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Bovine respiratory disease (BRD) is the most common and costly disease affecting beef cattle in the world.〔D. Griffin: ''Economic impact associated with respiratory disease in beef cattle.'' In: ''The Veterinary clinics of North America. Food animal practice.'' Band 13, Nummer 3, November 1997, , S. 367–377, PMID 9368983 (Review).〕 It is a complex, bacterial infection that causes pneumonia in calves and can possibly be fatal. The infection is usually a sum of three codependent factors: Stress, an underlying viral infection, and a new bacterial infection. The diagnosis of the disease is complex since there are multiple possible causes. The disease manifests itself most often in calves within four weeks of weaning, when calves are sorted and often sold to different farms. This gives it a common nickname, "Shipping Fever." It is not known whether the stress itself, commingling, or travel conditions are at most to blame, and while studies have identified general stressing factors like transport and cold weather conditions, there is still no conclusive evidence on more specific factors (e.g. distance, transport mode, temperature, or temperature volatility. ==Causative Agents== BRD is a "multi-factorial syndrome" that is dependent on a number of different causes.〔 A viral infection combines with a bacterial agent, which is often then aggravated by stress. Usually all three of these factors must be present in order to cause BRD.〔 Viral agents are often present in the herd for an extended time, with almost no symptoms, and only cause severe complications with a bacterial infection. 〔 The bacterial agents most commonly linked with BRD are Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. 〔 Viral agents include Bovine Viral Diarrhea (BVD), Infectious Bovine Rhinotracheitis (IBR), Bovine Respiratory Synctial Virus (BRSV), and Parainfluenza Type-3 Virus (PI-3). 〔(Bovine Respiratory Disease "Shipping Fever" in Cattle ), Ram Kasimanickam / Washington State University Veterinary Medicine Exension, 2010〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bovine respiratory disease」の詳細全文を読む スポンサード リンク
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