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 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:
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)|
Adapted from Hutcheson and Cole. 1986. J. Anim. Sci. 62:555-560.
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.
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:
Effective treatment of BRD requires planning instead of reacting. The following points should be implemented on any cattle operation:
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 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:
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.