The science of colic prevention

Studies can tell us about the influence of management factors on average. But geographic location, activity level, preventive care programs and other specific factors influence the experiences of individuals or small groups of horses.

Q: In article after article, EQUUS comments on how rare colic is when horses are on continuous pasture turnout. But all the horses I’ve ever lost to colic have been out on pasture. I believe this is partly due to a slower response time because their problem went unnoticed for a while. In fact, during the past 40 years of my caring for horses I’ve had equal amounts of colic in pasture horses vs. hand-fed horses, and all deaths from colic were in the pasture-horse group. I have to disagree with your observation and the information you give your readers on colic. I believe pasture horses are just as susceptible to colic as are hand-fed horses. I believe ulcers are less in the pasture feed group but not colic. I would like to see the data you use for your articles.

Scientific studies support the fact that horses who spend more time on pasture are less likely to colic than those who are kept in stalls.

A: Before addressing your specific question regarding management—particularly in relation to time on pasture and risk of colic—I think it is important to point out that data is typically generated from large numbers of horses, and within any data set there will be variability. That means that studies can tell us about the influence of management factors on average but these conclusions may not hold up when looking at small groups of horses or individual horses, because of other variables such as geographic location, type of showing, and preventive health care programs. Nonetheless, it is important to be aware of data, because lessons learned from larger populations of horses can be useful in managing individual horses.

Several studies have investigated the potential protective effect of pasture turnout (or conversely, confinement in stalls) and the risk of colic, and I will describe how I found these so that readers can do the same thing. I always start by searching for studies on PubMed, a medical search engine maintained by the National Institutes of Health. I would encourage anyone wanting the evidence for something they are reading or hearing about to try searching this site because the references are from peer-reviewed (by other scientists) journals, rather than testimonials, Internet posts, and other sources of information that can be difficult to verify.

Click here to learn if you really have to walk a colicky horse.

In this instance, I used the search terms “horse,” “colic,” “risk,” and “pasture”—which gave me 23 references (PubMed goes back to 1966). Not all veterinary journals are included on PubMed, but most of the best equine veterinary journals are. The first publication that comes up, as of January 28, 2020, is a systematic review in the journal PlosOne by Curtis et al., July 2019. (Here is the complete reference: Curtis L, Burford JH, England GCW, Freeman SL. Risk factors for acute abdominal pain (colic) in the adult horse: A scoping review of risk factors, and a systematic review of the effect of management-related changes. PlosOne 2019 Jul 11;14(7):e0219307)

This is a particularly powerful assessment of all of the scientific literature available on the subject of risk factors for colic because it includes as many studies as possible into one large study, taking advantage of the numbers of horses in all of the separate studies. This article also happens to be free to download (versus just the summary or abstract).

A quick review of the conclusion shows that, on the subject of housing/ turnout, risk factors for colic include:

• Number of hours stabled per day• No pasture or recent (within two weeks) decrease in acreage or pasture time• Increased risk of large colon volvulus (torsion) with increased hours stabled in the last 14 days• Crib-biting and increased duration of stabling• Recent change in stabling• Increased risk of enterolithiasis (colonic stones) if the horses spent less than 50 percent of their time outdoors• Increased risk of epiploic foramen entrapment (small intestinal strangulation) with increased stabling in the previous 28 days

Each of these bullet points comes with its own individual scientific reference collected by the systematic review, which could then be tracked down separately for even more specific information. Each of these factors has varying levels of risk, which is also indicated in the systematic review.

But going beyond the individual data points, this is the sort of evidence behind the general consensus that pasture turnout for horses is helpful at reducing the risk of colic. As a caveat to this, an owner’s individual experience with a single horse or smaller number of horses can vary from the overall “average.” A lot of stabled horses are very well managed, for example, in that they have access to forage (hay) for most of the day. In these cases, particularly when the management is very consistent, it would not surprise me if an owner reported a lower incidence of colic as compared to horses that might have intermittent access to hay.

Nonetheless, pasture turnout is recommended when possible because it provides horses with both continuous access to forage as well as lengthier periods of exercise. Turnout also makes sense physiologically because horses evolved to live off forage while grazing up to 18 hours per day. We have certainly changed horses a great deal with selective breeding, so that breeds like the Thoroughbred require additional nutrition to maintain their body weight (typically while being kept in stalls). However, the underlying principle of how the equine gut functions remains the same.

Anthony Blikslager, DVM, PhD
Professor of Equine Surgery and Gastroenterology
Department of Clinical Sciences
North Carolina State University

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