SELECTION OF ALFALFA FOR A LOWER INITIAL RATE OF DIGESTION AND CORRESPONDING CHANGES IN EPIDERMAL AND MESOPHYLL CELL-WALL THICKNESS

A modified nylon bag technique, described in detail in this paper, appears to be an effective method of selecting for a lower initial rate of digestion (IRD) in alfalfa. Breeding for reduced IRD in alfalfa resulted in a 15% reduction in 4-h dry matter disappearance (DMD) after three cycles of selection (ultimate goal of 25-30% reduction for a bloat-safe alfalfa). No further reduction in IRD occurred with a 4th cycle of selection. The IRD characteristic appears to be expressed at early stages of vegetative growth (pre-bud to early bud) and not at a more advanced stage of maturity (mid-bud to early bloom). The IRD characteristic also appears to be subject to environmental influence. Alfalfa plants selected for reduced IRD have consistently thicker cell walls compared to the unselected alfalfa check cv. Beaver. The advanced cycle 4 LIRD synthetic is being increased for subsequent pasture trials and assessment of bloat reduction.