As forages mature, portions of the plant (cell) wall increase in thickness due to the buildup of fibrous carbohydrates that are less digestible. As the plant becomes more mature, the stem makes up a higher percentage of the total plant area. The more nutritious leaf (legume) or blade (grass) makes up a proportionally small amount of the forage. With maturity, although more total forage is yielded or harvested, it will contain less digestible energy, protein, and fiber, resulting in a lower nutritional value.