The U.S. Meat Animal Research Center was the first entity in the United States to import the Romanov breed and it has been maintained as a closed flock for over 30 yr. Incorporating this super-prolific breed into crossbred and composite populations has resulted in large improvements in ewe productivity. However, few have quantified factors contributing to genetic and non-genetic variation in ewe reproduction and lamb growth within purebred Romanov populations, which were the objectives of this study. The pedigree contained a total of 8683 lambs born to 218 and 1600 unique sires and dams, respectively. Number of lambs born on a per ewe exposed (NLB_E) and lambing (NLB_L) basis were analyzed in univariate repeatability animal models. As expected, the proportion of phenotypic variance (σ_P²) in litter size attributable to additive genetic (0.06 – 0.08) and permanent environmental (0.05 – 0.07) effects of the ewe was low. The service sire permanent environmental effect contributed to a small but significant amount of σ_P² in NLB_E (0.03) but not NLB_L. However, the service sire additive genetic effect did not influence σ_P² in NLB_E or NLB_L. Lamb body weight was recorded at birth (BW_B) and upon weaning from either milk replacer (~30 d; BW_W-N) or their dam (~60 d; BW_W-D) and were analyzed in a 3-trait model with random additive direct and maternal effects. Estimated direct heritabilities were low for all BW traits (0.07 – 0.10). Maternal heritability was moderate for BW_B (0.34) but low for weaning BW (0.11 – 0.18). This was the first to report direct and maternal genetic correlations between BW of nursery- and dam-reared lambs, and both were estimated to be moderate (0.43 – 0.47). Additionally, direct and maternal effects of BW_B were more strongly correlated with BW_W-N (0.74 – 0.82) than BW_W-D (0.17 – 0.33). Despite inbreeding coefficients having increased at a rate of 0.33% per birth year (1986 – 2019) in this flock, they were not consistently associated with reductions in ewe or lamb performance. Parameter estimates generally agreed with those from less prolific breeds and results indicate selection can be an effective means of improving sub-components of ewe productivity.

中文翻译：

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影响罗曼诺夫封闭羊群母羊繁殖力和羔羊体重的遗传和非遗传因素。

美国肉类动物研究中心是美国第一个进口罗曼诺夫品种的实体，它作为一个封闭的鸡群保持了 30 多年。将这种超级多产的品种纳入杂交和复合种群，大大提高了母羊的生产力。然而，很少有人量化导致纯种罗曼诺夫种群内母羊繁殖和羔羊生长的遗传和非遗传变异的因素，这是本研究的目标。该谱系包含总共 8683 只羔羊，分别来自 218 只和 1600 只独特的公牛和母牛。在单变量可重复性动物模型中分析了在每头母羊暴露 (NLB _E ) 和产羔 (NLB _L ) 基础上出生的羔羊数量。正如预期的那样，表型方差的比例（σ_P ² ) 在产仔数中归因于母羊的加性遗传 (0.06 – 0.08) 和永久性环境 (0.05 – 0.07) 影响很低。在 NLB _E (0.03) 而非 NLB _{L 中}，服役公猪的永久环境效应导致了少量但显着的 σ _P ²。然而，在NLB _E或NLB _{L 中}，服务公牛加性遗传效应不影响σ _P ²。在出生时 (BW _B ) 和断奶时记录羔羊体重(~30 天；BW _W-N ) 或它们的母猪 (~60 天；BW _W-D) 并在具有随机加性直接效应和母体效应的 3 特征模型中进行分析。所有 BW 性状的估计直接遗传力都很低 (0.07 – 0.10)。BW _{B 的}母体遗传力中等(0.34)，但断奶 BW 的母体遗传力较低 (0.11 – 0.18)。这是第一个报告保育和大坝饲养的羔羊体重之间直接和母体遗传相关性的报告，两者都被估计为中等 (0.43 – 0.47)。此外，与BW _W-D相比，BW _{B 的}直接和母体效应与 BW _W-N (0.74 – 0.82) 的相关性更强(0.17 – 0.33)。尽管该羊群的近亲繁殖系数以每个出生年（1986-2019）0.33% 的速度增加，但它们与母羊或羔羊的性能下降并不一致。参数估计值通常与低产品种的参数估计值一致，结果表明选择可以是提高母羊生产力子组成部分的有效手段。