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Competency Area 7: Forage Harvesting Factors

PO 29. Know the optimum development stage for first cutting of alfalfa or perennial grasses.
A. Know the basic procedures for evaluating forage quality of grasses and legumes,
B. Know the ideal forage quality (NDF, ADF, CP, etc.) for alfalfa and perennial grasses.

A.) Know the basic procedures for evaluating forage quality of grasses and legumes.

A number of quality indicators, such as total fiber (NDF), digestibility, fiber digestibility, protein, and Relative Forage Quality (RFQ), are useful for evaluating the quality of a harvested forage. Animal rations can be relatively easily balanced to make up for a shortage of energy or protein, but not fiber. Therefore, forages should be harvested at the optimum fiber content (NDF) for the class of livestock being fed. Morphological stage in alfalfa is a NOT a good indicator of forage quality. Morphological stage in grass is a good indicator of forage quality at later maturity stages, but once the inflorescence emerges from the boot in grasses, optimum forage quality is lost. Spring alfalfa quality is best predicted using the PEAQ equations (Predictive Equations for Alfalfa Quality) developed in Wisconsin, that are based on the maximum height of alfalfa and the maximum growth stage.

 

The best estimate of harvest time for pure grass is less precise and is often based on calendar date (e.g. the last week of May in central NY). This will be between early and very late boot stage. Spring harvest of alfalfa-grass mixtures is based on alfalfa maximum height and the proportion of grass in the stand.
Estimated stand NDF of a mixed alfalfa-grass stand based on alfalfa height and the percent grass in the stand.

B. Know the ideal forage quality (NDF, ADF, CP, etc.) for alfalfa and perennial grasses.
Ideal forage quality is a function of the class of animal being fed the forage. For lactating dairy cattle, standing alfalfa in the field prior to harvest should be 38% NDF. At this stage CP (crude protein) will be approximately 19-20%. For pure grass stands, ideal NDF is approximately 50%. A lower NDF value would be associated with insufficient forage yield for a grass harvest. Grass should have sufficient N fertilization to result in CP of 17-18% at harvest. Optimum NDF in alfalfa-grass mixtures is a function of the proportion of grass in the stand.

Spring harvest of alfalfa-grass mixtures are based on the proportion of grass in the mixture.

Management to produce dry cow forage

  1. Regular soil testing.
  2. Set aside fields lowest in K.
  3. Avoid all forms of K fertilizer, including manure.
  4. If production declines, include some K fertilizer.
  5. Harvest spring grass after flowering.
  6. Use grass re-growth (lowest in K) for cows just prior to calving.