Diagnosing and managing BRD in post-weaned cows (Proceedings)

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Diagnosing and managing BRD in post-weaned cows (Proceedings)

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Aug 01, 2011

Key points

     • Bovine respiratory disease (BRD) is the most common illness of cattle after weaning, and accurate diagnosis impacts preventive and therapeutic program success.
     • Diagnosis of BRD in individual animals is often based on clinical signs and generating an accurate case definition helps identify a reasonable intervention point.
     • On a population level, predicting BRD is important when evaluating the potential efficiency of employing prevention or therapeutic measures.

Bovine respiratory disease (BRD) is the most common and costly syndrome afflicting beef cattle after weaning. A basic understanding of the disease syndrome is important to design a treatment and prevention program. Many bacterial pathogens associated with BRD are normal flora that can be isolated from the upper respiratory tract of healthy cattle. Other disease syndromes relevant to the cow-calf farm including reproductive pathogens, may also be found in animals without clinical signs. Contributing factors such as animal immune status, pathogen load, organism virulence, and environmental conditions influence disease severity. Managing for a single disease causing agent or risk factor will not eliminate disease from the population. The complete animal management program must be evaluated to maintain hope of diminishing disease impact.

BRD in individuals

Timely identification of clinically ill animals is critical because the best treatment protocol is ineffective if severe damage occurred prior to treatment. Recognition of disease is an art, not a science. The keys are systematic pen and animal appraisal, and diagnosis evaluation. Differentiation of specific diseases often depends on the epidemiology of the case presentation in the affected population.

Typical signs of respiratory disease include: anorexia, depression, animal isolation, increased respiratory rates, nasal discharge, coughing and diarrhea. A consistent method for evaluating pens and individuals within the group is important for accurate, timely identification of disease. Cattle are herd animals and considered prey in the predator-prey relationship of wild animals. In nature, predators feeding on the herd will pick out the weakest animals that may be easier to catch; therefore, the instinct for a sick calf is to blend in with the herd and not be found. Domesticated cattle have this instinct and try to avoid appearance of illness when possible.

A study of feedlot steers revealed that although only 35% of the animals were treated, 72% had pulmonary lesions present at slaughter.(Wittum, Woollen et al. 1996) The pulmonary lesions were directly associated with a significant reduction in ADG during the feeding period. One of the most remarkable findings of the study was that 68% of the untreated steers had pulmonary lesions. This indicates that visual evaluation was inadequate to prevent significant production losses attributable to respiratory tract disease. We should evaluate pens with these facts in mind. Walking or riding into the middle of the pen and trying to identify a sick animal is often fruitless unless the animals are very ill.