Horses and Thermoregulation, by Dr Clair Thunes

Posted on December 14, 2018 by Jerrilee.
Categories: breed, equipment, health, history, therapy.

winterhorses

Q.How do horses survive in the cold?
A. Horses are mammals and as such are warm-blooded just like humans and so when the air around them is colder than their body temperature, heat transfers from them to the environment and they get colder. To survive they must regulate this heat loss, however such heat loss is not always detrimental, for example if the horse is too hot and needs to cool down.  According to an article by the University of Maine Cooperative Extension, “estimates for the lower critical temperature (LCT) for horses are between 30 and 50 degrees Fahrenheit depending on hair coat, body condition, wetness and windchill”.  They go on to give the lower critical temperatures in degrees Fahrenheit based on hair coat as follows, wet or short hair 60, moderate length hair coat 50, heavy coat 30.  Once the average temperature reaches the LCT human intervention is required such as shelter, a blanket and or extra feed.

Q. Why should diet matter?
A. Once at the bottom of its comfort zone the horse reaches its critical temperature and the body speeds up chemical reactions within the body in order to burn more calories and to create more body heat. This requires an increase in dietary energy intake because if there are not enough calories in the diet to meet the additional needs for maintaining body temperature the horse will utilize its body energy reserves (fat).  If this deficit continues for too long then the body condition will be compromised and the horse will lose weight. Well-fed horses adapt better than those who are underfed.
Adaptation should be considered when contemplating a horse’s lower critical temperature.  A horse who has spent a good amount of time in Arizona where the average summer high is around 95 degrees Fahrenheit and average winter low is around 55 degrees Fahrenheit may hit its lower critical temperature at a relatively higher temperature than a horse who lives in Maine where the average summer high is only around 70 degrees Fahrenheit but the average winter low is around 20 degrees Fahrenheit. For the horse from Arizona the lower critical temperature may be 60 degrees even with thick haircoat. The age of the horse is also worth considering.  Older horses are generally less efficient at both digestion and thermoregulation and so are more susceptible to extremes in temperature.  They will therefore need a diet that is more easily digestible and may require intervention earlier than their younger counterparts to stay warm.  Young horses especially those under a year of age are also less able to handle cold weather in part due to the large amounts of energy that are being utilized for growth.  They should be provided with good shelter and ample access to good quality hay.

Q. Horses run around a lot when it’s cold. Does that help?
A. Exercise produces heat from energy burned by muscles so moving is another way the horse has to stay warm but the energy for movement has to come from somewhere, either the diet or body energy reserves.  This may be one reason why horses seem to run around more when the weather is cold.  Muscle contractions don’t just occur though as a result of the horse physically changing locations they also occur as a result of shivering.  The energy produced from these muscle activities raises the horse’s core temperature.
Also, like us, horses can make their hair stand-up, which is called piloerection (think of goose bumps), which acts to increase their hair depth and traps air next to their bodies creating an insulating layer.    It is because of this function that you might hear people say that well cared for horses are quite alright out in the cold as long as it is dry.  Once their coats get wet the hair is unable to stand up and create this insulating layer.  They then rely on the oils in their coat to prevent their skin from getting wet, which is why you should not bathe a horse that lives out in the winter or use a body brush which drags the oils through the coat, as they need the oils to stay near their skin to act as a protective barrier.  Horses living outside need to have access to adequate shelter such as a 3-sided shed as such shelter has been shown to reduce heat loss by 20% not only because it allows their hair to stay dry but it also reduces heat loss from wind chill. A blanket flattens the horse’s hair and prevents piloerection.  If in turn the blanket is not thick enough to adequately insulate or it leaks, the horse will be cold and will not be able to use piloerection to stay warm.  This is not to say that blankets should not be used. If you have a horse who does not carry much weight, with a thin hair coat or decide to clip your horse because it is in heavy work, a blanket will be necessary.

Q. What about stall protection?
A. Often the coldest part of the night is around 6am, as the sun comes up areas reached by sunlight warm up quickly compared to those areas still in shade such as the inside of stall, so horses in stalls are subjected to cold for far longer than those horses that can get out into the sun.  This can cause a real conundrum in spring and autumn when your stabled horses are blanketed at night and you need to take their blankets off early in the morning before you go to work because later in the day they will be hot.  In these instances you have to know your horse and know whether it is better for them as an individual to be too hot or too cold.  The hard keeper who is lean, gets cold and is stressed easily would probably be better left with the blanket on versus the horse carrying more condition who won’t be at any great detriment if he is a little chilly for a couple of hours.

In summary, horses do adapt to cold over time, according to Dr Cymbaluk of the ministry of Agriculture, Food and Rural Affairs in Ontario Canada. However, horses typically require a 10-21 day adaptation period.  A horse’s ability to adapt depends on the duration of the cold weather and the horse’s energy intake.  A horse isn’t going to be able to adapt to a sudden winter storm and so will require more intervention.  Therefore, energy intake is more critical.  Your horse will tell you if he/she is cold, pay attention to the warning signs and make adjustments to hay intake and overall management as necessary to insure that your horse comes out of the winter in good condition.

Dr Clair Thunes, PhD Nutrition. 2005. University of California, DavisMS Animal Science. 1998. University of California, Davis, BSc. Hons. Animal Science. 1997. Edinburgh University. web: summit-equine.com

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