Schmidt P I, Campos G S, Lôbo R B, Souza F R P, Brauner C C, Boligon A A
Animal Science Department, Federal University of Pelotas, 96010-900 Pelotas, Brazil.
National Association of Breeders and Researchers, 14020-230 Ribeirão Preto, Brazil.
Theriogenology. 2018 Mar 1;108:81-87. doi: 10.1016/j.theriogenology.2017.11.035. Epub 2017 Nov 27.
The female reproductive performance, productivity and size are strongly associated with production efficiency of herds raised in a tropical environment. The age at first calving (AFC), accumulated productivity (AP), stayability (STAY) and mature weight (MW) could be used as indicators of these traits. In this study, the genetic parameters and correlations between AFC, AP, STAY and MW measured in Nellore females were estimated, in order to provide support for the beef cattle evaluation programs. In addition, the genetic changes for these traits were obtained. The (co)variance components were estimated by Gibbs sampling by four-trait multivariate analysis, using a threshold animal model for STAY and linear animal model for the other traits (AFC, AP and MW). Heritability of AFC, AP and STAY showed low values, with posterior means of 0.13 ± 0.02, 0.14 ± 0.01 and 0.19 ± 0.03, respectively. On the other hand, for MW were estimated mean heritability of 0.44 ± 0.03 and repeatability of 0.77 ± 0.03, demonstrating the importance of genetic and permanent environmental effects for the expression of beef cows' size. The AFC showed null genetic correlation with AP (-0.06 ± 0.12) and MW (0.01 ± 0.09) and low and negative with STAY (-0.15 ± 0.11). The AP showed high genetic correlation with STAY (0.86 ± 0.03) and weak with MW (0.23 ± 0.09). Positive and moderate genetic association was estimated between STAY and MW (0.66 ± 0.05). Annual direct genetic trends of 0.19 kg, 0.30 units and 0.10 kg were estimated for AP, STAY and MW, respectively, and were significant (P < 0.05) for STAY and MW. For AFC, negative and favorable annual genetic change was estimated (-0.08 months, P < 0.05). In this population, the selection of heifers for an early reproductive age should have little influence, however favorable, in the time that the cows remain in the herd. The use of AP as a selection criterion should result in smaller changes in the females' mature weight when compared to selection based on STAY.
在热带环境中饲养的牛群，其生产效率与母牛的繁殖性能、生产力和体型密切相关。初产年龄（AFC）、累积生产力（AP）、留群率（STAY）和成熟体重（MW）可作为这些性状的指标。本研究旨在估计内洛尔母牛中AFC、AP、STAY和MW的遗传参数及相关性，为肉牛评估计划提供支持。此外，还获得了这些性状的遗传变化情况。通过四性状多变量分析，采用吉布斯抽样法估计（协）方差分量，对STAY使用阈动物模型，对其他性状（AFC、AP和MW）使用线性动物模型。AFC、AP和STAY的遗传力值较低，后验均值分别为0.13±0.02、0.14±0.01和0.19±0.03。另一方面，MW的平均遗传力估计为0.44±0.03，重复力为0.77±0.03，表明遗传和永久环境效应对于肉牛体型表达的重要性。AFC与AP（-0.06±0.12）和MW（0.01±0.09）的遗传相关性为零与STAY呈低负相关（-0.15±0.11）。AP与STAY的遗传相关性较高（0.86±0.03），与MW的相关性较弱（0.23±0.09）。STAY与MW之间估计存在正且中等的遗传关联（0.66±0.05）。AP、STAY和MW每年的直接遗传趋势分别估计为0.19kg、0.30单位和0.10kg，STAY和MW的趋势显著（P<0.05）。对于AFC，估计每年有负向且有利的遗传变化（-0.08个月，P<0.05）。在这个群体中选择初情期早的小母牛，对母牛留在牛群中的时间影响不大，尽管有一定益处；与基于STAY进行选择相比，将AP用作选择标准会使母牛成熟体重的变化更小
