Fit, frantic or fat?

Excitable-horse

Understanding Energy – Dispelling the Myths and Misconceptions

You know the basics: Eat less and move more to lose weight; eat more to gain weight and we’re all too familiar with its consequences: the jeans that are now a bit of a struggle to squeeze into… the belt that must be loosened out a notch…or the jodhpurs that have tragically shrunk a size in the wash…supposedly!

This basic fact is ground zero of human nutrition and applies in equal measure to our horses.

Yet far too few horse owners apply the same basics of metabolism to their horses and see the feed they give them as having some mythical properties that will make Neddy jump higher, gallop faster or perform a Valegro-like dressage test, depending on your own personal ambitions for said Neddy.

This article is ‘feed and energy 101’ for horse owners. Read on to understand the facts and dispel the myths of energy and calorie consumption in horses.


Energy – we all use it and we all need it, but it is one of the most misunderstood concepts in equine nutrition. There are many myths and misconceptions surrounding what energy is, how it is supplied, how much is needed and its effects. Dispelling these myths and misconceptions and knowing exactly what energy is and how it works is therefore, essential to ensure optimal health and performance

So, what is energy?

In its simplest sense energy is the fuel needed to carry out normal body processes and exercise. The more exercise your horse does, the more energy he or she needs. Whatever energy is used up needs to be replaced, and this replacement comes from your horses’ diet.

The food your horse eats contains calories which are just a measure of energy.   This means calories and energy are essentially the same. In the USA calories are quoted as mega calories or MCal but in the UK calories are quoted as Megajoules (MJ) of digestible energy. One Megajoule is equivalent to 239 calories – about the same that is in a Mars Bar!

The Digestible Energy (DE) in the information provided by feed companies is calculated from the Gross Energy (GE) of the feed, minus the energy content of the faeces, so basically the energy lost in poo! The DE gives us an idea of how much energy the horse is likely to obtain from a kilo of that feed.

How much energy does your horse need?

By looking at the digestible energy of a feed we know how much the horse can get, but how much do they need?

The amount of energy a horse requires largely depends on their level of activity. The higher the workload the more energy is used and the more dietary energy to replace it is needed:

A sedentary 500kg horse for example, needs around 63.5 DE MJ per day for maintenance but this rises to around 144.5 DE MJ per day for a horse in very hard work (NRC, 2007) so a significant difference!

If too little energy is fed the horse will lose weight. If too much energy is fed, the horse will gain weight, it’s as simple as that. So it’s good to know how much or how little your horse needs per day.

A great calculator to work out your horses’ energy requirements based on workload and how it may be supplied from the diet can be found here:

http://nrc88.nas.edu/nrh/

How does the diet supply energy?

There are 4 energy sources in the horses’ diet – these are: Simple Carbohydrates (starch and sugar), Complex Carbohydrates (fibre), Fats and Protein.  Protein is often thought to be a primary energy source, but this is a common myth!

Protein is used only when there isn’t enough energy and this is not an efficient process. Carbohydrates (simple and complex) and fats are the primary energy sources. An example of simple carbohydrates as a feed are cereals like oats and barley, sources of complex carbohydrates are forage and high fibre feed like sugar beet, and an example of fats would be linseed meal or soya oil.

Simple carbohydrates are broken down by enzymes in the Small Intestine (SI) to glucose. This is a very rapid process meaning that these simple carbohydrates are a source of ‘fast-release’ energy, and this is great for short bursts of fast or intense work.

Fats are broken down by enzymes in the SI to free fatty acids (FFA) but this is a much longer process than simple carbohydrates, meaning that fat is a source of ‘slow-release’ energy.

Complex carbohydrates are fermented by hindgut microbes to produce volatile fatty acids (VFA) – Acetate, Propionate and Butyrate, This, again is a lengthy process, so complex carbohydrates are also a source of slow-release energy. Slow-release energy is great for longer bursts of sustained exercise and provides stamina.

So, the type of energy you feed your horse is an important consideration. The types used should be tailored both to the amount and type of work your horse is doing and their individual needs and temperament.

The products of enzymatic digestion and microbial fermentation – glucose, FFA and the VFA are all absorbed into the bloodstream to be used for energy production if needed. Acetate is arguably the most important VFA as along with glucose and FFA it can be taken up and used directly for energy production – propionate and butyrate need to be further converted to glucose and FFA first.

What happens when the energy from feed isn’t needed straight away?

When dietary energy (glucose, FFA and VFA) is not needed immediately for exercise it is converted to a form to be stored.  Glucose is converted to glycogen, which is the animal storage equivalent of starch in plants and stored both in the liver and in muscles. Any extra glucose which goes beyond the glycogen storage capacity of the liver and muscles is converted to triglycerides and stored as fat.  Fatty acids are also converted into triglycerides and stored as fat.

In a nutshell, if your horse eats more calories than the energy he expends, he will put on weight – kind of like us humans! It’s really as simple as that.

Fat-horse

How is this energy utilised when it is needed?

When needed for exercise, glycogen and triglycerides are mobilised back into glucose and fatty acids. However, this energy cannot be used directly, so it needs be converted into a different form to power exercise and maintenance. This happens in the cells by a process of Anaerobic or Aerobic Respiration.

Anaerobic respiration takes place within the cell and Aerobic Respiration (which requires oxygen) takes place within specialised structures within the cells called mitochondria.  This ‘cellular’ respiration essentially breaks down glucose and fatty acids and produces molecules of Adenosine triphosphate or ATP for short.

ATP is the biological currency for energy and it fuels all maintenance and exercise processes. No matter what type of feed we put into our horses, all the nutrients capable of releasing energy (glucose, fatty acids and amino acids) are converted to this one crucial ingredient1.

ATP is the power behind every muscle contraction in the body from the limbs to the digestive tract! Without it your horse wouldn’t be able to move or even function!

Fitness has a significant impact on energy!

So, what if your horse is receiving the correct amount of energy for work but is still lacking in energy, should you feed more? – probably not!

A lack of fitness is commonly misinterpreted for the need to feed more energy but feeding extra energy will normally just result in the horse getting excitable in the short term (the equivalent of a sugar rush in us humans) or getting fat!

The key is to look at whether your horse is fit enough for the work he or she does rather than just feeding more energy.  A horse that has the optimum amount of fitness for their work should not be lacking in energy, simply because the amount of energy generated from feed increases with fitness.

Key takeaways (and no, we don’t mean McDonalds…)

To provide your horse with energy in the best way possible to meet their individual needs and workload, consider these key points:

  • Get familiar with how much energy you horse needs per day and how the diet is meeting this requirement
  • Think about the type of energy fed not just the amount, to tailor the energy supply to your horses’ needs
  • Don’t forget fitness! – consider this before feeding more energy.

 

1. Marlin, D. and Nankervis, K. (2002) Energetics of exercise In: Equine Exercise Physiology. Oxford: Blackwell Science, pp. 7-20

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