It’s summer! Most of us can enjoy the hot weather (as long as it doesn’t get too hot). Horses, however, have a thermoneutral zone different from that of humans, with ideal temperatures falling between -5 and +15 °C. Horses have more muscle mass to keep them warm, and less bare skin to cool them. In this issue of Science Sunday we discuss how equine bodies react to heat, what heat stress is, and how your horse can deliver optimum performance despite the heat.
Horses are homeothermic animals, meaning that their bodies work to maintain a constant internal temperature. At temperatures between 5 and 25 °C – the thermoneutral zone of the average horse – maintaining a constant body temperature doesn’t require much, if anything. This automatic body temperature maintenance works less efficiently above 25 °C, as equine bodies are not particularly efficient in releasing heat. They have lots of muscle mass and comparatively little skin surface, and it’s over this skin surface that most heat must be released. It all comes down to making sure that heat loss in the equine body is on par with its heat production and absorption.
Cooling off through sweat
In a horse at rest, heat is generated through the digestion of nutrients, i.e. metabolism. Physical exercise will generate more heat through muscle activity. Heat absorption depends on the temperature and moisture in the environment as well as sunlight and wind speeds. Heat loss is facilitated by shallow respiration (25%), perspiration (65%), and convection (wind).
When heat absorption and heat production are greater than heat loss, the body reacts, and the horse begins to sweat. Sweating is crucial to a horse; the sweat evaporates from the surface of the skin, transporting heat away from it. Horses do not cool off as easily as humans do – this is because they have relatively little skin surface and a large amount of muscle mass in relation to their body weight.
When a horse sweats, the blood vessels near the skin’s surface dilate, allowing for more heat to be released. The horse begins to display rapid, shallow breathing. Heart rate accelerates to pump the blood more quickly to the skin and release heat. On average, a horse loses 30 litres of fluids per day, and this can quickly increase to 60 litres. A hard workout can cause a horse to lose up to 15 litres of fluids per hour. Perspiration also comes with disadvantages, however, because the body loses electrolytes along with sweat. Fluids and electrolytes must be replenished after perspiration to prevent dehydration and to ensure that all biochemical processes in the horse’s body can continue without disruption.
Water first, then everything else
Electrolytes play a key role in the fluid balance of a horse’s body. They help to prevent dehydration, although naturally water is of utmost importance in this process. A horse weighing 500 kg needs to drink 25 to 30 litres of water on average per day. High temperatures and physical activity will increase this need to 50-100 litres per day. A substantial loss of fluids and electrolytes may impair the horse’s thirst mechanism, causing it to refuse to drink. A little salt applied to the horse’s tongue can help to motivate drinking.
Did you know that horses’ bodies are unable to store electrolytes? The equine body consists of billions of cells: electrolytes are found in the fluids around these cells and in the blood. The tissues and organs in a horse’s body are unable to store large quantities of electrolytes, which means that excess electrolytes are eliminated if they cannot be utilised immediately. This is why it is important that a horse be provided electrolytes before and right after it sweats to immediately compensate for losses caused by sweating.
Symptoms of heat stress
If a horse cannot release heat properly, its body temperature will increase. A body temperature that’s too high will disturb all sorts of processes and can be dangerous. The sensitivity to which a horse reacts to heat stress may depend on various factors: physical condition, coat thickness, or even acclimation to heat. There are also certain factors which we cannot control but should nevertheless keep in mind, such as age, coat colour, and breed. A dark-coloured horse, for example, may suffer more greatly from heat stress than a light-coloured one. A horse subject to heat stress will display a decreased appetite, reduced performance, stiff movements, increased heart rate, heavy breathing, uncontrolled movements, or swelling. Always consult with a vet if you are unsure about whether your horse is suffering from heat stress. Your vet can do a skin pinch test to determine whether the horse is suffering from heat stress.
Training in hot temperatures
Horses need time to acclimate to hot temperatures. When it’s suddenly hot from one day to the next, a horse from Central Europe will have more difficulty coping with the heat than will a horse that spent its entire life in Spain. If you want to exercise your horse on a hot day, make it as comfortable for him as possible!
Avoid working during the hottest hours of the day. And make adjustments to your training: give your horse ample breaks so that he can catch his breath. This will also help his body to regulate temperature. Logically, muscles warm up more quickly in warm weather, so you can shorten the time you normally need to warm up by a little bit. And make sure your horse is allowed to cool down after training.
Cool down, cool down, cool down. And as quickly as possible according to the intensity of exertion. One thing is key to keep in mind when training in hot weather: your horse will warm up quickly and will then need to release this heat. You now know that this heat can’t be so easily released. Cooling off a horse’s muscles isn’t so simple: there’s a lot to cool off with all that muscle mass. It takes a while for cold water to penetrate the fat layer and reach the large muscle groups. Studies show that the most effective way to cool off your horse is this: water the horse for 30 seconds, then walk him for 30 seconds. Repeat until the horse’s body temperature returns to normal.
Practical tips from our feed experts
1. Always encourage your horse to drink in hot weather
- Add a little flavour to your horse’s water, for example Cavalor Mash & Mix
- Apply a pinch of salt to your horse’s tongue to stimulate his thirst response.
- Give your horse electrolytes right after perspiration. The Cavalor product range includes electrolytes in powder and liquid form: Cavalor Electrolyte Balance and Electroliq Balance
2. Keep heat absorption to a minimum
- Give your horse access to shade and airflow, and avoid using rugs and bandages if possible
3. Keep the generation of heat to a minimum
- Work in the early morning or late evening
- Feed forage and concentrates in several small meals spread out over the day
4. Help your horse to release absorbed or generated heat