Istituto Zooprofilattico Sperimentale delle Venezie, Padua, Italy.
Verband der Südtiroler Kleintierzüchter, Bolzano, Italy.
J Anim Breed Genet. 2020 Jul;137(4):395-406. doi: 10.1111/jbg.12478. Epub 2020 Apr 21.
Scrapie is an ovine transmissible spongiform encephalopathy, and its susceptibility is associated with polymorphisms in the prion protein gene (PRNP). Genetic selection is currently the most effective mean for eradication of the susceptible VRQ allele in favour of resistant ARR allele. Maintenance of genetic diversity should be one of the major objectives in breeding programmes, especially in endangered breeds, and genetic information are an excellent alternative to pedigree data where these information are missing. The aim of our study was to determine changes of genetic variability in six native sheep breeds from autonomous province of Bolzano, northern Italy, following simulation of scrapie selection scenarios. A total of 684 rams were investigated for PRNP polymorphisms and for 10 microsatellite loci to estimate genetic variability. Across all loci, a total of 163 alleles were detected with a mean of 10.4 alleles per locus. Average observed (Ho) and unbiased expected (uHe) heterozygosity overall loci were 0.74 and 0.78, respectively, showing a statistically significant deviation from Hardy-Weinberg equilibrium (HWE) in all breeds. This heterozygosity deficit was confirmed by a positive fixation index (Fis), determining a moderate inbreeding in each breed. Simulating a soft selection, where only rams having at least a VRQ allele should be excluded from reproduction, Ho, uHe and Fis values remained almost unchanged, indicating that genetic variability should not be affected by the removal of these individuals. With a mild selection scenario, considering only rams with at least one ARR allele, we observed a decrease in the mean alleles per breed (8.9) and the maintenance of heterozygosity deficiency, except for two breeds, where it was any longer significant. These results showed that selection strategies allowing use of heterozygous as well homozygous ARR rams might be the right compromise to improve resistance to scrapie and to do not dramatically affect genetic variability of these breeds.
瘙痒病是一种绵羊传染性海绵状脑病，其易感性与朊病毒蛋白基因（PRNP）中的多态性有关。遗传选择是目前根除易感 VRQ 等位基因、有利于抗性 ARR 等位基因的最有效方法。保持遗传多样性应该是繁殖计划的主要目标之一，特别是在濒危品种中，遗传信息是在缺少系谱数据的情况下替代这些信息的极好选择。我们的研究旨在确定意大利北部自治省博尔扎诺的六个本地绵羊品种在模拟瘙痒病选择情景后的遗传变异性变化。总共对 684 只公羊进行了 PRNP 多态性和 10 个微卫星位点的调查，以估计遗传变异性。在所有位点共检测到 163 个等位基因，每个位点平均 10.4 个等位基因。所有品种的平均观察（Ho）和无偏期望（uHe）杂合度分别为 0.74 和 0.78，均表现出与 Hardy-Weinberg 平衡（HWE）的统计学显著偏差。这种杂合度不足通过阳性固定指数（Fis）得到证实，确定了每个品种的中度近交。模拟软选择，仅排除至少具有一个 VRQ 等位基因的公羊进行繁殖，Ho、uHe 和 Fis 值几乎保持不变，表明遗传多样性不应受到这些个体去除的影响。在轻度选择情况下，仅考虑至少有一个 ARR 等位基因的公羊，我们观察到每个品种的平均等位基因数量减少（8.9），并维持杂合度不足，除了两个品种不再显著。这些结果表明，允许使用杂合和纯合 ARR 公羊的选择策略可能是提高对瘙痒病的抗性而又不显著影响这些品种遗传多样性的正确折衷方案。
