Strategic Use of Antibiotics in Stocker Cattle
Livestock Update, April 2006
Dr. John Currin and Dr. Dee Whittier Veterinary Extension, VA-MD Regional College of Veterinary Medicine
Bovine Respiratory Disease Complex (BRDC) or Shipping Fever remains the most important health concern facing stocker producers. Despite numerous advances in our understanding of BRDC, vaccine technology, and new antibiotics in the last 40 years the percent of cattle that get BRDC as well as the number that die from it has remained about the same. There are several factors that play a role in this:
The most important of these facts are outside the control of the stocker producer. We must therefore design prevention and treatment protocols that make sense from a biologic and economic nature. While BRDC is often initiated by a virus, the problems that we see and treat are most likely pneumonia caused by one of the following bacteria:
There are 3 distinct types of treatments to consider for stocker calves:
Metaphylaxis is a newer term used to describe the treatment of an entire group of calves with an antibiotic on their arrival at your farm. There are currently several antibiotics that are labeled to be used for Metaphylaxis (see table 1).
Table 1. Drugs approved for use in metaphylaxis for Bovine Respiratory Disease Complex.
|Drug||Avg. national cost to treat a 500# calf|
In addition to injectable antibiotics chloratetracycline (CTC) can be added to the feed of newly arrived calves as a form of metephylaxis. The CTC can be fed at a rate of up to 1 gram per 100 pounds of bodyweight. The problems with the use of antibiotics in the feed is that grain intake is very variable among newly arrived calves and the calves that are having the most trouble adjusting to your farm and are the most likely to get sick are the very calves that are probably not eating enough grain to get enough antibiotic to help. Feeding the highest allowable level of CTC can also kill off enough good rumen bacteria to depress feed intake.
There are many factors that should be part of your decision to use metaphalaxsis (see Table 2).
Table 2. Risk Factors associated with a high risk of developing BRDC.
Source of cattle (weekly vs. special sales vs. on farm sales)
Vaccination, deworming history of cattle
Commingled vs. single-source cattle
Age/size of the cattle
Sex of the cattle (bulls vs. steers)
Time of the year (spring vs fall)
Weaned vs. unweaned
Your ability to detect and treat sick calves
Your history of BRDC
Comfort of your adjustment facilities
Value of the cattle (not a risk factor but important in the decision to use metaphylaxsis)
Even a careful assessment of these factors does not make it possible to predict with certainty what percentage of calves will get sick. The best rule of thumb is that if more than 25% of the calves are expected to get sick then metaphylaxis is a good idea. At this level of disease and with the value of today’s stocker calves being $500-$700, metaphalaxsis makes economic sense in most stocker operations to help cut down on losses associated with BRDC.
Treatment of the Individual Sick Calf
While the number of drugs available to treat calves with BRDC has increased greatly, the most important outcome predictor in treating BRDC has not. The most important outcome predictor in successfully treating BRDC is early recognition. Calves treated early in the course of the disease will have a much greater chance of responding to treatment than those calves that are pulled late. They are also much less likely to have severe lung damage that will impair their future ability to grow. Antibiotic selection needs to be discussed with your veterinarian and accurate records need to be kept to assess the results of the selected treatment. The newest generation of antibiotics, while expensive, is very effective at treating most cases of BRDC. If one of these antibiotics is being used without good success it is possible that there is a need to switch antibiotics. However, the most important thing needed is to evaluate whether sick calves are being identified early in the course of the disease. The most important reason for therapy failure is not treating calves early enough. See table 3 for a listing of the antibiotics most commonly used to treat respiratory disease.
Table 3. Antibiotics most commonly used antibiotics for treatment of Bovine Respiratory Disease Complex.
|Drug||Dose||Frequency||Avg national cost to treat a 500# calf|
|200 mg oxytet||4.5cc/100#||Repeat if needed in 48 hours||$1.00-$2.00|
|A180||1.5cc/100#||Repeat in 48 hours||$13.50|
Mass medication is a variation on metephalaxis. In the middle of an outbreak, there comes a point when the best course of action is to stop treating individual calves and get the entire group of calves up and treat them all. The best rule of thumb for when to do this is when 10% or more of the calves have been treated for 3 days in row or >25% of the calves need treatment on any one day. While not perfect, using these rules of thumb will help make careful decisions instead of reacting in the heat of the moment or failing to consider this option until after 60-80% of the calves have been treated.
Prior to 2000 Mycoplasma was almost unrecognized as a source of disease in Virginia. Since then, the dairy and beef industries have seen a steady rise in illness associated with Mycoplasma. Mycoplasma is a tiny bacteria that can cause pneumonia, head tilt, droopy ears, and or swollen joints. Unlike the Pasturella bacteria that tends to cause severe toxemia so calves look sick very quickly, Mycoplasma tends to be much more subtle. It is not unusual for calves to go unnoticed until they have lost 50% or more of their lungs. Producers should suspect Mycoplasma when they see a single drooped ear in calves or when they see a high percentage of calves (>25%) that relapse (get sick again after initial treatment).
Mycoplasma is very difficult to treat. Several of the commonly used antibiotics do not work well for Mycoplasma. Penicillin, Polyflex®, Naxcel®, Excenel®, and Excede® all kill bacteria by destroying the cell wall. Since Mycoplasma does not have a normal cell wall, these antibiotics are ineffective in treating Mycoplasma. Micotil® shows little or no activity against Mycoplasma as well. Oxytetracycline has produced mixed results in treating Mycoplasma with some reports of good results while others report poor responses. The drugs available to treat calves that show the best results are Nuflor® and Draxxin®. Baytril® and A180® can also be effective in treating Mycoplasma when there is a mixed infection with M. haemolyticia and Mycoplasma. Two factors in the treatment of Mycoplasma are important: 1) early recognition, and 2) prolonged treatment. Calves that are treated early in the course of the disease respond fairly well but unless these calves are treated for longer than typical treatment regimes for other causes of pneumonia, 50-70% of the calves will relapse and get sick again. Each time the calf relapses it will have more lung damage and be less likely to get better. Current recommendations are to provide continuous levels of antibiotics to these calves for 10-14 days. If you suspect problems with Mycoplasma, work with your veterinarian to come up with a treatment protocol that will fit these guidelines. Chlortetracycline can be added to the feed as part of the extended therapy protocol.
What other drugs may help? It is important to note that these drugs may be used in addition to, not in place of, antibiotics.
Banamine® is an anti-inflammatory drug which helps reduce fever and damage to the lungs, and therefore may help sick calves get back on feed quicker.
Providing calves with 1 gallon of warm water and electrolytes per 200 lbs. of body weight causes a stimulation of appetite and corrects the dehydration a calf usually suffers if sick and off feed for more than 24 hours.
B Vitamins and probiotic pills and pastes can be used to try to help stimulate appetite.
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