Equine Energy Metabolism

Question 1

Energy

Answer 1

• Most important nutrient (not itself but what we take out of various nutrients)
• Measure of feed’s potential to fuel body processes
• End products of digestion provide the starting point for metabolism
• chemical energy to ATP using metabolism

Question 2

energy metabolism - Source metabolites

Answer 2

Substrate - site of digest - end product

• sugar/starch - small intestine - glucose
• fibre - large intestine - VFAs
• fat - small intestine - fatty acids
• Horses do not eat during exercise. End products of digestion stored for later use

Question 3

energy metabolism - storage components

- 2 stages of glucose metabolism

Answer 3

• glucose stored as glycogen
• VFAs converted into body fat and glycogen
• fatty acids stored as body fat
• Glucose/Glycogen is metabolised in two stages ~ Glycolysis
  ~ Citric acid cycle

Question 4

Glycolysis - about

Answer 4

• sequence of reactions
• glucose [6C] to 2 pyruvic acid [3C] and ATP product
• anerobic process that occurs in cytoplasm
  (process on pages in folder)

Question 5

glycolysis - outcome

- if oxygen is/not available

Answer 5

• ATP use = 2 ATP
• ATP gain = 4 ATP
• net gain = 2 ATP and 2 NADH
• if oxygen unavailable 2 NADH used to converted pyruvate into lactic acid (need the empty NAD to keep glycolysis happening)*

*2 Pyruvic acid (3C) to 2 Lactic acid (3C) using 2 NADH and 2 NAD produced

• lactic acid Accumulates in muscles causing stitch and cramp, fatigue
• All of the above is ANAEROBIC – doesn’t need O2
• if oxygen available: after glycolysis
  ~ pyruvate enters the citric acid cycle
  ~ 2 NADH oxidised to yield 6 ATP
  (via oxidative phosphorylation and the electron transport chain)

Question 6

Citric acid cycle

Answer 6

(pages in folder)

Question 7

other energy sources

Answer 7

• We have accounted for glucose, but what about the other products of digestion?
• Carbon ‘skeletons’ of deaminated amino acids
• Fate depends on length of carbon chain of amino acid
  ~ glucose
  ~ As VFAs below
• VFAs
  ~ Propionate [3C] end up as glucose in the liver
  ~ Acetic [2C]
  ~ Butyric [4C]
• Fatty acids [long-chain]

Question 8

Muscle fibre types

Answer 8

• 3 muscle types with different metabolic characteristics
  ~ type 1 - slow twitch - resistant to fatigue - aerobic
  ~ type 2A - fast twitch - high and low oxidative - both
  ~ type 2B - fast twitch - low oxidative - anerobic
• muscle type mainly influenced by breed and training
  ~ quarter horse = mainly type 2B
  ~ thoroughbred = type 1 and type 2A
  ~ arab = mainly type 1

Question 9

Quarter horses - muscle fibre type and why

Answer 9

• mainly type 2b muscle fibres
• can respond quickly (anerobically) and produce great power
• cant sustain the process for long
• rapid high energy activity (rodeo, sprint)

Question 10

thoroghbred - muscle fibre type and why

Answer 10

• higher proportion of type 2A and type 1
• within one minute, slower aerobic energy suplements anerobic metabolism
• good pace maintained over most of race

Question 11

arab - muscle fibre type and why

Answer 11

• higher proportion of type 1
• requires more energy than anaerobic metabolism can deliver
• energy supplied from body fat
• steady and sure over vast distances

Question 12

energy and exercise intensity

Answer 12

• Ability to take in oxygen (oxidative capacity) influences energy substrate metabolism and performance
• Aerobic energy to Anaerobic energy using Exercise intensity
• At lower exercise intensity oxidative capacity sufficient to allow utilisation of aerobic substrates
• At higher exercise intensity oxidative capacity insufficient. Anaerobic substrates more important

Question 13

anaerobic threshold

Answer 13

• At speeds > 650 m/min ATP requirement cannot be satisfied by aerobic pathways. Anaerobic pathways become more important.
• ‘Anaerobic threshold’
• Above anaerobic threshold glycogen use and lactic acid accumulation increases exponentially.
• Actual oxidative capacity and anaerobic threshold can be influenced by training. and cope with anerobic conditions

Question 14

practical application (anerobic threshold)
- racing

Answer 14

exercise:
- racing = speed
- endurance = distance
- draft = load carrying
Racing: 
~Energy (ATP) demand not satisfied by aerobic metabolism. 
~ High anaerobic metabolism. 
~ Fatigue quickly due to lactic acid accumulation.

Question 15

endurance riding

Answer 15

• Energy (ATP) demand satisfied by aerobic metabolism.
• Little anaerobic metabolism.
• Fatigue slowly (due to eventual glycogen depletion).
• Dietary considerations
  ~ aerobic substrates - fat (body tissue and diet), acetic and butyric acid (dietary forage)
  ~ anerobic substrates - glycogen (body tissue), glucose and propionic acid (dietary concentrate, e.g. starch to optimise glycogen storage but not too much as limit to horse digestion)