June 24, 2010
Immunostimulants boost the immune system to fight disease.
This is the last of a two-part series. Need to review Part 1?
Sales and Training
Young horses are faced with formidable challenges to their immune systems when they leave the farm for the first time to travel to sales, training centers or racetracks, putting them at high risk for illness.
- Their naïve immune systems encounter pathogens to which they previously have not been exposed
- The first trip on a trailer usually is stressful emotionally and physically
- The pace at sales often is hectic and grueling for youngsters
- Training is stressful and physically demanding
- The large horse population and high traffic in and out of sales, training centers and racetracks facilitates the spread of disease.
Immunostimulant therapy begun before youngsters leave home will help them fend off disease and, if they do become ill, they could have less severe or shortened illness.
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According to Cornell University researcher Dr. Dorothy M. Ainsworth, racehorses often suffer from exercise-induced depression or abscesses when the horse breathes bacteria into the lungs and the immune system fails to launch a good antibody response against the invaders.
“Exercise-associated immunosuppression also enables viral infections to become established in the respiratory tract, which, in turn, predispose (the horse) to the development of secondary bacterial infections,” she says. “Theoretically, if this immune suppression could be reversed or attenuated, the prevalence of infectious pneumonia, bronchitis or lung abscessation should dramatically decrease in the equine athlete.”
Blood Work First
Dr. Elizabeth Davis warns that immunotimulants should not be used when a horse’s immune system already is operating at maximum levels, “smack-dab in the middle of a challenge,” she says. “So if we have a horse that has very severe pneumonia, peritonitis or any serious gastrointestinal disease, we’re probably not going to use an immunostimulant at the time.”
In certain situations, Dr. Davis says, it is prudent to perform blood work on the horse to determine the status of its immune response before administering an immunostimulant.
“If it is a horse that is getting ready to travel across the country and it is apparently healthy, it is probably very reasonable to go ahead and initiate the immunostimulant therapy without relying on blood work,” Dr. Davis says. “But if it is a horse that is sick, I would want to do some blood work beforehand.”
A high white-cell count shows the horse is mounting a good immune response; a normal-to-low white-cell count indicates the horse’s immune system has been compromised. Because immunostimulants should be used only under veterinary supervision, Dr. Davis suggests relying on the treating veterinarian’s recommendations on when to use immunostimulants, which product would be most effective and whether blood work should be performed before treatment.
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She also says that some immunostimulants, such as certain types of interferon-a, should not be given repeatedly because the horse’s immune system will begin to create antibodies to destroy it because it is a foreign protein.
“But it is uncommon that we would have to give it time and time again if we had the diagnosis right,” she adds.
Other immunostimulants developed from bacteria that are harmless to horses are safe and effective for repeated use.
“EqStim is not going to be a problem; every time you give that, it is still going to be effective,” Dr. Davis says.
She adds that immunostimulants rarely cause adverse side effects, other than a mild fever.
“We’re seeing the immune system do what we want it to do, so that is why we might see a fever spike, which is usually mild, self-limiting and in the range of 102-102.5 degrees. One immunostimulant is labeled to be administered in three doses, and I sometimes see a fever after the second or third dose.”
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As with any medication, a horse can be hypersensitive to an immunostimulant, which makes it doubly important that a veterinarian administer the immunostimulant and monitor the horse for signs of distress.
“Then if there is a problem, the veterinarian can treat it quickly and effectively,” Dr. Davis says. “Those reactions, fortunately, are very minimal.”