Prognosis for colic in geriatric horses
The prognosis for horses with colic, particularly those requiring colic surgery, has improved dramatically during the past 10 to 15 years, with survival rates upwards of 80 percent for horses recovered from general anesthesia after colic surgery.1
Louise Southwood, BVSc, PhD, Dipl. ACVS, Dipl. ACVECC, associate professor in the Department of Clinical Studies at New Bolton Center, University of Pennsylvania, has the clinical impression that older horses do just as well as younger mature horses after colic surgery. However, not all veterinary specialists agree, and the veterinary literature is limited and not definitive on this topic.
"Horse owners who bring in their 18- to 20-year-old horses with colic are concerned that their horses are older," says Southwood. "They're worried about putting them through surgery and think they're probably not going to do well with regards to survival and postoperative complications."For this reason, Southwood and her colleagues did a study2,3 meant to provide horse owners and veterinarians with "as accurate information as possible regarding the survival and complication rates for geriatric horses with colic."
Although it might seem logical that geriatric horses—those 16 years of age or older—would show decreased survival rates compared with younger, mature horses, according to Southwood and colleagues, recent studies show this may not be the case.
Why geriatric horses may have decreased survival rates
Southwood investigated several aspects of why geriatric horses might have poorer prognoses. One of the hypotheses was that geriatric horses are more compromised at admission and do worse because of their increased illness upon presentation.
"Looking at the whole population of horses upon admission, we found geriatric horses were not more compromised than mature nongeriatric horses," says Southwood. "Geriatric horses presenting with signs of colic had a similar cardiovascular status at admission based on heart rate, packed cell volume (PCV), plasma creatinine concentration, blood lactate concentration, etc.—parameters that have been used to characterize critical illness and determine the chance of survival. Therefore, we concluded that geriatric horses were not more critically ill than mature nongeriatric horses.
"With these older horses, often they'll stand quietly not showing obvious signs of colic, even with a strangulating lesion," says Southwood. "It seems that such horses may be more stoic. A dose of flunixin meglumine will keep them comfortable for a relatively long period of time."
However, the results of Southwood's investigation showed that this stoicism did not correspond to any delay in referring geriatric horses. There was no difference in the duration of colic before referral between geriatric and mature nongeriatric horses, which is also important when looking at outcomes after colic surgery.
Southwood's study also looked at the severity and type of disease at admission, comparing clinical signs such as the level of pain, intestinal sounds and peritoneal fluid analysis. The findings suggested that geriatric horses did tend to have more serious disease than their younger counterparts. "Our study showed that among the horses admitted to New Bolton Center, the geriatric ones were more likely to have a strangulating lesion than the younger mature horses were," says Southwood. This finding was supported by another study published around the same time.4
Therefore, the significant difference between older and younger mature horses was that geriatric horses tended to have different, and possibly more severe, gastrointestinal disease. As a result, the overall short-term survival rate of geriatric horses was in fact less than that for mature horses (59 percent vs. 76 percent), and the survival rate for medically managed geriatric horses was also decreased (58 percent vs. 80 percent). Contributing to these results was the fact that geriatric horses (16 years of age or older) were more likely than mature horses to be euthanized during surgery or without surgery (surgery declined by owner). These findings are consistent with the increased likelihood that the geriatric horse had a strangulating lesion. The overall survival of surgically managed geriatric horses between the ages of 16 and 20 years was not significantly different from that for the younger horses (59 percent vs. 70 percent, respectively). However, for geriatric horses (20 years of age or older), the surgically treated survival rate did decline more considerably (53 percent).
Importantly, when looking at the types of gastrointestinal disease and the related outcomes, Southwood's study found there was no difference in survival between geriatric (16 years of age or 20 years of age or older) and younger mature horses, with either small (86 percent, 84 percent and 83 percent, respectively) or large (78 percent, 75 percent and 70 percent, respectively) intestinal strangulating lesions or those requiring intestinal resection and anastomosis.
While the survival rate for geriatric horses with large intestinal simple obstruction (80 percent) was less than that of mature horses (97 percent), the prognosis was still good. "I do not have a good explanation for this finding," says Southwood. "However, the important thing is that even though their survival was lower than that for mature horses, the prognosis is still very good for geriatric horses with large intestinal simple obstructions."
One of the most critical factors with regard to successful colic surgery is early surgical intervention. "From what I see in the hospital, from every perspective looking at any horse (with colic), the sooner we get them in the better," says Melanie Perrier, DrMedVet, clinical assistant professor, Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee. "If people are transporting horses for long periods of time, it may be too late for surgery. I always tell my clients that sometimes it's better to come earlier, so we might have a better prognosis, and maybe it's even going to be cheaper. You might not have to resect a lesion, or you may have a horse that's not as ill when it arrives, so it might need less supportive care."