Exercise physiology of the horse encompasses:
- the cardiovascular system
- the respiratory system
- the muscular system
- the neurological system
- the endocrine system
- metabolic pathways
Why is oxygen uptake of the most importance?
Required to harvest energy and produce work
List the channels of heat transfer
- infrared thermal radiation from vegetation
- sunlight (direct & reflected)
- infrared thermal radiation from atmosphere
- wind
- evaporation
- thermal radiation
- infrared thermal radiation from ground
Factors affecting heat exchange
Conduction, convection, radiation, evaporation
What is conduction
two things beside each other exchanging heat
What is convection
how heat is dissipated
- wind may increase this by increasing movement of air from animal
What is radiation
Controlled by surface-environment exchange
Different levels of heat:
- inside vs. outside
- concrete (cooler) vs. brick/rubber
- straw (warmer) vs. shavings
What is evaporation
vapor pressure gradient is the major controlling mechanism
- hair can help dissipate heat or keep heat in
What is the LCT?
lowest temp (-15) when a horse has to up regulate energy expenditure in order to maintain body heat - when wet --> LCT is decreased (feels colder at warmer temperatures)
What is UCT?
highest temp (+15) when horse must use energy to dissipate energy (e.g. sweat, seek cover)
What mechanisms are used to change body temperature
- postural (turn butt to wind, huddle, seek shelter/shade/water)
- vasoconstriction/vasodilation
- piloerection (raise hairs = winter coat –> provides air barrier)
- behavioural adjustments (walk/eat)
- shivering (muscular movements to generate heat)
- feed intake to change heat increment of feeding/fermentation (more heat when fermenting hay in cecum/colon)
Which is more adaptable, LCT or UCT
LCT
- lowering LCT = horse feels colder at same temperature
- increased win, rain, cloud cover = increased energy requirement
Factors affecting LCT include:
Insulation
- body size
- hair thickness
- fat
- posture
Regulating metabolic rate
- age is inversely related
- feed/fiber intake
- thyroid status
- pregnancy/lactation
Prior thermal history
- insulate capacity changes (individual variability)
Wind speed
- lowers LCT
Rain
- lowers LCT
Cloud cover
- lowers LCT
- sun –> thermoregulation
What guidelines should be taken for cold weather?
- growing horses have higher LCT than mature horses and need additional DE
- ~1.3% addition for each degree drop in lCT in young horses (~2.5% in mature horses) - doesn’t count for foals - provide heated water (2-10 degrees C)
- to maximize consumption - Well bedded run in with sufficient room for all horses, facing south or east
- horses should all be able to lie in recumbent position) - if transporting, horses need to be protected from wind chill (especially foals)
What guidelines should be taken for hot and humid weather?
- water and salt must always be provided
- shelter from radiant sun
- ventilation will help to facilitate maintenance of BT through evaporative cooling
- no blankets/hoods
- if possible, avoid periods of the day where there is a lot of sunlight (whether riding and certainly for transport)
To make ATP, nutrients need to be oxidized, therefore, the increased energy demand of exercise demands:
- myoglobin has greater affinity for oxygen than Hb –> facilitating its movement into muscle
- increased oxygen consumption which is accompanied by an increase in lung volume and respiratory rate
- increased circulation/blood pressure which is accompanied by increase in heart rate and stroke volume
- increased oxygen carrying capacity which is accompanied by an increase in RBC due to spleen concentration and increased generation of RBC during exercise
- increase in oxygen saturation of Hb (increases the release of oxygen to tissues) –> further mediated by lactate production, increased p CO2 and increased temperature which decreases pH, increases oxygen dissociation which facilitates oxygen release
Storage energy used during exercise
Muscle + ADIPOSE –> triglyceride
MUSCLE and Liver –> glycogen
- aerobic exercise
Describe Type I muscle fibers
- slow twitch
- high oxidative capacity
- intermediate glycolytic capacity
- high lipid content
- intermediate glycogen content
- low fatigability
Describe type IIa muscle fibers
- fast twitch
- high oxidative capacity
- high glycolytic capacity
- intermediate lipid content
- high glycogen content
- intermediate fatiguability
Describe type IIb muscle fibers
- fast twitch
- high oxidative capacity
- high glycolytic capacity
- low lipid content
- high glycogen content
- high fatiguability
Explain the role of the spleen in the horse and how it satisfies exercise demands
The spleen stores RBC
- During exercise increased RBC’s are produced
- When the spleen contracts it releases RBCs –> increases oxygen carrying capacity
How does digestible energy relate to the feedstuff fed?
- foods with a higher GI (corn) will have a faster and higher DE compared to low GI feed (hay)
- Low glycemic index feed will have a more sustained digestible energy
