by Paul D. Siciliano, PhD Colorado State University Fort Collins, Colorado

Hay makes up a significant portion (50 -100%) of the equine diet. It is a source of energy, protein, vitamins, minerals and, most importantly, fiber that is necessary for normal gastrointestinal function in the horse. The quality of hay, and therefore its nutritional value, varies considerably between different lots of hay. Understanding the factors responsible for variability in hay quality will increase the chances of getting the best value when buying hay.

Quality of hay can be measured in terms of qualitative and quantitative characteristics. Qualitative characteristics are most often visual appraisals. Quantitative characteristics are actual chemical measures of various nutrients and other components influencing nutrient amount and digestibility.

Qualitative measures
Two primary factors that influence forage quality are nutrient concentration and nutrient digestibility. Both of these are heavily influenced by the stage of maturity of the forage plant. Most of the highly digestible nutrients in forages are present in the leafy part of the forage. Less digestible components are present in the stem and other structural components of the forage plant. As a plant matures, the relative proportion of leaves to stem decreases. Therefore, the nutrient rich and highly digestible proportions of the plant decrease with age, while the less digestible and less nutrient rich components of the plant increase. The ratio of leaves to stems provides a simple visual measure of maturity that can be used as a relative estimate of digestibility and nutrient content when comparing different lots of hay. The degree of maturity can also be estimated by the appearance of the seed heads on grasses and flowers on legumes. When a plant becomes fully mature, its seed head/flower will be fully developed. Therefore, a lower proportion of fully developed seed heads/flowers is desirable.

These qualitative methods can provide some estimate of maturity that is useful for making comparisons between different lots of hay that are being considered for purchase. However, they do not provide any information regarding nutrient concentration. Furthermore, without knowledge of the appearance of different plants in various stages of maturity, the qualitative estimates (stem to leaf ratio and degree of seed head/flower development) can be inaccurate. Therefore, the combination of qualitative and quantitative measures (laboratory analysis) will result in selection of a hay that more closely meets the nutrient needs of your horse. Qualitative measures may be used initially to narrow down the choices to two or three different lots. Quantitative measures can be used to make a final decision.

Hay should also be examined closely for dust, mold and foreign material (plant or other).

Quantitative measures
The first step to having a hay sample analyzed by a forage testing lab (quantitative measure) is to obtain a representative sample. To properly sample hay, a core sampler should be used (figure 1). Core samplers can be purchased at most feed and farm supply stores. Several bales (10-20) should be sampled and then pooled for final analysis. The amount of forage sent to the laboratory for actual analysis is approximately one pound. It is important to choose a certified forage laboratory. Many forage labs can be found in the yellow pages under analytical laboratories or by calling 402-333-7485. The average cost for analysis is approximately $20.00.

Hay sample analysis generally takes one to two days. Most analyses include the following information: Dry Matter (DM) (percent DM = 100 - percent water), crude protein, minerals (calcium, phosphorus, potassium, magnesium, etc.), acid detergent fiber (ADF) and neutral detergent fiber (NDF). Vitamins and some minerals (e.g. selenium) usually cost extra and must be requested in addition to the standard analysis. If you live in an area of high selenium soils (e.g. Great Plains), you should have the selenium content analyzed to detect and prevent possible toxicities. The upper safe limit for selenium is estimated at 2 ppm. However, levels greater than 0.5 ppm should be cause for concern.

Although all of the analyzed items are nutritionally important, the key items for assessing forage quality are acid detergent fiber (ADF) and crude protein (CP). ADF is an indication of the cellulose and lignin content of a forage. Cellulose is a structural carbohydrate present in forages that has very low digestibility in the horse. Lignin is an organic compound present in forages which is essentially indigestible. It also interferes with the digestion of other nutrients. Therefore, the higher the ADF level, the higher the cellulose and lignin content and the lower the digestibility of a forage. ADF can also be used in conjunction with crude protein (CP) to determine a digestible energy (DE) value. The CP content and DE value are very important pieces of information when buying hay because energy and protein are the two primary nutrients supplied by hay.

Some analyses may contain estimates of the energy concentration of the hay, which are listed as Total Digestible Energy (TDN), Digestible Energy (DE), Metabolizable Energy (ME) and Net Energy (NE). These values are generally intended for use with cattle and should not be used for horses unless specifically stated that they have been calculated for the horse. If no energy concentration is listed on the analysis, then it can be calculated using percent crude protein and percent ADF with the following equation:

DE(Mcal/lb) = {4.22-0.11(%ADF)]+[0.03632(%CP)]+[0.00112(%ADF)2]}/2.2

Requirements
The hay that is purchased should meet the horse's requirements. Table 1 lists a range of crude protein and ADF values suitable for meeting the nutrient requirements of various classes of horses.

Table 1. Crude protein, acid detergent fiber and neutral detergent fiber requirements for various feeding classes of horses (expressed on a 100% dry matter basis).

Evaluation of nutrient content and digestibility of forages using both qualitative and quantitative techniques enables the horse owner to select the best value hay related to cost and nutrient requirements, thereby enhancing feeding efficiency.

Dr. Paul Siciliano is an Assistant Professor of Animal Sciences specializing in Equine Nutrition. He completed his BS in Animal Sciences at The Ohio State University and received his PhD in Equine Nutrition from the University of Kentucky. He joined the Colorado State University faculty in January of 1996. Dr. Siciliano's research focuses on the nutrient requirements of the growing horse.