12/30/2017
Yates Equine Veterinary Services
I am frequently asked, and I wondered myself, about working horses in extremely frigid weather like what we are currently experiencing. It can be frustrating for all of us who are trying to keep horses reasonably fit over the winter if they are unable to be safely worked for a long period of time. I've seen this question come up on several pages today, with answers such as: just turn horses out, to ride them in coveralls with 1 of their blankets still on.
I made it my mission today to search PubMed to see if any true scientific studies have been done regarding horses exercising in cold weather. Note: this is not about hacking (walking) or horses playing in turnout. I wanted to know if actual work (trotting, cantering, jumping) was harmful, and at what temperatures.
Unfortunately, there are really only 3 studies that show up for cold weather research in horses-most of the research has been done about cooling hot horses surrounding the 1996 and 2008 Olympics.
1. Equine Vet J Suppl. 2002 Sep;(34):413-6.
Airway cooling and mucosal injury during cold weather exercise.
Davis MS1, Lockard AJ, Marlin DJ, Freed AN.
2. Equine Vet J Suppl. 2006 Aug;(36):535-9.Cold air-induced late-phase bronchoconstriction in horses. Davis MS1, Royer CM, McKenzie EC, Williamson KK, Payton M, Marlin D.
3. Am J Vet Res. 2007 Feb;68(2):185-9. Influx of neutrophils and persistence of cytokine expression in airways of horses after performing exercise while breathing cold air. Davis MS1, Williams CC, Meinkoth JH, Malayer JR, Royer CM, Williamson KK, McKenzie EC.
In the first study, scientists found increased ciliated epithelial cells in the broncho-alveolar lavage in horses that exercised in cold weather, indicating damage to the respiratory tract. This is a similar finding to studies that have been performed in cold weather human athletes, and led the authors to conclude that breathing unconditioned (not warmed or humidified) air does in fact contribute to airway inflammation in horses.
Study 2 tested horses breathing 23 degree F air at 5h, 24h, and 48h post exercise. The authors did find bronchoconstriction (narrowing of the airways) at 48 hours post exercise, and concluded that exercising in cold weather may be a cause for lower airway disease in horses.
Finally, the third study looked at horses 24 and 48 hours after exercise breathing 23 degree F air, and concluded that there were increased neutrophils (white blood cells), as well as inflammatory proteins, up to 48 hours after exercising in cold air. The authors were concerned that these findings could mean that horses were more susceptible to viral infections after exercising in the cold.
Where does that leave all of us? My decision after viewing the literature today is that I'm going to avoid true exercise (cantering/jumping) when the temps are below 20 F. We really need more studies done in a natural environment (outside, not using treadmills) in colder weather for more information, but there is enough scientific evidence currently to show that at least some damage is done to the respiratory tract at temperatures 23 and below.-Dr. Yates
*********Edited on Dec 30: I posted this in the comments but it's buried at this point, so I wanted to move it up here:*********
I wanted to jump back into the conversation to clarify some of the questions that have been asked and debated. First, I want to ask people to please be respectful of one other. Some of these debates have become overly contentious.
Secondly, since this post has now been seen over 400K times in different parts of the world, I wanted to reiterate that the original intent was to get guidance on sport horses (h/j, dressage, eventers) WORKING (NOT trail riding or turned out) in the Midwest USA/Great Lakes region. For those not familiar with our weather, we tend to have wild temperature swings in the winter, where it may be 30 deg F, but then have 2 weeks of 10 deg F-minus 0 temps. Our horses are most assuredly NOT acclimated to extreme temperatures, but the question always arises if it is too cold to ride.
Many people have mentioned racehorses/Amish/working ranch horses. I'm very aware that there are many northern tracks that race in the winter, as well as ranch horses and Amish buggy horses that continue to work cattle and drive their families to town. It would be interesting to scope and do serial BALs on those horses to determine if their cytokine/neutrophil levels match these studies or are significantly different.
Finally, several people have asked for the specific materials and methods for the studies. I don't have the full text of the first 2 papers, but the M and M for the third is as follows: 9 adult horses (no breed mentioned) trained on a treadmill 3 times/week for 12 weeks. The exercise test was 5 min walk at 1.8 meters/s, 5 minutes trot 4 meter/sec, and 5 minutes canter 6.8-9.5 meters/sec. The samples were collected at 24 and 48 hours post exercise test.
Thank you to everyone for the great discussion!
