EFFECTS OF ADDITIVES AND GROWTH ENVIRONMENT ON PRESERVATION AND DIGESTIBILITY OF WHEAT SILAGE FED TO HOLSTEIN HEIFERS

Wheat grown in two separate years under different environmental conditions was fed as silage to investigate effects of additives on forage preservation and digestibility. Direct-cut wheat was harvested in an early head stage of maturity. Wheat was drought stressed in yr 1 and averaged 41.6% DM, and yr 2 averaged 23.0% DM at harvest. Forage was ensiled in 10 900-kg concrete stave silos; 2 per year were assigned to one of five treatments with an enzyme-chemical product, or treatment with one of three different types of lactic acid bacterial inoculants. Each year, during two 12-d periods, forage from five different silos was fed individually for ad libitum intake, separate from concentrate (1.1% of BW) to 15 Holstein heifers (average BW 228 +/- 32 kg). Wheat forage and silage from yr 1 was lower in CP but higher in NDF, ADF, lignin, and starch than that harvested in yr 2. Silage additives decreased DM and NDF recovery in yr 1 and increased DM, NDF, and neutral detergent solubles recovery in yr 2. Additives increased the ratio of lactic to acetic acid and decreased ammonia in silage both years. Additives increased DM and fiber digestibilities of wheat silage-based rations fed to Holstein heifers in yr 2. In vitro digestibility indicated that these improvements were associated with a reduction in the lag phase of forage digestion. The rate of in vitro DM digestibility was positively correlated with silage DM recovery, suggesting an association with nutrient preservation. Wheat preservation and digestibility both were improved by silage additives when wheat was grown under normal environmental conditions, but losses were greater with additives in drought-stressed forage.