Hay used to be widely viewed as having little or no nutritional value beyond being a source of fiber which provided horses with chew time and made them feel full between meals. That has largely changed but even those who recognize hay’s place in the diet may not appreciate how really vital it is.
If you think commercial grain mixes are the most important thing in your horse’s diet, think again. Let’s say your horse is in moderate to heavy work. If you follow the feeding directions of a top of the line 14% protein feed you will supply 40 to 45% of your horse’s protein needs using NRC guidelines (which may be too low). Where does the rest have to come from? The hay.
Substituting grain calories for hay calories always cuts protein intake. Grain mixes have easily 2.5 times more calories than hays so to equal them in protein they would also have to have 2.5 times more protein. A good quality grass hay is typically around 10% protein but commercial grains are 14% tops for premium products, not 25%.
Vitamins and minerals aren’t as expensive as protein and feeds do better there. The top of the line feeds provide at or close to the minimum recommended intake of correctly balanced minerals, vitamin A and vitamin D when fed at the full recommended amount. The A and D are not necessary with a quality hay. The minerals would be a nice insurance package if minerals in hays were also balanced. The fact is that while hays can also provide minimums or more of many minerals, they are rarely, if ever, balanced and the feeds do nothing to correct this. These imbalances can interfere with absorption.
The B vitamins come predominantly from bacteria in the intestinal tract, as well as hay. The horse can manufacture vitamin C and if more is needed it will have to be supplemented separately since C in a grain mix is not stable. Neither is vitamin E and this too needs to be supplemented separately.
Hays lose about half the fat that was present in the fresh grass when they are cured. Commercial grains certainly add plenty of fat but it’s the wrong kind. The fat lost in curing is the omega-3 fatty acids which are not stable in a grain mix and need to be supplemented separately as flax or flax and Chia.
The energy that comes from hay has unique advantages. Unlike starch and sugar calories, which peak quickly then bottom out, fermentation of fiber and complex plant carbohydrates that are not digestible in the small intestine produces a steady, uninterrupted flow of volatile fatty acids (VFAs). The horse uses these VFAs to fulfill a large percentage of his calorie requirements.
Acetate is the major VFA produced from hay. It is immediately available as an energy source to be burned in the mitochondria. Aerobic (with oxygen) generation of energy in the mitochondria is the most efficient pathway. Glucose and fatty acids can also be burned this way but require processing first. Acetate can enter the reactions “as is”. Because it substitutes for glucose, glucose can then be used to keep blood levels up or replace glycogen after exercise and glycogen is not broken down as quickly during work when acetate is available.
Propionate is another VFA. Propionate feeds the organisms in the bowel and is converted by the horse’s liver into glucose. Glucose will be released into the blood if needed or stored as glycogen. The VFA butyrate is an important fuel for intestinal lining cells and directly stimulates cellular turnover. It also has a stimulating effect on the immune system and favors the growth of beneficial organisms over pathogens in the intestinal tract.
In summary, hay of good quality can meet or exceed protein needs. It has a full complement of vitamins except E, which drops with curing and storage. It is a major mineral source but will need some supplementing and balancing because domestic horses do not have the same plant variety in their diets. VFAs from hind gut fermentation are a source of calories and provide unique health benefits. Hay also satisfies their drive to eat almost continuously, for digestive and behavioral health.
It’s much more than just fiber.
Eleanor Kellon, VMD