Article: Burton Keakile
Forage quality is a function of nutrient concentration, intake, nutrient availability, and partitioning of metabolized products within animals. Of these factors, intake potential is the major determinant of production by animals fed forage-based diets. It is however one of the most difficult aspects of forage quality to determine or predict because variation among animals has a large influence on intake. Physical fill limits intake of forages with high cell wall concentrations when fed to animals with high energy demand. Hence, grasses, with their higher cell wall concentration, typically have lower intake than legumes.
Energy availability of forage is also limited by cell wall concentration because cell contents are almost completely digested, whereas forage cell walls are slowly digested. When crude protein concentration in herbage drops below 7% of dry matter, ruminal fermentation of forages may be limited and protein requirements of animals may not be met. Efficiency would be improved if a larger portion of forage protein passed from the rumen under-graded so that it can be degraded in the intestines where absorption is more efficient. Another important plant factor influencing forage quality is herbage maturity. Systems are now available for determining maturity of both legumes and grasses that will become more important as aids for predicting forage quality before forages are harvested or grazed.
Forage quality may also be influenced by the environment in which forages are grown and by soil fertility and these cause year-to-year, seasonal, and geographical variation in forage quality even when herbage is harvested at the same stage of maturity.
There are some factors that influence forage quality and they may include palatability, and this is where some animals will select forage based on smell, feel, and taste. Palatability may therefore be influenced by texture, leafiness, fertilization, dung or urine patches, moisture content, pest infestation, or compounds that cause a forage to taste sweet, sour, or salty.
A farmer may also know the quality of forage consumed by the animals from the amount of intake. Animals must consume adequate quantities of forage to perform well. Typically, the higher the palatability and forage quality, the higher the intake. Digestibility is one other way to check for the quality. This is to say the extent to which forage is absorbed as it passes through an animal’s digestive tract varies greatly. Immature, leafy plant tissues may be 80 to 90% digested, while less than 50% of mature, steamy material is digested.
Animal performance is the ultimate test of forage quality, especially when forages are fed alone and free choice. Forage quality encompasses “nutritive value” which is the potential for supplying nutrients, that is to say the digestibility and nutrient content, how much animals will consume, and any anti-quality factors present. Animal performance can be influenced by any of several factors associated with either the plants or the animals. Failure to give proper consideration to any of these factors may reduce an animal’s performance level, which in turn reduces potential income.
Legumes generally produce higher quality forage than grasses. This is because legumes usually have less fiber and favor higher intake than grasses. One of the most significant benefits of growing legumes with grasses is improvement of forage quality.
