The U.S. Maternal Hair index was designed by the National Sheep Improvement Program (NSIP) to increase total weight of lamb weaned per ewe lambing (TW). Producers are interested in adding gastrointestinal nematode (GIN) resistance to this breeding objective since parasitism causes substantial economic losses. The NSIP provides producers with estimated breeding values (EBV) for post-weaning fecal egg count (PFEC), an indicator of GIN resistance. Our objective was to gauge the effects of including PFEC as another selection criterion and goal trait. Selection index theory was used to construct 11 indexes. First was a benchmark index with TW as the goal. Weaning weight, and number of lambs born and weaned, were selection criteria. An index was then designed with PFEC added as a selection criterion. In 9 more indices, PFEC was also included as a goal trait, where the economic value of TW was scaled relative to that of PFEC. PFEC received a scaled economic value of -1 with that of TW increasing from +1 to +5 at +0.5 increments. Selection criteria were modelled as EBV or phenotypes. Annual genetic responses in goal traits were predicted. The top 3% of males and 26% of females were selected. Breeding values and phenotypes were simulated for 200 lambs by Cholesky decomposition and used to generate index scores, with 100 replicates run. Concordances with the animals selected in the benchmark scenario were determined. Using EBV as selection criteria, TW increased by 1.46 kg/yr in the benchmark scenario. However, unfavorably, PFEC increased by 2.24%/yr. When using phenotypic criteria, TW increased by 0.52 kg/yr and PFEC by 0.28%/yr. Once added as a goal trait, PFEC decreased regardless of the scaled economic value of TW. However, responses in TW were also reduced, although less so as its scaled economic value increased. A scaled economic value of +3 for TW appeared reasonable over other choices with 79% of the emphasis placed on TW in the breeding objective. With EBV as selection criteria, PFEC declined by 7.96%/yr with 98% of the response in TW retained. Also, on average, 64% of males and 80% of females were chosen in common with the benchmark. With phenotypic selection criteria, PFEC declined by 5.13%/yr and 94% of the response in TW was retained; 61% of males and 80% of females were chosen in common with the benchmark. Implementing an index with scaled economic values of +3 for TW and -1 for PFEC would balance gains in TW with reductions in PFEC.

中文翻译：

---

将胃肠道寄生虫抗性添加到毛羊的育种目标中：初始步骤


美国母体毛发指数由美国国家绵羊改良计划 （NSIP） 设计，旨在增加每只母羊羔羊羔羊 （TW） 断奶羔羊的总重量。生产者有兴趣将胃肠道线虫 （GIN） 抗性添加到该育种目标中，因为寄生会导致巨大的经济损失。NSIP 为生产者提供断奶后粪便蛋数 （PFEC） 的估计育种值 （EBV），PFEC 是 GIN 抗性的指标。我们的目标是衡量将 PFEC 作为另一个选择标准和目标特征的效果。采用选择索引理论构建 11 个索引。首先是以 TW 为目标的基准指数。断奶体重以及出生和断奶的羔羊数量是选择标准。然后设计一个指数，添加 PFEC 作为选择标准。在另外 9 个指数中，PFEC 也被列为目标性状，其中 TW 的经济价值相对于 PFEC 的经济价值进行了缩放。PFEC 的经济价值为 -1，TW 的经济价值从 +1 增加到 +5，增量为 +0.5。选择标准被建模为 EBV 或表型。预测目标性状的年度遗传反应。前 3% 的男性和 26% 的女性被选中。通过 Cholesky 分解模拟 200 只羔羊的育种值和表型，并用于生成指数评分，运行 100 次重复。确定了与基准情景中选择的动物的一致性。使用 EBV 作为选择标准，在基准情景中，TW 增加了 1.46 kg/yr。然而，不利的是，PFEC 增加了 2.24%/年。当使用表型标准时，TW 增加 0.52 kg/年，PFEC 增加 0.28%/年。一旦添加为目标性状，无论 TW 的比例经济价值如何，PFEC 都会下降。 然而，TW 的反应也有所减少，尽管随着其规模经济价值的增加而减少。与其他选择相比，TW 的 +3 比例经济值似乎是合理的，在育种目标中 79% 的重点放在 TW 上。以 EBV 为选择标准，PFEC 下降了 7.96%/年，保留了 TW 中 98% 的响应。此外，平均而言，64% 的男性和 80% 的女性被选择与基准相同。根据表型选择标准，PFEC 下降了 5.13%/年，保留了 TW 中 94% 的反应;61% 的男性和 80% 的女性与基准相同。实施 TW 经济值为 +3 和 PFEC 为 -1 的指数将平衡 TW 的收益与 PFEC 的减少。