Forage for Horses

By J. Kathleen Young, Ph.D

Why should horse owners be concerned about forages for their horses? Horses need to be fed at least one percent of their body weight daily (dry matter) as forage. Most horses are fed more than that; many receive two or more percent of their body weight per day in grass or hay. This means that a 1000 pound horse may easily eat 15-20 pounds per day of hay, along with 3-6 pounds of a grain ration. When problems occur that may relate back to nutrition, people usually look at the grain ration. However, when the vast majority of the horse’s diet is hay or grass, we must pay more attention to the important nutritional role that the forage plays in the horse’s nutritional status.

Quality of Forages

There are several factors that affect the quality of hay, therefore the nutrient content. The higher the quality of the hay, the better the horse’s digestive tract is able to digest and absorb the nutrients contained in the hay.
The factors that affect the quality of the hay include plant species, fertilization, maturity at time of harvest, season at which hay is harvested, climate conditions, storage conditions, and age (time since cutting). The maturity of the plant at time of harvest determines the hay quality more than any other factor. Young, leafy, immature plants contain more protein, energy and minerals than older, stemmier plants. As a plant matures, it contains more indigestible fiber (lignin), therefore is less digestible for the horse, as well as containing less protein, energy and minerals. To ensure high quality hay, plants should be harvested at the proper stage of maturity, for instance, timothy should be cut in the pre-bloom or early-bloom stages for the highest nutrient content.

Plant species (e.g. grass vs. legume) has an impact on the nutrient content of the hay, but not as much as most horse owners believe. The maturity of the plant when it was cut has much more influence. Alfalfa tends to have more protein, energy and calcium than grass hays, but research has shown that a good quality grass hay may provide more nutrients than a medium or low quality alfalfa because the higher quality grass hay is more digestible (less fibrous). For example, for protein to be of value to a horse as amino acids, it must be digested and absorbed (as amino acids) in the horse’s upper gut (stomach and small intestine). Since the fiber in hay can only be digested by microbes in the horse’s hind gut, the more fiber in the hay, the more that hay is digested in the hind gut. In one study, when horses were fed medium quality alfalfa hay, only 2% of the protein was digested in the upper gut. This means that 98% of the protein was of no benefit as amino acids to the horses. Horse owners sometimes feel that alfalfa is always a better choice for horses than grass hays, but that is not necessarily true. Further, high quality alfalfa may not provide enough fiber to maintain a healthy hind gut in the horse. A certain amount of indigestible fiber (bulk) is necessary to ensure the health of the microbes in the hind gut, as well as helping to maintain proper motility in the hind gut.

Fertilization primarily affects yield per acre rather than nutrition of any one bale of hay. The season at which the hay is harvested affects quality in that digestibility is highest for forages harvested in the spring, somewhat lower in mid to late summer, and then it rises slightly in autumn. Climate conditions, such as excessive moisture or drought can affect the quality of hay, especially since climate conditions can affect when the hay is cut. Often the plants become more mature than optimum because climate conditions are not conducive to harvesting at the best time.

Storage conditions and age (time since cutting) primarily affect vitamin content of hays. Many vitamins are not very stable over time and lose biological activity. Environmental conditions such as heat, sunlight and rain can hasten the loss of vitamin activity in hay.
Characteristics to look for in choosing high quality hay include:
· High leaf to stem ratio (indicates less mature plants)
· Small diameter stems (less mature plants)
· Fresh smell and appearance
· Cleanliness
· Color (faded, yellow or brown color may indicate aged hay or poor storage conditions)
· Few seed head or blooms (less mature plants)
Hay analysis may provide more information, but the results need to be interpreted with caution. For instance, the crude protein determined by analysis does not indicate the site of digestion in the horse. A hay that tests high in crude protein and also high in acid detergent fiber (ADF) is not well digested in the horse’s upper gut, thus the amino acids from the protein are not readily available for absorption in the upper gut. A hay with lower crude protein and lower ADF may actually provide more nutrients, including protein, energy and minerals to the horse.