Hay Quality

By Donna Foulk, Extension Educator, Penn State Cooperative Extension 

Forage is a very important part of a horse’s diet.  The horse evolved as a grazing animal with a digestive system designed to process a nearly continuous supply of high fiber food.  A horses’ nutritional program should focus on forage first. A horse has fewer digestive upsets when forage is the main component of the ration.  Grain concentrations and supplements should be used when necessary to complement the forage.

All commercial hay falls into one of two categories – grass or legume.  The most common types of grass hay are timothy, orchardgrass, or brome.  Canarygrass and endophyte-free varieties of tall fescue are also used to produce grass hay.  Alfalfa and clover are examples of legume hays.  Legumes have nodules on the roots that allow plants to utilize nitrogen from the air in the production of protein.  Legume hays are generally higher in protein and calcium than grass hays of equal maturity.

Hay varies greatly in protein levels and digestible nutrients and therefore an understanding of hay quality is critical in developing a sound nutritional program.  Grain rations are formulated at protein levels of 10% to 16% to match the needs of individual classes of horses, but hay can range in protein from less than 5% to over 30%.  Many factors influence hay quality and no one factor can be used to make prediction about nutritional value.  Health of the stand, soil fertility, weeds and pests in the field, forage species and variety, maturity of the plant at harvest, drying and baling conditions, and how the hay is stored all contribute to hay quality. In general the type of hay selected is not as important as when and how the hay was produced.  All types of hay can be low or high in quality depending on when and how the hay was made.

The maturity of the plant at harvest is an important indicator of hay quality.  In early spring, forage plants are in a vegetative stage and are young, leafy, and high in protein and digestible nutrients. Grass hay in the vegetative stage can contain protein levels as high as 20%.  As the hay plants begin to mature and produce a seed head or flower, the carbohydrates and other nutrients in the plants are converted to cellulose and lignin, structural materials that allow the plant to stand tall and disperse seeds.  Structural materials are not readily digested by horses and supply little nutritional value.  The food value of the plant declines as the plant ages. Protein levels can drop to less than 5% if the plant is overly mature when the hay is cut.

The seed head is a good indicator of plant maturity.  In the vegetative stage, seed heads are absent and protein levels will be as high as 20%. By the time the seed head starts to emerge (early heading), the protein level will have declined to about 11%. Seed heads at early heading are small, soft, and tight.  If the hay is not cut at early heading, the plant will continue to mature. The seed heads become large and coarse. Protein levels in overly mature hay will fall below 6% and the hay will be high in fiber. 

After the first cutting of hay is harvested, the plants regrow but will remain vegetative and will not produce seed heads.  Second and later cuttings of hay are leafy, lower in fiber, and generally higher in protein and digestible nutrients. The hay is more easily digested by the horse and more readily consumed. Therefore, second cuttings of hay are ideal choices for growing foals, horses in heavy training, older horses, and horses that are difficult to keep weight on.

Legume hays follow the same progression in protein loss through maturity.  Alfalfa will fall to protein levels of around 11% when past bloom and can exceed 30% protein in later cuttings that are harvested pre- bloom. Although alfalfa can safely be fed to horses, the high protein, and nutrient levels in later cuttings of alfalfa exceed nutrient recommendations.   The unused protein is excreted as ammonia in the urine of horses. Excessive calcium levels in alfalfa may require phosphorous supplementation for growing foals.

Lack of insects and weeds is another important factor in forage quality.  Weeds can be difficult to dry and cause hay to mold in storage.  In addition, weeds that are toxic in the field will retain their toxic properties when dried in hay.  Blister beetles are found in warmer climates and can be baled in hay causing serious health consequences for horses. The insect contains the toxin cantharid which is very irritating to the horses’ digestive tract. Other frequently encountered insects like aphids, cereal rust mite in timothy, and weevils and leaf hoppers in alfalfa do not present a health problem for horses but may present production challenges for farmers.

One of the single most important factors in evaluating hay quality is lack of mold.  If hay is baled at high moisture levels, in the range of 20 to 35%, molds grow as the predominant microorganism in hay.  Mold is undesirable because molds consume nutrients, carry on respiration that can cause heating and fires, and produce toxins and spores that are detrimental to horse health.  Moldy hay should not be fed to horses.

Conditions at harvest also influence hay quality.  Plants continue to carry on respiration after being cut, which reduces the sugars and carbohydrates in the hay. The longer the hay lies in the field, the greater the loss of nutrients becomes.  If hay is rained on after it is cut, the soluble nutrients can be leached from the hay. The quicker the hay is dried and baled, the less loss of nutrients that occurs. Good environmental conditions (hot and windy days with low relative humidity) and management techniques that allow for quicker baling of hay, (use of mower conditioners, drying agents, preservatives, and hay dryers) can minimize loss of quality. Bright green hay is higher in vitamin A and is an indicator that the hay was cut and dried quickly. 

Visual appraisal based on smell, sight, and texture is the most commonly used method of selecting hay but is not always an accurate indicator of hay quality.  Sugar and starch levels in have vary greatly based on environmental conditions such as sunlight, temperature, moisture, and humidity when the hay was made. Many forage testing laboratories will provide an analysis of a hay sample for a nominal fee. Grain concentrates and supplements can then be chosen to offset any deficiencies in the forages. Local Cooperative Extension offices can supply a list of forage testing laboratories.

When choosing hay for your horse, remember to match the quality of the hay to your horse’s nutritional needs. High quality hay is not always the best choice for all horses. A heavy milking brood mare or a horse in heavy training may benefit from a diet of second cutting alfalfa or alfalfa/grass mixed hay that is high in nutrients and protein and low in acid detergent fiber.  Many pleasure horses and “easy keepers” would be best maintained on a diet consisting of a first cutting grass hay that supplies adequate levels of protein without too many calories.