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Topics : Forage Quality & Testing : Putting Forage Quality in Perspective

Putting Forage Quality in Perspective

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Additional Forage Quality Information via the Forage Information System (FIS)


Ranking of Major Factors that Influence Forage Quality

Six major factors affecting forage quality (not yield), ranked by their impact on forage quality, include: 1) maturity, 2) crop species, 3) harvest and storage, 4) environment, 5) soil fertility, and 6) variety. The relative importance of each of these factors, along with some exceptions to the ranking, are described below.

  1. Maturity (harvest date). Maturity is the most important factor affecting forage quality. Forage quality is never static; plants continually change in forage quality as they mature. As plant cell wall content increases, indigestible lignin accumulates. In fact, forage plant maturity changes so rapidly that it is possible to measure significant declines in forage quality every two or three days.
  2. Crop species. Differences in forage quality between grasses and legumes can be very large. The protein content of legumes is typically much higher than that of grasses, and legume fiber tends to digest faster than grass fiber, allowing the ruminant to eat more of the legume.
  3. Harvest and storage. Improper harvest techniques can seriously reduce forage quality, primarily through the loss of leaves. Storing a hay crop at an incorrect moisture content, or improper ensiling of a forage crop, can dramatically lower its quality.
  4. Environment (climate). Moisture, temperature, and the amount of sunlight influence forage quality. Rain damage is very destructive to forage quality. When bad weather delays harvesting, the forage crop becomes more mature and hence lower in quality. High temperatures may increase lignin accumulation and decrease quality, but drought stress may actually benefit quality by delaying maturity.
  5. Soil fertility. Soil fertility affects forage yield much more than it does quality. While it is possible to produce high quality forage on poor, unproductive soils, it is generally very difficult to produce high yields of high quality forage with an unproductive soil resource. Proper soil phosphorus (P) and potassium (K) levels help to keep desirable legumes in a mixed seeding and also reduce weed problems. It is necessary to balance soil fertility to avoid mineral imbalances in ruminants. Low soil fertility, as well as very high fertility, has resulted in reduced forage quality.
  6. Variety (cultivar). After decades of breeding foraged for yield and persistence, attention has recently been focused on developing or identifying varieties with improved quality. Variety or cultivar can affect forage quality, but not as greatly as the other five factors. In alfalfa, selection for improved quality is underway by most commercial companies, and several U.S. firms have initiated selection in corn silage hybrids for improved forage quality.

Other factors affecting forage quality. Several lesser factors also can influence forage quality. Weeds can negatively affect quality, especially in the case of noxious weeds. Insect pests can lower forage quality, particularly if they cause significant leaf loss. Plant diseases can affect quality when they result in a shift in the species present in the field and when they promote leaf senescence. Insects and diseases generally have their greatest impact on yield and persistence of forages.

Exceptions to the ranking

Forage crops that accumulate a significant quantity of grain may increase slightly in overall quality with maturity as grain content increases in the plant. Some species contain antiquality factors that can lower animal performance. Variety can become the most important forage quality factor in cases where varieties are developed to significantly reduce or eliminate species antiquality factors, as in low-alkaloid varieties of reed canarygrass. Harvest and storage of a forage crop at a moisture content leading to spontaneous combustion would plainly become a most important factor. Or, if prolonged flooding or drought threatens a forage crop, environment becomes as important as any of the other factors. Certain soil fertility conditions, such as a very low pH, could eliminate alfalfa from a mixed seeding, thereby changing the species composition of the stand and greatly diminishing its quality.