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Scientific and Equine Consultant

Cooling Your Horse’s Lower Legs! Why, Why Not and How!

COOLING YOUR HORSE’S LOWER LEGS! WHY, WHY NOT AND HOW!

Dr David Marlin

WHY MIGHT YOU WANT TO COOL YOUR HORSE’S LOWER LEGS?

Knocks and slight strains (muscle, joint, tendon, ligament, skin bone) lead to inflammation.

The 5 key features of inflammation are:

-Heat
-Redness
-Swelling
-Loss of function
-Pain

When a horse knocks its leg or bruises the foot by standing on a stone or gets a slight soft tissue strain, this will result in an inflammatory response. There may be no significant structural damage but the body still responds with an inflammatory response. This may cause the horse to become lame. Furthermore, when training there is usually a small amount of tissue damage that occurs even in healthy horses. In cases where there is inflammation (e.g. swelling and heat) but before the horse is lame or following training, the use of cold therapy can be used to decrease the inflammatory response and possibly preserve function (prevent the development of lameness). Cold therapy may also help to reduce the inflammatory response within tissues over time e.g. tendons, joints even where there is no obvious injury. The reason for this is that low-grade chronic inflammation within a tendon may lead to an increasing lesion and eventually a severe injury (tear).

WHY MIGHT YOU NOT WANT TO COOL YOUR HORSE’S LOWER LEGS?

For a lameness where the cause is unclear or where the lameness has been ongoing for some time, aggressive use of ice may enable the horse to continue training and competing. However, without a proper veterinary diagnosis of why the horse is lame, the long-term management of an injury with ice may eventually result in a serious injury e.g. a severe tendon rupture.

HOW DO YOU REMOVE HEAT?

Heat moves according to 4 processes
1) Convection (heat gain or heat loss)
2) Radiation (heat gain or heat loss)
3) Conduction (heat gain or heat loss)
4) Evaporation (heat loss ONLY)

How heat moves depends on the temperature difference! For example in the air around a horse is hotter than then skin then heat moves in. If the air around is cooler than the skin then heat moves out.

CONVECTION – movement of heat without contact. If the skin is 30°C and the air temperature is 20°C, then heat will move from the skin to the air. The bigger the temperature difference the faster the heat transfer. If there is also a breeze then this will increase the speed at which heat moves out of the horse; known as forced convection.

RADIATION – We are most familiar with GAINING heat by radiation. The SUN produces radiant heat. We feel warmer when the sun is out and colder when we stand in the shade or a cloud comes across the sun. Horses gain heat by radiation in the sun. Horses can lose heat by radiation. When a horse is standing in a cold stone stable the horse becomes like the sun and radiates (loses heat) to the stone walls.

CONDUCTION – how heat moves between two surfaces in contact. Heat moves from the warmer to the cooler object until the two are the same temperature. How fast the heat moves is dependent on how much surface is in contact and the difference in temperature (the bigger the difference the faster the heat moves). Horses lose heat by conduction when they lay on cold ground in the winter or when cold water is poured over them.

EVAPORATION – When water or sweat on a horse’s skin evaporates (changes from a liquid to a vapour) there is a loss of energy which reduces the temperature at the skin.
When we cool a horse’s legs with hosing or application of water or ice-boots we are cooling by the processes of CONDUCTION AND OR EVAPORATION.

WHAT IS THE MOST EFFECTIVE WAY OF REMOVING HEAT?

Ignoring radiation as its not relevant in the context of cooling limbs, if convection is 1, evaporation would be a 5 and conduction a 20!

WAYS OF COOLING A HORSES LEGS

COLD-HOSING – cold-hosing removes heat by conduction. How much heat is removed and how quickly is determined by how cold the water is, the flow-rate of the water and how long you hose for. The most heat will be removed by hosing for a long time, with very cold water from a high flow-rate hose.

STANDING IN COLD WATER – Horses (if compliant) can be stood in buckets of water with ice melting in it (this achieves a temperature of 0°C) or they can be stood in large shaped rubber boots which are filled with ice and water (with or without circulation).

REFRIGERATED COOLING BOOTS – Refrigerated systems (such as Zamar, Frio-Horse, Ice horse) which pump circulate a coolant through the boot cool purely by conduction. The advantage of a pumped system is that the temperature of the coolant always remains at the “set” temperature as the heat is removed from the coolant within the refrigeration unit. These systems can also be set to a temperature lower than °0C due to the properties of the coolants used which increases the rate of heat removal and or the minimum tissue temperature achieved but carry an increased risk of cold burns if not used correctly!

BOOTS THAT ARE SOAKED IN WATER – boots that are soaked in water and which have a gel inside to absorb and hold water cool mainly by evaporation. There is an initial transfer of heat from the skin to the boot by conduction which depends on the difference in temperature between skin and boot when the boot is applied. So soaking a water boot in ice-cold water before application will increase the rate of heat removal. Further cooling is then achieved by evaporation of the water. The effectiveness with which these type of boots cool is highly dependent on the climate. When it is hot, dry and breezy they work well. When it is high humidity and low temperature they are ineffective.

BOOTS THAT ARE PLACED IN THE FREEZER – boots that are placed in the freezer or have ice packs inserted into them cool by conduction. The rate of heat removal is dependent on the skin to boot temperature difference and the area of the boot in contact with the skin. A close fit over a large area of leg is ideal. These boots may contain water, gels or powders (usually in sealed pockets within the boot) which all have slightly different cooling capacities. The more coolant material in the boot the longer the boot will cool for and or the more heat it will remove. If the boots are used directly from the freezer (-5°C to -25°C) there is a risk of ice burns. If using boots in this way then consider using a layer of bandage or other thin material between the boot and the leg!

TOPICAL COOLING PRODUCTS – Products such as gels or clays which are applied to the lower leg cool by evaporation. Those that contain alcohol will work better in humid conditions. Water based clay products will face the same problems as water cooling boots in that if its humid and or cool then the rate of evaporation and hence the cooling effect will be small. Topical cooling products only cool whilst they are wet! Once they dry out they cease to remove heat and become insulators, causing the skin to warm-up again.

WHICH COOLING METHODS ARE LIKELY TO BE THE MOST EFFECTIVE?
Anything which cools primarily by CONDUCTION will be the most effective.

HIGHLY EFFECTIVE
Standing in water with melting ice
Boots that are placed in the freezer (depending on fit and type and volume of coolant)
Refrigerated coolant circulation systems
Cold-hosing (Water ~0-10°C)

MODERATELY EFFECTIVE
Cold-hosing (Water ~10°C-15°C)

SLIGHTLY EFFECTIVE
Products that rely on evaporative cooling
Cold-hosing (Water >15°C)

APPROPRIATE USES OF COLD THERAPY

1) As directed by a vet or physiotherapist
2) In the case of an acute (sudden) injury e.g. a knock, stone bruising, acute filling
3) In order to reduce inflammation following training in horses without known injuries e.g. icing feet, lower limbs.

Date: July 22, 2016