Department of Genetics, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
Advanced Beef Cattle Research Center, Animal Science Institute/APTA/SAA, Sertãozinho, São Paulo, Brazil.
PLoS One. 2021 Apr 2;16(4):e0248186. doi: 10.1371/journal.pone.0248186. eCollection 2021.
The objective of the present study was to evaluate the effects of different selection practices on the environmental sensitivity of reproductive and growth traits in males and females of three Nellore selection lines [control (NeC), selection (NeS), and traditional (NeT) lines]. Moreover, genetic trends for the intercept and slope were estimated for each line, and the possible reranking of sires was examined. A total of 8,757 records of selection weight (SW), 3,331 records of scrotal circumference (SC), and 2,311 records of days to first calving (DFC) from Nellore cattle born between 1981 and 2017 were analyzed. (Co)variance components and genetic parameters of all traits were estimated using a reaction norm model with Gibbs sampler. In all cattle lines, the mean heritability of the studied traits ranged from 0.39 to 0.75 for SW in both males and females, from 0.46 to 0.68 for SC, and from 0.06 to 0.57 for DFC along with the environmental descriptor. In all cattle lines, the genetic correlation coefficients between the intercept and slope ranged from 0.03 to 0.81 for SW, from -0.14 to 0.39 for SC, and from -0.87 to -0.42 for DFC. Genetic trends for the slope and proportion of plastic genotypes indicated that the NeS line was more responsive to environmental changes, whereas the NeC and NeT lines tended to respond more modestly. Reranking of sires was observed for all traits, specifically in the NeC and NeT lines, because of the weak correlation between the opposite extreme environments. In the NeS line, reranking of sires was observed for DFC alone. Our results indicate that the effects of genotype-environment interaction are important and should be considered in genetic evaluations of Nellore cattle. Moreover, different selection practices affected the environmental sensitivity of the Nellore selection lines tested in this study.
本研究旨在评估不同选择实践对三个尼洛拉（Nellore）选择系（对照（NeC）、选择（NeS）和传统（NeT）系）雄性和雌性繁殖和生长性状的环境敏感性的影响。此外，还估计了每个系的截距和斜率的遗传趋势，并检查了可能的重新排名。总共分析了 1981 年至 2017 年间出生的尼洛拉牛的选择体重（SW）记录 8757 次、阴囊周长（SC）记录 3331 次和首次配种日龄（DFC）记录 2311 次。使用 Gibbs 抽样的反应规范模型估计了所有性状的（协）方差分量和遗传参数。在所有牛系中，研究性状的平均遗传力在雄性和雌性中均为 0.39 至 0.75，SC 为 0.46 至 0.68，DFC 为 0.06 至 0.57，同时还有环境描述符。在所有牛系中，截距和斜率之间的遗传相关系数范围为 0.03 至 0.81，SC 为 -0.14 至 0.39，DFC 为 -0.87 至 -0.42。斜率和塑性基因型比例的遗传趋势表明，NeS 系对环境变化的反应更为敏感，而 NeC 和 NeT 系则倾向于反应更为温和。所有性状都观察到了系谱的重新排名，特别是在 NeC 和 NeT 系中，这是由于相反极端环境之间的相关性较弱。在 NeS 系中，仅观察到 DFC 的系谱重新排名。我们的结果表明，基因型-环境互作的影响是重要的，在 Nellore 牛的遗传评估中应予以考虑。此外，不同的选择实践影响了本研究中测试的 Nellore 选择系的环境敏感性。
