The quality of the forage in any given pasture is a function of three separate but related factors; the kinds of plants present, their stage of maturity, and the time of year. Generally, the leaves of legumes are higher in quality than the leaves of grasses, grass leaves are almost always of a higher quality than the stems of either legumes or grasses, and young green leaves and stems are higher in quality than those that are old and dead brown. As a rule, the younger the plant or plant part, the higher the quality. Conversely, as individual plants or plant parts increase in age, they tend to decrease in quality.

While most pasture plants in the actively growing or vegetative stage are comprised primarily of leaves, as they progress through their normal growth and development stages to maturity, the proportion of low quality stems and dead leaf material increases while the proportion of high quality green leaf material decreases. As a result, pasture quality tends to be higher in the spring and fall as compared with midsummer.