Between Sweat and Shiver
Posted on January 25th, 2018
Everywhere they live, horses have an opportunity to get too cold or too warm, and owners have an opportunity to underdress or overdress their steeds.
We cannot trust local custom to decide when to dress our buddies, because local custom varies so widely from place to place.
- In the eastern U.S., where I live, it is often colder than we’d like, and horses spend much of the winter season wearing heavy blankets. In the summer, when it is hot, these same horses often wear “fly sheets”, but because fly sheets are not as sturdy as blankets, other horses are more likely to eat them, and most of our horses must endure the flies without assistance.
- In the western U.S., where winters are usually much colder than in the east, most horses find themselves without blankets, and some without run-in sheds.
- In Australia, judging from past articles in Horses and People, there are owners like those in the eastern U.S., who are likely to overdress their horses in winter.
Where I live, the local customs are very local. Driving down the road, you’ll see a pasture full of blanketed horses, and at the next farm a pasture in which none has a blanket. So the advice you’ll get on blanketing will depend on who you ask.
If we can’t quite trust the opinion of others for our winter blanketing decision, and we trust our own instincts? We love our horses, and try to follow the Golden Rule: Do unto them as we would have them do unto us. This would be splendid advice if we were horses, or if they were people. But that’s not the way things worked out. Our horses are already wearing a fine fur when winter approaches.
I sometimes imagine that I can put myself in my mule’s shoes, and experience the world as she does. I regularly find that I’m wrong when I do this. For instance, when it is bitterly cold where I live, I imagine that all of the horses in pastures would be huddled in their run-in sheds. Not so. They choose to stand out in the snow, as if it was just another day at the beach. My trouble in imagining their comfort is because I’m not built like a horse. Humans evolved to be able to run ultra marathon distances in Africa, and you may have seen nature films in which a human eventually outran an antelope. The hunter benefitted from a ratio of surface area to mass that favored cooling, as well as from the quart of water he carried with him in a goatskin. So a horse will be hot when we are warm, and comfortable when we are cold. We should not dress him as we would dress ourselves. When it comes to blanketing, we cannot trust our instincts.
If we cannot trust the advice of others, and cannot trust our own instincts, we are left with just two options: ask science, or ask the horse.
Science has become easy to ask. Take your browser to http://Scholar.Google.com. Uncheck “include patents”, and search away. Google Scholar will give you a brief abstract, a link to the full abstract or sometimes the full article, links to various versions of the article, links to related articles and articles that have cited it, etc. When you need to know more than what you can learn from the abstract, you can read the full article at Sci-Hub (currently available at http://sci-hub.tw/). Sci-Hub is a site that provides free access to almost every article ever published by a scientist.
Science has much to teach us, we quickly learn.
- Many believe that blanketing a horse after winter exercise is a good idea. But researchers in Sweden found otherwise: unclipped horses who exercised and were then blanketed became overheated, as judged from respiratory rate and rectal temperature.[Wallsten, Hanna, Kerstin Olsson, and Kristina Dahlborn. “Temperature regulation in horses during exercise and recovery in a cool environment.” Acta veterinaria scandinavica54.1 (2012): 42. ]
- Horses adapt well to a wide variety of climates, and have seldom been observed to be indicating any discomfort (such as shivering) in temperatures ranging from -40 to +40 C.[Mejdell, Cecilie M., and Knut E. Bøe. “Responses to climatic variables of horses housed outdoors under Nordic winter conditions.” Canadian journal of animal science 85.3 (2005): 307-308. ]
- Horses have many effective responses to the cold. Their coats thicken, and guard hairs lengthen, so that rain and snow take longer to reach the skin. They increase their food intake, move more, and stay closer together. If a run-shed is available, they may take advantage of it to block wind and precipitation.[Autio, E., M. L. Heiskanen, and J. Mononen. 2007. Thermographic evaluation of the lower critical temperature in weanling horses. J. Appl. Anim. Welf. Sci. 10:207–216.; Mejdell, C. M., and K. E. Bøe. 2005. Responses to climatic variables of horses housed outdoors under Nordic winter conditions. Can. J. Anim. Sci. 85:307–308.]
What are a horse’s preferences in temperature? In one study, mature horses had a “thermoneutral zone” of -15C to 10C [McBride, G. E., R. J. Christopherson, and W. Sauer. “Metabolic rate and plasma thyroid hormone concentrations of mature horses in response to changes in ambient temperature.” Canadian Journal of Animal Science 65.2 (1985): 375-382. ] Beyond that range, the horse began expending energy to keep cool or warm. Are you listening? The horses in that study didn’t need blanketing until the temperature had dropped to -15C.
But Mr. Horse is surely better than Science in telling us when to use a rug, and what rug to use.
Horses are quite happy to tell you if they are too warm or too cold. If they are too warm, you’ll feel them sweating. If they are too cold, they’ll shiver. Horses will also talk to you with their feet. If the breeze is pleasant, they’ll face it; if unpleasant, they’ll turn away from it. If the sun is too hot, they’ll stand in the shade of a tree or their run-in shed.
One of the most fundamental jobs of a horse’s body is to keep body temperature constant. A horse’s body is great at producing heat. They have a high metabolic capacity and large mass — which produces heat — and a relatively small surface area — which dissipates heat. When he exercises, 20% of the metabolism in the muscles is used for work, and the remaining 80% becomes heat. A horse usually has no trouble getting its body temperature up to about 37°C. In Australia, though, where ambient temperatures are often close to that, a horse’s most common problem will be a need to cool.
Keeping their Cool
Horses have few strategies for cooling: they can stand in the shade or they can sweat. On a trail ride, they may try to splash their faces with water at a stream crossing. Sweat solves the overheating problem through “evaporative cooling”. To make sweating more efficient, horses produce “latherin”, a surfactant protein that is found in both the sweat and saliva of their genus. In their saliva, latherin helps the saliva dampen their dry food and make it more digestible. In their sweat, latherin breaks down the waterproofing of their fur, improving the evaporation of the sweat. Sweat only cools when it evaporates. [good idea for photo: horse showing latherin] Toweling or scraping a sweating horse removes the latherin and the sweat, leaving your horse hot and less hydrated.
When summer temperatures climb, horses need our help. We must provide ample shade so that all of the horses of the pasture can simultaneously get out of the sun. Abundant water must be within reach, to help the horses remain hydrated as they sweat. And because sweat will contain some salts, replacement salts in the form of powder or blocks should always be available. A small breeze will help sweat do its job, and keep the flies away as well. Consider outfitting run-in sheds with fans. An arrangement of solar panels and motion sensors can help you provide breeze and shade for horses who live off the grid. A flysheet (fine mesh net, not a blanket!) in the summer might help block some sunlight and flies while allowing for air circulation. But check under the sheet to see whether your horse seems cooler or warmer with it. Flysheets with a zebra pattern seem to deter flies better than solid colors, but the pattern won’t prevent other horses from chewing on it.
Some owners think that clipping their horse is a fine way to cool him, but I think this destroys your horse’s ability to use his coat in self-defense: to block rain and flies, to protect against bites from other horses, to stay warm on a cold night. If you want to make sweating more efficient, consider a bath with a gentle hypoallergenic unscented detergent that will do the job of latherin: breaking down the oils in the fur to help sweat evaporate. Give this bath before you ride, and let him roll when you are done. (Rolling feels good, restores the scent of his herd, and adds his scent to the wallow. When others in his herd think he’s one of them, his life becomes easier.)
Any animal creates heat with its mass, and loses it with its surface area. An Arabian or Thoroughbred has a more modest core and relatively longer, thinner limbs than a draft horse, and so has a ratio of mass to surface area that favors cooling, and are relatively more comfortable than draft horses when it is warm.
Arabs developed in the heat of Arabia because this phenotype was better able to haul warriors great distances in the heat. Those that couldn’t stand the heat seem to have gotten out of the fire and moved north or to the dinner table. Viking adventurers visiting merry old England helped themselves to local horses, and took some home. Those horses, too, had differential mortality rates, and today’s survivors are stocky and thickly coated, much like their ancestors in Mongolia.
Australia’s climate is more like Saudi Arabia’s than Iceland’s, so if you are considering what horse to buy, I’d vote for a hot blood, who will be better able to keep its cool on a hot day.
Dodging the Draft
In much of the world, horses never get blankets in the winter. Do a Google image search for “Icelandic pony winter” and see how many blankets you can count. But wherever you find horse owners who like to dress for success, you’ll find overdressed horses as well.
In bed at night, we are handy with our own blankets, adjusting them to maintain the temperature we want. But a blanketed horse can do nothing about his plight. Sometimes a blanket will warm too much, triggering sweating, then preventing the sweat from evaporating, triggering even more sweat. Sometimes a blanket will not warm enough because its weight has mashed the fur down, making it less effective as insulation or because it has lost its waterproofing, and is allowing rain to get through. So the burden is on you to make sure that your blanketing doesn’t overheat or chill your horse.
There are no blanket scientists who will tell us when to blanket, and no blanket police who will make sure we behave. So your guidelines must be to always keep your horse mid-way between shivering and sweating, and trust that he can handle the rest. When all of the horse owners at your barn are blanketing, it takes some courage to do otherwise.
My mule grew up in a hot part of the world, and is now experiencing a very cold northern winter. I brought her up here in September, and worried that she wouldn’t be able to adapt to life as a northern gal. But she is doing fine. Her coat has grown in thick and lush, and I’ve never seen her shiver. I’ve been swayed by the arguments in this piece, and never use her light-weight waterproof sheet if the temperature will be about 5C. Since there is no run-in shed in her pasture, this sheet helps with wind, rain, and snow.
Horses are like us: they must thermoregulate, and wish to do this with the least effort; they can sweat or shiver to help with thermoregulation; they have a preferred ambient temperature range; there are individual differences (and differences by breed, size, age, and phenotype) in these preferences.
Horses are not like us: they prefer cooler temperatures, on average, than humans; they have fewer options for controlling the temperature of their environment than we have. (locked in a paddock without shade, in a stall without sun, into a rug…)
Horses and humans can adapt, but both have their limits. Per capita human productivity seems to be higher for those living in temperate parts of the world than for those living outdoors at the equator or poles. (heating and air conditioning overcome latitude for us, but we don’t invite our horses indoors.)