Forage quality is a relative term. From a nutrition perspective, forage quality relates to the feeding value of the hay, or the ability to convert hay into milk, meat, and fat. Forage quality is a function of both forage intake and digestibility increase. Like all living organisms, plants are composed of cells. Cell wall content is the most important factor affecting forage utilization and, thus, forage quality.
Fiber analyses can indicate the cell wall content of hay.
Low-quality hay has a high proportion of cell wall material, and the cell walls are composed of a relatively large amount of indigestible compounds, such as lignin. Lignification of the cell wall, which occurs as hay plants mature, is the primary factor limiting forage digestibility. Not only is high-quality hay more nutritious, but it is also more palatable and digestible. Therefore, animals consume it in larger quantities. Supplements can only partially compensate for low-quality hay in the diet.