Equine colic: Still serious, but successful outcomes more likely

Horses with colic can respond to surgery or medical intervention; the key is to evaluate pain levels, experts say. (Shutterstock.com)In December 2016, Kentucky Derby champion Nyquist was taken to Hagyard Equine Medical Institute in Lexington, Kentucky, after a bout of gastrointestinal discomfort and was successfully treated surgically for colic. Today, successful outcomes are more common in colic cases due to early diagnosis, improved medical treatment, and enhanced surgical technique and experience.

“The most common type of surgical colic we see in Lexington is what Nyquist had-a large colon volvulus,” says Hagyard's Liz J. Barrett, DVM, MS, DACVS. “Horses are predisposed to it because the majority of their large colon is free within the abdomen with no attachment to the body wall. It's very common in postfoaling mares (a huge part of our equine population here in Kentucky), likely due to the increased room and pressure changes in their abdomen after foaling.”

The team at Hagyard also sees medical cases-those that never have an exact diagnosis because they respond to basic medical treatment-as well as impactions, gas colics, entrapments and various causes of strangulating lesions.

When surgery is the best choice

While colic surgery involves cost, prolonged recovery time and various risks associated with general anesthesia and surgery, in some cases it's clearly the best option. Often bowel can be saved before it needs to be resected or before it contaminates the abdomen. The team at Hagyard takes most colic cases into the barn to be worked up, Dr. Barrett says, but those horses that are in significant pain-often thrashing violently in the trailer-go straight into the induction box to be considered for surgery.

Once a horse is in the induction box, the team sedates it heavily. “Those painful cases we can't get comfortable even with heavy sedation go directly to surgery,” Dr. Barrett says.

Otherwise, the case proceeds through a systematic process. The team first performs a basic colic exam (physical exam, passing of a nasogastric tube, ultrasound of the abdomen and a brief rectal exam) to confirm there's not something other than colic going on. They then assess whether the case is best handled medically or surgically.

“We try to identify certain indicators that say they require surgery immediately rather than an attempt at medical treatment,” Dr. Barrett says. “Throughout the workup these indicators move the horse's likelihood of needing surgery either up or down, and the combination of all the factors makes the final decision for us.”

On physical exam, a finding that would move the case “down” the treatment scale is fever, as most febrile horses have some sort of medical issue. When the nasogastric tube is being passed, a finding of reflux without fever would move the case “up” the surgical chain.

“During our ultrasound exam, if we see thickened bowel wall-i.e. large colon edema greater than 9 mm-that usually fits with large colon volvulus,” Dr. Barrett explains. Those horses require surgery to correct the issue. “Also, on ultrasound exam, distended loops of small intestine … can mean the horse needs to go to surgery immediately,” Dr. Barrett says.

“On rectal exam, if you feel distension of small intestine or certain types of cecal impaction, those are things you cannot wait on,” Dr. Barrett cautions. “That's going to move the horse up the scale to towards requiring immediate surgery. Finally, abdominocentesis-i.e. surgical puncture of the abdominal wall to withdraw fluid, and looking at values within the fluid-can help tip the scales on a decision to take the horse to surgery or not.”

Sometimes surgical intervention is necessary to prevent necrosis of bowel and abdominal contamination, and sometimes it's necessary because the condition causing the colic is extremely painful for the horse. “A displacement will occasionally resolve on its own, but sometimes it causes the horse too much pain,” Dr. Barrett says. “Other often-painful things like volvulus, epiploic foramen entrapment or mesenteric rent-things that cut off the blood supply-require surgery to correct the problem and prevent necrosis.”

Some colics appear to be medical but are so painful the horse is taken to surgery anyway, and the team finds a clotting disorder or ischemic bowel as the cause of the enteritis. “Also you can find lipomas that cause obstruction of the bowel or of vasculature so that contents can't move or blood flow is obstructed and causes pain,” Dr. Barrett says.

Sometimes stones are to blame: Enteroliths or fecaliths block intestinal transit and cause obstruction and pain. “In foals, you see small intestinal volvulus that cuts off the blood supply,” Dr. Barrett states. “You can see diaphragmatic hernias, either postfoaling, after trauma or in foals soon after birth, and all these issues require surgical intervention.”

One year Dr. Barrett's team was seeing more tapeworm infestations than normal and saw a corresponding increase in intussusception colic cases, Dr. Barrett says.

“Small colon impactions are cases we try to manage medically, but some of the horses get so gassed up that we need relieve that distension and the impaction before we see deleterious effects of the increased pressure in the abdomen,” Dr. Barrett says.

When medical management is the best option-with one exception

According to James N. Moore, DVM, PhD, DACVS, of the University of Georgia College of Veterinary Medicine, the most common form of colic veterinarians see is spasmodic colic.

“Presumably this type of colic occurs because the smooth muscle in the wall of the intestine spasms, or there's an accumulation of an excessive amount of gas in the intestine,” Dr. Moore says. “Either of those could cause the horse to feel abdominal pain. I say ‘presumably' because intestinal spasms are rarely, if ever, identified during a rectal exam. Horses with these problems are treated symptomatically with analgesics, primarily NSAIDS. With time and appropriate care, the spasm and distension subside, and those horses do perfectly well.”

Another common cause of colic is obstruction of the intestinal lumen, the most common being impaction of the large colon due to the accumulation of ingesta at the pelvic flexure. “This is the region of the colon where its diameter decreases markedly over a short distance,” Dr. Moore explains. “If the ingesta is dry, it may cause an obstruction where the colon narrows. When that happens, the ingesta entering that part of the colon accumulates proximal to the obstruction, the colonic wall stretches and the horse feels abdominal pain.”

Horses with large colon impactions are treated with analgesics to relieve the pain, intravenous fluids to restore fluid volume, and intestinal lubricants such as mineral oil by stomach tube. “These treatments help to rehydrate the ingesta to allow it to pass through the rest of the horse's gastrointestinal tract,” Dr. Moore says. “Horses with large colon impactions treated in this manner have an excellent prognosis for survival.”

There are two other diseases that result in obstruction of the large colon, Dr. Moore says: “One is left dorsal displacement, also known as nephrosplenic or renosplenic entrapment. In this condition, the large colon becomes displaced between the spleen and left kidney, causing obstruction of the lumen of the colon. Fortunately, the blood supply to the wall of the colon is not impaired. The other condition, right dorsal displacement, results in displacement of the large colon around the cecum. Again, the blood supply to the colonic wall is not affected. Horses with either of these displacements have an excellent prognosis for survival when treated appropriately.”

Horses also experience abdominal pain as a result of inflammation, either of the intestine or the lining of the abdominal cavity, Dr. Moore says. “Inflammation of the small intestine is called enteritis, inflammation of the colon is colitis, and inflammation of the lining of the abdominal cavity is peritonitis,” he elaborates. “While horses with these conditions often are very sick and require intensive medical therapy, they do not require abdominal surgery.”

According to Dr. Moore, another cause of colic to be considered is strangulating obstruction, which can affect either the small intestine or colon. In these instances, the intestine is twisted or has passed through either a natural opening in the abdomen or a defect in the intestinal mesentery. In these cases, obstruction of the intestinal lumen occurs and the blood supply to the wall of the intestine is impaired. As a result, that portion of the intestine becomes strangulated and dies. “Horses with strangulating obstructions require emergency surgery to treat them. Fortunately, if the condition is recognized and treated early, the prognosis for survival is very good,” Dr. Moore concludes.

Pain is key to the treatment plan

“Even with all the tests and checklists we've developed, I still think whether or not we can control a horse's pain is the most critical factor in deciding if the horse requires surgery or not,” Dr.  Barrett says. “The new tests are best for horses that are a little bit too stoic and don't show us how much pain they're in or those that are overly dramatic in response to minor pain they feel.”

Dr. Barrett recalls the words of a practitioner she worked for during veterinary school. He said, “There are two types of colic-those that respond to Banamine [flunixin meglumine] and those that don't,” she recalls. “I finished veterinary school, an internship and a residency and that phrase still rings true. If we can control the pain the horse has, it can allow the medical issue to resolve without the horse being a danger to themselves or their handlers. Basic medical treatment includes enteral fluids to help to increase GI motility and, if it makes it to the colon, hydrate an impaction.”

Further therapy includes using intravenous fluids. “You can add motility agents to the fluid therapy, i.e. lidocaine or metoclopramide, if they have enteritis. We also provide other forms of supportive care including decompression of the stomach, electrolyte balance, antiulcer therapy or antibiotics as necessary,” Dr. Barrett says

More successful outcomes

Overall, Dr. Barrett says the main reason colic treatment and surgery outcomes have improved for her team is the speed with which they can make a diagnosis and correct the problem. “Today our ability to maintain horses safely under anesthesia is much improved due to better anesthesia products and better skill,” she says. “Our surgical techniques have also improved from where we were 20 years ago. We have more skilled, more experienced surgeons, which leads to better training. … Our collective knowledge is so much more than it used to be.”

They can also provide better postop care. “Horses are grazers, and at Hagyard we try to get them back eating as early as possible,” Dr. Barrett says. “I think this helps avoid a lot of postop problems, such as ileus and diarrhea. If only a study on this would be easy to perform!” Motility enhancers such as lidocaine, metoclopramide and similar medications are good adjuncts as well, she says, as is the ability to follow up with blood work to make sure electrolytes and everything else are in balance.

“I think something special about Hagyard Equine Medical Institute, and equine practice in general, is our excellent team approach, which is helpful, especially with a horse like Nyquist,” Dr. Barrett says. “Nyquist was admitted to our medicine department, where we have an excellent ICU and boarded internists doing the initial workup and management. And then he came down to surgery, where we have boarded surgeons and people who are trained and do a lot of anesthesia on critical cases like this, and then if necessary we have the ability to transfer those cases back to ICU. We work together through these cases as a team, similarly to the way human medicine has gone, each specialized in our particular areas and all contributing various expertise and experience to each case. I think that has allowed us to move ahead with horses having a much better prognosis after colic surgery.”

Suggested Reading

1. Moore JN. Diseases associated with colic by anatomic location. In: Aiello SE, Moses MA, eds. Merck Veterinary Manual. 11th ed. Whitehouse Station, New Jersey: Merck & Co., 2016.