Thermoregulation and exerciseassociated heatstress Part 3

1
Thermoregulation and exercise-associated
heat-stress Part 3

• AVS 435 Equine Exercise Physiology

2

• Age and thermal heat load
• Older horses reach 40C core temp (104F) 50
  faster than young horses with same SET, despite
  higher sweat rate
• Less total body water
• Less fluid available for sweat production

3

• Minimizing hyperthermia and hydration losses
• Adequate acclimation to hot, humid environments
• 1996 Atlanta Olympic Games
• Arrive at least three weeks prior to competition,
  with minimal heat training during first week
  after arrival

4

• During transport, horses average 3 kg fluid loss
  per hour of travel
• Equates to .8 gallons/hr
• 1 dehydration per 90 minutes of travel
• Remember thermoregulation and performance is
  affected at 2-3 dehydration

5

• Voluntary fluid intake decreased in unfamiliar
  environment
• May take 3-4 days to correct fluid losses
• Often increase rate of rehydration via IV or NG
  fluids
• Up to 10 liters/30 minutes via NG tube
  gravity-flow to horses with normal gastric
  emptying

6

• Minimizing fluid losses
• Offer water during travel (duh)
• Before, during, after travel, syringe with
  electrolytes
• Increase plasma sodium to encourage thirst
  response, voluntary drinking

7

• Ensure good ventilation in trailer
• Forced convective heat loss
• Better air quality, lessen irritation to upper
  respiratory tract
• Offer hay in trailer
• Horses drink 3-4 kgs water for 1 kg dry matter
• BUT trailer must allow enough room to clear
  URTs via coughing

8

• Provide water via buckets
• Horses drink on average 10 more water than from
  paddle automatic waterers
• Flavoring water
• Cider vinegar, molasses, Kool-Aid, Gatorade,
  apple juice, Horse Quencher

9

• Allow for increased water intake
• Water consumption increases 30-50 during heat
  acclimation period

10

• Hyperthermia
• Any horse with a rectal temperature above 103
  within 20 minutes of cessation of exercise will
  benefit from active cooling

11

• Horses with persistent rectal temperature 105 or
  higher is at danger of developing more severe
  metabolic disease

12

• Non-veterinary strategies to cool
• Immerse in cool pond or stream
• Fans or misting sprayers
• Ice boots on lower legs, neck
• Alcohol baths (1 pint rubbing alcohol to 1 gal
  water)
• Increases rate of evaporation

13

• Continuous spraying or sponging with cool water
• Utilizes convection and conduction
• Dont let water just sit there
• Spray, scrape, repeat
• Thin layer water heats to skin temp, acts as
  insulating layer if not removed
• Evaporation too slow
• Dripping only removes minimal heat

14

• Cool water is better than icy water
• Localized vasoconstriction less skin surface
  blood circulation less convective transport of
  heat from core to surface
• Dont drape with wet towels
• Absorbs heat, then becomes insulating layer

15

• Cooling strategies that require a vet
• IV fluids
• Dehydration almost always a component of
  hyperthermia
• Nasogastric fluids
• Up to 10 liters (2.65 gals) per 30 min via
  gravity flow if normal gastric emptying

16

• Cool/ice water enemas
• Very effective, but also risky
• Rectal mucosa easily perforated in horses (cows
  much tougher)
• If dehydrated tissue paper