Glycogen Sparing Effect in Endurance Horses or Feeding Fat to the Endurance Horse

There have been several studies done on the addition of fat to endurance horse diets. Fats can be useful in 2 ways. Up to 30% of a horses total diet can be fats, or 20% of concentrates. 10% total is the most common baseline that is followed, as higher percentages are sometimes refused by the horse due to texture and taste issues.
Commonly fat has been added to a horses diet for 2 reasons.

1. To add 'bloom' or gloss to a horses coat.
2. To and or maintain weight in a horse with a large energy requirement.

The more scientific or factual reasons fats are added to a diet, that are directly beneficial to the high level endurance horse are.

1. Fat is the most energy dense feed available - considering that it is also highly digestible, energy that remains available for production is increased by 60%! Minimal amounts are lost through body functions or heat.

2. Fats decrease the heat load (meaning that the horse isn't required to use to heat to metabolize fats, unlike proteins or fibre. In a study where 10% fat was added to the horses total diets, heat production was actually reduced by 14% - hence possibly one of the reasons the monikor of 'cool calories' originated. This is an essential fact that is of high value to the endurance horse - as when processing fats in a working environment - the heat load (sweat) % is reduced as the horse relies on fats for energy.

3. The most important facet of feeding fats (and the least understood) is the glycogen sparing effect in endurance horses. In horses fed a 10% fat total diet - the horse's metabolism shifts (this takes approx 90-120 days to come into effect) whereby the horse begins to use fat stores more effectively and consistently during work periods - essentially 'sparing' glycogen.

Glycogen is the carbohydrates that are stored in the horses body - during aerobic exertion the horse use glycogen as it's primary source of energy. Fatigue becomes apparent when the horse runs out of glycogen - or is working at a rate where the horse can longer produce glycogen at the rate that is required (anaerobic activity) and/or glycogen depletion.

By having a horse's base metabolism shift to using fats as a primary energy source, glycogen is then spared - by the fact that glycogen stores are used only to burn the fat that the base energy rather than glycogen itself being the primary source of energy during exertion. Glycogen stores last longer, resulting in longer mileages available before fatigue sets in.

The horse can utilize glycogen without fats, but cannot utilize fats without glycogen. when the horses metabolism relies solely on glycogen, workout sessions will be shorter, simply due to the onset of fatigue. If a horses metabolism is shifted to relying mainly on fats, fat stores are comparatively endless.

This is an important point, so when planning to enhance an endurance horses diet with fats, the ability of the horse to create glycogen must also be accounted for.