By William C. Rebhun.
Bacterial bronchopneumonia is the most common cause of contagious respiratory infections in calves and adult cows. There are several bacteria capable of inducing pneumonia, but the most common organisms are Pasteurella multocida, Pasteurella hemolytica, and Hemophilus somnus.
These organisms may create disease individually, in cooperation with one another, or work in combination with viruses and mycoplasma organisms which will be discussed separately.
When bacterial pneumonia occurs in calves, it usually involves 10 to 80 percent of the calves on a farm and is termed Enzootic Calf Pneumonia. In adult cows, bacterial pneumonia is termed Shipping Fever and occurs in outbreaks that involve a high percentage of cattle on the premises.
Laymen and veterinarians called bacterial pneumonia Shipping Fever because it frequently developed in cattle shipped long distances, transported to shows and fairs, or assembled in sales or feedlots.
The signs of bacterial pneumonia include fever, coughing, nasal discharge, increased respiratory rate, depression, and decreased appetite. Inflammatory cells and exudates in the airways of the lungs cause abnormal sounds called "rales" as air moves into and out of the airways (bronchioles) of the lungs. These sounds can be heard only with a stethoscope and are important diagnostic signs for the veterinarian examining calves or cows affected with bacterial bronchopneumonia.
The majority of the damage occurs in the lower lung area and, in severe cases, the infection results in consolidation or total destruction of the lower lungs. This results in chronic pneumonia, poor growth, or death in these severely affected animals.
Spread by Air
The organisms are spread from one animal to another through the air or through nasal discharges and coughing of infected secretions. This airborne transmission makes it easy for the causative organism to infect many cattle when they are confined to a barn or feedlot area. The infection rate is high if cattle are confined in a poorly ventilated area or a totally enclosed structure, since air movement and subsequent diffusion of organisms is reduced in these settings.
Fortunately, humans and other species of animals are not at risk from bacterial bronchopneumonias in cattle since each species (including man) tends to suffer from species-specific pneumonias.
This disease occurs all across the United States but has a higher incidence in the mid-fall and early spring, when the weather is changeable, and especially in the cold months in the Northern United States since cattle are confined in smaller units or barns during these months.
Good ventilation will help eliminate ammonia fumes from urine and manure that can damage the cattle's normal defense mechanisms against respiratory diseases.
The disease has a tremendous economic impact on cattle owners and consumers due to decreased production, drug costs for treatment, and mortality of affected cattle.
In beef animals, cattle affected with bacterial bronchopneumonia may grow poorly, need more time and feed to reach market weight, or may die. All these problems result in higher costs of beef for the consumer.
Treatment requires antibiotics to kill the causative bacteria, nursing care, well-ventilated shelter, and supportive drugs that may hasten recovery. Supportive drugs and antibiotics are selected by veterinarians based on their experience as well as specific cultures of bacteria obtained from affected calves or cows.
Cultures are obtained from the airways of affected live cattle or the lungs of cattle that have died from the disease. Antibiotics such as penicillin, tetracycline, sulfas and erythromycin may be used, but antibiotic selection should be at the discretion of the attending veterinarian.
When ventilation is poor, ammonia fumes from urine and manure build up and cause chemical damage to defense mechanisms of the lungs. Humidity also builds up and predisposes to cross infection through aerosol transmission. Unless ventilation is improved immediately, further spread of the disease may occur and affected animals may fail to improve following therapy.
Prevention is difficult since many predisposing factors such as transport of cattle, confinement of cattle, and grouping of calves and cattle are inevitable and necessary management components of the livestock industry.
Vaccines are available for some bacterial causes of pneumonia such as Hemophilus somnus and can prevent this disease if ventilation and management are good. Vaccines against Pasteurella pneumonias are controversial and most veterinarians agree that these vaccines cannot adequately protect cattle against Pasteurella especially if management techniques or ventilation predispose to disease.
Viral infections of the respiratory tract in cattle occur frequently and damage tissue in the upper airway, trachea (windpipe), or bronchi and lungs. There are many known viruses capable of causing respiratory disease in cattle, and probably some viruses which are yet to be isolated or discovered.
Viral infection sometimes occurs before or in conjunction with bacterial pneumonia in cattle and is thought to predispose to bacterial pneumonia because it weakens the defense mechanism and lining tissues of the respiratory tract.
Because of this interaction of viruses and bacteria, the term Shipping Fever Complex often is used to describe the myriad of organisms involved in an outbreak of respiratory disease in cattle or calves. This term is especially appropriate if management factors such as grouping, transporting, or poor ventilation for cattle are present in addition to bacteria and viruses.
Stresses created by management allow infections to develop more easily because cattle are weakened by these stresses. This is exactly like the situation in a human being when lack of sleep, driving long distances, or attending meetings where one encounters hundreds of other people predispose all of us to the common cold. This common cold is a viral disease but may develop into a bacterial pneumonia if we are further stressed or chilled.