Gastrointestinal nematodes are a major constraint in sheep production. Breeding for resistance has proven to be an effective and feasible approach to address this problem. The use and investigation of genetic markers for resistance traits could accelerate genetic progress and lead to a better understanding of underlying molecular mechanisms. Thus, the aim of this study was to evaluate if five single nucleotide polymorphisms SNPs OAR2_14765360, OAR6_81718546, OAR11_62887032, OAR12_69606944 and OAR15_59871543 are associated with resistance and resilience traits in a flock of the Morada Nova sheep breed. Lambs were submitted to two consecutive parasite challenges by oral infection with 4000 infective larvae L3) of Haemonchus contortus. Fecal egg counts (FEC), packed cell volume (PVC) and body weight were measured every one or two weeks for 42 days in each trial. DNA samples from 287 lambs, 131 ewes and 4 rams were amplified by ARMS-PCR or PCR-RFLP and genotypes were determined. Analysis of variance (ANOVA) was used for association analyses between genotypes and phenotypes. In case of significant association, the allele substitution effect was calculated based on a linear model. OAR2_14765360 and OAR12_69606944 were associated with FEC, and OAR12_69606944 also had significant effects on PCV and weight gain, showing favourable associations of the CC genotype with all evaluated traits. Both OAR6_81718546 and OAR11_62887032 were associated with weight gain, and OAR6_81718546 had an additional effect on PCV. OAR15_59871543 was not polymorphic in the population. OAR6_81718546 and OAR12_69606944 presented significant allele substitution effects of -1.06 ± 0.52 kg for the T allele on final body weight and 0.74 ± 0.32 for the C allele in PCV of the same sampling date, respectively. This is the first report of SNPs associated with gastrointestinal nematode resistance in this sheep breed. Our findings support the existence of quantitatice trait loci (QTL) for resistance and resilience in linkage disequilibrium with the polymorphic SNPs and suggest their future use for explorations of these traits in Morada Nova sheep.

中文翻译：

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四个单核苷酸多态性（SNPs）与巴西Morada Nova绵羊对弯曲杆菌的抗性和复原力有关。

胃肠道线虫是绵羊生产的主要限制因素。事实证明，抗病育种是解决这一问题的有效途径。抗病性状的遗传标记的使用和研究可以加速遗传进程，并导致对潜在分子机制的更好理解。因此，本研究的目的是评估五个单核苷酸多态性SNPs OAR2_14765360，OAR6_81718546，OAR11_62887032，OAR12_69606944和OAR15_59871543是否与Morada Nova绵羊品种的群中的抗性和韧性相关。羔羊通过用4000只弯曲变形金门氏菌的感染性幼虫L3）口服感染而经受两次连续的寄生虫攻击。粪便卵数（FEC），在每个试验中，每1或2周测量一次填充细胞体积（PVC）和体重，持续42天。通过ARMS-PCR或PCR-RFLP扩增了287只羔羊，131只母羊和4只公羊的DNA样品，并确定了基因型。方差分析（ANOVA）用于基因型和表型之间的关联分析。在显着关联的情况下，基于线性模型计算等位基因替代效应。OAR2_14765360和OAR12_69606944与FEC相关，而OAR12_69606944也对PCV和体重增加具有显着影响，显示CC基因型与所有评估的性状均具有良好的关联。OAR6_81718546和OAR11_62887032均与体重增加相关，而OAR6_81718546对PCV具有附加影响。OAR15_59871543在总体中不是多态的。OAR6_81718546和OAR12_69606944在相同采样日期的PCV中，T等位基因对最终体重的显着等位基因替代作用分别为-1.06±0.52 kg和C等位基因为0.74±0.32。这是该绵羊品种中与胃肠道线虫抗性有关的SNP的首次报道。我们的发现支持与多态性SNP连锁不平衡中抗性和复原力的数量性状基因位点（QTL）的存在，并建议将其用于在Morada Nova绵羊中探索这些性状。