Nutritional needs of horses fed all-hay diets.

Can we meet the nutritional requirements of horses with hay alone?

An article by William Schurg P.H.D, Department of Animal Sciences, University of Arizona.


Feeding and general nutritional needs are probably the most important factors affecting the proper development, maintenance and reproduction of the horse. Furthermore, feed constitutes the single greatest cost item in owning horses. Since the horse is an athlete, owners must feed them as such, but can the nutritional needs of the horse be adequately supplied by hay alone?

All horses are herbivores, that is animals made to live primarily on plants or forages. Approximately 65% of the digestive tract capacity of the horse is in the lower gut, which includes the cecum and colon. The cecum and colon contain many microbial populations which allow for the digestion of fibrous feeds, similar to cattle and sheep. Since the horse possesses this large fermentation vat in a vast lower gut, the horse is designed to utilize great amounts of forage in their diet. Horses that are fed adequate amounts of forage normally will have fewer digestive upsets and behavioral vices.

Horse rations that are based primarily on hay under most circumstances will be more economical than using extensive amounts of concentrate feeds to provide nutrients. Regardless of the feedstuff used, a horse requires an absolute amount of nutrients daily. For proper digestive tract function, horses should be fed a minimum of 1% of their bodyweight per day in long-stem dry matter. It is know that when the particle size of the total ration is below 1” in size, increases are seen with behavioral vices and problems with rate of passage and digestion. Thus, using long-stem, good quality hay is imperative in any horse feeding situation.

The hay's value in terms of quality is determined buy the nutrient composition of the feedstuff rather than by its physical appearance. However one can estimate quality by looking at the hay and taking into account such factors as:

• Stage of maturity
• Relationship of leaves to stems
• Color, odor and the freedom of foreign materials.

Regardless, the actual nutrient composition will be the only true way to determine the quality of the feed. The closer the nutrient composition of the hay matches the requirements of the horse being fed, the fewer supplements that will be needed and the ration typically will be cheaper.

So, can we meet the nutritional needs of the horse by using hay alone? This question can be answered by saying that depending on the use or classification of the horse, hay alone may supply 50-100% of the horse’s needs. Horses will normally consume from 1.5-2.5% of the body weight daily in dry matter. This intake will be dependent upon the quality of the forage available. Older more mature forage with higher fiber values limit intake and require that more nutrients be provided in the form of concentrate supplements. The five nutritional classifications of horses are:

• Maintenance
• Pregnancy
• Lactation
• Growth
• Work

For this article, I will explore meeting the needs of the horse at maintenance and lactation only when fed a hay alone diet. Maintenance is defined as maintaining body weight. The animal is typically mature and not pregnant, lactating, breeding or being worked. This class of horse can often meet all of its requirements with forage alone.

The minimum requirements are 8-10% crude protein, 0.3% calcium, 0.2% phosphorus and 1Mcal of digestible energy per pound of the total ration. Lactation occurs in mares during the first three months after foaling, and mares can be expected to produce milk equivalent to about 3% of their body weight per day and 2% per day during months four to six.

The requirements for energy are about 80% above maintenance for the first three months and 50% above maintenance for the next three months of lactation. Minimum requirements during the first three months of lactation are 14% crude protein, 0.6% calcium, 0.4% phosphorus and 1.2Mcal of digestible energy per pound of total ration. Thus you can easily see how much the nutrient needs change when we add lactation onto the maintenance horse.

In the example below we will be feeding a typical 1,000 pound maintenance mare whose requirement for energy is 15.5Mcals per day and who requires 1.32 pounds per day of protein. This horse will be fed 16.5 pounds of either Bermuda grass, alfalfa or a 50-50 mix. In this example: Bermuda grass alone meets 99% of the maintenance horse’s need for energy and 150% of the protein need. Alfalfa provides 115% of the energy and 218% of the protein need. The mixed hay provides 107% of the energy and 184% of the protein requirements.

As you can see, for the most part hay alone , regardless of the type, adequately provides the energy and protein needs of the adult mare as long as the hay source is very good quality! In these examples, the nutrient composition of the Bermuda grass hay is 0.9Mcal/lb digestible energy with 12% crude protein, and the alfalfa hay contains 1.05Mcal digestible energy with 17.5% crude protein. These would be very acceptable hay compositions. Horse owners should be aware that hay may well be considered lower in quality than what is described above, thus the need for various types of supplementation.

The second example will to be to feed the lactating 1,000 pound mare an all hay diet using the same types of hay as in example one. This time, due to her lactation function, she will be consuming about 22 lbs of hay daily. An all Bermuda grass hay diet for this animal will only meet about 76% of the mare’s energy needs and 91% of her protein needs, thus the use of some concentrate supplements is appropriate. When we feed her an all alfalfa diet, it only meets 89% of her energy requirement, but more than adequately meets her protein requirement. The mixed hay again falls short of meeting the energy needs at 82%, but will meet the protein requirements.

Typically, horse owners can balance these all hay based rations with a variety of feedstuffs. The important consideration is to base the ration on the nutrients provided in the base forage being used. One should balance the ration to meet the nutrient needs of the horse by using the most economical sources of these nutrients. Local costs of hay and grain supplements vary greatly, thus it is critical that the horse owner evaluate their rations and calculate costs.

So, can we meet the nutrient needs of horses by using diets of hay alone? Yes. But we must take many things into consideration to use feedstuffs of high quality. Lastly, remember to feed your horse by weight and not by volume, feed regularly, don’t feed moldy or dusty feed, inspect the feed box for cleanliness, feed horses as individuals, provide proper amounts of exercise and grooming and keep clean, fresh water available at all times.

Some general rules of thumb for feeding horses follow:

• Feed alfalfa and/or grass hay at about 1-1.5lbs/100lbs BW daily for maintenance and for the non-breeding stallion or mare during the first 8 months of pregnancy.
• Grain is only necessary to maintain condition or meet a specific requirement. During working regimes and lactation, feed grain in addition to the hay recommendations at:
  
  Maintenance: (0-0.5 lbs/horse/day)
  Light Work: (0-0.5 lbs/horse/day)
  Medium Work: (2-3 lbs/horse/hour of work)
  Heavy Work: (4 or more lbs/horse/hour of work)
  Lactation: (0-0.5 lbs/100 lbs BW/day fed with 2-2.5% BW hay daily)

Reprinted with permission: University of Arizona Dept of Animal Sciences, 2002.