Question: I’ve owned horses for decades and I’ve noticed something interesting about colic incidence. When the air is stagnant in the fall, horses seem to be a higher risk of gas colic. Has any research been done on this? I was thinking it might be the increase in pollution concentration coupled with seasonal hormone cycles. Breeds in my experience are mostly Quarter Horses and Paints. The ponies and Mustangs in my care seem to be unbothered. At any rate, I have learned to be ready for gas colic if it is foggy in the fall. Has there been any research done on this subject?

Answer: Thank you for this interesting question. There is no research that I can find on fog, stagnant air or pollution and their potential effects on colic. But I did find some related studies that may provide some answers.

What the research says

To search for this research, I used PubMed, which is maintained by the National Institutes of Health. I also used the North Carolina State University library search to pick up research that may not make it to PubMed because of low numbers of citations. Two articles are of particular interest. The first study is “Lack of Association Between Barometric Pressure and Incidence of Colic in Equine Academic Ambulatory Practice” (Cianci J, Boyle AG, Stefanovski D, Biddle AS J Equine Vet Sci 2021;97:103342). This study was performed by the University of Pennsylvania Field Service during the years 2015-2017. During that time, the researchers looked at 3,108 horses with medical “events.” These events included colic. The researchers then cross-referenced corresponding weather data from the National Weather Service. When examining the data, they noted that barometric pressure was not statistically associated with a diagnosis of colic.

Geographic and seasonal factors

However, in this study the likelihood of colic diagnosis significantly increased with increasing latitude (further north). In addition, horses were more likely to be diagnosed with colic in the fall compared with winter. If you take these risk factors together, this research does indicate there are geographic and seasonal factors that you may be encountering where you live that do, in fact, put your horses at a higher risk of colic. One specific thing I would do (for your own research) is to keep a daily log of all the horses on the farm, and note when they colic. This might help you see trends more clearly.

The second study is “A two-year, prospective survey of equine colic in general practice” (Proudman CJ. Equine Vet J 1992;24:90-3). In this study, performed in the United Kingdom, there was no statistically significant correlation of the seasonal incidence of colic when assessing monthly temperature, change in monthly temperature and monthly rainfall. However, as the prior article showed, there may be geographic differences that could affect horses in other areas. More research is, therefore, warranted to look at regional changes in weather and air quality.

An ongoing question

As an overall point of view, factors such as season, air quality and weather have and will continue to be discussed by veterinarians and horse owners related to the potential risk of colic. Each local environment will likely give different results—so more research is needed. In addition, changes in temperature or environmental conditions may make horses behave differently, in terms of grazing patterns. Management can change as well. For example, horses may be kept in stalls during more severe changes in weather.

Horses’ gastrointestinal tracts are sensitive to changes in feed or management because they have a delicate balance of a large microbial population (the microbiome) in the colon. It is a “best practice” to maximize forage intake versus concentrate intake, and to give horses as much turnout as is feasible to reduce changes in the microbiome. Forage and exercise both affect the microbiome, which in turn produces gas often talked about in relation to colic.

Anthony Blikslager, DVM, PhD
North Carolina State University
Raleigh, North Carolina

Anthony Blikslager, DVM, PhD, DACVS, is a professor at North Carolina State University, where he received his doctorate in gastroenterology. He earned his veterinary degree from the Virginia–Maryland Regional College of Veterinary Medicine in Blacksburg, Virginia. Blikslager is on the editorial review board for the Equine Veterinary Journal. He won the Merial Applied Equine Research Award in 2011.