Bacterial pneumonia in feedlot beef cattle

细菌性肺炎是加拿大饲养场肉牛最常见和经济上重要的疾病，也是牛肉行业预防性使用抗生素的主要原因。该病主要发生在犊牛抵达饲养场后的头2-3周，是细菌、病毒、压力、不利气候条件和遗传因素相互作用的结果。该项目包括该疾病的两个方面：对肺部细菌感染的先天免疫，以及由牛支原体引起的一种特殊形式的细菌性肺炎的发病机制。该项目先天免疫部分的目标是确定肺部和血液中有助于抵抗/易感性细菌性肺炎的先天免疫蛋白。将评估这些蛋白质的遗传变异与疾病易感性的关系，测量这些蛋白质的测试可能对确定患病风险增加的小牛有实际好处，并允许更有针对性的抗生素治疗。第二部分侧重于牛支原体肺炎，它最近已成为加拿大牛肉和奶牛慢性抗生素耐药肺炎的主要原因。该项目是对这种疾病自然发生的病例进行深入检查，调查免疫反应以及牛肺中牛支原体细菌数量和遗传类型的变化，比较患病犊牛与健康犊牛，以及在发病前以及肺炎急性和慢性阶段发生的变化。将比较当代和存档的牛支原体分离株的基因型和抗菌素耐药性，以寻找可能解释该疾病最近出现的差异。这些结果对于了解疾病如何发展，特别是控制措施是否应针对疾病的易感原因或针对牛支原体的毒性菌株具有重要意义。

Bacterial pneumonia is the most common and economically important disease of Canadian feedlot beef cattle, and is a major reason for preventative use of antibiotics in the beef industry. The disease occurs mainly in the first 2-3 weeks after calves arrive in feedlots, and results from interactions among bacteria, viruses, stress, adverse climatic conditions, and genetic factors. This project encompasses two aspects of this disease: innate immunity against bacterial infection in the lung, and the pathogenesis of a particular form of bacterial pneumonia caused by Mycoplasma bovis. The objective of the innate immunity component of the project is to identify innate immune proteins in the lung and blood that contribute to resistance/susceptibility to bacterial pneumonia. Genetic variation in these proteins will be evaluated for their association with disease susceptibility, and tests to measure these proteins may be of practical benefit to identify calves at increased risk of disease, and permit more focused antibiotic treatment. The second component focuses on Mycoplasma bovis pneumonia, which has recently emerged as a major cause of chronic antibiotic-resistant pneumonia in Canadian beef and dairy calves. The project is an intensive examination of naturally occurring cases of this disease, investigating immune responses and changes in the numbers and genetic type of Mycoplasma bovis bacteria in the lungs of cattle, comparing calves that develop disease to those that remain healthy, and changes that occur prior to disease and during acute and chronic stages of pneumonia. The genotype and antimicrobial resistance of contemporary and archived isolates of Mycoplasma bovis will be compared for differences that may explain the recent emergence of this disease. These results are important to understand how the disease develops, and specifically whether control measures should be directed at the predisposing causes of disease or at virulent strains of Mycoplasma bovis.