Hay Curing and Water Soaking: Effects on Composition and Digestion of Alfalfa Leaf and Stem Components

Progress toward improved hay harvesting technology is limited by a lack of information on the sources of yield and forage quality losses that occur during curing of alfaffa (Medicago sativa L.) hay, especially with exposure to rain. Two trials were conducted to determine the relative contributions of separate leaf and stem components to losses in yield and quality and to changes in dry matter and cell-wall digestibility of alfalfa during hay curing and soaking with water. Concentrations of N, ash, in vitro dry matter disappearance (IVDMD)₁ and neutral (NDF) and acid (ADF) detergent fibers were measured for leaf and stem components from alfalfa herbage just after harvest, and for field-cured and water-soaked hay. Leaf concentration averaged 386, 330 and 280 g kg⁻¹ in herbage, dry hay, and soaked hay, respectively. Neither hay treatment affected component N concentrations but whole-shoot N concentration was reduced in both hays due to reduced leaf concentrations. Increased component fiber concentrations and reduced leaf concentration in soaked hay both contributed to large NDF and ADF increases on a whole-shoot basis. The extent and rate of NDF disappearance were reduced in soaked hay compared with herbage. Leaf accounted for 78% or more of the respiration and shatter losses of DM, N, ash, and in vitro digestible dry matter (IVDDM) and 60% or more of the soaking losses of the same constituents. Onethird of the leaf N content was lost in soaked hay compared with 10% of the stem N content. Leaf and stem each lost 3% of their NDF content. Ash content losses during soaking exceeded 50% for leaf and 30% for stem. Because nearly all of the respiration and shatter losses, and most of the soaking losses, of chemical constituents came from the leaf component, reducing leaf loss offers the greatest opportunity for reducing alfalfa hay harvesting losses. Productive value of hay might be impacted more by severe wetting than constituent concentrations alone would indicate becaus extent and rate of fiber digestion are reduced.