Abstract
A comparative study of microbiota of the respiratory tract and joints of bovine respiratory disease (BRD) cattle mortalities was undertaken. Nasopharynx, trachea, lung and joint samples were collected from 32 cattle that died of BRD, “cases”, and 8 that died of other causes, “controls”. Bacterial diversity was lower (p < 0.05) in the nasopharynx, trachea and lungs of cases as compared to controls. In cases, alpha-diversity (p < 0.05) was lower in the lungs and joints than the nasopharynx. Proteobacteria, Tenericutes, Bacteroidetes, Firmicutes and Actinobacteria were the most abundant phyla in all samples. Relative abundances of Mycoplasma spp. in the lung, Pasteurella spp. in the trachea and lung, and Histophilus spp. in the lung, trachea and nasopharynx of cases were higher (p < 0.001) than controls. Mycoplasma spp. comprised 20.5% of bacterial flora in the joint, 36.0% in the lung, 22.4% in the trachea and 8.8% in the nasopharynx. Mannheimia spp. (21.8%) and Histophilus spp. (10.4%) were more abundant in lungs. Cattle that died of BRD possessed less diverse respiratory microbiomes with a higher abundance of respiratory pathogens. Mycoplasma spp. were prominent members of pneumonic lungs and joints displaying septic arthritis.
Highlights
Bovine respiratory disease (BRD) is the most significant cause of mortalities in newly arrived feedlot calves [1], costing the North American feedlot industry over $4 billion annually due to treatment and prevention costs as well as lost productivity [2,3]
This is the first study to characterize the microbiome of the respiratory tract and joints of feedlot cattle afflicted with arthritis and/or pneumonia
Previous microbiome studies of feedlot cattle have been limited to samples from the nasopharyngeal passages of healthy and sick animals, or the upper and lower respiratory tracts of healthy cattle [5,7,8,16,18], whereas the current study utilized tissue samples obtained at the time of postmortem examination from cattle that had either been euthanized or died naturally of nonresponsive arthritis or pneumonia
Summary
Bovine respiratory disease (BRD) is the most significant cause of mortalities in newly arrived feedlot calves [1], costing the North American feedlot industry over $4 billion annually due to treatment and prevention costs as well as lost productivity [2,3]. BRD is a multifactorial disease precipitated by various stressors (e.g., weaning, transportation, and commingling) that predispose cattle to viral and bacterial infections, with bacterial pathogens being considered the principle etiological agents. Primary bacterial pathogens associated with BRD include Pasteurella multocida, Mannheimia haemolytica, Histophilus somni and Mycoplasma bovis [4,5], all of which can colonize the upper respiratory tract as commensals in healthy cattle [6,7,8]. P. multocida is associated with a fibrinopurulent bronchopneumonia, which results in less fibrin and necrosis and is less fulminant. H. somni is associated with purulent bronchopneumonia, severe fibrinous pleuritis, and a septicemia that may lead to secondary infections in other organs. P. multocida, M. haemolytica and H. somni are associated with
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