Page 22 - The Game July 2006

22 The Game, July 2006 Your Thoroughbred Racing Community Newspaper HORSES AND HEAT WAVES
Equine Health
by Karen Briggs
Dave Landry Photo
Welcome to another Canadian summer. From my non-air-condi- tioned, sticky home office, I’m not only feeling sorry for my sweaty little self, I’m also feeling a bit sorry for the horses who go to work in these purgatorial conditions every day.
Dehydration and heat stress are very real risks under conditions like these. Horses evolved as cold-weather critters, good at maintaining their core body temperature when arctic winds blow across the Mongolian steppes, but less skilled at getting rid of excess body heat when the weather gets humid and steamy. The fact that they can sweat is a major advantage, of course, they’re one of the only domestic animals who do so, but in the process of sweating, they can lose 7-8 litres of fluid per hour when exercising (and sometimes up to 15 L in extreme conditions). That’s not the only way in which they suffer water losses. Increased respiration in hot conditions, especially when they’re exerting themselves training or racing, adds to the fluid debit column.
Under normal circumstances, the horse’s body is approximately 60% water. Lose 5-7% of his bodyweight in water loss, and he is mildly dehydrated (which can be assessed by pinching a fold of skin on the horse’s shoulder and releasing it; if it takes more than two seconds to snap back, it’s an indication of dehydration). Depression, dry mucous membranes (check the gums), and a prolonged capillary refill time are other indications.
At 8-10% water loss, dehydration is classified ‘moderate’, but there’s little that’s moderate about symptoms like weak pulse strength, poor jugular vein
distension, and elevated heartrate. Even the ability of the skin cells to retain a healthy fluid balance is affected.
By the time a horse’s water loss is more than 10% of his body weight, he’s in big trouble. With severe dehydration, he’ll look shocky, colicky, and disoriented, with cold extremities and looming multiple organ failure. Emergency rehydration measures must be implemented to save such a horse but it should never get that bad if we pay attention to hydration status and do everything we can to maintain a healthy water intake, particularly when horses have to exercise at 30 degrees Celsius or above.
Along with fluid, horses lose electrolytes, the positive - or negative- ly-charged trace mineral salts that help their cells maintain their normal functionality, when they sweat. If the diet is not adequately replacing these lost minerals (primarily sodium, chloride, potassium, magnesium, and calcium), horses can suffer muscle cramping, cardiac arrhythmias, gastrointestinal distress, even loss of brain function.
Commercial electrolyte mixes, or a 50/50 mix of regular table salt and ‘lite’ salt (potassium chloride, or KCl) can help a horse replace the salts he loses through sweat, and they’re a good idea anytime you’re asking an animal to exert himself in severely hot or humid conditions. A couple of caveats regarding electrolytes though: avoid those with a high glucose or sugar content (listed as one of the first few ingredients), as the sugar will cause a glucose surge in the bloodstream, in
turn triggering an insulin release and resulting in hypoglycaemia while exercising. Also, don’t use electrolytes which contain bicarbonate, a sweating horse is already alkalotic, and bicarb will just compound this pH imbal- ance.
Electrolyte preparations
can be offered in a pail of
water, but often it’s better to administer them mixed with
some applesauce or vegetarian babyfood, and syringed into the mouth. Some horses will refuse electrolyte- flavoured water and cheat themselves of the water they need, and using a syringe also assures you of a certain level of intake.
Don’t wait until a horse is already dehydrated before you give electrolytes. High concentrations of these salts in the gut at that time, may actually pull water from the blood, increasing the body’s dehydration level. Instead, go for the pre-emptive strike, administering electrolytes one to two hours before a stressful event (hard workout, race, or long-distance shipping).
Afterwards, allow him to drink until satisfied, and administer more electrolytes by syringe. (Studies done by the University of Guelph before the 1996 Atlanta Olympics taught us that many of our traditional ideas about cooling hot horses were wrong, including the idea that drinking deeply after exercise would trigger colic.)
Some other tips for preventing dehydration:
1. A horse’s daily fluid requirement is about 60 mL/kg. For an average- sized 500 kg (1100 lb.) horse, that’s about 30 litres of water per day, or 1-2 litres per hour. If that amount of water isn’t available to your horses, it’s time to make some management changes.
2. Make sure water is always available in both stalls and paddocks and that it’s clean and fresh. Some horses will turn up their noses the instant there’s a hint of algae or dead bugs floating in the trough, so scrub buckets and troughs regularly with baking soda. Check the levels in the troughs daily, and not just from a distance. Last summer I found my herd all standing around looking desperately thirsty next to a trough I’d filled the day before. On closer inspection, I found there were two drowned chipmunks floating in there!
3. Monitor hydration status with the skin-pinch test, capillary refill (press your thumb firmly on the horse’s upper gum, under the lip, and watch that the area becomes pink again within 1-2 seconds of releasing the pressure), listening for gut sounds, and checking the moistness or tackiness of the mucous membranes.
4. Encourage extra water intake by feeding wet feeds, such as sloppy soaked beet pulp or hay cubes, and feeding juicy vegetables and fruits (apples, lettuce, carrots, or whatever tempts the appetite). Just don’t depend on these foodstuffs to do the whole job, fresh water is the first consideration.
5. With a horse who refuses to drink, try putting a tablespoon of salt on his tongue. The salty taste might encourage him to put his nose in the bucket.
6. Four to five hours prior to a stressful event (a hard workout, race, or shipping in a hot, closed trailer), feed hay; the fibre in the horse’s gut will help hold water in the gut which will be available to him when dehydration starts to develop.
7. Make sure your horses have access to a plain or iodized salt block, or have a tablespoon or two of salt added to their daily feed. (Some horses don’t like the taste of the brown mineral blocks and as a result won’t take in enough salt.) NaCl is the most important electrolyte to replace and the only one about which horses have ‘nutritional wisdom’, meaning they’ll seek out what they lack.
8. Many horses refuse to drink away from home, especially if the water has an unfamiliar taste. For the finicky ones, accustom them to water flavoured with a bit of instant-drink- mix powder, peppermint flavouring, or apple juice, and then bring that same flavouring when you ship in to another location to fool their taste buds.
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