Changes in availability and nutritive value of different corn residue parts as affected by early and late grazing seasons.

Two early- (EG) and two late-season (LG) corn-residue grazing trials were conducted either from October to December or from December to March (1987 and 1988) using both nonirrigated and irrigated fields. Initial availability, disappearance, and nutritive value of different corn residue components were estimated. Stocking rates were 1.97, 2.20, 1.36, and 2.58 animals/ha for the two EG and LG nonirrigated fields (NIF), respectively, and 3.96 animals/ha for EG irrigated fields (IF). Samples were collected three times throughout the grazing period. In one of the LG trials, samples were collected 30 d before the grazing season began for measurement of weathering damage. Composite samples were analyzed for CP, ADF, ADIN, and in vitro DM (IVDMD) and OM (IVOMD) disappearance. Ruminal escape protein (EP) content was assessed using a Dacron bag technique. Weathering reduced (P less than .02) the amount of leaf blade available by 42% during a period of 30 d before the LG season in Trial 2. Grain, husks, and leaf blades disappeared to the greatest degree (P less than .05) during either grazing season. More than 90% of the grain disappeared during the first 30 d, regardless of grazing season. Overall IVDMD for NIF grain, husks, leaf blades, stems, and cobs across the EG and LG trials were 98.6, 68.4, 42.0, 41.0, and 48.1%, respectively. Corn residue fractions from IF had a lower (P less than .05) IVDMD than did NIF fractions. Grain from NIF was 20% higher (DM basis) in EP than grain from IF (Trial 2). Grain left in the field was the most important source of CP and EP for calves grazing corn residues. Husks and leaf blades were selected by calves; husks were the roughage fraction with the highest nutritive value.