Centre for Genetic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada, N1G 2W1.
Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, 2500 University Dr. NW, Calgary, Alberta, Canada, T2N 1N4.
J Dairy Sci. 2018 Mar;101(3):2724-2736. doi: 10.3168/jds.2017-13554. Epub 2018 Jan 10.
Mastitis is a disease of major economic importance to the dairy cattle sector because of the high incidence of clinical mastitis and prevalence of subclinical mastitis and, consequently, the costs associated with treatment, production losses, and reduced animal welfare. Disease-recording systems compiling data from a large number of farms are still not widely implemented around the world; thus, selection for mastitis resistance is often based on genetically correlated indicator traits such as somatic cell count (SCC), udder depth, and fore udder attachment. However, in the past years, several countries have initiated collection systems of clinical mastitis, based on producers recording data in most cases. The large data sets generated have enabled researchers to assess incidence of this disease and to investigate the genetic background of clinical mastitis itself, as well as its relationships with other traits of interest to the dairy industry. The genetic correlations between clinical mastitis and its previous proxies were estimated more accurately and confirmed the strong relationship of clinical mastitis with SCC and udder depth. New traits deriving from SCC were also studied, with the most relevant findings being associated with mean somatic cell score (SCS) in early lactation, standard deviation of SCS, and excessive test-day SCC pattern. Genetic correlations between clinical mastitis and other economically important traits indicated that selection for mastitis resistance would also improve resistance against other diseases and enhance both fertility and longevity. However, milk yield remains negatively correlated with clinical mastitis, emphasizing the importance of including health traits in the breeding objectives to achieve genetic progress for all important traits. These studies enabled the establishment of new genetic and genomic evaluation models, which are more efficient for selection to mastitis resistance. Further studies that are potential keys for future improvement of mastitis resistance are deep investigation of the bacteriology of mastitis, identification of novel indicator traits and tools for selection, and development of a larger female reference population to improve reliability of genomic evaluations. These cutting-edge studies will result in a better understanding of the genetic background of mastitis resistance and enable a more accurate phenotyping and genetic selection to improve mastitis resistance, and consequently, animal welfare and industry profitability.
乳腺炎是奶牛养殖业中具有重要经济意义的疾病，因为其临床乳腺炎发病率高、亚临床乳腺炎流行，因此与治疗、生产损失和动物福利降低相关的成本很高。在全球范围内，仍未广泛实施疾病记录系统来汇总大量农场的数据；因此，乳腺炎抗性的选择通常基于与体细胞计数（SCC）、乳房深度和前乳房附着等遗传相关的指标性状。然而，在过去几年中，一些国家已经启动了临床乳腺炎的收集系统，这些系统通常基于生产者记录数据。所产生的大量数据集使研究人员能够评估这种疾病的发病率，并研究临床乳腺炎本身的遗传背景，以及其与奶牛养殖业感兴趣的其他性状的关系。临床乳腺炎与其先前代理性状之间的遗传相关性被更准确地估计，并证实了临床乳腺炎与 SCC 和乳房深度之间的紧密关系。还研究了来自 SCC 的新性状，最相关的发现与泌乳早期的平均体细胞评分（SCS）、SCS 的标准差和过高的测试日 SCC 模式有关。临床乳腺炎与其他经济重要性状之间的遗传相关性表明，对乳腺炎抗性的选择也将提高对其他疾病的抗性，并提高生育力和寿命。然而，产奶量仍然与临床乳腺炎呈负相关，这强调了在育种目标中包括健康性状的重要性，以实现所有重要性状的遗传进展。这些研究为建立新的遗传和基因组评估模型奠定了基础，这些模型对于乳腺炎抗性的选择更有效。乳腺炎抗性的进一步研究是乳腺炎细菌学的深入研究、鉴定新的指示性状和选择工具、以及开发更大的雌性参考群体以提高基因组评估的可靠性，这些研究是未来改善乳腺炎抗性的关键。这些前沿研究将有助于更好地了解乳腺炎抗性的遗传背景，并使乳腺炎抗性的表型和遗传选择更加准确，从而提高乳腺炎抗性，最终提高动物福利和产业盈利能力。
