Failure with antimicrobial drugs: does it mean resistance?

When there is no improvement in the animal’s condition after giving it antibiotic therapy, what next?

Often it involves weaned calves being treated for respiratory disease, but it could also be a sick cow or baby calf as well.

There are several reasons why antibiotic treatments might fail. One of the most common is because the animal has not been treated in a timely fashion. This is usually a result of waiting too long before initiating treatment or failing to identify the sick animals in the early stages of the disease.

In these cases, the disease is too advanced and the pathology caused by the disease is too severe. The pathology may have walled off the infection and made it impossible for the antibiotics to penetrate or it may have caused severe organ damage, such as in the lung, and there is no hope for the animal to heal and recover.

It’s a common scenario and one that can be quite frustrating because there is often little that can be done once the disease has progressed to an advanced state. One of the important rules of antibiotic use is knowing when to stop treating.

It makes little sense from either an economic point of view or a scientific one to be using expensive antibiotics on animals that have no hope of recovery.

Another possible reason for treatment failure is a wrong diagnosis. Antimicrobial drugs are an important tool for livestock producers and we want to maintain their usefulness. However, antibiotics are only useful in treating bacterial infections.

Diseases caused by viral infections, nutritional deficiencies, toxins and parasites are not going to respond to antibiotic therapy. For example, a case of scours caused by a viral infection in a young beef calf might be treated with antibiotics if an accurate diagnosis has not been made.

Unfortunately, this viral disease will not respond to antibiotic therapy at all, and oral fluids or intravenous fluids might be the more appropriate and useful therapy. The phrase “not all bugs need drugs” has been coined to promote appropriate antimicrobial use in human medicine and it also holds true for livestock diseases. Having an accurate diagnosis made by a veterinarian will help pinpoint correct therapy.

Another potential scenario is having management problems beyond a simple bacterial infection. Cattle with nutritional deficiencies or that are in a stressful environment such as muddy or overcrowded conditions may have a diminished immune response and, despite therapy, may not respond as expected.

It is important to minimize disease risk through other means so we are not reliant on antibiotic therapy to improve bad situations. The use of biosecurity, vaccination programs, maintaining sanitation and hygiene, avoiding overcrowding, maintaining good nutrition and parasite control are vital to minimizing disease risk and will help to minimize the use of antibiotics.

Another reason for failure of therapy could be that the bacterial organism is not sensitive to the antibiotic being used. We are fortunate that this is a relatively uncommon scenario in beef cattle bacterial infections.

Antibiotic resistance does occur but it is not usually the most common reason for the failure of animals to respond. Your veterinarian may want to occasionally send samples to the laboratory to determine whether the organisms being treated are resistant to some of the common antimicrobial drugs. There is no doubt that using antibiotics tends to select for bacteria that are resistant to antibiotics.

It is important to minimize our use of antimicrobials through good management and husbandry practices to avoid antimicrobial resistance. These resistant genes can then be spread to other types of bacteria and transmission of antibiotic resistance from cattle to people can occur through food, environmental contamination and other sources.

The regulations around antimicrobials are changing and the federal government has recently announced that all medically important antimicrobials will require a veterinary prescription by Dec. 1, 2018. This will require your veterinarian to have a valid client relationship with you and your cattle operation before he or she can sell you any medically important antimicrobials for your animals.

This was already in place for a number of antimicrobial drugs, but now antibiotics such as penicillin, tetracycline and others will be included in the list. It will become even more important for you and your veterinarian to work together to develop treatment protocols and decision points for how and when to treat cattle with antimicrobials.

We are fortunate to have such valuable tools as antibiotics at our fingertips to help us treat and prevent disease in our animals. We want to preserve their usefulness and be good stewards of antibiotics to minimize antibiotic resistance in bacteria that can infect our animals and in those that may be passed on to humans.

Not all bugs need drugs. Work with your veterinarian to establish treatment protocols and disease prevention programs that will promote good antibiotic stewardship.

About the author


Stories from our other publications