Intracellular pH regulation of ruminal epithelium and its impacts on rumen acidosis

本研究的目的是评价细胞内pH调节相关蛋白质编码基因的单核苷酸多态性（SNP）及其对瘤胃pH调节的影响。瘤胃酸中毒是一种对反刍动物健康和生产力产生负面影响的代谢紊乱。饲喂高谷物日粮通常会引起过度发酵，导致瘤胃内发酵酸积累，导致采食量减少、肝脏衰竭、跛行和乳脂减少。然而，动物对高发酵性饮食的耐受程度存在显著差异;一些动物容易发生瘤胃酸中毒，而另一些动物在几乎没有瘤胃酸中毒症状的情况下提高生产力。因此，确定使动物更耐受瘤胃酸中毒的因素是极其重要的。基于先前的研究结果，编码参与瘤胃上皮细胞内pH调节的转运蛋白的基因（如NHE 3和MCT 1）是SNP发现的初始目标，将通过测序分析进行，其中通过比较使用基于已报道的基因组序列或靶基因的cDNA序列设计的引物扩增的基因组序列来鉴定潜在的SNP。使用卡方检验比较酸中毒敏感和酸中毒抗性动物组之间的SNP基因型和等位基因频率，SNP基因型和/或等位基因频率的显著差异将表明基因SNP与对瘤胃酸中毒的抗性之间的推定关联。对于酸中毒敏感和酸中毒抗性动物组之间显示基因型和/或等位基因频率显著差异的SNP，将对更多动物进行基因分型。该项目有望为改善动物健康和提高生产效率提供新的分子方法。标记辅助选择酸中毒抗性和营养管理考虑动物遗传学，预计将有助于可持续的乳制品生产在加拿大，减轻瘤胃酸中毒问题。

The objective the proposed research is to evaluate the single nucleotide polymorphism (SNP) in genes coding proteins involved in intracellular pH regulation and its impacts on regulation of rumen pH. Rumen acidosis is the metabolic disorder that negatively affects health and productivity of ruminants. Feeding high grain diets often causes excess fermentation and results in accumulation of fermentation acids in the rumen, leading to feed intake reduction, liver abscesses, lameness, and milk fat depression. However, a significant variation exists among animals in the extent of tolerance to a highly fermentable diet; some easily experience ruminal acidosis while others improve productivity with little symptom of ruminal acidosis. Therefore, it is extremely important to identify factors that make animals more tolerant to ruminal acidosis. Based on findings from previous research, genes coding transport protein involved in intracellular pH regulation in ruminal epithelia such as NHE3 and MCT1 are initial targets for SNP discovery, and it will be performed through sequencing analyses, in which potential SNP will be identified by comparing genomic sequences amplified using primers designed based on reported genomic sequences or cDNA sequences of the target genes. The SNP genotype and allele frequencies will be compared between the acidosis-susceptible and acidosis-resistant animal groups using a Chi-square test, and significant difference of SNP genotype and/or allele frequencies will indicate a putative association between the gene SNP and resistance to rumen acidosis. The SNP that shows significant difference of genotype and/or allele frequencies between the acidosis-susceptible and acidosis-resistant animal groups will be genotyped for a greater number of animals. The proposed project is expected to provide novel molecular approaches to improve animal health and production efficiency. Marker-assisted selection for acidosis resistance and nutritional management considering animal genetics are expected to contribute to sustainable dairy production in Canada by mitigating ruminal acidosis problems.