Thursday, 11 August 2011

Heat Stroke and Acclimatisation

After writing a post on thermoregulation I wanted to go further into heat stroke and how training and acclimatisation would help to prevent it. Most of this is with regards to exercising horses in hot climates.

Heat stoke is an emergency which requires immediate recognition and treatment. The horse will try to lose heat by rapid heat exchange or panting, they must be cooled down and electrolytes given to aid recovery. Humidity effects heat loss because there is more moisture in the air, therefore it is harder for the sweat to evaporate into the air due to a smaller difference gradient between the horse's body surface and the air. Humidity therefore limits sweat evaporation and heat loss.

There are a number of ways in which to prevent horses getting heatstroke, exhaustion and dehydration. Knowing the signs of dehydration is helpful. These are as follows;

  • Skin loses pliability (skin test)
  • Not wanting to graze or eat
  • Listlessness (lacking in energy)
  • Loss of normal colour from membranes of gums and eyes and reduced capillary refill time (the time it takes to go from white to pink after being pressed)
  • Muscles quiver
  • Weaker pulse
  • "Thumps"
  • Thick, patchy sweat
  • Panting (only with heat exhaustion)
Pinch test on the neck of a horse.

The pinch test can be done to check for dehydration. This is when a fold of skin on the neck is picked up between the finger and thumb. When it i released it should return to normal within 5 seconds. 

Horses should freely be allowed water until around an hour before a cross country competition. After the competition the neck and extremities should be sponged with water and allowed to evaporate, the loins and croup should be avoided to prevent the back from becoming stiff.

The aim of training a horse is to get the adequately fit so it can compete with a reduced level of fatigue, this also reduces fatigue related injuries such as rotational falls. Interval training is a good method of getting a horse fit, this is when short periods of exercise are carried out followed by a break and repeated. The speed and length of the exercise can be increased as their fitness improves.

Training has a number of effects on the respiratory system. When the horse is not active the alveoli become blocked by mucus and debris, exercise removes this from the lungs. This gives the horse a greater ability to get oxygen into the blood. The muscles that control breathing in the chest can develop. The blood supply to muscles increases and the muscles have an increased ability to store glycogen to use as energy. There is an increased amount of blood flowing to the skin for the same rise in temperature before training allowing more heat to be lost. There is also a rise in plasma levels in the blood which enhances sweat production and helps with the cardiovascular demands.

Training acts as a form of heat acclimatisation by putting a heat load on the body, this stimulates the heat loss mechanisms and they improve as they have to do it more often. More sweat is produced and it starts being produced at a lower intensity. There is also a better transfer of heat from the core of the body to the periphery allowing the horse to cool down more quickly.

Horses may have to perform under very different conditions when they travel for championships. High temperature and humidity are especially dangerous. They can cause heat related stress. Horses should be monitored and not pushed when they are showing signs of fatigue. Fans can help to cool them down as the moving air promotes evaporation. Water can be sponged over the horse and scraped off. The horses temperature may rise to 41 oC but it should be 39 oC within 30 to 40 minutes.

When horses sweat they lose electrolytes. This can cause thumps which is also called synchronous diaphragmatic flutter. This is when the diaphragm contacts in the same rhythm as the heart beat so the horse's flank synchronises with the pulse. Veterinary advice should be sought immediately. Electrolytes can be given in solution in drinking water before, during and after a competition. Salt (sodium chloride) can be given in water and as salt licks to help with this.

Hope you found this interesting!

Love Laura

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