An expert addresses the possibility that post-trailering episodes of colic may be related to the trip.
Q: Has a link been established between trailering and colic? Twice in the past year my mare has walked off the trailer after a day of showing looking very uncomfortable. Both times, the veterinarian came out, diagnosed mild colic and gave her a dose of Banamine. She recovered within a few hours, but now I’m scared to put her on the trailer. What could be going on?
A: This is a very interesting question, because trailering and colic have been linked for many years. However, this link is most discussed for the opposite question: “Can trailering resolve colic in my horse?” The latter likely happens in some cases either because a medical episode of colic has resolved by the time the horse arrives at a veterinary hospital, or possibly because the horse has gas accumulation in the colon and the trailer ride provides sufficient motion to allow the gas to pass through.
However, you are asking about the opposite scenario: “Can transport in a trailer cause colic?” There is one article I am aware of that assesses this possibility (Padalino et al., PLoS One, 2016;11: e0162371). This study, which reports on an online survey in Australia, did not find an association between trailer transport and colic.
Without scientific proof, the only way I can answer this question is by conjecture based on my experiences and some physiological facts. A lot is made of the effect of “stress” on equine health and performance, but the term is not particularly well defined. Nonetheless, I think that the stress of trailering or showing (or both) may for some reason have started to trigger colic in your horse. In response to stress, the pituitary gland beneath the brain releases cortisol-releasing factor (CRF) into the bloodstream, and that, in turn, stimulates the adrenal glands to release cortisol. Because these processes are initiated by the horse’s perception of its environment, they are variable and can change
Both CRF and cortisol are hormones that have effects on the gastrointestinal tract. Recently, studies in pigs have shown that these hormones can have a direct effect on the gut via an interaction by a group of cells within the gut wall called mast cells, and this is likely the same in horses. These cells are more commonly associated with allergy. When activated, mast cells release substances that alter gut function and lead to changes in the microbial community within the gut (the microbiome). This could cause a horse to colic.
From a practical standpoint, I would try to figure out whether something has changed about the way your horse copes with trailering or showing. You are likely already providing constant access to hay when you transport your horse, but you may want to consider other measures to make her more comfortable, such as bringing along a companion, or switching to a stock trailer or another model that provides more space.
I also wonder if you have noticed any change in your horse’s behavior after showing. Have you been showing more frequently recently or enter-ing classes that are more challenging? I would ask your veterinarian to help you think through some of these factors and determine whether there are some practical solutions to any of the potential problems you identify.
In addtion, I would consider asking a veterinarian on call at the show to take a close look at your horse before the trailer ride home. That could lead to early treatment of colic, and hopefully a better understanding of why the problem is occurring.
Anthony Blikslager, DVM, PhD
North Carolina State University
Raleigh, North Carolina