Relating sugar fluxes during bale storage to quality changes in alfalfa hay

Negative quality changes that occur when alfalfa (Medicago sativa L.) is baled at moisture levels in excess of 200 g kg-1 have been well documented, however, relatively little is known about changes in nonstructural carbohydrate pools during bale storage and how these changes are involved in depression of forage quality. The objectives of this study were to quantify nonstructural carbohydrate pools at specific time periods during bale storage and to relate these findings to accumulated heating degree days and traditional quality indices. Alfalfa forage was field-dried to high and low-moisture concentrations of 299 and 197 g kg-1, respectively, and packaged as conventional (CONV) and laboratory-scale (LAB) bales. During the first 4 d of storage, reducing sugar concentrations appeared to increase in high-moisture conventional bales and high-moisture laboratory bales made at twice the density of conventional bales (treatments that most favored spontaneous heating). Between 4 and 11 d in storage, reducing sugar concentrations for these treatments decreased sharply and continued a gradual decline thereafter, effectively mirroring the concurrent increases in acid-detergent insoluble N (ADIN). Nonreducing free sugar, total free sugar, and total nonstructural carbohydrate (TNC) concentrations declined rapidly during storage; these responses were linearly related to increases in heating degree days 30 degrees C. For high-moisture treatments, ADIN concentrations were strongly correlated with total free sugar and TNC levels (r = -0.90 and -0.90, respectively). Correlations between ADIN concentrations and reducing sugars (r less than or equal to 0.72) appeared weaker. At the low moisture level, reducing sugar concentration was not related (P greater than or equal to 0.05) to ADIN concentration