Casellas J, Caja G, Piedrafita J
Grup de Recerca en Remugants, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
Animal. 2007 Jun;1(5):637-44. doi: 10.1017/S1751731107727477.
Birth weight plays a central role in lamb survival and growth, and the knowledge of its genetic determinism has become essential in worldwide selection programmes. Within this context, within-litter birth weight variation (BWV) has been suggested as an attractive trait to homogenise litters in prolific species, although it has not been analysed in sheep. The objective of this study was to ascertain whether maternal additive genetic variance exists for BWV in Ripollesa ewes, and to study its genetic, permanent environmental and residual relationships with litter weight (LW) and litter size (LS) at birth. Data were recorded in the Ripollesa experimental flock of the Universitat Autònoma of Barcelona, between 1986 and 2005, and included 1 662 litters from 380 ewes, with 712 records of BWV and 1 530 records of LW. Traits were analysed with a multivariate animal model solved through Bayesian methodologies, and with a threshold characterisation of LS. Additionally, the effect of BWV on lamb survival was studied. Additive genetic variance was observed for BWV (h2 = 0.061), as well as for LW (h2 = 0.200) and LS (h2 = 0.141). Nevertheless, genetic correlations among those traits were not substantial (BWV and LW = 0.151; BWV and LS = - 0.219; LW and LS = - 0.320) and suffered from a high degree of uncertainly, with the null correlation included within the highest posterior interval at 95%. Within-litter birth weight variation and LS showed a negative and large permanent environmental correlation ( - 0.872), and LW and LS were negatively correlated due to residual ( - 0.762) and permanent environmental ( - 0.449) random sources of variation. Within-litter birth weight variation influenced lamb mortality during the first 7 days of life (P < 0.05), increasing and decreasing survivability in heavier and lighter littermates, respectively. Nevertheless, stillbirths and lambs died after the 1st week of life were not affected by BWV (P>0.05). The low heritability found indicates that slow genetic progress may be expected from selecting for BWV. Close to zero genetic correlations suggest that this selection will probably not affect LS and LW, although some significant permanent and residual correlations must be taken into account. Further studies are needed to understand better the genetic architecture among these three reproductive traits.
出生体重在羔羊存活和生长中起着核心作用，了解其遗传决定因素在全球范围内的选择计划中已变得至关重要。在此背景下，窝内出生体重变异（BWV）被认为是使多产物种的窝均匀化的一个有吸引力的性状，尽管尚未在绵羊中进行分析。本研究的目的是确定里波列萨母羊的BWV是否存在母体加性遗传方差，并研究其与出生时窝重（LW）和窝产仔数（LS）的遗传、永久环境和残差关系。数据记录于1986年至2005年巴塞罗那自治大学的里波列萨实验羊群，包括来自380只母羊的1662窝，有712条BWV记录和1530条LW记录。采用贝叶斯方法求解的多变量动物模型对性状进行分析，并对LS进行阈值特征描述性分析。此外，还研究了BWV对羔羊存活的影响。观察到BWV的加性遗传方差（h2 = 0.061），以及LW（h2 = 0.200）和LS（h2 = 0.141）的加性遗传方差。然而，这些性状之间的遗传相关性并不显著（BWV与LW = 0.151；BWV与LS = -0.219；LW与LS = -0.320），且存在高度不确定性，零相关性包含在95%的最高后验区间内。窝内出生体重变异与LS显示出负的且较大的永久环境相关性（-0.872），LW与LS由于残差（-0.762）和永久环境（-0.449）随机变异来源而呈负相关。窝内出生体重变异影响出生后前7天的羔羊死亡率（P < 0.05），分别增加和降低较重和较轻同窝羔羊的存活率。然而，死产和出生后第1周后死亡的羔羊不受BWV影响（P>0.05）。发现的低遗传力表明，选择BWV可能预期遗传进展缓慢。接近零的遗传相关性表明，这种选择可能不会影响LS和LW，尽管必须考虑一些显著的永久和残差相关性。需要进一步研究以更好地理解这三个繁殖性状之间的遗传结构。
