Department of Animal Science, Universidade Federal de Viçosa, 36570-000, Viçosa, MG, Brazil; ABCZ, Associacão Brasileira dos Criadores de Zebu, Pq. Fernando Costa, 38022-330, Uberaba, MG, Brazil.
ABCZ, Associacão Brasileira dos Criadores de Zebu, Pq. Fernando Costa, 38022-330, Uberaba, MG, Brazil.
Anim Reprod Sci. 2020 Mar;214:106305. doi: 10.1016/j.anireprosci.2020.106305. Epub 2020 Jan 28.
Scrotal circumference of bulls is correlated with pubertal age of female offspring. Hormonal control of reproductive function is similar in males and females, which may result in genetic correlation among different reproductive traits measured in the two sexes. The estimation of heritability and genetic correlations allows for the computation of direct and correlated genetic gains which are important for predicting of outcomes as a result of genetic-based selection. The aim of this study was to estimate genetic parameters and relative efficiency of indirect selection for age at first calving (AFC), stayability (STAY) and scrotal circumference at 365 days of age (SC365) in Nellore cattle. The STAY variable can be defined as the probability of a cow remain in the herd enough time to raise a certain number of calves that pay for her development and maintenance costs. A bivariate Bayesian analysis was used to estimate variance components using a linear-animal model for SC365 and AFC and threshold-linear model for SC365 and STAY and for AFC and STAY. For STAY, the value of 1 was assigned to cows that calved at least three times by 76 months of age; otherwise, the value 0 was assigned. The posteriori means of heritability estimates were 0.29, 0.08 and 0.09 for SC365, AFC and STAY, respectively. Genetic correlations were favorable from a cow productivity perspective between SC365 and AFC, and SC365 and STAY (-0.45 and 0.12, respectively). Indirect selection approaches were more efficient than direct selection for AFC (ERS = 1.87) when animals were selected for SC365.
公牛的阴囊周长与雌性后代的青春期年龄相关。雄性和雌性的生殖功能受激素控制，这可能导致在两性中测量的不同生殖性状之间存在遗传相关。遗传力和遗传相关的估计可以计算直接和相关遗传增益，这对于预测基于遗传的选择的结果非常重要。本研究旨在估计Nellore 牛的初配年龄（AFC）、留用率（STAY）和 365 天阴囊周长（SC365）的遗传参数和间接选择的相对效率。STAY 变量可以定义为奶牛留在牛群中的时间足以养育一定数量的小牛，以支付其开发和维持成本的概率。使用线性动物模型对 SC365 和 AFC 进行双变量贝叶斯分析，使用阈值线性模型对 SC365 和 STAY 以及 AFC 和 STAY 进行方差分量估计。对于 STAY，将值 1 分配给在 76 个月龄时至少生育过三次的奶牛；否则，分配值 0。SC365、AFC 和 STAY 的后验遗传力估计值分别为 0.29、0.08 和 0.09。从奶牛生产力的角度来看，SC365 和 AFC 之间以及 SC365 和 STAY 之间的遗传相关性较好（分别为-0.45 和 0.12）。当选择 SC365 时，间接选择方法比直接选择 AFC 的效率更高（ERS=1.87）。
