Dunc's Diatribe: Fats - the good, the bad and the ugly.
Monday, October 25, 2010 by Duncan McLaughlin
Any discussion about your endurance horse’s diet must include discussion on fat : fat is so important in the energetics of sustained exercise. But before we begin, lets cover some terms:
Adipose fat is what we commonly think of as ‘fat’; fat storage depots around the body. Think ‘love handles’ and you get the idea.
Intramuscular Triglycerides (IMTGs) are specialised fats stored in-between muscle fibers and are an important source of fuel for sustained exercise.
Essential Fatty Acids (EFAs) are fats that must be supplied in the diet. These include your Omega3s and Omega6s. Simply put, Omega3s are involved in anti-inflammatory responses and Omega6s are involved in inflammatory responses but both are required by your horse’s body for many metabolic processes.
Volatile Fatty Acids (VFAs) result when microbes in the hindgut breakdown fiber. The VFAs are then absorbed by your horse’s digestive system for use. The most important VFAs are acetate, butyrate and propionate.
1. Acetate is easily converted to acetyl-CoA and used directly as an energy source by muscle for aerobic exercise. Excess is converted by the liver to fat.
2. Butyrate is mostly used as energy source by the cells lining the digestive tract but excess can also be converted by the liver to fat.
3. Propionate is either converted by the liver to glucose and then transported to muscle for use or storage as glycogen or it is converted by the liver to amino-acids and/or fat. Estimates suggest as much as 50% of blood glucose is derived from propionate.
So you can see, we need to take VFAs seriously.
Free Fatty Acids (FFAs) come from the breakdown of fat, either long-chain dietary fat in the digestive system or adipose fat from body stores, and are moved by the circulatory system to muscle, where they can be used as fuel for aerobic exercise.
Horses don’t eat, or need, much fat. The evolved diet (grasses, forbes, shrubs) was low in fat, no more than 5% of total calories. This explains why horses don’t have gall bladders: instead a continuous but very small amount of bile, important for fat digestion, trickles in to the small intestine.