Timothy hay is an excellent source of roughage for equine diets. Horsemen often have to decide if they should purchase the first or second cutting of timothy hay for their horses. Many believe that the nutritional quality of first-cutting timothy hay is inferior to the second cutting. While this may be true in some cases, this assumption is really erroneous if first-cutting hay is harvested from a weed-free field at an early stage of growth before the stem becomes larger and coarser.
While timothy hay quality is influenced by many factors, including plant variety, weather conditions during growth and harvest, and day length, it is the stage of plant maturity that really dictates nutritional quality. First or second cutting doesn’t provide much information about plant maturity and thus, quality.
Timothy plant maturity can be visually determined by the number of seed heads present. Timothy grass in the vegetative stage will not have visible seed heads. But, how does plant maturity affect quality? As timothy matures, the plants pass from the vegetative stage, when they are producing leaves, to reproductive stages where the plants use energy stores to begin producing seeds instead of leaves. As a result, the stem-to-leaf ratio increases and nutritive quality decreases. During this time, the concentrations of structural components in the stem, including hemicellulose, cellulose, and lignin, are increasing, while crude protein levels are decreasing.
The best way to know the nutritional quality of timothy hay is to take a representative sample from the hay lot and send it to a laboratory for analysis. Analyses of timothy hay harvested at several stages of maturity are shown in Figure 1. When timothy is cut at the joint stage, the crude protein content is about 11%, but it is almost 30% lower when timothy is harvested at the full-head stage. Fiber content, which is reported as neutral detergent fiber (NDF) and acid detergent fiber (ADF), increases as timothy matures. Neutral detergent fiber is a measurement of cell wall content (hemicellulose + cellulose + lignin) and is an indirect measure of how readily a forage will be consumed. In general, forage intake decreases as NDF increases. Immature timothy hay (harvested at joint and pre-bloom stages) has lower levels of ADF than hay harvested at the full-head stage. Acid detergent fiber is a measurement of cellulose and lignin. Hay digestibility decreases as ADF increases. Bacteria in the horse’s hindgut can partially digest hemicellulose and cellulose, but they cannot digest lignin. For this reason, forage dry matter digestibility decreases three to four percent with every one percent increase in lignin.
Timothy hay is worth more to the horse owner when it is harvested at an immature stage of growth. It will have higher levels of crude protein and lower amounts of both NDF and ADF. The nutritional quality of timothy hay is not related to a particular cutting, but rather to the stage of maturity of the plant when it was cut. Absence of seed heads indicate that timothy hay is immature, but analysis by a laboratory is the only way to know the actual nutritional quality of the hay.
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