What is fluid?
water, electrolytes and many other molecules (either dissolved or suspended)
What makes up total body water?
~67% lean body mass (~300L)
Extracellular fluid volume (1/3 = ~100L) = Na and Cl
Intracellular fluid volume (2/3 = ~200L) = K
What are electrolytes?
generally salts that dissolve in water
How much water is lost per hour of shipping during May-Sept?
15-20L
what is dehydration?
Loss of fluids from the body exceeds intake of fluids
- lost from intracellular or extracellular fluid
What are the effects of dehydration?
Even ~1% dehydration results in:
- decreased mental performance
- decreased physical performance
What are the signs of dehydration?
Larger losses contribute to
- lack of well being
- fatigue
- loss of interest in activities and surroundings
- inappetence
- intolerance to heat stress
How can hydration be assessed?
- skin pinch test –>longer than one second = dehydration
- capillary refill test
- cardiac recovery index
- elevated plasma protein concentration
How and why do horses get dehydrated?
- sweating rates exceed intake of water AND electrolytes
- sweating required for thermoregulatory cooling
- evaporation of sweat from skin cools the skin –> and blood perfusing the skin
- eliminates heat produced by muscles
How efficient in conversion of chemical energy –> mechanical
25% –> locomotion
- 75% –> heat –> heat storage –> heat dissipation
Human sweat or horse sweat is more concentrated?
Horse
- lose ability to retain sodium as sweating continues
- Cl concentrations must balance K, Na, Ca, Mg –> losses very high to balance losses of all the cations
- K concentrations higher in sweat than blood –> implies intracellular dehydration
What is the key to preventing heat strain?
minimize or prevent dehydration
- water and electrolytes!!
- to keep water within fluid compartments (Na, K, Cl, Mg, Ca)
Effective electrolyte supplementation should enhance?
- gastric emptying
- intestinal absorption
- body distribution
- exercise performance
- well being
What factors affect gastric emptying and intestinal absorption?
- solution osmolarity
- volume ingested
- temperature of solution
- presence of non-electrolytes
An effective electrolyte will?
- use water to replace sweat losses
- minerals to replace sweat losses
- use energy source (dextrose) to promote absorption
- increase palatability to encourage consumption
What should be in a good electrolyte product?
- electrolytes to balance what was lost in sweat
- dextrose (D-glucose) to enhance small intestine absorption of Na and water
- fructose may enhance small intestine absorption of K
- easily dissolved in water
- NOT easily dissolved not absorbed by the intestine (e.g. magnesium carbonate)
When buying an electrolyte the following should be considered?
- cost
- taste
- will it be absorbed by GIT
- ease of administration
What is the problem with giving just water?
- diluting osmolarity in ion concentrations
- kidneys don’t like this = volume overload –> excretion –> getting rid of electrolytes –> more electrolyte depleted/dehydrated
What are sweating rates for moderate work?
10L/hour
- ~110 grams of electrolytes/10L
- want to give enough to balance water losses from sweating
What will happen if too much electrolytes are given?
if with adequate amounts of water:
- will have no negative effect on horse’s health
- extra will be excreted by kidneys
If not with enough water:
- electrolytes may sit in stomach
- further dehydrates fluid compartments
- water moves from blood –> GIT
- water move from cells –> blood
- only later will water and electrolytes move from GIT back into blood/cells
- discomfort
- movement of water into gut from EC fluids –> extracellular dehydration
How does a well hydrated horse perform
- feels well
- is bright and alert
- is energetic
- shows appetite
