Post-Mortem of a Steer Calf on Feed: Answer

Fig. 1. The open-chest view shows cranioventral consolidation and fibrin on the pleural surface ( (Credit Feedlot Health Management Services) )

 

Fig. 2. The lung cross-section image shows consolidation with fibrin in interlobular septae.

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From the experts at Feedlot Health Management Services

The team diagnosed this case as a representative example of Fibrinous Pneumonia, which is a costly yet commonly observed disease that continues to affect cattle around the world.

Pathogenesis: 

  • Impairment of pulmonary defense mechanisms due to stress (e.g. weaning, transport, handling, etc.) and/or viral infection allows for proliferation of Mannheimia haemolytica, a normal inhabitant of the upper respiratory tract, in the lower airways and lung. During infection, the bacteria produces virulence factors (e.g. leukotoxin and lipopolysaccharide) which contribute to the clinical signs and post-mortem lesions generally observed.

Epidemiology: 

  • More commonly observed within the first 60 days of feeding rather than later.
  • Seems to happen more frequently in the fall (October through December), but this is confounded by the extremely large number of high-risk feedlot placements during the same timeframe, especially in northern latitudes.

Ante-Mortem Clinical Signs: 

  • Animals will commonly exhibit one or more of the following signs:
  • Depressed mentation status/dull appearance
  • Anorexia (appear gaunt)
  • Reluctance to move
  • Increased respiratory effort and/or rate
  • Fever (104.0°F or higher)
  • Lack of signs attributable to body systems other than the respiratory tract

It is very difficult, if not impossible, to accurately differentiate between different forms/causes of bovine respiratory disease in live animals using clinical assessment. As a result, the term “undifferentiated fever” may be a more accurate ante-mortem term to describe these animals than “pneumonia” or “pasteurellosis.” Additional diagnostic tools may help improve the specificity of diagnosis in the future, but for animals that succumb to disease, a post-mortem exam remains the gold standard. 

Management:

General management of BRD, including fibrinous pneumonia, centers around prevention of disease, which includes reduction of stressors, adequate vaccination for both viral and bacterial BRD pathogens, and targeted metaphylaxis when applicable. Treatment of BRD, including fibrinous pneumonia, centers around early detection of animals with disease and timely antimicrobial +/- supportive therapy.

Post-Mortem Lesions:

  • Upon initial observation of the open thorax (see Fig. 1), typical findings often include: cranioventral consolidated that is often associated with mild to moderate amounts of fibrin and proteinaceous material on the pleural surface.
  • Upon observation of the parenchyma on cut-sections of lung (see Fig. 2), typical findings often include: lobular hemorrhage and necrosis, yellow fibrin in the interlobular septae, and bronchi may contain fibrinous coagulum but not frank pus. As the lesion progresses, coagulation necrosis becomes the predominant lesion and is observed as large, pink-tan foci within affected parenchyma that may or may not cross lobular borders.

Post-Mortem Series presented in partnership with Feedlot Health management Services, Okotoks, Alberta. For more information, visit their website at www.feedlothealth.com

Feedlot Health’s large team of professional consultants serve feedlots and calf growers in Canada, the United States, Mexico, Brazil, Kazakhstan and elsewhere, representing about 4 million head per year
Working with crews at client operations, Feedlot Health conducts post-mortem exams on all feedlot and calf-grower mortalities, using a standard protocol for recording the animal’s history, digital images, and post-mortem findings. The group compiles images and post-mortem findings in a central database, for review by the professional team, as an educational tool and to track disease trends within an operation or across their client base. 

Working with crews at client operations, Feedlot Health conducts post-mortem exams on all feedlot and calf-grower mortalities, using a standard protocol for recording the animal’s history, digital images, and post-mortem findings. The group compiles images and post-mortem findings in a central database, for review by the professional team, as an educational tool and to track disease trends within an operation or across their client base. 

For the previous article in this series, see Post-Mortem in a Feedlot Heifer on BovineVetOnline.

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