GASTROENTEROLOGY

Should You Refer a Foal for Colic Surgery? Maybe

By Marie Rosenthal, MS

Foals treated surgically for strangulating small intestinal lesions appear to have postoperative outcomes similar to those in adults, according to a retrospective study by Sara J. Erwin, DVM, a PhD candidate at North Carolina State University.

“We think that this means there should be more optimism toward surgical treatment of foals with suspected small intestinal strangulating lesions,” she said at the 68th AAEP Annual Convention in San Antonio.

The team performed a retrospective study evaluating the clinical outcomes of foals with surgical strangulating lesions of the small intestine and compared them to those of adult horses.

“Strangulating small intestinal lesions cause ischemic injury, and the length of ischemia increases the damage to the intestinal lining that eventually kills the epithelial cells of the intestinal lining. Epithelial cell death starts to occur with as little as 15 minutes of ischemia, so a strangulating lesion is a medical emergency, Dr. Erwin explained. By about 4 hours of ischemia, one can see total loss of small intestinal architecture, which can lead to sepsis, systemic inflammatory response syndrome and death of the patient.

“Surgery is often required to restore perfusion to these areas and to prevent this sequela,” she said, adding that colic accounts for more than 30% of deaths in horses between the ages of 1 and 20 years. Strangulating lesions are the most likely to cause morbidity in adult horses.

Small intestinal volvulus is the leading cause of strangulation in foals. “There's a commonly held thought that foals tend to do worse than adults with these lesions,” Dr. Erwin said.

So, she and her colleagues set out to see if that was true.

“Adult survival of small intestinal strangulation ranges from 50% to 80%, and foal survival ranges from 27% to 50%. And while age-dependent outcomes have been examined in adults, these have not been compared directly between foals and adult horses,” she explained.

In many of the studies, the primary veterinarian plays a key role in referring the horse for surgery.

“The referral process is complicated in the foal due to varying degrees of visible or recognizable pain in these younger patients,” she explained. Veterinarians cannot perform physical rectal palpation in foals, and while abdominal radiographs and ultrasonography can be useful in determining possible lesions, they are not commonly used in the field with colic workups, especially in these younger patients.

Other factors also determine whether a young horse is referred. Finances often are key—foals tend not to be insured and not many people want to send an animal for an extensive work up and surgery if they don’t think it is going to survival anyway.

Because of how quickly ischemia can impair a foal’s chances of survive, distance from a referral hospital also plays a role. Every minute counts in these situations.

“The distance to the nearest referral hospital and the prognosis and cost estimate that's usually provided by the referring veterinarian” all play a role in whether the foal is referred, Dr. Erwin said.

Dr. Erwin and her colleagues thought that updated survival statistics could help guide these conversations among referring veterinarians and owners, as well as among the surgeons.

“Our objective in designing this study was to directly examine differences in clinical outcomes between foals and case-matched adult patients undergoing surgical correction of strangulating small intestinal lesions,” she said.

They collected small intestinal strangulating surgery cases from 2000 to 2020 from five veterinary university from around the country: North Carolina State University, the University of Pennsylvania, UC Davis, The Ohio State University, and Colorado State University.

“We collected signal lesion and resection information, short-term survival information—which we defined as the time from recovery from surgery to hospital discharge—and long-term survival information when it was available. We defined foals as being 6 months of age or younger, and adult cases were between 2 and 20 years of age,” she said. They did not look at horses 2 months to 2 years in case there were physiologic changes due to weaning that could influence outcome. They also excluded horses that were older than 20 because they were more likely to have comorbidities that could also play a larger role in outcomes.

They saw no trend toward any certain breed being more or less likely to be recovered from surgery.

In total, they reviewed the records from 41 foals and 105 adults. “Each foal case that was recovered from surgery was case-matched by year, by lesion and resection type to 3 adults that were also recovered from surgery cases,” she said.

In a separate analysis that was not case matched, they looked at horses that were euthanized during surgery.

Most of the horses were Thoroughbreds (28 adults; 13 foals) from California or the tristate area around Pennsylvania, which they thought was due to the number of Thoroughfare breeding farms in those areas. There were also fewer horses from Colorado State because of the delay in time to recognition of colic and the average trailer ride to the university.

Other horses represented in the foal group were Standardbreds (9), Warmbloods (7), Quarter Horses (3), Andalusian (3), Arabian (2) and other or unspecified (4). In the adults, after Thoroughbreds, they saw Quarter Horses (15), Arabians (13), Warmbloods (11), Standardbreds (7), Morgans (5), American Saddlebreds (4), Paints (3), Ponies (3) and other or unspecified (16).

They saw trends in the ages of presenting horses, with many more foals presenting younger than 2 months of age. There was another, smaller increase in foals around 120 to 150 days of age. Among the adults, they saw a peak between 6 and 9 years and then again between 17 and 20 years.

More than half of the lesions (22) in the foals were volvulus, and the most common lesion in adults was strangulating lipoma (38), followed by volvulus (31).

“Volvulus was pretty common,” Dr. Erwin said. “It was the most common foal lesion and the secondmost common adult lesion followed closely to strangulating lipomas,”

Recovery trends were similar among all the horses and did not differ by age, sex, breed or type of lesion, according to Dr. Erwin.

“We saw no trend toward any certain breed being more or less likely to be recovered from surgery. We also saw no trend toward any certain sex being recovered or not from surgery as well.

“Interestingly, once all the adult horses recovered, volvulus was the most common lesion. But there was still no trend toward any certain lesion type being more or less likely to recover from surgery,” she explained.

Of the 41 foals that went to surgery, 25 (60%) of them recovered from surgery. Of the 105 adults, 75 (71%) recovered.

Few horses needed a resection in the foal group, but all seven of the foals that received a resection survived short-term and 17 of the 18 that did not need a resection survived short-term,” she said.

“We saw 28 of 33 adults that needed a resection survive short-term and 38 of the 42 that did not need a resection survived short-term. So similar proportions here as well.”

Of the 25 foals that recovered from surgery, only 1 of them was euthanized while still in the hospital. And 66 of the 75 adults that recovered from surgery survived to hospital discharge.

The investigators only had long-term information for 13 adults and 5 foals. Two in each group were euthanized 2 months after discharge because of the formation of adhesions, but the numbers were too small to draw any conclusions.

The retrospective nature of the study, as well as the often-incomplete medical records were limitations of the study, she admitted.

“Overall, we saw similar incidents of intraoperative euthanasia and resections between age groups, and we saw no significant difference in short-term outcomes of foals compared with adults undergoing surgical correction of small intestinal strangulating lesions,” Dr. Erwin explained. MeV

For more information:

Erwin SJ, Blikslager AT, Ziegler AL. Age-dependent intestinal repair: implications for foals with severe colic. Animals (Basel) 2021;11(12)3337.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8697879/