0.22 (AFC) and 0.03 (CI). Little or no gain from selection is apparent in the genetic trend analysis over the 45 years of the study. However, environmental improvement has allowed phenotypic progress in growth traits and age at first age calving.

摘要。巴西半干旱区域约占东北部领土总面积的57%。该区域的核心经济活动为农牧业，多数情况下采用传统生产技术开展经营。但目前针对巴西东北部半干旱地区肉牛养殖的公开研究资料较为稀缺。本研究旨在估算巴西东北部半干旱地区饲养的内洛尔牛（Nellore cattle）生产与繁殖性状的遗传参数及遗传趋势。研究收集了1965年至2011年间出生的牛只的如下数据：205日龄校正体重（W205）、365日龄校正体重（W365）、550日龄校正体重（W550）、首产犊龄（AFC）、产犊间隔（CI）以及550日龄阴囊周长（SC）。本研究通过吉布斯采样器（Gibbs sampler）开展单变量分析，估算得到协方差与方差组分。本次估算得到的遗传力（众数）分别为：W205为0.27、W365为0.36、W550为0.39、SC为0.37、AFC为0.22、CI为0.03。对本研究45年周期内的遗传趋势分析显示，通过选择育种几乎未获得遗传进展。但环境条件的改善推动了生长性状及首产犊龄的表型提升。