Treating respiratory disease in feedlot cattle (Proceedings)

Respiratory disease is cited as the most common health problem encountered in U.S. feedlots. Bovine Respiratory Disease (BRD) is a multi-factorial disease that affects the lower respiratory system. There are a multitude of viruses and bacteria that can potentially contribute to BRD. However, there are typically one or more predisposing factors that allow pathogens optimal access to the lower respiratory tract. Stress from weaning, transportation, castration and/or dehorning, nutrition and ration changes, enteric disease, immunity, ventilation and weather changes contribute to the onset of BRD.

Metaphalactic treatment protocols are used for "high risk" calves during initial processing upon arrival at the feedlot. A typical pen of high risk calves in the U.S. are Southeastern calves who have originated from multiple herds, have no prior vaccination history, and have been shipped a long distance to the feedlot. Often these stressed calves will already be in initial stages of BRD during transit to the feedlot.

Sick calves should be pulled as they are identified to be morbid and treated with a parental antibiotic. Ancillary treatments such as vitamins or anti-inflammatories are rarely used as there is no evidence that they decrease treatment success or performance. With the advent of long acting antibiotic formulations, most cattle are returned to their pen immediately after treatment instead of convalescing in a hospital pen. Many veterinarians are now recommending treatment moratoriums with antibiotic formulations of 3 to 8 days depending upon drug. Since antimicrobial resistance is not as critical as the antibiotic being able to adequately penetrate diseased lung, treating with more or different drugs following initial treatment is often not beneficial. The stress of pulling from pen and treating is probably worse than benefit of treating with additional drugs. Remember that the primary goal of any respiratory treatment program is to keep the calf alive long enough for the calf's immune system to clear the infection with the assistance of targeted and appropriate antibiotics

Treatment protocols are usually tailored to fit the needs of type cattle and the requirements of management and cattle owners. Low-risk cattle can often be treated with tetracyclines as a first line treatment. These low-risk cattle should have an immune system capable of handling respiratory disease and a broad spectrum antibiotic like tetracycline is sufficient. Cattle that fail to respond to initial therapy can be given a new "more potent" antibiotic. A third treatment with one of these newer antibiotics will be given if necessary. If cattle do not respond after a third treatment they are classified as a "chronic" and removed from the pen. Treatment protocols for higher risk cattle may incorporate one of the newer antibiotics as the first and second therapy since the immune system is not as capable of responding the bacterial insult. However, if calves require a third treatment, tetracycline is usually used. Traditionally, treatment protocols switched antibiotics for second and third treatments. However, since it is less a question of efficacy of antibiotic and more related to severity of insult and time for recovery, more veterinarians are using the same antibiotics for their 1st and 2nd therapies.

More important than which antibiotic is administered is when therapy is instituted. The earlier calves are identified and treated the less lung damage which leads to consolidated and necrotic areas of lung with limited blood supply to deliver antibiotic therapy. Calves should be observed daily for signs of respiratory disease. Initial signs of respiratory disease are more easily identified as subtle changes of behavior instead of obvious respiratory signs. Calves should be assessed on both their overall attitude and specific signs of respiratory disease. It is sometimes beneficial to use a scoring system until personnel are comfortable assessing cattle and can reliably identify sick cattle. A typical scoring system would be:

Attitude

0 – Normal, cattle are bright and alert, hold their head up and readily move away from the observer

1 – Mild depression, cattle's attitude is slightly depressed but respond quickly to observer and appear normal

2 – Moderate depression, cattle stand with head down, ears droop, abdomen lack of fill and may appear floppy, cattle move away slowly from observer

3 – Severe depression, cattle stand with head down and very reluctant to move, very noticeable gauntness of abdomen

Respiratory

0 – Normal, eyes clear, nose is clean with no discharge, normal breathing

1 – Mild Respiratory, serous discharge from eyes and\or nose, slight cough

2 – Moderate Respiratory, mucco-purulent discharge, cough, increased respiratory rate

3 – Severe Respiratory, excessive mucco-purulent discharge, harsh cough, open mouth breathing

Typically, cattle are not pulled until they are at least a 2 for either attitude or respiratory symptoms. Remember that cattle will show attitude symptoms before respiratory symptoms so most cattle will be pulled with an attitude score of 2 and a respiratory score of 1. If morbidity is high in the pen or cattle have not been responding to initial therapy satisfactorily, it may be prudent to pull deeper and select cattle that have an attitude score of 1. It is usually best to observe cattle in the morning at approximately the same time each day. Personnel should make sure that they move and observe all of the cattle. Cattle are a prey animal and will try to hide when they are sick. These sick animals will hide behind other cattle when moving and often stand beside healthy cattle at the bunk but will often not eat. Cattle that have been pulled will then be evaluated. Rectal temperature greater than 104° F is primary tool used to determine if treatment is necessary. If temperature is below 104° F, then evaluate to determine the presence or absence of other important disease entities such as sub-clinical acidosis.