The length of ewe productive life (LPL), defined as the number of days between the first and last lambing, is a key indicator of ewe longevity and is directly related to the sustainability of the sheep industry. Therefore, the primary objective of this study was to investigate systematic effects influencing LPL in Katahdin sheep. The LPL of 10,474 Katahdin ewes (69.5% with uncensored and 30.5% with right-censored observations) born between 1992 and 2021 in 58 flocks located across the United States were analyzed. The Kaplan-Meier (K-M) and Cox Proportional Hazard (Cox PH) methods were used to estimate survival probability. Four Cox PH models were evaluated. Model 1 included contemporary group (CG; flock-year-season of ewe birth) as a random effect and the ewe’s dam’s age (EDA), ewe’s own birth-rearing type (BR; 1/1, 2/1, 2/2, 3/2, 3/3, with the digit-3 including lamb counts ≥3), and age at first lambing (AFL) as fixed effects. Models 2 to 4 were an extension of model 1. Model 2 also included average lamb birth weight (ABW) per ewe lifetime, while model 3 included average lamb weaning weight (AWW) per ewe lifetime. Both ABW and AWW were fitted as fixed effects. Model 4 fitted all previous effects together. The factors CG, BR, ABW, and AWW affected LPL (P < 0.05) in all models in which these effects were fitted. The EDA effect only influenced LPL (P < 0.05) in model 1, while AFL had no effect (P > 0.05) in any model. The median LPL ranged from approximately 2 to 3 yr, depending on the risk factors analyzed. In general, Katahdin ewes themselves born in multiple litters, and that produced lambs weighing ~5 kg at lambing and 20 to 25 kg at weaning (over their lifespan) had better survival probability. Although the LPL of Katahdin sheep is relatively low, it appears to be a consequence of voluntary culling due to its association with both ABW and AWW. Future studies should quantify the rate of involuntary culling in Katahdin ewes to identify whether longevity indicator traits should be included in more comprehensive breeding objectives.

中文翻译：

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影响美国 Katahdin 母羊生产寿命长短的因素


母羊生产寿命 （LPL） 的定义是第一次和最后一次产羔之间的天数，是母羊寿命的关键指标，与绵羊产业的可持续性直接相关。因此，本研究的主要目的是调查影响 Katahdin 绵羊 LPL 的系统效应。分析了 1992 年至 2021 年间在美国 58 个羊群中出生的 10,474 只 Katahdin 母羊（69.5% 未经删失，30.5% 右删失观察）的 LPL。采用 Kaplan-Meier （K-M） 和 Cox 比例风险 （Cox PH） 方法估计生存概率。评估了四个 Cox PH 模型。模型 1 包括当代组 （CG;母羊出生的羊群年季节）作为随机效应，母羊的母羊年龄 （EDA）、母羊自身的出生饲养类型 （BR;1/1、2/1、2/2、3/2、3/3，其中数字 3 包括羔羊数量 ≥3） 和首次产羔年龄 （AFL） 作为固定效应。模型 2 到 4 是模型 1 的扩展。模型 2 还包括每只母羊一生的平均羔羊出生体重 （ABW），而模型 3 包括每只母羊一生的平均羔羊断奶体重 （AWW）。ABW 和 AWW 均作为固定效应进行拟合。Model 4 将之前的所有效应拟合在一起。因子 CG 、 BR 、 ABW 和 AWW 影响了所有模型 的 LPL （P < 0.05）。EDA 效应仅影响模型 1 中的 LPL （P < 0.05），而 AFL 在任何模型中均无影响 （P > 0.05）。中位 LPL 范围约为 2 至 3 年，具体取决于分析的风险因素。一般来说，Katahdin 母羊本身在多窝中出生，并且产生的羔羊在产羔时重 ~5 公斤，断奶时重 20 至 25 公斤（在其生命周期内）具有更好的存活概率。 尽管 Katahdin 绵羊的 LPL 相对较低，但由于它与 ABW 和 AWW 有关，这似乎是自愿扑杀的结果。未来的研究应量化 Katahdin 母羊的非自愿淘汰率，以确定是否应将长寿指标性状纳入更全面的育种目标。