Colic has long been one of the most common and most deadly conditions for horses in this country. Because “colic” refers to a set of symptoms (primarily abdominal pain) rather than a specific cause of symptoms, veterinarians and researchers are still learning about the best types of treatment and prevention for different causes of colic.
In a recent edition of its Vet Chats series, the Grayson-Jockey Club Research Foundation asked two veterinarians at North Carolina State University to provide some updates on new research into the illness that is every horse owner's worst nightmare.
According to Drs. Anthony Blikslager and Amanda Ziegler, researchers are learning more about how to detect signs of serious pain in colicking horses. While some signs, like rolling, thrashing, and flank-biting, are well-known to be classic colic symptoms for many horses, there are some whose instinct as prey animals can make them more stoic and less inclined to be demonstrative of their discomfort.
Blikslager cited recent research on “equine pain face” in which the muscles around the eye tense, producing an angled effect around the top edge of the eye, and ears are frequently held asymmetrically and turned slightly toward the sides of the head. In addition to pain face, Blikslager said more subtle signs can also correspond to signs of pain like increased heart rate. Horses who are inclined to stand with their heads lower than their withers, particularly those parked at the back of their stall, unwilling to move, showing no interest in activity by the door may also be in pain and trying to be low-key about it.
“We are now beginning to understand that a horse that's just standing still like that, with his head a little bit low, ears back, trying not to be noticed toward the back of the stall, is actually a horse showing behavioral signs of pain,” said Blikslager.
A really tuned-in owner will notice if the horse's behavior is atypical for that individual, even if it's not classic for a painful colic. That's information veterinarians need when they get a call from an owner who has spotted a problem, or as they try to assess how a horse is feeling after treatment. Heart rate is also an important indicator for a horse's pain level, which is why owners and managers need to be familiar with using a stethoscope. Heart rates at or above 48 beats per minute are at an elevated risk for requiring surgery.
This slide shows a normal horse and a rendering of a horse displaying behavioral signs of pain
Owners who have called a veterinarian for a colic case before know that there is a menu of potential treatments a horse can receive. Blikslager explained why each option is used at a specific point during a colic treatment.
A veterinarian's initial goal upon arriving to the barn is to provide some temporary pain relief that will allow a thorough examination to try to detect the cause of symptoms. Veterinarians want something that will wear off fairly quickly so they can see if the pain recurs or not. Xylazine or butorphanol are good options for this stage, though the former will lower heart rate, which can be deceptive for veterinarians. The latter, which is an opiate, has the undesirable effect of constipation, which is not ideal for a colic case, but research shows it doesn't inhibit the horse's overall recovery.
“The horses you really want to watch out for, regardless of how you start treating them, is the ones that are in recurrent pain,” said Blikslager. “Those are the ones who are in a higher risk category for needing something more than what you can do in the field.”
For longer-term pain relief, Blikslager tends to reach for flunixin or firocoxib. The trick to longer-term management is it becomes important for owners to know when pain recurs, and what to do if they see the horse acting painful again. Horses that don't respond to initial sedation treatment need a shorter exam and a heavier-hitting drug like detomidine or potentially a trip to a clinic, as surgery may be necessary.
Ziegler presented data from recent studies examining the action of different non-steroidal anti-inflammatories (NSAIDs) on the lining of intestines. NSAIDs can operate on two different types of prostaglandins referred to as COX-1 and COX-2. COX-1 supports normal physiological function, while COX-2 is involved in pain and inflammation. Some NSAIDs are selective about their actions and focus on fighting COX-2 prostaglandins, while others are nonselective, meaning they operate on COX-1 also.
Ziegler has conducted research to see whether this nonselective action can sometimes cause problems.
In the case of colic caused by intestinal twists, bacteria can enter the blood, causing widespread inflammation in the body (lots of COX-2). (This, by the way, is why dark purple gums are a sign of a more serious colic case, because they are a sign toxins have entered the bloodstream.)
A twist can cause part of the intestine to lose some of its blood supply, which is why that type of colic is so dangerous to horses. Unfortunately, COX-1 is needed to help intestinal lining bounce back after blood supply is restored, so an NSAID that reduces both types of prostaglandins may help relieve pain but could also make recovery more difficult.
Flunixin, firocoxib, and meloxicam will all go to work against COX-2 prostaglandins, and flunixin will also work against COX-1.
On a microscopic level, Blikslager said the healed gut lining didn't immediately appear different in flunixin-treated horses, but on the cellular level there are some gaps in cells that didn't close properly, leaving a risk for bacteria to enter the bloodstream. In a 2007 study in the American Journal of Veterinary Research showed both flunixin and meloxicam seemed to do similarly well controlling pain in horses post-surgery, but by 48 hours post-surgery, horses receiving flunixin did show increased endotoxin levels in the blood compared to those on meloxicam. A 2009 study showed similar impacts to firocoxib.
Ziegler presented a recent study that sought to quantify whether those microscopic differences in cells were actually impactful on a clinical level. In that study, horses undergoing surgery for intestinal twists were given either flunixin or firocoxib post-surgery and they were monitored for post-operative pain and signs of endotoxins. Both drugs did well on pain control and heart rate measurements. When researchers looked at enzymes to gauge COX-1 and COX-2 inhibition, both drugs did similarly well against COX-2, but by 48 hours post-surgery, COX-1 markers were significantly lower in horses treated with flunixin as compared to firocoxib-treated horses. The group also found elevated levels of biomarkers indicating endotoxin presence in horses treated with flunixin as compared to firocoxib by the time they hit that 48-hour mark.
That doesn't mean it isn't safe to use flunixin in colicking horses or after surgery, Blikslager cautioned — it depends on the root cause of the colic symptoms.
“It isn't something you'd worry about in a standard field colic; it is something you'd worry about with a horse who'd had an intestinal twist,” said Blikslager. “This initial observation wasn't all that popular with veterinarians, because we felt like we were doing the right thing using Banamine. It's a side effect we have to be aware of.”
With repeated cases of colic, the veterinarians agreed they encourage owners to look to see whether there are any environmental triggers that could be contributing.
“It's really easiest to think of as a management disease, not meaning anyone's doing something incorrectly, but the first places to look for cases of recurrent colic are changes in diet, changes in exercise, or even just whether the diet or the exercise you're already giving that horse is the right combination,” said Blikslager. “The ones that probably recurrently colic are the ones like the show horses where you're probably trying to push them a bit on the energy of the feed, and they get these changes in their bacterial populations and they get a little gassy periodically. Also, they're under some level of stress, and also they're being shipped and stalled more often. That's kind of a combination for a repeat colic patient.”
Catch a replay of the seminar here:
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