How Horses Adapt to the Winter Season

For many of us in the northern hemisphere winter has truly arrived. What does this mean for our horses? They have survived through the ice ages, with very long and cold winters and horses have a very low thermo-neutral zone. The lower end of the ‘zone’ allows horses to cope quite easily with 32-28° Fahrenheit without requiring additional energy to maintain their body-weight.

This is partially due to their coats growing denser and longer during the winter months and due to their nutritional strategy and metabolic adaptations. For coat thickness there are some slight differences between breeds, but as with behavior, little has changed as the common ancestors of our domesticated horses (equus ferus caballus) evolved to survive well in cold winters. They are from a lineage of the wild horses (equus ferus ferus) which populated the holarctic region (northern hemisphere covering the northern regions of earth as far as northern Africa) for the last 12 000 years. Their only remaining common ancestor is the now endangered Thaki or Przewalski horse (equus ferus przewalski). Interestingly, up to 30 species of equids survived through the last glacial period (ice age) to around 11 000 years ago, however, it is now believed that excessive human hunting caused the extinction of most of those. This possibly allowed homo sapiens to survive the harsh winters.

Photo: Equus Prszewalski in late autumn – fat deposits and thick winter-coat ready to survive temperatures as low as -4°F

So, we have established that our modern equids can survive well in cold winters due to their ancestry and even, what we term as ‘thin’ coated horses with Arabian background, will grow thick coats to protect them against cold and wind. What about nutrition during the winter?

Living off the land

Metabolically their body has also developed a system which allows them to gain excess weight in the summer months, by ‘ignoring’ some of the appetite regulating hormones which signal ‘stop eating’ such as leptin. In the late autumn the sensitivity to these hormones rises again possibly preparing horses to a scarcer environment and the reduction in thyroid regulating hormones puts their body on a ‘energy conservation’ setting by reducing movement and their metabolic rate. This effect also has been seen through reduced Heart Rates in the ‘low light’ season. The digestive system has evolved alongside the climate to cope with poor winter foraging conditions. The process of forage fermentation in the hindgut itself acts  like a little like a central heating system for the horse and as less forage is ingested, the passage through the tract slows down leading to greater fermentation and with that heat production. A natural weight loss occurs during the winter month and this seems to have a protective effect against conditions which develop when the body condition remain too high for too long.

What are the consequences of such an innate ‘survival’ system for keeping our domestic equines happy and healthy through the winter?

Behavior and Exercise

The horses’ behavior is likely to change somewhat in the winter months, they become a little more lethargic and less happy to exercise, as the downregulation of thyroid related hormones occurs even if sufficient feed is available during this period. Therefore, the very old-fashioned assumption that the horse ‘needs’ more energy in response to this leading to an increase in concentrate feed, will at best have no effect and at worst set the horse up for metabolic problems in spring, as the body is more likely to accumulate internal bodyfat during an energy conserving metabolism. Just give your horse a little extra time to warm up when exercising and consider reducing exercise. Although there seems to be no direct link with photoperiod, for performance horses kept indoors light quality may influence preparedness to exercise. This is purely speculation at this point, but daylight simulators during the winter have been shown to have a positive effect on human mental health.

‘Shaggy’ equine outdoor management in the winter

If horses are less exercised during the winter, think twice about taking their nice warm coat away, instead use less or no rugs. Horses prefer to be outdoors in all weathers, bar heavy rain and wind. A study in Sweden has shown that only then will they seek shelter. Ensure that there always is a shelter from rain. Things to look out for include rain-scald (if not rugged up) and mud-fever. Both a linked to bacteria (Dermatophilus) penetrating the outer layer of the skin, which may be damaged from excess ‘soaking’ in water/wet mud. Generally, the coat and ‘feathers’ around the fetlock will protect horses well. However, our activity of brushing, cleaning and tidying up will cause the loss of protective hair and oils making them more prone to develop skin conditions outdoors. It’s a matter of balance between keeping them in a manner that is most ‘natural’ and species-specific to their behavior requirements and our requirement to ride and exercise them as well as our desire to ‘make them look nice’. Turned out horses should be checked regularly and ‘crusts’ forming around the fetlock or on the back are a sure sign that treatment is necessary.

A little note here for our ‘donkey’ friends. Donkeys have evolved and survived in much warmer climates than the ancestors of our domestic horses and therefore are poorly adapted for cold and/or wet conditions. They do not have a thick undercoat like horses do and their top coat is not as ‘water resistant’ even if they do look ‘woolly’ at times. This means they are utterly miserable out in the cold and wet and suffer much more from rain-scald and mud-fever. Donkeys must have access to a well enclosed shelter with warm bedding all year round.

Winter water

Also ensure there is always a good access to water when horses are outdoors and indoors. In more severe climates this means ensuring the water source does not freeze up. Horses tend to drink less when the water gets below 44 °F and this can be a risk factor for colic, especially if food intake also reduces. Adding some warm water to hay or feeding steamed forages can help increase water intake. Also ensure that indoor water drinkers do not become too cold and if necessary provide additional warmer bucket water.

Feeding in the winter season

There is also no harm in some natural reduction in body weight over the winter months. Body condition will tell you a lot about the nutritional status of your horse. If your horse has accumulated body-fat during the summer (anything above a Body Condition Score of 5 out of 9), now’s the time to allow it to lose this excess weight before the lush spring grass returns. In staled horses this may mean reducing access to feed slightly more and a slow feeder /slow feeding system will keep them to keep busy and allow them to fulfill their ‘quota’ of natural foraging behavior. As such, if horses are slowly acclimatized to it, edible straw bedding should be kept clean to allow for this behavior as well.

For easy keepers, kept indoors soaking and steaming hay can help reduce easily digestible carbohydrates somewhat and for horses which may be prone to respiratory conditions, feeding steamed hay will take away the many irritants which accumulate in winter stabling, when doors and windows are closed more often. Behavior wise feeding times can become very stressful, specially first thing in the morning if not enough forage was provided overnight. Horses should never fast for more than 4 hours. Always feed forage at least an hour before concentrate feed to reduce risk of colic.

For horses prone to lose too much body-weight in the winter, feeding good quality forage may often be enough. Haylage may provide more energy than hay, as it is often slightly earlier cut and also seems to be digested more efficiently. In addition, some Lucerne chaff (alfalfa) can provide good quality protein. Do not forget to introduce any new feed stuffs slowly. If your horse spends most of the summer outdoors do not move from grass to inside suddenly, first introduce some conserved forage outside for a couple of weeks. It may be worth consulting a nutritionist or have your forage analysed before the winter feeding begins to ensure that the most important nutrients are balanced.

Feeding hay or haylage outdoors has to be done with care – a slow feeder system has to provide access to several horses safely or conserved forage needs to be spread across stations/feeding areas to allow even the ‘lowest’ member of the herd access without being bullied. This forage ideally should be put in the field before the horses. If feeding when horses are in the area already special care needs to be taken to ensure human and horse safety. Spread the forage along a long line and ideally away from fencing to avoid injury.

Feeding concentrate outdoors

This poses a special challenge. Options can be individual taped off electric fence areas or even solid fence pens horses can be temporarily brought into to allow them to feed slowly and without harassment. When feeding concentrates to a group of horses in one field the dominant horses have to be fed first (there is little other choice) or they need to be restrained. Adding a little more chaff to the feed of dominant horses will keep them busier for longer and allow the lower ranking horses to finish their feed. Sometimes just a small amount of feed is necessary as a carrier for a balancer or supplement and this can be hand fed during the daily horse check. Safety for horses and humans is the priority and should be thought through carefully.

In and out management

Although living outdoors is ideal for most horses, many are kept in at night in the winter, partially so that we can fulfil our hobby of horse riding (often disguised as ‘exercise them’) and to protect limited grassland. Turning out in the winter then leads to additional problems, such as boggy field entrances, horses galloping around more to make up for being cooped up in between and the need to understand herd dynamics when turning out. It is well worth taking some time to understand this and establish a routine ‘order’ of turnout where possible. As such the two ‘lowest’ ranking horses (the ones likely to be pushed away by others) should be turned out together first (always avoid ‘single’ horses in paddocks out of sight of other horses), followed by the rest. Horses do congregate at the gate during the ‘established’ bringing in time, which can make things difficult. One option is to have several access points to a field and to rotate between them. This way the horses never know where you will turn up and the gate areas become less worn.

Key take home messages

• Horses naturally slow down a little in the winter
• Horses do not always need a stall or rugs in the winter
• Horses always need shelter from rain, plenty of forage and access to water
• Forage can provide enough energy, even in the winter
• Take some time to check nutrient balance before using supplements 
• Stabled horses will benefit from slow feeders and may need steamed or soaked hay

Written by: Andrea Ellis

Scientific references:

Azzaroli, A. (1992). "Ascent and decline of monodactyl equids: a case for prehistoric overkill"(PDF). Ann. Zool. Finnici. 28: 151–163.

Brinkmann, L., Martina Gerken, Catherine Hambly, John R. Speakman and Alexander Riek (2014) Saving energy during hard times: energetic adaptations of Shetland pony mares, The Journal of Experimental Biology (2014) 217, 4320-4327 doi:10.1242/jeb.111815

How are mud-fever and rain-scald treated? https://www.ed.ac.uk/files/imports/fileManager/dveprainscald.pdf

Janne Winther Christensen, Katarzyna Olczak, Rupert Palme, Karen Thodberg, Journal of Veterinary Behavior, 2018. The effect of shelter design on shelter use by Icelandic horses in the winter period. 27 (), 47 – 54

Mejdell, C.M., Bøe, K.E., 2005. Responses to climatic variables of horses housed outdoors under Nordic conditions. Can. J. Anim. Sci. 85, 301e308.

Moore Colyer M.J.S., Taylor J. L. E., James R. (2016) The Effect of Steaming and Soaking on the respirable Particle, Bacteria, Mould and Nutrient Content in Hay for Horses. Journal of Equine Veterinary Science. 62-69, 39.