What is Digestible Energy?

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What is Digestible Energy?

It’s clearly written on the colourful bag of horse feed in big bold letters – “contains SUPER FIBRES that provide an enhanced level of digestibility!” That sounds awesome…but what does it actually mean

In this article by Karen Richardson, of Better Health & Nutrition for Your Horse or Pony, she explains that comparing the Digestible Energy content of feed products can be like comparing apples with oranges. 

The term Digestible Energy is used to estimate the amount of calories your horse can potentially extract from a feed product.

Digestible energy estimates for grains, fats/oils, low fibre products may be quite accurate due to the way they are digested, but this is not the case for fibrous products, particularly those containing high levels of fibre (over 35% eg. soyhulls) or those with a high content of highly fermentable fibres (eg. sugarbeet pulp, soyhulls) – the so called “super fibres”.

Super fibres are primarily digested in the hind gut. Whilst there is some digestion of sugars, fats and proteins in the small intestine which will contribute to energy production, mostly they are digested in the hind gut by microbial fermentation.

The processes and formulas used to estimate Digestible Energy cannot accurately take into account the quantity of energy substrates produced via microbial fermentation and the subsequent absorption of these substrates by the body. There are too many variables such as individual variations in the microbial make up of the hind gut, metabolic status of the individual and the individual’s ability to assimilate energy substrates. For example, a horse on a grain containing diet will have a different microbial composition to a horse on an all forage diet and this will impact how well fibres are digested in the hind gut. A horse suffering from intestinal inflammation will not be as efficient at absorbing energy substrates produced by microbial fermentation compared to a horse with a healthy hind gut. A horse with a healthy, efficiently functioning hind gut will have the potential to produce more energy substrates than a horse with an unhealthy, inefficient hind gut, or one in between.

What we do know is that super fibres not only increase the number of healthy, fibre digesting bacteria in the hind gut but they also enhance the production of the energy substrates that are converted by the body to energy. It is possible that a horse with a poorly functioning hind gut can improve and in time will be able to achieve more digestible energy from the same quantity of a super fibre than it did when it first received it.

It might be tempting to look at the numbers and see that grain has a higher digestible energy value than sugarbeet pulp or soyhulls, and perhaps feeding more grain will produce more digestible energy than adding a super fibre. I would urge you to think again.

The digestible energy from grain is achieved via enzymatic digestion in the small intestine. Feeding large quantities of grain are not efficiently digested in the small intestine. Transit through the small intestine is relatively quick and undigested grain is passed on to the hind gut where it adversely affects the microbial population – the acidity of the environment is increased and this kills good fibre fermenting bacteria. The potential digestible energy content of the grain has decreased substantially not only because it was not fully digested in the small intestine but it has further decreased the quantity of energy substrates able to be produced by the microbes of the hind gut.

Research has shown that digestible energy values for sugarbeet pulp and soyhulls may be more comparable to that of oats and barley (I have a scientific review article published on the topic). The point of my post is to point out that when it comes to considering digestible energy contents of feeds there is more to it than numbers. 

 

Karen Richardson BSc(Hons), MSc Equine Science

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