Bovine Respiratory Disease (BRD)

Agricultural Disaster Preparedness and Recovery November 04, 2011|Print

Bovine respiratory disease (BRD) is a respiratory disease complex that accounts for a significant portion of annual cattle/calf losses in the beef industry. This complex is manifested as one entity, bronchopneumonia, but it can be caused by a variety of factors that interact to cause severe respiratory distress and even death.

BRD in beef calves is called shipping fever because the greatest incidence of bronchopneumonia occurs after shipment of cattle to stocker operations or feedlots. The main cause of BRD in calves is exposure to infectious agents along with stress associated with weaning, commingling, and transportation.

 

Clinical Signs

Clinical signs of BRD often develop 5 to 14 days following management or environmental stresses. Signs can be variable due to the many causative agents possibly involved in the disease complex. Signs include:

  • Anorexia (not eating)
  • Rapid and labored breathing
  • Depression and weakness
  • Droopy ears
  • Coughing
  • Nasal and ocular discharge (runny nose and eyes)
  • Fever (up to and over 104oF; normal is 101.5oF)
  • Stiff and/or staggering walking/movement
  • Hanging back from the rest of the herd
  • Sudden death

The onset of BRD can be quite dramatic and rapid. The discovery of dead cattle and a high percentage of animals exhibiting depression and other signs of illness are not uncommon.

The most common early signs of BRD are appetite depression and fever, so it is very important to diligently examine newly-stressed cattle. Are they eating well? Tracking feed intake with records can be very helpful. Cattle that have been off feed for over a day may appear gaunt.

Early in the course of BRD, cattle may appear slightly depressed, including holding their head slightly lower than normal, droopy ears, and showing less interest in their surroundings than their herdmates. A stiff gait and diarrhea are also often associated with BRD.

Respiratory involvement progresses quickly. A soft, repetitive cough is usually associated with the disease's course. Watery eyes and a clear nasal discharge are often exhibited as well. Left untreated, animals can progress to heavy, labored breathing. Ultimately, animals die from asphyxiation.

Table 1 shows the effect of transit stress on calves at the feedlot following shipping. The decrease in dry matter intake (and consequently, reduced absorption of essential nutrients) by diseased calves can compound health problems and decrease performance. Lowered dry matter intake can last up to 2 months.


Table 1. Dry matter intake (% of body weight) of newly arrived calves to feedlots.

Days After Feedlot Arrival Healthy (% BW) Diseased (% BW)
0-7 1.55 0.90
0-14 1.90 1.43
0-28 2.71 1.84
0-56 3.03 2.68







Adapted from Hutcheson and Cole. 1986. J. Anim. Sci. 62:555-560.

 

Diagnosis

The objective for diagnosing any disease is improvement in the overall health of a herd or feeding operation. If obtaining a diagnosis will not cause a change in health management practices, then diagnostic procedures will be a waste of time and money. However, no diagnosis leaves conjecture as to the true nature of the disease condition. A veterinarian should be consulted regarding health management in specific herds.

One of the most effective tools for diagnosis of BRD is the use of a rectal thermometer. Animals suspected of having BRD should have temperatures taken and be treated based on rectal temperature.

When submitting samples to a diagnostic laboratory, a detailed case history needs to be included, such as the animal species, age, sex, number of animals in the herd, number of animals affected, and number of animals dead. The date of onset and duration of illness are also important for diagnosis. Was there any previous treatment such as vaccination, medication, or nutritional supplementation? Were there any animal movements such as additions to the herd (from outside sources) or pasture rotation?

Animals or tissues should be submitted for diagnosis as soon as possible after death. Once death occurs, tissue changes and decomposition starts, which will quickly make diagnosis difficult. This problem is exacerbated during periods of warm and hot weather.

 

Treatment

Even with modern vaccines and prevention programs, BRD still occurs and can cause catastrophic losses. In 1968, Dr. George L. Crenshaw said "Respiratory diseases of cattle, particularly those associated with shipping fever, are extremely complex, and it is questionable that they will ever be solved completely with our present methods of weaning, processing, shipping, and handling after arrival at the feedlot." This statement is still accurate. Any treatment program objectives should include:

  • Reduction of death loss
  • Reduction in the rate of chronic cases
  • Improvement of performance in convalescing calves
  • Improvement of animal welfare
  • Cost effectiveness

Effective treatment of BRD requires planning instead of reacting. The following points should be implemented on any cattle operation:

  • Treatment schedules for primary disease conditions need to be formulated in advance by veterinarians who are familiar with the operation and include a specific therapy, length of treatment, dosage for each drug, route of administration, size of needle used, site of injection, and withdrawal time.
  • Sick animals should be isolated from other animals in the herd to keep them from spreading the infection to others. Moving high risk animals to sick pens also reduces the stress of competition for fresh feed, water, and space and facilitates monitoring and treatment.
  • Revaccination in problem pens may be needed. Underlying viral infection can result in illness rates greater than 5% per day and response rates to first-time antibiotic therapy of 80% or less.

 

Mass Medication vs. Individual Animal Treatment

Should individual animals be medicated or the whole herd? Without treatment, each sick animal has a very high risk of death. If illness is complicated by bacteria, appropriate antibiotic selection can be made through consultation with a veterinarian and using culture and sensitivity tests performed on samples collected at necropsy.

Mass medication--antibiotics given on arrival to all cattle--is a management strategy that has gained acceptance and has been demonstrated to be effective and economical under certain conditions. The exact mechanism by which mass medication therapies work to improve health is not known. One explanation is that pathogenic bacteria residing in the nose and throat are eliminated or greatly reduced, which in turn reduces the likelihood of calves becoming clinically ill with bacterial pneumonia. Bacteria are the only agents impacted by mass medication; the spread of viruses does not decrease. In outbreak situations when mass medication has been used and response to antibiotic therapy in sick cattle is poor, a primary viral component is likely to be responsible.

University of Nebraska research indicates mass medication with Micotil® upon arrival at the feedlot resulted in a significantly lower number of cattle requiring treatment (11.8% vs. 33.7%). However, mass medication upon arrival also resulted in higher cost of gain and less profit compared to individual treatment for respiratory disease.

 

Prevention

Prevention of BRD requires proper planning and careful attention to herd health management. There are only two ways to prevent and control outbreaks of infectious disease: 1) break the disease cycle or 2) alter immunity of the herd. Risks of BRD outbreaks can be reduced by:

  • Developing a proper pre-weaning vaccination procedure (vaccinating 2 to 3 weeks prior to weaning, followed by booster vaccinations at weaning)
  • Purchasing source-verified cattle from herds with a known health history
  • Weaning cattle and acclimating them to eating from a bunk prior to shipment
  • Reducing stresses related to shipping and handling cattle
  • Eliminating commingling of cattle from various sources at weaning and shipment
  • Observing freshly weaned calves and new arrivals for signs of sickness at lots several times daily
  • Isolating sick cattle in a separate pen
  • Developing a sound nutritional program for incoming cattle which will ensure they adapt easily to eating from a feed bunk and avoid compromising their ability to fight disease

 

Summary

Prevention rather than treatment of BRD is the primary objective of a herd health management plan. To be successful in combating BRD, a well thought-out treatment plan needs to be in place. Components of the plan should include prevention, disease detection, diagnostics, monitoring for treatment failures, and a treatment schedule. Good records will allow analysis of these activities and help determine if the herd health management plan is meeting goals and expectations.

Finally, people who care for sick animals must be properly trained, motivated, and assigned a reasonable workload. It is people making decisions that affect the health outcome of these animals.

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