FIBER ANALYSES AND IN-SACCO DEGRADABILITY OF PLANT FRACTIONS OF 2 CORN VARIETIES HARVESTED AT VARIOUS TIMES

Twenty maize plants each of the varieties Boss and Bezemara were harvested on four (4 September, 16 September, 30 September and 14 October) and three ( 1 6 September, 30 September and 14 October) dates, respectively. The plant stem below the ear was divided into 5-cm height portions, and the stalk over the ear and the ear formed two further fractions. Neutral detergent fibre (NDF), acid detergent fibre (ADF), hemicellulose, cellulose and lignin were determined for selected fractions (height 0-5 cm, 5-10 cm, 20-25 cm, 40-45 cm, over ear and ear). Rumen dry matter degradability (DMD) of all fractions was evaluated in situ using three rumen fistulated male sheep. The rumen incubation time for all samples was 48 h. Later harvest dates increased the cell wall content of all stalk fractions of the variety Boss (NDF: 55.2%, 64.9%, 75.4% and 85.7%; ADF: 35.3%, 41.5%, 48.8% and 58.6%; lignin: 6.6%, 7.7%, 8.7% and 11.6% of DM for harvest dates 4 September, 16 September, 30 September and 14 October, respectively). The latest harvest date did not enhance the fibre content of Bezemara (NDF: 60.8%, 76.6% and 76.1%; ADF: 38.8%, 49.6% and 49.1%; lignin: 7.5%, 9.9% and 8.5% of DM for 16 September, 30 September and 14 October, respectively). The lignin content decreased with height of stem (0.5 cm: 11.0%; 20-25 cm: 9.3%; 40-45 cm: 8.5%; over ear: 5.0% of DM). The cell wall content of ears was reduced with later harvest date. The in sacco DMD of residual plants of both varieties decreased with later growing stages. The higher fractions of residual plants showed a higher DMD than the lower ones (0-5 cm: 59.3%; 20-25 cm: 65.3%; 40-45 cm: 67.3%; over ear: 72.2%). The DMD of ears was less influenced by harvest date (88.5-93.8%), and was closely correlated with lignin content of fractions (r = -0.93). A higher cut of com plant may increase the digestibility of com silage and probably also the performance of ruminants.