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

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.

BRD diagnosis in populations

Population-level BRD treatment and prevention strategies may most efficiently be employed soon after cattle arrive to the stocker or feeder operation; however, utilization of these tools is based on an accurate estimation of the population risk for BRD.

Immediately prior to and after feeding is a good time to evaluate a pen for clinical illness. Animals exhibiting anorexia can be identified and animal movement toward the bunk can be used to assess locomotion or potential signs of lameness. After viewing the pen from outside, the pen should be entered and the cattle examined from the exterior to the interior in a circumferential spiral pattern. All individuals within the pen should be viewed to assess for potential signs of illness.

Individual pens need to be examined differently based on cattle type and length of time they have been on the farm. Appropriate labor should be allocated to ensure adequate evaluation of cattle in the highest risk category and time frame. Cattle that arrived in the last 2-3 weeks are at highest disease risk and these cattle may need to be ridden twice a day, while cattle that have been in the yard for over four weeks may only need to be ridden once per day. Treatment records and necropsy results also dictate pens needing a concentrated effort.

Cattle identified with illness should be removed from the pen and taken to the treatment facility in a low stress manner. Careful, slow management is important because respiratory disease decreases lung capacity. The bovine removes excess body heat through respiration and diminished capacity can lead to overheating if animals are stressed.

Evaluation of number of animals pulled from the pen is an important tool for continual improvement of diagnosis techniques. Rectal temperature can provide a quick, general guide for assessment of pulling patterns. A good rule of thumb is 5-10% of the pulls with a rectal temperature of 104° F or less. If more than 10% has a lower temperature, there may have been too many animals pulled or the diagnosis may not be infectious respiratory disease. If all the pulls have a rectal temperature of 105º F or higher then it is likely that there are more animals in the pen that need to be segregated and treated. If only a handful of the animals pulled for treatment have a fever, we may have misdiagnosed illness in some of the animals and pulled too many.

Treatment of clinically ill animals

Treating sick calves should not be confused with processing. These animals are the weakest, highest stressed animals in the facility and should be handled with extreme care. Low stress, isolation, good husbandry and nutrition may be the best treatments sick calves receive. No antibiotic injection can replace careful animal handling. Increasing undue stress in the treatment process can increase the odds that the animal will return to the hospital; thus, taking a few more minutes to perform this task in a calm, efficient manner can save future expense and labor.

Animals brought to the treatment facility should be evaluated for illness type and treated accordingly. Rectal temperature is a good tool for evaluating disease, but the thermometer should not be used to make the final treatment decision. A treatment protocol should be created to address common disease classifications found on the farm. Provision of a written treatment protocol to the farm by the veterinarian makes communication clear and precise. The guidelines should include specific drugs, dosages, withdrawal times, and appropriate post treatment interval. Adherence to the preset regime provides consistency in treatment and better evaluation of animal response to treatment. The protocol should be constantly evaluated and changes implemented as needed.

Individual animal treatment records are important not only for evaluating animal response, but also for ensuring adherence to drug withdrawal guidelines. All individual treatments should be recorded on a daily basis including the date, animal treated and the drugs administered. It may also be helpful to institute a simple visual measure such as notching an ear tag or placement of a special treatment identification to determine how many times an animal has been treated.

Summary

Operations differ significantly in management techniques and health programs. Critical control points should be identified for each farm and used to ascertain the biggest areas for potential improvement to allow proper allocation of resources. A customized wellness program couples medicine and management to minimize the negative impact of disease.