Many horses and ponies are fairly hardy and can live without a rug all year round.
As horses are mammals they maintain their internal body temperature at around 38°C through a well-developed mechanism, known as thermoregulation.
Thermoregulation: How horses stay at the right temperature
Thermoregulation is an efficient system of anatomical, physiological and behavioural mechanisms which have developed through evolution so that the body temperature is maintained within a narrow range.
Fluctuations outside these normal temperature ranges can lead to health problems and even death, so these highly developed systems need to be efficient and effective.
Domestic horses have the same built-in mechanisms as wild horses and we are often guilty of forgetting this! How often does your horse use a field shelter in winter to keep warm? Horses mainly use them in summer to escape the heat and the flies.
So before we reach for the rug catalogue and order the warmest and most expensive rug for our horse, it’s worth taking a minute to consider if they really need rugs – or indeed if rugs could actually be detrimental to their health.
How do horses maintain their body temperature?
It is much easier for a horse to warm up than it is for them to cool down. Most of their thermoregulation mechanisms will be reversed if they are trying to cool down. They also have the ability to sweat to reduce heat - but we will focus on keeping warm.
Physiological and anatomical mechanisms
- The horse’s coat is an effective insulator which depends on the depth and thickness of the hair layer. A thicker, longer coat grows in winter months, particularly in certain breeds used to colder climates. The hair is covered in natural grease, which repels water and stops the skin from becoming wet. Over-grooming can remove some of these oils, so in winter in particular take care not to over-groom. The longer hairs on the outside of the horse’s coat means that water runs down and off the coat without seeping in to the bottom layer of hair and the skin. However wet the outer coat, it is very likely that the inner layer is dry.
- The coat also adapts and changes according to seasonal differences. Sensors react to daytime light and length of days. So as the days grow shorter in autumn, the horse starts to develop his winter coat. The hair also has the ability to rise or stand on end (thanks to the pile erector muscles), which keeps horses insulated by trapping warm air in between the hair and the skin. The hair can also stand up in different directions to aid warming or cooling, depending on air flow.
- In a natural state, horses will graze for around 19 hours a day. As the horse eats, the digestive process of breaking down long fibres in the hind gut generates heat through the peristaltic movement of the gut (contractions) and associated blood flow. This is a very important heating mechanism and therefore access to forage should be readily available, particularly in very cold weather.
- Large body muscles generate heat through movement and activity and the associated blood flow – not only during the natural process of movement through grazing, but also by having a play in cold weather!
- In extreme cold, horses will reduce blood flow to the surface of their skin and divert this to their internal organs to maintain core temperature. This is why the tips of horses’ ears may feel a little cold as blood flow is diverted away from extremities. If you want to feel how warm your horse is, put your hand in their arm pit or deep into their hair.
- Fat is also a natural insulator. In the wild it is normal for horses to put a little weight on in summer and lose it during the winter months. Overweight domestic horses don’t often lose weight in summer however, and this can prevent them from growing such a thick or efficient winter coat. This is another reason why it is important to keep your horse at the right weight during the summer.
- Horses learn to adopt the typical stance in extreme weather by turning their backs on wind and rain to protect their heads, necks, eyes, ears and belly. They may seek natural shelter such as trees or hedges and they will keep together as a herd to share body warmth.
- When we see horses with snow and frost on their backs it shows just how well insulated they are. A little body heat escapes through the hair to melt the frost - a bit like houses with good insulation in their lofts! This is proof that your horse is warm.
Rugs and horses
Horses have evolved to adapt and survive in their surroundings and did this for many thousands of years before domestication. It is very easy to anthropomorphise how we think our horses are feeling, often resulting in stabling and feeding unnecessarily and over-rugging. Cute as we think Shetland ponies may look in little rugs – they really are designed to live without them!
Rugging a horse may affect the natural stimuli to trigger thermoregulation mechanisms. The hair erector muscles, need ‘exercising’ (like any muscle) in order to work efficiently. Over-rugging or putting a rug on too soon can compromise a horse’s ability to do this.
Over-rugging may also mean the horse warms up under the rug but not in other exposed areas. If he is hot under his rug, his ability to cool down naturally is lost too.
We mustn’t forget that horses are designed to use fat reserves over winter to keep warm. Modern trends are to over-feed so that horses come out of winter in an unnaturally fat state, but this increases the risk of further weight gain and potentially laminitis in the spring. By putting a rug on we are affecting his natural weight control systems.
When should I rug my horse?
There are of course some exceptions to the rule. Lighter breeds and elderly or poorly horses may benefit from the additional warmth of a rug; likewise clipped horses and those with restricted movement, for example if they are stabled.
Horses are very well adapted to deal with the cold, as long as other basic management needs are in place; such as access to forage 24 hours a day, the company of other horses and access to shelter. Late summer and early autumn is the time for your horse to naturally develop his winter coat and adapt his natural heating systems.
So, think before you rug! Your horse maybe healthier without one!