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How to make rugging decisions

March 2018 by Dr David Stang, PhD, www.horsesciencehorsesense.com
Dr Stang (1946-2018), was a computer security expert and software developer with a PhD in Experimental Social Psychology. He published a dozen books and about 150 journal articles. David loved nature, horses and mules, computers, horses and mules, writing, and horses and mules - in that order. You can find more of his work at: www.HorseUserManual.com

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 blanket, because local custom varies so widely from place to place, so how are we to make the best decisions for our horses?

In Australia, judging from past articles in Horses and People, there are horse owners like those in the eastern United States and, because of the particular climate, they are likely to overdress their horses throughout the year.

In the eastern United States, where I live, it is often colder than we’d like and horses spend much of the Winter season wearing heavy blankets (you may call them rugs or covers where you are). In the Summer, when it is hot, these same horses often wear fly sheets. However, because fly sheets are not as sturdy as Winter blankets, other horses are more likely to eat them and most of our group-housed horses must endure the flies without assistance.

In the western United States, where Winters are usually much colder than in the east, most horses find themselves without blankets, and some without run-in sheds and shelters. 

Where I live, the local customs are very local. Driving down the road, you’ll see a pasture full of covered 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 blanketing decisions, can 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 finally approaches.

I sometimes imagine I can put myself in my mule’s shoes and experience the world as she does. I regularly find I’m wrong when I do this. For instance, when it is bitterly cold where I live, I imagine 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 ultramarathon distances in Africa and you may have seen nature films in which a human eventually outran an antelope. 

The two-legged hunter benefitted from a ratio of surface area to mass that favoured 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, and so on. 

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 and we quickly learn…

  • Many believe blanketing a horse after Winter exercise is a good idea. But, researchers in Sweden found otherwise: unclipped horses who exercised and were then covered with a blanket 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 ,once adapted, have seldom been observed to be indicating any discomfort (such as shivering), in temperatures ranging from -40oC to +40oC. [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 rain and snow take longer to reach the skin. They increase their food/fibre intake, move more and stay closer together. If a run-in 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 -15oC to 10oC [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 horses 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 -15oC. 

But, surely Mr. Horse is better than Science in telling us when to use a blanket and what blanket to use...

Horses are quite happy to ‘tell’ you if they are too warm or too cold. If they are too warm, you’ll see and 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 they exercise, 20% of the metabolism in the muscles is used for work and the remaining 80% becomes heat. A horse usually has no trouble getting their body temperature up to about 37°C. In Australia, though, where ambient temperatures are often close to that and much hotter, 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. 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 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 or electrolytes, replacement salts, in the form of powder and blocks, should always be provided. 

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 fly sheet 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. Fly sheets with a zebra pattern seem to deter flies better than solid colours, but the pattern won’t prevent other horses from chewing on it.

Some owners think clipping their horse is a fine way to cool him, but this also destroys your horse’s ability to use his coat in self-defence: 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 own scent to the wallow. When others in his herd think he’s one of them, his life becomes easier.)

Hot bloods

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 heavy Draft horse, for example, so they have a ratio of mass to surface area that favours cooling, and this is why they are relatively more comfortable than Draft horses when the weather is warm.

Arabians developed in the heat of Arabia, because this phenotype was better able to haul warriors over great distances in the heat. Those that couldn’t stand the heat seem to have gotten out of the fire, and either 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 ride in the heat, I’d vote for a hot blood, who will be better able to keep their cool on a hot Summer 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 covered horse can do nothing about his plight. Sometimes, a blanket will warm too much, triggering sweating, preventing the sweat from evaporating and, in turn, triggering even more sweat. 

Other times, 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 the blankets you use don’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 always be to keep your horse between shivering and sweating, and trust they can handle the rest. When all of the horse owners at your barn are over-blanketing or under-blanketing, it might take 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 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 I don’t use her lightweight, waterproof sheet if the temperature will be above 5oC. Since there is no run-in shed in her pasture, this sheet helps with wind, rain and snow.

Did you know?

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, including 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. For example, when locked in a paddock without shade they can’t take their own rug off.

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 working outdoors at the equator or poles. Indoor heating and air-conditioning overcome latitude for us, but we don’t invite our horses indoors.

Further reading:

What’s best for your horse? When we can’t trust the advice of others and we can’t trust our own instincts, we are left with two options: Ask Science or ask the Horse.

Thanks to the wonders of the internet, science has become easy to ask. Try a search using Google Scholar to read the actual abstracts and sometimes full papers - straight from the equine scientists' mouths.

Here are some we found:

Temperatures horses prefer:

  • http://bit.ly/2Edibv7
  • Read the background section of http://bit.ly/2E85h1f

Inter-breed variations:

  • http://bit.ly/2nJX9Ol
  • http://bit.ly/2shjW8T

Acclimatising to heat:

  • http://bit.ly/2EKYJ9X
  • http://bit.ly/2C2w11v

Shelter design preferred by horses in summer:

  • http://bit.ly/2nMERfi

Cipping, rugging and temperatures that trigger metabolic changes:

  • http://bit.ly/2EMQ2Mk
  • http://bit.ly/2E85h1f

Effective ways of cooling after exercise and good measures of heat-induced stress:

  • http://bit.ly/2EOKyAF
  • http://bit.ly/2BMI9Ij

Read also this excellent article by Dr David Marlin which dispels myths about the best ways to cool horses.

And this article by veterinarian Katelyn McNicol on helping horses cope in the heat.