This is an abbreviation of unit 7 from the Advanced Equine Nutrition course. The complete text, a video, and quiz questions are available with The Horse’s Advocate membership. You can also purchase them separately. Note: Passing the Basic Equine Nutrition Course is required before starting the Advanced Course.

Unit 7- Fat And Carbohydrate: Not So Essential Nutrients

Horses Can Make Sugar And Fat

The word “essential” in nutrition signifies that a horse must consume that “nutrient” to survive. This is because the horse cannot produce it. We saw its use when discussing protein. Horses need a diet with all the essential amino acids. This prevents deficiencies in making proteins that utilize them. However, fats and carbohydrates can be made by horses when they are absent in the diet. They still must eat them for efficiency in the energy flux of life. They can survive for a long time without them in their food.

In the Basic Nutrition Course, you learned that forage contains starch and sugars. Sugars are also known as “Non-Structural Carbohydrate” or NSC. Forage also has cellulose, referred to as “Structural Carbohydrate” or SC. Starch is the ordered storage of glucose made by the plant through photosynthesis. Sugars include glucose, sucrose, and fructose. There is no daily requirement for sugar intake. Horses can consume starch and sugars in the plants they eat. They can use these nutrients for fuel. They also help maintain glycogen in muscles and the liver, as well as body fat.

The Basic Nutrition Course taught us that no animal can digest cellulose or SC (structural carbohydrates). However, the trillions of bacteria in the horse’s hindgut (cecum and colon) can digest cellulose. They create short-chain fatty acids and other postbiotics. Horses use these products as fuel.

All animals, including horses, can eat starch and cellulose. They will consume these until they reach their daily fuel requirements. Consuming these foods preserves the fat and glucose stored in the horse. It prevents a catabolic crisis, where protein converts into glucose for fuel over long periods without food. This variation occurs in seasons. In the summer, a horse will eat more than it needs. It stores the excess for winter when access to starch and sugars is less. This adaptive behavior of horses reassures us about their resilience to adverse conditions. Daily eating of carbohydrates and fat does occur, but the word “essential” is not required when discussing these nutrients.

Key Points:

1. Horses make glucose by converting amino acids and lactate via gluconeogenesis. Therefore, glucose is not an essential daily nutrient in horses.
2. Glucose sources for horses are starch and free sugars found in forage and seeds of plants.
3. Protection from free glucose is necessary because glycation from unbound glucose will damage the proteins it touches. The methods used are binding glucose to insulin, storing it as glycogen, breaking it down via glycolysis, and converting it into a fatty acid.
4. Glucose can cross the cell membrane using the insulin-dependent GLUT-4 transporter. It also uses insulin-independent transport across the blood-brain barrier. Additionally, glucose can move without insulin into muscles when they are exerted.
5. Lack of glucose availability in the brain may precede brain illnesses. 
6. A catabolic crisis can occur during starvation when no dietary glucose is available. Paradoxically, excess dietary glucose causes insulin to hoard glucose, making it unavailable, which also causes protein loss.
7. Increasing body fat is evidence that excess glucose is being consumed, among other reasons.
8. Fat (fatty acids) are consumed in forage but are predominately made by the hindgut bacteria when they break down cellulose. There are no “essential” fatty acids in horses.
9. Fatty acids move freely in the blood and across cell membranes. They are stored in tiny fat droplets within cells.
10. Seed oils should be avoided in horse feeds. They can cause a leaky gut when bound to pieces of gut bacteria (lipopolysaccharides). In humans, these bound oils pass into joints, causing inflammation and stiffness. Older horses not fed seed oils reportedly move more freely.
11. Horses can go without eating sugars or fats for a while. When seasonal, avoidance helps them improve energy flux.