Direct selection for litter size or weight at weaning in pigs is often hindered by external interventions such as cross-fostering. The objective of this study was to infer the causal structure among phenotypes of reproductive traits in pigs to enable subsequent direct selection for these traits. Examined traits included: number born alive (NBA), litter size on day 21 (LS21), and litter weight on day 21 (LW21). The study included 6,240 litters from 1,673 Landrace dams and 5,393 litters from 1,484 Large White dams. The inductive causation (IC) algorithm was used to infer the causal structure, which was then fitted to a structural equation model (SEM) to estimate causal coefficients and genetic parameters. Based on the IC algorithm and temporal and biological information, the causal structure among traits was identified as: NBA → LS21 → LW21 and NBA → LW21. Owing to the causal effect of NBA on LS21 and LW21, the genetic, permanent environmental, and residual variances of LS21 and LW21were much lower in the SEM than in the multiple-trait model for both breeds. Given the strong effect of NBA on LS21 and LW21, the SEM and causal information might assist with selective breeding for LS21 and LW21 when cross-fostering occurs.

中文翻译：

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推断猪分娩和断奶性状之间的表型因果结构。

断奶时直接选择产仔数或体重通常会受到交叉寄养等外部干预的阻碍。本研究的目的是推断猪繁殖性状表型之间的因果结构，以便随后直接选择这些性状。检查的特征包括：活产数 (NBA)、第 21 天的窝产仔数 (LS21) 和第 21 天的窝重 (LW21)。该研究包括来自 1,673 个 Landrace 水坝的 6,240 窝和来自 1,484 个 Large White 水坝的 5,393 窝。归纳因果关系 (IC) 算法用于推断因果结构，然后将其拟合到结构方程模型 (SEM) 中以估计因果系数和遗传参数。基于IC算法和时间和生物信息，特征之间的因果结构被识别为：NBA → LS21 → LW21 和 NBA → LW21。由于 NBA 对 LS21 和 LW21 的因果影响，LS21 和 LW21 的遗传、永久环境和剩余方差在 SEM 中远低于两个品种的多性状模型。鉴于 NBA 对 LS21 和 LW21 的强烈影响，SEM 和因果信息可能有助于在发生交叉培育时对 LS21 和 LW21 进行选择性育种。