EFFECT OF WHEAT SILAGE MATURITY ON IN-SITU DEGRADATION OF ORGANIC-MATTER, CRUDE PROTEIN, STARCH AND FIBER

Winter wheat (Triticum aestivum L.),,harvested at late milk (LM), earl y dough (ED) and hard dough (HD) stages of maturity was ensiled. Rate and extent of degradation of feed fractions contained in wheat silages were determined. Polyester bags filled with 3 g silage dry matter wer e incubated in the rumen of six fistulated steers for 9 different time s (0, 2, 4, 6, 8, 12, 24, 48 and 288 h) in a repeated 3 x 3 Latin squa re design. Starch contents of the silages increased markedly and fibre contents decreased-with maturity. Zero time (0 h) disappearance of cr ude protein. (CP) was > 85% across maturities and mainly in the form o f water-soluble CP assumed to be instantaneously degradable. 0 h value s for starch were > 89% across maturities, mainly in the form of water -insoluble; small particles. After 12 h of ruminal incubation, greater than or equal to 98% of starch of all silages had disappeared from th e bags. The extent of organic matter (OM) degradation increased with a dvancing maturity, whereas, the rate of OM degradation decreased. Effe ctive degradabilities of the OM were greater for the ED and HD silages than for the LM silage at all the three assumed ruminal passage rates (2, 5 and 8% per h). Stage of silage maturity had no consistent effec t on degradation kinetics of cell-wall constituents. Extent and direct ion of silage maturity effects varied with fibre:fi action and maturit y stage. In conclusion, increased content of rapidly degradable starch with maturity and overall lack of negative effects of maturity on fib re degradation parameters resulted in favorable ruminal degradation ch aracteristics of the ED and HD silages compared with the LM silage. Th is observation is consistent with findings on the same silages that vo luntary intake of the ED and HD silages was greater than consumption o f the LM silage, although OM digestibilities were not affected by stag e of maturity.