by Jim Morrison, Extension Educator Crop Systems
Forage quality can be defined as the extent to which a forage has the potential to produce a desired animal response or level of performance (for example, daily gain or milk production).
Forage quality is a function of voluntary intake and nutritive value. The forage quality need of an animal depends upon its age, sex, and production status. It is a simple concept, but yet encompasses much complexity.
Let’s take a quick look at the major factors that influence forage quality.
Species differences. Legumes generally produce higher quality forage than grasses. This is the result of less fiber in legumes and thus intake will be higher when legumes are consumed. Cool-season grass species (orchardgrass, bromegrass, perennial ryegrass, etc.) are generally higher in quality than warm-season grasses (bermudagrass, switchgrass, corn, etc.). Digestibility and crude protein are typically higher in cool-season grasses than in warm-season grasses. Warm-season grasses convert sunlight into forage more efficiently than cool-season grasses, but their leaves contain a higher proportion of highly lignified, less digestible tissues.
Maturity stage. Maturity stage at harvest is the most important factor determining forage quality of a given species. Forage quality declines with advancing maturity. Reduced leaf-to-stem ratio is a major cause of the decline in quality with maturity. Leaves are higher in quality than stems, and the proportion of leaves in forage declines as the plant matures. Maturity at harvest also influences forage consumption by livestock. As plants mature and become more fibrous, forage intake drops dramatically. The intake potential decreases and neutral detergent fiber (NDF) concentration increases as plants mature. This is because NDF is more difficult to digest than the non-fiber components, thus digestion slows greatly as forage becomes more mature.
Harvesting and storage effects. Leaf shatter, plant respiration, and leaching by rainfall during field drying of hay can significantly reduce forage quality, especially with legumes. Rainfall during curing damages legume leaves the most. Damage from rain increases as forage becomes dryer, and is especially severe when rain occurs after the hay is ready to bale. Quality losses also occur due to weathering, plant respiration, and microbial activity during storage. In high rainfall areas, losses can be large for round bales stored outside, due to the weathering of the outer layers.
Secondary factors that affect forage quality include soil fertility and fertilization, temperatures during forage growth, and variety.
The ultimate measure of forage quality is animal performance. This winter, plan your strategies for producing the forage quality needed in your operation. Additional information is found in the publication entitled “Understanding Forage Quality”, available at Extension offices.