Chemical composition and digestibility of forage mass in irrigated aruanagrass pastures or oversown with a mixture of winter forage species

A mixture of two winter forages: black oat (Avena sirigosa Schreb. cv. Common) and Italian ryegrass (Lolium mulliflorum Lam. cv. Common) was introduced in a pasture of aruanagrass (Panicum maximum Jacq. cv. Aruana), grazed by sheep in an intensive production system (irrigation, fertilization and rotational stocking) with the objective of increasing the forage nutritive value during the dry winter period. From 04-14-00 to 01-18-01 and 06-07-01 to 02-22-02, the chemical composition and digestibility of pregrazing forage were evaluated in six grazing periods. A completely randomized block design with replication within blocks was used. The treatments were 1) grass alone and 2) the grass oversown with the mixture of winter forages. Samples of pre-grazing forage mass and components (aruanagrass, black oat and Italian ryegrass) were taken to evaluate the forage botanical composition, contents of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and lignin and ill vitro dry matter digestibility (IVDMD), in the six grazing periods. In the first year, the control had a greater CP content than oversown pasture in the third period and similar in the others periods, as well as greater NDF, ADF and lignin contents in the overall mean of the six grazing periods. Forage IVDMD from the two treatments were similar in all grazing periods. In the second year, the control had a greater CP content than oversown pasture ill the fourth period and similar ill the others periods, as well as greater NDF, ADF, lignin and IVDMD contents in the overall mean of the six grazing periods. Nitrogen fertilized and irrigated aruanagrass pastures and aruanagrass pastures oversown with black oat and Italian ryegrass exhibited the same values of chemical composition and digestibility.