Effects of drying procedures on chemical composition and nutritive value of alfalfa forage
The effects of various drying procedures of alfalfa forage were evaluated on chemical composition, in vitro neutral detergent fibre (NDF) and dry matter (DM) digestibility, in situ DM, organic matter and crude protein (CP) degradability. The alfalfa had been harvested in the spring growth (early bud and flowering) and first regrowth (late bud and late flowering) periods. The samples were dried at 30 °C (T30), 40 °C (T40), 50 °C (T50), 60 °C (T60) and 100 °C (T100) in a forced-air oven or frozen for one month and then freeze-dried (TFD) or oven-dried at 50 °C (TFREE). Another drying procedure included pre-treatment by heating in a microwave oven (TMO) or in a forced-air oven at 100 °C for 1 hour (T100+50) and then oven-dried at 50 °C. The freeze-drying method was chosen as a reference method. Freeze-dried samples had the lowest NDF, acid detergent fibre (ADF), acid detergent lignin (ADL), neutral detergent insoluble protein (NDIP) and acid detergent insoluble protein contents (P <0.05). Additionally, freeze-dried products had the highest CP, in vitro true digestibility of DM and CP degradability values (P <0.05). There was no added benefit of the TMO in the chemical composition, in vitro digestibility or in situ degradation compared with T50. This study showed that T50 can yield chemical composition, in vitro and in situ results that are similar to those obtained with the freeze-drying method and that this procedure is useful for forage analyses and evaluation.
Keywords: freeze-drying, insoluble nitrogen, in vitro digestibility, oven-drying, ruminants