Forage Quality Considerations of Alfalfa Dr. Dan Undersander University of Wisconsin
Alfalfa Forage Quality Needs Protein Energy/fiber Anti-quality components of alfalfa
Protein in Alfalfa High protein content Dairy animals need about 19% in ration Protein supplementation has been cheap but not likely to continue Higher protein in alfalfa is of greater value as more other forages used in ration, especially corn silage (low protein)
Protein in Alfalfa High protein content Bypass protein Need certain amount of protein to avoid degradation in the rumen If new genetics increases amount of by-pass protein (as occurs in red clover) this could greatly increase alfalfa use in dairy rations.
Energy and Fiber of Alfalfa Low fiber and high energy Especially true of leaves
Forage Quality Changes with Advancing Maturity IVDDM (g/kg) 840 790 740 690 640 590 540 490 440 leaves 1981 leaves 1982 stems 1981 stems 1982 Leaves change little in quality Stems decline in digestibility -1 0 1 2 3 4 5 6 Weeks from early bud stage
Forage Quality Changes with Advancing Maturity Leaf:Stem Ratio 1.5 1.2 0.9 0.6 0.3 1981 1982 Leaf:stem ratio declines at the plant matures resulting in lower forage quality Need to reduce leaf loss 0-1 0 1 2 3 4 5 Weeks from early bud stage
Reducing leaf loss to increase forage quality can be accomplished by: increased leaf disease resistance reduced senescence reduced abscission of senesced leaves appropriate management during harvesting
Some Considerations of Alfalfa Digestibility Leaf Percentage (Weight DM Basis) Fig 1. Comparison of ADF to Leaf Content of Alfalfa in MN and UW Trials 80 75 70 65 60 55 50 45 40 y = -2.8419x + 155.58 R 2 = 0.659 30 32 34 36 38 40 Some varieties have greater leaf content Additional low fiber mechanism - some varieties have lower fiber in stems Acid Detergent Fiber (ADF)
Some Considerations of Alfalfa Digestibility Alfalfa changes daily in forage quality as it matures. Rainy weather may delay harvest and result in low quality. Slowing the rate of change of alfalfa quality with maturity would be of economic value to farmers.
Energy and Fiber in Alfalfa Low fiber and high energy Especially true of leaves Fiber Forms Some fiber types more rapidly digestible
Rate of Alfalfa Digestion dry matter digestion (%) 90 85 80 75 70 65 60 55 50 48h dig 24h dig 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 sample Higher intake level in dairy cattle causes forage to pass through the rumen faster, i.e. 24 hours for dairy, 48 hours for beef, dairy heifers Alfalfa germplasms vary greatly in their rate of digestion
Rate of Alfalfa Digestion dry matter digestion (%) 90 85 80 75 70 65 60 55 50 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 48h dig 24h dig sample Of fiber fractions order of digestion from slowest to fastest is: Lignin < Hemicellulose < Cellulose < Pectin Therefore replacing other fiber with pectin will increase rate of digestion
Antiquality Components of Alfalfa Alfalfa can accumulate compounds causing photosensitization Makes light-colored cattle, horses and sheep more sensitive to sun will get sunburned Can cause liver damage May need medical treatment but most common remedy is to remove feedstuff from diet Occurs most commonly on pasture (most of causal compounds eliminated during curing) but can occur in hay high in chlorophyll
Antiquality Components of Alfalfa Reduced intake with water stress Alfalfa contains Acremonium, endophytic fungus (same species as in tall fescue) Alfalfa accumulates secondary compounds to withstand water stress that reduces palatability of alfalfa Most such compounds decompose during field curing
Antiquality Components of Alfalfa Host to Fusarium Fungus can produce mycotoxins at times during field curing or silage fermentation Cause reduced intake Negatively affect immunological system Predisposition to animal to several diseases Raise cell content of milk (reduce milk quality) Some resistance appears to be available
Alfalfa Forage Quality needs Protein Energy/fiber Anti-quality components of alfalfa Many changes underway will improve alfalfa in the future for use in animal rations.