Institute of Animal Breeding and Genetics, Justus-Liebig-University Gießen, Gießen, Germany.
Clinic for Obstetrics, Gynaecology and Andrology of Large and Small Animals, University of Giessen, Giessen, Germany.
J Anim Breed Genet. 2023 Mar;140(2):132-143. doi: 10.1111/jbg.12752. Epub 2022 Dec 30.
Tail docking is routinely conducted in long-tailed sheep breeds to prevent flystrike infections, but it is not in agreement with legal guidelines and animal welfare issues. Selection on short tails is a sustainable alternative in this regard, but side effects on other breeding goal traits are unclear. In consequence, the present study aimed to estimate genetic parameters for tail length (TL) at birth, birth weight (BW), weaning weight (WW) and postweaning weight (PWW) at the slaughtering date considering single-trait (STM), multiple-trait (MTM) and structural equation models (SEM) with different random effects, and accordingly, different covariance structures. The SEM considered time-lagged recursive relationships among response variables in three different pathways. The first path pertained to the effect of TL on WW and of WW on PWW. The second path reflected the effect of BW on WW and of WW on PWW. The third path was the recursive effect of TL on PWW. The phenotypic data consisted of 2803 records for TL, 13,042 records for BW, 1556 records for WW and 3986 records for PWW from Merinoland lambs. Lambs were born in the period from 1995 to 2021 and kept at the university Gießen research station, Germany, with their naturally long tails. Genetic statistical model evaluation based on Bayesian and Akaike's information criteria suggested models simultaneously considering direct genetic, maternal genetic and maternal permanent environmental effects and respective covariances. For statistical models including the same random effects and covariance structures, SEM were superior over MTM. The direct heritability for TL from the best-fitting STM was 0.60 ± 0.08, indicating the potential for genetic reduction of tail length within a few generations. For growth traits, the direct heritabilities ranged from 0.16 ± 0.03 for BW to 0.31 ± 0.09 for PWW. The maternal heritabilities were 0.03 ± 0.03 for TL, 0.12 ± 0.02 for BW, 0.04 ± 0.03 for WW and 0.07 ± 0.03 for PWW, reflecting small, but the non-significant influence of uterine characteristics on the tail development. The direct genetic correlations between TL and all weight traits were positive and very similar to MTM and SEM but reflected antagonistic genetic relationships from a breeding perspective. Oppositely, the structural equation coefficients reflecting trait associations phenotypically were negative (favourable) for the time-lagged effects of TL on WW and on PWW. As an explanation, lambs with long and woolly tails have an increased risk for contamination with dirt and dust causing infections, which in turn impairs the body weight development. In conclusion, breeding on short tails should consider trait-associated environmental risk factors, for example, disease susceptibility, which can be mimicked via SEM approaches.
断尾是长尾绵羊品种中常见的操作，以防止蝇蛆感染，但这与法律准则和动物福利问题不符。选择短尾是一种可持续的替代方法，但对其他繁殖目标性状的副作用尚不清楚。因此，本研究旨在估计出生时的尾巴长度（TL）、出生体重（BW）、断奶体重（WW）和屠宰日的断奶后体重（PWW）的遗传参数，考虑单性状（STM）、多性状（MTM）和结构方程模型（SEM），使用不同的随机效应和相应的协方差结构。SEM 考虑了三个不同途径中响应变量之间的时间滞后递归关系。第一条途径涉及 TL 对 WW 的影响，以及 WW 对 PWW 的影响。第二条途径反映了 BW 对 WW 的影响，以及 WW 对 PWW 的影响。第三条途径是 TL 对 PWW 的递归影响。表型数据包括来自 Merinoland 羔羊的 2803 个 TL 记录、13042 个 BW 记录、1556 个 WW 记录和 3986 个 PWW 记录。羔羊于 1995 年至 2021 年期间出生，在德国吉森大学研究站饲养，保留其自然生长的长尾。基于贝叶斯和赤池信息量准则的遗传统计模型评估表明，模型同时考虑了直接遗传、母体遗传和母体永久环境效应及其协方差。对于包括相同随机效应和协方差结构的统计模型，SEM 优于 MTM。来自最佳拟合 STM 的 TL 的直接遗传力为 0.60±0.08，表明在几代内有减少尾巴长度的遗传潜力。对于生长性状，直接遗传力范围为 BW 的 0.16±0.03 至 PWW 的 0.31±0.09。母体遗传力为 TL 的 0.03±0.03、BW 的 0.12±0.02、WW 的 0.04±0.03 和 PWW 的 0.07±0.03，反映了子宫特征对尾巴发育的微小但无显著影响。TL 与所有体重性状之间的直接遗传相关性为正，与 MTM 和 SEM 非常相似，但从繁殖角度来看，反映了拮抗的遗传关系。相反，反映表型特征关联的结构方程系数对于 TL 对 WW 和 PWW 的时滞效应为负（有利）。解释是，长尾且毛茸茸的羔羊有被污垢和灰尘污染的风险，从而导致感染，这反过来又会损害体重发育。总之，短尾繁殖应考虑与性状相关的环境风险因素，例如疾病易感性，这可以通过 SEM 方法来模拟。
