Hay Quality

Martin W. Adams, PhD, PAS - Equine Nutritionist for Southern States

Good quality hay or pasture should make up at least half of most horse’s diets. Horses will readily eat many types of grass and legume hay, especially if it is of high quality. The most common problems that horse owners have when purchasing hay are finding a dependable and consistent supply and determining if it is good quality for their horses. Cattle have a different digestive system than horses, and can break down fibrous material with greater efficiency, so they can utilize lower quality or more fibrous sources of hay. Horses consuming poor quality hay cannot digest it well enough to maintain body weight and are at greater risk for impaction colic. So make sure you can determine if the hay you purchase is “horse quality” instead of “cow quality”.

There are two main methods to determine the quality of hay for horses; evaluation of physical factors and chemical factors. Physical factors that horse owners can use to determine hay quality are maturity, color, smell, species, and leafiness.

The maturity of the plant is the single most important factor that influences the nutrient content and quality of hay. As the forage plant matures, protein, leafiness, energy digestibility and intake decrease because the amount of fiber, lignin and stem of the plant increases. Legume hay (alfalfa, clover, etc.) that is past full bloom, and grass hay (timothy, fescue, orchard grass, etc.) that has already formed a mature seed head, are usually too mature and poor quality to make acceptable hay for horses.

The vitamin A precursor, carotene, is responsible for the bright green color of freshly cut hay. After forage is harvested for hay, prolonged storage time and exposure to sunlight will reduce the carotene content of hay and reduce the green color. While color is not always a reliable indicator of hay quality, for example, bright green weeds in a bale of hay may have a lower nutrient content than the brown hay that is more nutritious, it is usually indicative of a short storage time and good quality. Hay bales with some beige to yellow color on the outside are likely sun-bleached and still good quality. Hay with an overall yellow color could be very mature and resemble straw, which would be poor quality hay. Another situation could be hay that was rained on excessively after harvest and many nutrients leached out, this hay would likely not have a green color and be very poor quality. Hay with black or white powdery spots could be mold, and should be inspected more closely as toxins produced by some plant molds, or mycotoxins, can cause colic and respiratory problems in horses that consume them. Moldy hay should not be fed to horses.

Good quality hay will have a pleasant, sweet aroma. Hay with a musty, moldy or sharp smell is likely to have heat damage or mold from being harvested without being dried properly. Heat damaged hay will have less digestible protein but is not harmful to the horse's health. Moldy hay can cause sickness in horses due to the presence of mycotoxins (mold toxins), so if a bale doesn't smell right, don't feed it to your horse.

Legume hays tend to contain higher levels of protein, energy and calcium than grass hays of the same maturity stage. Legume and mixed hays would be recommended over grass hays, for performance, lactating and growing horses as their nutrient requirements are greater.

Leaves contain more digestible nonstructural carbohydrates, protein, minerals and vitamins than stems. When forage plants mature, the leaf to stem ratio decreases, and nutrient values decrease. Hay with a greater leaf to stem ratio, and with smaller leaves and small, fine stems (indicating a earlier harvest or cutting date) will have a higher calorie and protein content due to a less mature state.

The only way to be certain of hay quality is to have it analyzed for chemical factors. Chemical factors that are used to evaluate hay quality include crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), total digestible nutrients (TDN), relative feed value (RFV), and digestible energy (DE). These values can be determined by sending a sample of hay to a laboratory that performs nutrient analysis on hay. A basic hay test analysis will cost $10 to $15 per sample and will usually include CP, calcium, phosphorus, ADF, NDF and some measure of energy value, such as TDN, RFV or DE. Most state land grant universities have an extension service that has a laboratory testing service available to test hay, and there are also private companies that provide this service. For a complete list of certified hay testing laboratories go the National Forage Testing Association’s web site at www.foragetesting.org.

ADF is a measure of hay indigestibility. The test for ADF includes the plant cell wall components cellulose and lignin. The greater the ADF value, the less digestible the hay fiber is, and the lower the calorie content available for the horse. NDF is a measure of the entire plant cell wall and measures the amount of cellulose, hemicellulose and lignin. NDF is a measure of forage intake. As the value for NDF is increased, consumption of hay is limited or decreased. Less mature hay provides more calories to the horse because a greater amount can be consumed (lower NDF content) and because it has greater digestibility (lower ADF content). The greatest concerns about poor quality hay, besides the fact that the horse may not be able to eat enough to maintain his body weight, is that consumption of poor quality hay is correlated with a greater incidence of impaction colic, especially when the horse is dehydrated.

RFV is an index of the relative value of hay based on its ADF and NDF values. It was developed as a convenient and less technical method for beef and dairy cattle owners to decide on purchasing hay for their animals’ feed needs. The value for horse owners is not as great, but sometimes these values will be provided on a laboratory analysis report when a hay sample has been submitted for testing and it can be used as a general guideline. A higher RFV represents a higher quality or more nutritious forage for horses.

TDN or total digestible nutrients is based on an older system of analysis that reports the percentage of digestible material in the forage. A larger value or percentage indicates greater calorie content, and this would be indicative of higher quality forage.

DE or digestible energy provides the energy content of the forage in megacalories (Mcal) or kilocalories (Kcal) per pound. A higher DE value would be more desirable and would indicate less mature and more nutritious forage, with less hay needed to maintain body condition, growth rate or milk production of the horse.

Table 1 lists quality estimates for legume, mixed and grass hay for horses. Average quality grass hay will test 8% to 14% CP and contain at least 850 Kcal per pound. Any class of horse could utilize average quality grass hay well, and commercial horse feeds can provide sufficient amounts of protein, energy, vitamins and minerals to balance the horse’s nutrient requirements. But performance, lactating and growing horses would benefit more from higher quality hay due to their higher protein and energy requirements, and less supplemental feed would be required. Avoid low quality hay of any type for all horse classes, but especially for performance, lactating and growing horses.

Table 2 lists quality standards for hay that have been developed by the American Forage and Grassland Council. Categories of Prime, 1, 2, 3, 4 and 5 are given and values for CP, ADF, NDF and RFV are listed. Hay that is tested and compared to these guidelines, or sold according to these guidelines, should have a rating of no less than 3 on this table if intended for use by horses. A quality standard of 3 will have a CP value of 11% or greater, a maximum ADF value of 42%, a maximum NDF not greater than 60%, and a RFV of at least 100.

Table 3 lists the marketing grades for grass hay, which has grades 1 through 4, with 1 being the most desirable. Grass hay purchased for horses according to these marketing grades, or laboratory values from hay samples compared to this table should be from grades 1 through 3. Hay for horses with tested CP values of less than 8%, ADF values greater than 41% and NDF values greater than 65% should not be fed, due to low energy content, poor intake and increased risk of impaction colic. A good rule of thumb is to use the 8/40/60 rule, only purchase hay that tests 8% crude protein or more and less than 40% ADF and less than 60% NDF, all on as fed basis.

Table 4 shows the marketing grades for legume hay, with grades 1 through 4, with 1 being the most desirable. Like with grass hays, legume hay to be purchased for horses according to these marketing grades, or laboratory values from a hay sample using this table for comparison should be from grades 1, 2 or 3. Although CP values for legume hay in grade 4 are relatively high compared to grass hay, legume hay at this market grade has very large stems and high NDF values, and is not very palatable to horses. This would result in poor consumption and difficulty in maintenance of body condition, especially for younger horses.

Hay Buying Tips

• Don’t buy hay with excessive dust or a musty smell. These can indicate mold formation and the presence of mycotoxins, which could be harmful to your horse.
• Purchase hay from a recommended source or supplier, preferably from someone who can provide a laboratory analysis of the hay.
• Buy as much hay as possible at one time to provide a consistent supply to minimize changes in your horse’s feed supply. See if the hay supplier will sell you a few bales that you can inspect and feed to your horses before making a larger purchase.
• Grab a handful of the hay and give it a hard squeeze. If it hurts your hand, it is too stemmy and mature to be good quality horse hay.
• Look for seed heads in grass hay, if they are numerous, large and well-formed, and there are large stems present, the hay is probably too mature and fibrous to be acceptable for horses.
• Inspect the bale and if you see a bright green color, and lots of small leaves and small stems, the hay should be good quality for horses.
• For legume hay, the presence of flowers and large stems are indicative of maturity and this may not be of acceptable quality for your horse.

Acceptable Forms of Hay

Hay is not just an important part of the horse’s diet, but is also needed to maintain normal chewing time and digestive health. A minimum 1½ inch particle size is important to minimize colic and abnormal behavior. Hay can be provided in the following forms:

Square bales. Small (40 to 80 pounds) square bales of hay are most commonly used by the horse owner. Square bales are comparatively easy to move and store and should be stored indoors or under cover to prevent weather damage.

Round bales. Large (800 to 1,200 pounds) round bales are more efficient to produce and can be used for horses. Storage of round bales should be indoors or on a well-drained base and covered with plastic. The use of a feeder that contains hay and controls wastage is recommended. Be sure that enough horses are consuming hay quickly enough to prevent wastage and molding to occur. Remove hay that has become moldy and in contact with the ground. Moldy hay can make horses sick from the formation of mycotoxins. Botulism poisoning is also more common with round bales due to the greater incidence of inclusion of dead rodents and increased contact of hay with organic material from soil contact.

Hay cubes. Cubes can be made from a variety of coarsely chopped hays, but the most common are alfalfa and timothy-alfalfa cubes. Advantages include less storage space and handling ease, and decreased feeding waste. Cubes have adequate particle size to maintain normal digestive health and prevent wood chewing, so they can be used to totally replace baled hay. Be careful when adapting horses to hay cubes, horses may consume them too quickly and choke. Feed hay cubes close to the ground so horses must chew hay cubes before swallowing. If you provide hay cubes as treats or add to other feeds in above-ground feeders, break cubes into small pieces or wet or soak cubes with water to soften them first to prevent choking.

Chopped hay. Hay chopped to a length of 1½ inch or more can be used to replace baled hay. Advantages are similar to hay cubes, with less storage space required, ease of handling, and decreased feeding waste. Chopped hay can be dusty and should be treated with a small amount of molasses or oil to decrease dustiness.

Pelleted hay. When fed as the only source of fiber, hay pellets don’t have adequate particle size to allow enough chewing time for normal digestive health and behavior for horses. Horses can have increased rates of impaction colic, obesity, and chew on wood, trees and other horse’s manes and tails when fed diets with only pelleted hay or total pelleted diets and no source of long-stemmed fiber.

Table 1. Quality Estimates for Types of Hay for Horses¹

¹Values are expressed on 100% dry matter basis.

Table 2. Quality Standards for Hay ^1,2

¹Hay Market Task Force of American Forage and Grassland Council.
²Values are expressed on 100% dry matter basis.

Table 3. Marketing Grades for Grass Hays ^1,2

¹Hay Market Task Force of American Forage and Grassland Council.
²Values are expressed on a 100% dry matter basis.

Table 4. Marketing Grades for Legume Hays ^1,2

¹Hay Market Task Force of American Forage and Grassland Council.
²Values are expressed on a 100% dry matter basis.