Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Abstract only
Publication Acceptance Date: 10/9/2003
Publication Date: 10/9/2003
Citation: Fulton, R.W., Blood, K.S., Panciera, R.J., Confer, A.W., Ridpath, J.F., Saliki, J.T., Welsh, R.D., Johnson, B.J. 2003. Respiratory disease in feedlot cattle: isolation of infectious agents and lung lesions in fatal feedlot cases. American Association of Veterinary Laboratory Diagnosticians. p. 147. Interpretive Summary:
Technical Abstract: Respiratory tract diseases represent major economic losses to beef cattle producers. Severe pneumonia, "Shipping fever" is a major cause of production losses including high morbidity and mortality of both stocker and feedlot cattle. Severe bacterial pneumonia associated with "Shipping Fever" is caused by Mannheimia haemolytica, Pasteurella multocida and Haemophilus somnus. Several viruses such as bovine herpesvirus-1 (BHV-1), bovine viral diarrhea viruses (BVDV), parainfluenza-3 virus (PI-3V), bovine respiratory syncytial virus (BRSV), bovine adenoviruses, and bovine respiratory coronaviruses and various Mycoplasma spp., particularly M. bovis are associated with those diseases. The purpose of this study was to identify infectious agents and lesions in lungs of calves dying of respiratory disease in an Oklahoma feedyard. Lung samples and fixed tissues were submitted from cattle dying of suspected respiratory disease from May 2002 - May 2003. These cattle were either in the sick pen or died acutely without prior treatment. Samples from the lungs were submitted for isolation of bacteria, viruses, and Mycoplasma spp. In the later stages of the project, ear notches were tested for BVDV antigen by immunohistochemistry (IHC) and selected ear notches were tested using an antigen capture ELISA test. There were 287 sets of samples from cattle in this study. The percentages of bacteria and Mycoplasma spp. recovered from 254 lungs were: M. haemolytica, 28%; P. multocida, 28%; H. somnus, 10%; Archanobacterium pyogenes, 33%, Salmonella spp., 0.5%; and Mycoplasma spp., 69%. Viruses recovered by cell culture isolation from 249 lungs included: BVDV noncytopathic (NCP), 8%; BVDV cytopathic, 2%; BHV-1, 2%; unidentified, 1%; and BHV-4, 0.5%. The BVDV were sequenced to determine which BVDV subtypes were present. The morphologic diagnoses for 250 lung samples were categorized into three listings: pneumonia, duration, and bronchiolar changes. Percentages for pneumonia category included: fibrinous, 28%; fibrinous pleuropneumonia, 49%; interstitial, 6%; septicemia, 1%; other, 4%; normal tissue submitted, 9%; and autolyzed tissue, 3%. Duration of lesions included: acute, 24%; subacute, 16% chronic, 37%; healing, 3%; and 20% for uncategorized, normal, autolyzed, and septic. Bronchiolar changes were 40% with bronchiolar obliterans, and 30% with bronchiolar necrosis. There were 5% of the ear notches positive for BVDV IHC. These calves were most likely persistently infected (PI) with BVDV. Results of this study indicate that while feedlot studies of pneumonias have M. haemolytica as the predominant etiologic agent, the recovery rate in animals treated may be reduced to approximately 30%. Also, P. multocida identified by a rate similar to M. haemolytica should also be considered in the etiology of feedlot bacterial pneumonias including fibrinous and fibrinous pleuropneumonia. The predominant virus recovered from this study was BVDV. It is important to subtype BVDV isolates to differentiate field strains from vaccinal strains (BVDV1a and BVDV2) plus identifying other subtypes such as BVDV1b. The use of BVDV IHC on ear notches of all cattle dying in the feedlot permits a retrospective analysis of BVDV PI.