Equis ISSN 2398-2977

Nutrition: energy

Contributor(s): Derek Cuddeford, Zoe Davies, David Frape, Deborah Lucas, Katie Williams (nee Lugsden)

Energy requirements

Sources
  • Hydrolysable carbohydrates, eg starch:
    • Usually supplied by cereal grains.
    • Converted to glucose in small intestine or to volatile fatty acids and lactic acid in the hind gut for immediate use or storage as glycogen or fat.
    • Where larger rations of cereals are given to performance horses the risk of colic   Abdomen: pain - adult   and laminitis   Foot: laminitis  is reduced by using micronized cereals.
  • Non-starch polysaccharides, eg cellulose:
    • Supplied by dietary fiber.
    • Converted to volatile fatty acids (VFA) and then to fatty acids (FA), or to glucose and FA from propionic acid. These products are used immediately or stored as fat and as glycogen from glucose.
  • Fats:
    • Typically low in horse's natural diet but can be utilized remarkably efficiently.
    • Converted to fatty acids for immediate use or stored as fat.
  • Protein   Nutrition: protein  :
    • Least preferred by the horse as very inefficient break down process involved.

Physiology

  • Maximum performance depends on reducing the depletion rate of energy sources and minimizing the accumulation of end waste products.
  • There are two mechanisms by which the horse regenerates ATP:
    • Oxidative phosphorylation breaks down carbohydrates, fats and protein using oxygen and is therefore considered aerobic.
    • Glycolysis breaks down glucose or glycogen without oxygen resulting in the production of lactic acid. This is anaerobic.
  • Different exercise intensities utilize different metabolic pathways to generate energy and so fatigue occurs for different reasons:
    • Prolonged aerobic exercise, eg endurance, eventually   →    the depletion of muscle and liver glycogen stores. The horse is unable to maintain normal blood glucose levels   →    fatigue.
    • Anaerobic exercise, eg sprint racing,   →    accumulation of lactic acid in muscles and a fall in pH to 6.5 or less. ATP production will decline thereby reducing muscle power output    →   fatigue.

Energy utilization

  • At walk muscle contraction is slow and energy generation is entirely aerobic. Fat is the predominant energy source as stores are plentiful and it can be broken down quickly enough to meet demands.
  • As the pace increases to trot and canter a combination of fat and glycogen will be used as energy sources. Glycogen can be broken down twice as fast as fat and so as requirements increase the more rapid delivery of energy from glycogen stores is required to meet demands.
  • As speed increases to a fast gallop anaerobic pathways are initiated. Anaerobic glycolysis is the fastest way to generate ATP but lactic acid is produced which will   →    fatigue relatively quickly.

Dietary energy provision

  • Gross energy (GE) of a feed is the heat evolved when it is subjected to complete combustion in oxygen, ie the conversion of chemical energy to heat energy.
  • The horse is unable to utilize all the gross energy and so a digestible energy (DE) value is calculated by subtracting the energy lost in the feces from the gross energy.
  • In other species metabolizable energy (ME) is calculated which subtracts the energy lost in urine as well as fecal losses from the gross energy value.
  • Calculation of energy requirements for maintenance according to the National Research Council (NRC) is as follows:
    • DE (MJ/day) = 5.9 + 0.13 W, where W = bodyweight in kg.
  • For heavy horses (675-839 kg):
    • DE (MJ/day) = 7.61 + 0.1602 W - 0.000063 W².
  • Typical DE/kg, 88% DM values of feed stuffs commonly found in diets of horses:
    • Pature: 8-12 MJ/kg (values will vary throughout the year).
    • Grass hay: 5-8 MJ/kg.
    • Grass haylage: 6-9 MJ/kg.
    • Oats: 10.5-12 MJ/kg.
    • Barley: 12.5-13 MJ/kg.
    • Maize: 14.2 MJ/kg.
    • Wheat: 14.1 MJ/kg.
    • Molassed beet pulp: 12 MJ/kg.
    • Alfalfa chaff: 9 MJ/kg.
    • Full fat soya: 19 MJ/kg.
  • Typical DE values of compound feeds (88% DM):
    • Resting/light exercise: 8-10 MJ/kg.
    • Working feeds: 10-11 MJ/kg.
    • Competition/performance: 12-14 MJ/kg.
    • Conditioning: 11-14 MJ/kg.
    • Veteran: 11-12 MJ/kg.
    • Stud rations: 12-14 MJ/kg.

Print off the Owner factsheet on Nutrition - keeping your horse on top form to give to your clients.

Energy sources for different requirements

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Timing of feeding

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Further Reading

Publications

Refereed papers
  • Watts K A & Chatterton N J (2004)A review of factors affecting carbohydrate levels in forage. J Equine Vet Sci24(2), 84-86PubMed.
  • Hintz H F (1992) EdClinical nutrition.  Vet Clin North Am6, (2).

Other sources of information

  • Frape D (2004)Equine Nutrition and Feeding.3rd edn. Blackwell Publishing Ltd, Oxford, England. ISBN: 1405105984.
  • Pagan J D (1999)Is Time of Feeding Critical for Performance?In: Proceedings of the BEVA Specialist Day on Behaviour and Nutrition. BEVA, UK.


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