14/ JULY 2017 THE RIDER Developing the Sport Horse: The importance of hydration

By Dr. Bri Henderson BVMS MRCVS ACVSMR- resident Cheltenham Veterinary Cen- tre, Caledon, Ontario 905-838-3451

As we move through the

height of our summer com- petition season, it is not un- common to have multiple days of severe heat and hu- midity – the days when you sweat standing still. Heat and humidity can

be harder on your horse than it is on you. Most of us have worked to motivate a slug- gish horse through the final jump off or day 3 of a com- petition but why does it hap- pen? Was our training off the mark? Perhaps they need a different energy source in their feed? Or was it that en- ergy zapping heat and hu- midity? In the next few pages we will take a close look at the role of sweating in the horses’ ability to cool and how extreme heat and humidity can affect their ability to perform.

What happens to horses while exercising in the heat? As the horse begins to

work, heat is produced as a by-product of muscle con- traction at a 4:1 ratio! As the body temperature climbs and adrenaline levels in- crease, sweat glands re- spond by producing a hypertonic (highly concen- trated) salt solution that coats the hair. Under normal circumstances horses cool

by evaporative cooling and convection. The movement of air over their body is paramount to both of these mechanisms.

Evaporative cooling: The sweat coats the hairs and as air flows over them it pulls the moisture and the heat off the horse. Convection: Blood vessels near the skin dilate and allow the transfer of heat from the blood into the air. During intense exercise,

horses can lose up to 10-15L per hour in sweat alone! Once their body temperature reaches greater than 42C, the respiratory system kicks in to help “blow off” some of the extra body heat (ap- proximately 15% of the body heat can be dissipated via respiration).

How does heat and humid- ity affect the horses’ abil- ity to perform? Perhaps the single most

important calculation when determining the risk to your horse during hot and humid conditions is the “Heat Stress Index”.

H.S.I. = Ambient

Temperature (*C) + % Hu- midity

The Cole’s notes ver-

sion of the H.S.I. is that it is that the temperature and % humidity must be consid- ered together to explain their full impact on an ath- lete’s ability to perform. For example, during the

day’s heat stress index with everyone at the barn so that all team members are aware of the risk and what they need to watch for over the course of the day. Early recognition is key!

2) Teaching horses at home to drink electrolyte solutions or accept syringed elec- trolyte supplementation is also a good place to start. Electrolytes can also be sup- plemented in the grain ra- tions. Remember that horse sweat is a highly concen- trated salt solution – there is approximately 10g of elec- trolytes per litre of sweat! Offer water frequently in between classes and ensure buckets are topped up when the horse returns to their stall.

early morning session it’s 20C and 98% humidity. H.S.I. = 15C + 98% = 112 H.S.I.

Based on the informa-

tion in the chart above, you would need ice water to cool your horse appropriately after

a period of

moderate/intense exercise. Now let’s compare that

situation with a typical af- ternoon weather report! By the afternoon, typically the humidity has burnt off and the temperature has in- creased: H.S.I. = 26C + 70% = 96 H.S.I.

We are now safely down

in the yellow zone where we would only need cold water for cooling after a hard ef- fort.

air is already saturated with moisture. This

In humid conditions, the reduces

evaporative cooling, allow- ing sweat to cling to the hair like a hot blanket and causes a rapid increase in body temperature. Horses’ that are struggling with over- heating will often be “in- verted” or seen to “pant”.

Inversion: when the respi- ratory rate is higher than the heart rate (over a 1 minute count). It can look like the horse is ‘panting’. Once fluid loss (dehy-

dration) has reached 5% of body mass (approximately 20-25L in your average sad- dle horse) there is a notice- able

reduction in performance. Dehydration

levels above 5% cause the athlete to feel ill as organ and brain function are im- paired. It is also interesting to note that dehydrated ath- letes sweat less than nor- mally hydrated horses (as the body tries to conserve any fluids it can). This fur- ther reduces the cooling mechanisms of the body, starting up a vicious cycle that can only lead to an overheated and severely de- hydrated horse if not cor- rected early. How can we improve

our athlete management under these circumstances?

“An Ounce Of Prevention Is Worth A Pound Of Cure” 1) Make a plan – discuss the

Not all electrolytes are

created equal – and differ- ent electrolytes are designed for different types of work. A thoroughbred sprinting on the track requires different support than a sport horse competing over 3-4 days, in the same way a track star is managed differently from a marathon runner. Your safest bet is to discuss your options with your regular veterinarian and include them in the discussion of how to support the horses through a hot and humid competition. 3) Ensure horses (and rid- ers) get frequent breaks out of the sun, have access to cool water and stable fans. If you notice a horse showing signs of heat stress (soaked

in sweat, inverted respira- tory pattern, dull eyes) get the horse into the shade and start cooling immediately while someone contacts the attending or show veterinar- ian.

For veterinarians and

riders if endurance horses, cooling horses becomes sec- ond nature with experience and education. The horse industry is littered with fal- lacy. Start by hosing or sponging cold water down the neck over the jugular veins, along the belly and in between the hind legs (look for the big dilated veins!). The repetitive application of cold water is the KEY to re- moving excess heat from the body. Continue to apply water to the body until the water coming off is not gaining heat. The addition of air movement will en- hance heat removal from the body (natural breeze or fans can be used). You can soak the horse from “ears to tail” with cold water if necessary – “tying up” isn’t from the application of cold water, it happens inside the muscle as a result of dehydration and accumulated “cell garbage”.

Heat Stress in horses

can be very serious with po- tentially long-lasting impact on the ability of your horse to exercise during the heat. So take care to reduce the heat load of your horse dur- ing exercise, particularly during hot and humid weather.

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