Basic treatment for equine colitis includes administering fluid therapy and electrolytes, restoring flora imbalance and providing
supplemental protein because the animal's serum protein concentration decreases rapidly.
Javsicas says, "The use of antibiotics depends on the case and whether antibiotic use might have been the cause of the colitis.
We reserve antibiotics for cases where the horse has a very low white blood cell count or those that are persistently febrile.
In cases in which we're worried about the specific cause, such as those with Potomac horse fever, we'll start them on treatment
for that right away. Because if we treat early, we're much more likely to have a positive outcome."
When treating colitis in horses with several complications, secondary disease may occur.
"In the acute period, the concerns are shock from endotoxemia and hypovolemia," Magdesian says. "The consequences of these
can include laminitis and disseminated intravascular coagulation, where the horses become hypercoagulable—or at risk for thrombosis
in blood vessels, especially at catheter sites. They can develop peritonitis and can experience hypoproteinemia and edema.
And they can become immune-compromised and develop secondary infections such as pneumonia or infections at catheter sites."
Thal says, "We try to know what organism we're treating so we can use an antibiotic with a spectrum that actually is doing
some good and not doing harm. One of the biggest mistakes I've made when treating these cases is overdoing it with antibiotics."
Thal thinks the horse is one of the most sensitive species regarding antibiotic-associated diarrhea and colitis. "We treated
a number of cases with antibiotics for other problems such as musculoskeletal infections and other diseases and ended up with
severe antibiotic-associated diarrhea. The key question is whether to treat these horses with antibiotics at all. I've had
this conversation with colleagues over the years. We assume that if it's a gram-negative infection, it's probably Salmonella. Of course, Potomac horse fever is a possibility as well, though it is not responsive to our typical course of antibiotics,
but it is responsive to tetracycline. We can at least identify that organism, which is truly rare in our area. But if so,
we would target it."
When treating a colitis case in which a definitive diagnosis cannot be made, Thal says he treats for gram-negative enterics,
(e.g., Salmonella) and uses a narrow-spectrum gram-negative microbe treatment, usually gentamicin. He no longer uses penicillin unless he thinks
it's needed, nor does he use metronidazole unless he is confident he is treating a clostridial infection. "And that's really
rare in some geographical locations," he says.
One good development in treating these cases is the use of panel-type PCR tests, whose results can give a good idea of the
organism present. "It's better than relying on culture, which is inherently insensitive and sometimes slow," Thal says. "The
panels test for the common organisms. I'm still getting probably less than 50 percent return on them, and most of the time
they all come back negative. So I'm left with a diagnosis that it's either an antibiotic-associated diarrhea or I've got an
organism growing that's causing this condition. What do I do? I just keep the spectrum narrow with the antibiotics."
New treatment methods are under investigation as well. Thal says four to five years ago he started treating these horses with
filtered manure from a healthy horse. "The effectiveness of probiotic use in the horse is pretty sketchy. I've tubed a fair
number of horses with really bad colitis with large quantities of filtered manure from a healthy horse to try to alleviate
the problem. We use three to five pounds of fresh manure from an apparently healthy, well-dewormed horse. We mix with water,
and filter off solids to two to three gallons of filtrate, so it can be pumped through a stomach pump and tube. I administered
this one to two times per day."
The procedure of tubing horses with fecal filtrate is extrapolated from human medicine, Magdesian says. "The administration
of fecal enemas—a fecal liquor from a healthy relative—is a recognized treatment for recurrent forms of C. difficile infection in humans. We've adopted that for horses."
He first treats the horse with omeprazole to increase the stomach pH so the acid of the stomach doesn't kill the microflora
(within the manure mixture). He then uses a tube to administer the horse fresh fecal liquor (with large fibers filtered out)
from a healthy donor horse, one that has been cultured negative for Salmonella and other dangerous pathogens.
"No studies have proven the procedure definitively works in horses," says Magdesian, "but it's done in some cases. And a lot
of clinics use the technique in an attempt to restore a healthy GI microflora in sick individuals. Though there've been no
studies to prove it's effective, and since we use so many treatments, it's hard to say whether this makes a difference in
outcome without clinical trials. It's one of many in our treatment armamentarium that we use. The idea is good, and there
are certainly models in human patients where it helps."