Bovine respiratory disease (BRD)

Bovine respiratory disease (BRD) is the most common cause of illness and death in Australian feedlot cattle. It is most common in the first four weeks after entry to a feedlot.

BRD is caused by a combination of stress and disease-causing agents, including viruses and bacteria.

BRD is a multifactorial disease, triggered by stressors which weakens the immune system, and disease-causing agents such as viruses and bacteria that cause severe respiratory illness.

Stressful conditions include:

• saleyards
• transport
• injury
• dehydration
• co-mingling, pen competition, pen 'add-ons' and movements
• handling
• weather extremes and dust
• feed and water changes.

The viruses most commonly associated with BRD in Australia are bovine herpesvirus, bovine viral diarrhoea virus (BVDV or bovine pestivirus), bovine parainfluenza, and bovine respiratory syncytial virus.

Several bacterial species have also been recognised as important in the BRD complex; these include Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Trueperella pyogenes and Mycoplasma bovis.

Ante-mortem

• During ante-mortem inspection, animals showing the following clinical signs would be suspected as being affected by bovine respiratory disease:
• fever (<40°)
• depression and loss of interest in surroundings
• lethargy and unwillingness to move
• extended head
• droopy ears
• discharge from the eyes, nose and mouth
• coughing
• rapid shallow breathing

Post-mortem

Key post-mortem findings:

• Bronchopneumonia, characterized by inflammation and consolidation of lung tissue. Lungs can appear congested and reddened due to inflammation.
• In severe cases, there may be haemorrhage in the lung’s parenchyma. Lungs with consolidated tissue are firm to the touch and heavy due to the accumulation of exudates. When cut open, they exhibit a firm and solid consistency, typically reddish or greyish, lacking the normal spongy texture.
• In acute cases, fibrinous pleuritis is observed, which is inflammation of the pleura with fibrin accumulation, leading to adhesions between the pleura and the thoracic cavity. (Photos 1 & 2)
• If the infection is advanced and involves bacteria like Mannheimia haemolytica or Pasteurella multocida, pulmonary abscesses can be found in various stages of encapsulation and development.  (Photo 3)
• In chronic cases, abscesses can be walled off as abscesses or fibrous capsules
• Regional lymph nodes—including bronchial and mediastinal lymph nodes—may undergo changes like enlargement, reddening, necrosis, or formation of abscesses.
• Acute cases of BRD with a primary involvement of viruses, may exhibit nasal and tracheal lesions, such as redness ulceration, and the accumulation of mucous or purulent secretions in the nasal cavity and trachea (Photo 4).
• In acute cases, fever and septicaemia are common. (Photos 5, 6,7 & 8)

Inspection procedure

BRD is commonly detected through routine inspection procedures of the body cavities and pulmonary structures.  

The critical issue is determining whether the disease is chronic or acute. In AS4696- 2023, the third schedule 3.4 states:

Pleurisy - acute infectious with evidence of septicaemia, petechial haemorrhage, polyserositis - Carcase and all its parts condemned.

Photos 5, 6,7,8,9,10 & 11 depict these three conditions.

Note: Redness of subcutaneous fat and darkness of muscle tissue. The liver & kidneys will be enlarged and deep clay red brick colour.

Polyserositis

Polyserositis refers to inflammation affecting several serous membranes at one time. When the pleura, peritoneum, and pericardium become inflamed, it may indicate the presence of bovine respiratory disease (BRD).

Disposition

Australian Standard AS4696-2023

Depending on the extent and severity of the disease one of the dispositions outlined below in Schedule 3 applies.

DAFF Post-mortem decision notes

Pneumonia/Pleurisy (Respiratory Disease Complex)

Several bacteria, often in conjunction with viral infection, are associated with severe bacterial pneumonia and pleurisy in cattle, buffalo, sheep and goats. These bacteria include Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Trueperella pyogenes

For pigs, typical gross lesions seen in this disease complex are indicative of infections of Enzootic Pneumonia, Porcine Pleuropneumonia (APP) and Pnuemonic Pasturellosis. Other infections which may be involved include Streptococcus suis type 2 and Trueperella pyogenes.

Resolved pleural and peritoneal adhesions of a nonsuppurative and chronic nature are removed before the remainder of the carcase is passed for human consumption. Following stripping of pleura, the carcase is reinspected:

If the ribs appear normal following pleural stripping, the removed parts (in other words, stripped pleura) are condemned, and the carcase may be passed for human consumption.

If the ribs do not appear normal, the affected ribs or whole forequarter are removed, and the carcase is reinspected (refer to Appendix A: Respiratory Disease Complex Disposition Criteria for further guidance):

If there is evidence of systemic pathology (in other words, cachexia, fevered carcase, septicaemia, peritonitis, polyarthritis or polyserositis), then the carcase is condemned.

If there is no evidence of systemic pathology, then the carcase may be passed for human consumption and the removed parts condemned (in other words, ribs or forequarter).

Where uncertainty regarding the final carcase disposition remains, additional testing to determine safety and wholesomeness may be undertaken (Australian Meat Standard (clause 10.17)) (e.g. pneumonia/pleurisy complex in beef).

For pigs with evidence of tail bite, the lungs should be palpated for signs of multiple pulmonary abscesses resulting from embolic pneumonia to assist with final disposition judgement (Table 4, Schedule 2, Australian Meat Standard). Lung abscesses of pigs are not associated with foodborne hazards (refer to Conditions predisposing towards food poisoning and Pointon et al. 2018). Affected carcases should be assessed for pneumonia/pleurisy complex with disposition judgements for severity (acute or chronic) applied accordingly (refer to Definitions).

Disposition should be based on the risk-based criteria for Respiratory Disease Complex, refer to Appendix A: Respiratory Disease Complex Disposition Criteria and Appendix B: Disease stage and role in assessment of risk and wholesomeness for carcasses with Bovine Respiratory Disease complex (BRD) (Pointon et al. 2017) table.