Dietary energy can be a confusing matter for horse owners, because the term ‘energy’ is most often used to describe a horse’s behavioural energy, or how forward going he is. But dietary and behavioural energy are not the same thing and the former does not have a direct result on the latter, regardless of the feed source.
Dietary energy is the body’s fuel that is extracted out of the feed, more specifically the carbohydrates (including sugar, starch and fibre) and oil. Energy is not extracted to any great extent out of protein so dietary protein level does not affect dietary energy availability (unless the animal is starving and using body tissue to survive). Just like for us, too much dietary energy for a horse causes weight gain in the form of excess body fat, and too little dietary energy causes weight loss as the horse’s body uses up fat stores. The correct amount of dietary energy and the horse’s condition will stay the same.
Dietary energy for horses is commonly called ‘calories’, which is not strictly correct because we use the description joules rather than calories for horse feeds in the UK. It does, however, help owners to consider energy with regard to their horse’s body condition rather than their temperament, since we commonly use the term calories to describe our own dietary energy intake.
Horse’s temperaments vary widely in terms of how much natural forwardness or exuberance they have. This innate level of forwards (or not, as the case may be) can be altered a little with environment and feed, but not nearly to the extent as it can by training and exercise. So although riders tend to think of energy as the horse’s capacity or willingness to work, the only situation where a lack of dietary energy would cause a lack of energy in work or lethargy would be if the horse was starving, or if it had run low in muscle fuel stores (muscle glycogen). A horse running low in muscle stores would apply only to high level performance horses either training for endurance (over 60 miles) or repeated sprinting with inadequate ‘easy’ or rest days.
The most common reasons for a lack of energy in work, a lack of stamina or lethargy are either a lack of fitness for the work the horse is being asked to do, or a poorly motivated horse without much natural forwardness. Feeding more dietary energy to both these cases will simply result in weight gain.
There does seem to be a link between dietary energy and behavioural energy with a specific type of feedstuff – starchy cereal grain. In some horses – classed as susceptible horses – feeding cereal grains (processed or not) seems to cause excess exuberance (or fizziness) and often, reactiveness and spookiness. It’s not known why cereals seem to have this effect on some horses, but it could be due to the starch content, which is relatively high compared to other horse feeds. All cereals can have this effect on a susceptible horse, not just oats. Interestingly, oats contain the lowest amount of starch and energy, and the highest amount of fibre out of all the cereal grains that horses are fed (including wheat, maize and barley).
Energy requirement is probably the easiest dietary factor to assess, because the horse’s body condition will tell you whether or not the intake is balanced, and if your horse is maintaining his weight and condition then he is not short of dietary energy, regardless of how he feels in his work.