Heat Stress and the Horse

Heat Stress and the Horse

During hot weather and high humidity, our horses are at risk of Heat induced illnesses.

The primary types of heat illnesses include:

Heat exhaustion – this is where the horse’s temperature has increased and the pulse rate rises significantly – to 50-100 beats per minute and the rate of breathing has increased to more than 30 breaths per minute. The horse becomes lethargic and shows signs of dehydration (pinch test on the skin and the skin does not bounce back).

Heat Cramps – particularly found in horses that are sweating while doing work in the heat. You may see spasms, muscle twitching and obvious cramping of the muscles.

Hyperthermia or Overheating - this is the most common and can be caused in hot weather (over 30degrees) by prolonged exposure to direct sunlight, excessive work, transportation, lack of ventilation or high humidity. Again, the horse can show an elevated heart rate, fast breathing and can be sweating while standing, have dark urine, be dull and listless, the mucous membranes in the mouth can become dark and they show signs of dehydration in a pinch test (slow for the skin to bounce back). The horse may also exhibit muscle tremors and even collapse.

Heatstroke or sunstroke - this is even more serious. Horses worked hard or fast, exposed to direct sunlight without shade, young horses, old horses, horses in poor condition, pregnant mares and horses with long coats are most susceptible to heatstroke or sunstroke. Signs include many of the above but sweating may also stop, they can become uncoordinated (tripping, stumbling etc) and may even move through to delirium and convulsions. Emergency veterinary care is required in this circumstance.

Horses most at Risk:

• Horses worked on hot days
• Horses being travelled
• The young, old, sick or unfit/unconditioned horse
• Imported horses (that have not grown up with the heat)
• Horses without shade
• Rugged horses

Prevention is Better than Cure

As a knowledgeable horse owner, we would all like to think that we are sensible and don’t overstress a horse in the heat. No one wants to intentionally make their horse sick. The reality is that it is quite easy to do so without realising, with heat related illness.   

Here’s some common, basic precautions:

• Work your horse in the early hours of the morning (or late in the evening – although they are likely to be flat (lowered energy) from the heat of the day) while the air is cool and before/after the sun is up.   
• Work them light on hot days – use this as stretching or light hacking out days. Try not to do full/hard training days on hot days.
• Work in a well ventilated indoor if possible.
• Cool your horse off fully after work and hose down completely to ensure the horse goes back into the stable or paddock, cool.
• Ensure your horse always has access to shade – a solid shelter or protective stand of trees that depart a solid shade at all times of the day. Shade is imperative in horse care. (Sometimes horses are crazy creatures and chose to stand outside so they can see their friends or for some other, unknown reason. In these circumstances, you may need to bring them in for their own health).
• Remove heavy (even cotton) rugs that do not allow a flow through of air to the horse’s skin
• Ensure the horse has a huge quantity (more than 100 litres) of CLEAN, FRESH, COOL water (be careful of exposed pipes as they will heat up and any water flowing through them will become Hot! – this water must be run through before filling a water trough). Water troughs may need to be topped up 2-3 times a day in extreme hot weather if manual filling is required.
• Clip horses with long hair (but not if they are not unrugged as the skin will burn if left outside)
• Remove all rugs from stabled horses and ensure there is free flowing air
• Use a fan (or multiple fans) in your stables to ensure ventilation if necessary
• Transport horses at cool times of the day – if you don’t have a back cover on your float/trailer, ensure the direct sun will not burn your horse’s rump if the sun is behind you as you travel - use a mesh or shadecloth cover if possible.
• When travelling, make sure vents/windows are open and there is maximum ventilation in the float/trailer/truck.
• If you’re at a competition, make your warmup as short as possible and ensure your horse has water straight after the test. Really consider how important that ribbon or score is to you if your horse is not fit and conditioned to the heat. Forget competing unless you’re out for an Olympic qualifying score if the temperature is really hot (over 38degrees) – there will always be another competition – is it worth the risk to your horse?
• When hosing down (in the shade), put the water on and scrape it off quickly (water staying on the skin surface actually heats up and locks the heat in). Wet/scrape/wet/scrape/wet/scrape… continue until the breathing and heart rate slow and the horse is fully recovered.
• Bring horses, foals and mares into a shade paddock or the stables during the day – put them back out at night.

What to do if you think your horse is Heat Affected

1. Get them out of the heat to a shady area immediately – bring their friend if they’re going to get stressed
2. Offer them cool, fresh, clean water. If they are in a severe state, a few mouthfuls then a break for a few minutes, then some more. Continue slowly while doing the following.
3. Hose the horse off – as above, hose to wet, then scrape, then wet/scrape/wet/scrape…
4. Monitor the horse’s temperature and heart rate (see how to do this here)
5. Fan the horse or get moving air onto the skin if possible
6. If you have ice boots, put these on the legs to help bring down the temperature.
7. Walk the horse to keep the air moving if necessary but in the shade and if they are lethargic or stumbling, stop and allow them to stand in a cool place only.
8. If the horse is not responding (breathing slower, temperature reducing) quickly within 10-15 minutes, call the vet (the horse may require intravenous fluids and further veterinary treatment)
9. If you’re at a competition, don’t travel the horse home straight away if you think the horse has become heat affected. Stabilise and cool the horse first as travel can also induce or escalate heat related illnesses.
10. If you have a problem with a foal (or a difficult to hose horse), get them in the stable and use a wet towel if you cannot hose it off. Keep wetting the towel (easiest from a bucket of cool water – even with ice in it) and keep wiping it down without stress until you see improvement.
11. Once stabilised and safe, you may consider giving the horse some electrolytes. There are various forms available – from pastes to water additives to licks. Always keep some kind of paste on hand for summer and use particularly the night after competitions or a heat related incident. You may use a 1/3 or a ½ a tube initially, and then the balance some hours after. Read the label or speak to your vet regarding the best course of treatment for your horse.
12. If in doubt at any time, call your vet.