Page 103 - Speedhorse April 2021

FEEDING FAT
by Nancy S. Loving, DVM
An equine athlete usually has a sleek, well-
defined physique, rippling with muscle. Energy demands of athletic exertion necessitate provi- sion of ample calories to support the efforts. Decades of documentation has proven that grains are a problematic feed for horses, poten- tially leading to gastric ulcers, colic, obesity, insulin resistance, and laminitis.
There is an invaluable dietary tool that provides energy and calories in substitution for grain yet without the adverse effects of grains – feeding fat. Forage components, like hay or pasture, have little fat content, and what little there is, is not readily absorbable. Not only that, but unlike most mam- mals, horses don’t have a gall bladder. So, how is
it that fat can serve a useful function to maintain body condition or to fuel equine locomotion?
FUELING EXERCISE
For a horse to maneuver and run, he is depen- dent on two sources of energy stores in the body: fat and/or glycogen. Fat is used in the presence of oxygen during aerobic exercise. Glycogen is stored in the muscles and liver to be used in intense, anaerobic exercise when oxygen is in limited supply to hard-working muscles, such as in sprint activities and racing. Depletion of glycogen stores is a known cause of fatigue in the equine athlete.
Research studies have shown that fats are digested and well absorbed in the equine gas- trointestinal tract. A horse’s pancreas produces an enzyme (lipase) that digests (hydrolyzes) triglycerides (fats) in the intestine.
Digestion of fat produces a lower heat increment than digestion of starch or fiber,
so a higher fat diet results in reduced produc- tion of internal heat. A diet of oats, hay and oil generates 5% less heat production than a diet of oats and hay, and 16% less when compared to a hay-only diet. Besides being a “cooler” burning energy source, supplemental dietary fat leads to less intake of “hot” burning hay. Horses fed a fat-supplemented and reduced hay diet experi- ence 12% less water loss, which is important in performance where hydration is a concern.
Fat as a fuel substrate for locomotion also lessens the degree of acidosis of the blood stream. Lactic acid is a waste product of glyco- gen utilization, so any strategy that diminishes internal heat or acidosis helps delay the onset of fatigue for both aerobic and anaerobic exercise. A high-fat diet improves a horse’s use of glyco- gen from the muscles while doing high speed work. Studies have shown that fat-supplemented horses engaged in relatively short but high-speed exercise are able to run faster and maintain a steady heart rate for a longer time before lactate (acidosis) concentrations rise in the bloodstream.
For a horse performing aerobic exercise, a high-fat diet spares glycogen stores for longer, thereby delaying fatigue – fat is used as a fuel source for longer periods, for maintenance, and for a wider variety of sub-maximal work intensities, such as during warm up periods
or less intense levels of performance. This leaves the more limited muscle glycogen stores untapped and full for use when work intensity is ratcheted up to require use of glycogen.
These positive effects from fat supplemen- tation occur if a horse is fed a diet with some carbohydrates to allow for muscle glycogen replenishment and storage. Regular exercise and training enable a horse to adapt to using fat
VETERINARY VIEWS
A high-fat diet improves a horse’s use of glycogen from the muscles while doing high speed work.
SPEEDHORSE April 2021 101
Marie Littlefield