在乳牛牧場中，牛呼吸道疾病(Bovine respiratory disease，BRD)是造成小牛死亡與發病的重要疾病。BRD是一種多重病因疾病，參與BRD的主要細菌包括Mannheimia haemolytica (M. haemolytica)、Pasteurella multocida (P. multocida)、Histophilus somni (H. somni)、Mycoplasma bovis (M. bovis)。呼吸道病原體的調查是一種重要的方法，其可調查區域內病原體的分佈及農場中可能造成BRD的原因，利用來尋找預防和控制方法以減少經濟損失。因此，本研究收集了來自台灣小牛呼吸道的樣本以調查小牛的BRD細菌病原，並探討呼吸道臨床狀況和細菌存在與否的關聯。本研究以鼻咽拭子採樣台灣32個不同的牛群共400頭未斷奶小牛，其中感染BRD 為27頭、沒有感染BRD的小牛為373頭，並使用問卷調查各場的經營管理模式以分析其與BRD之間的關係。實驗牛群大小在137到2,000頭之間，且各場未斷奶小牛數為4到130頭，小牛年齡為1到135天。M. haemolytica、P. multocida、H. somni以聚合酶連鎖反應檢測，M. bovis則以巢氏聚合酶連鎖反應檢測。本研究發現台灣小牛上呼吸道中，最常見的細菌是P. multocida可於65.6% 場中發現，其次分別為M. bovis (16.5%)、H. somni (13.3%)及M. haemolytica (3.3%)。感染BRD的小牛中，最為常見的細菌為P. multocida (59.3%)，其次分別為H. somni (44.4%)、M. bovis (22.2%)、M. haemolytica (0%)。18.5%的BRD感染小牛沒有被檢測出這4種細菌。出現P. multocida和H. somni與動物的臨床症狀有相關(p<0.05)。其他病原則與臨床症狀沒有關聯。以廢棄乳餵飼的小牛在呼吸道中有較高的M. haemolytica, P. multocida及M. bovis盛行率。小牛被餵飼沒有加熱過的初乳會有較高的P. multocida和H. somni檢出率。總結，在台灣無論是BRD陽性或陰性小牛都可在呼吸道中分離出呼吸道相關細菌病原。在牧場中，餵飼廢棄乳或乳房炎乳、太晚給予第一次初乳以及餵飼沒有加熱的初乳都屬於較差的小牛管理方式，會增加呼吸道細菌病原的盛行，因而導致小牛罹患BRD的風險上升。

Bovine respiratory disease (BRD) is an important disease causing of mortality and morbidity in calves. In respiratory tract of healthy and stressed calves contain commensal bacterial pathogens that involve BRD such as Mannheimia haemolytica (M. haemolytica), Pasteurella multocida (P. multocida), Histophilus somni (H. somni) and Mycoplasma bovis (M. bovis). Survey of pathogens in respiratory tract and farm management are very important to enlightenment about distribution of pathogens in area and management factors that associate with them. Therefore, the purpose of this study was to investigate BRD bacterial pathogens from calves and assess the association between bacterial pathogens and farm management. A total of 400 samples from pre-weaned calves with (n=27) and without (n=373) BRD were sampled by nasopharyngeal swab (NPS) from 32 herds in Taiwan (Jan. 2018- Jan. 2019). A questionnaire was designed for investigating the farm information, calf’s management and used for analyzing the relationships with bacterial pathogens occurrence. The herd size ranged from 137 to 2,000 cattle and 4 to 130 pre-weaned calves. The calves age ranged from 1 to 135 days. Bacteria including M. haemolytica, P. multocida and H. somni were detected by PCR and M. bovis was detected by nested-PCR. The most common bacteria in upper respiratory tract of calves were P. multocida (65.6%) followed by M. bovis (16.5%), H. somni (13.3%) and M. haemolytica (3.3%). The association between the presence of P. multocida and H. somni with BRD calves were found (p<0.05). P. multocida, M. bovis and M. haemolytica were significantly higher in calves feeding by waste milk or mastitis milk, M. bovis and H. somni were significantly higher in delaying first colostrum feeding calves. P. multocida and H. somni were significantly higher in no heated colostrum. In conclusion, this study indicated that respiratory bacterial pathogens are commonly found in both healthy and BRD dairy calves in Taiwan. Feeding calves by waste milk or mastitis milk, delaying first colostrum feeding and no heated colostrum are poor calves management that can be risk of BRD in calves due to higher prevalence of bacterial pathogens in respiratory tract.

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