Rego et al., 2006. Rev. Bras. Zootec., 35 (3): 691-698

Steer forage intake rate (IR) was evaluated in pastures of Brachiaria brizantha, Panicum maximum cv. Tanzania, Arachis pintoi and a mixed of Brachiaria brizantha with Arachis pintoi. The objectives were to define sward structural characteristics and chemical composition nutrients of each pasture most determinant of forage intake rate by grazing steers. The steers grazed in pairs, passing through all grass species maintained at different sward heights in successive days. After three hours fast the animals were allowed to graze each experimental area for 60 minutes and had their grazing time and bite numbers registered. Forage intake was estimated by the double sampling technique. Sward structural characteristics used in the model for estimation of IR were: average sward height, morphological component proportion (%), morphological component mass (ton DM/ha) and density of morphological components (kg DM/ha/cm). The chemical composition was expressed as crude protein (CP) and neutral detergent fiber (NDF). Sward variables were selected using the stepwise statistical procedure. The IR equations defined from the studied characteristics were: Marandu grass: IR = 59,8980 + 0,7299 GL + 3,5777 DMA - 1,2459 NDFL + 0,2882 SH (GL - proportion of green leaves, FM – forage mass, NDFL - NDF of leaves, SH – average sward height). Tanzania grass: IR = 111,762 -4,1532 CPL + 0,3469 GL - 0,5207 NDFL (CP of leaves, GL – proportion of green leaves, NDFL - NDF of leaves). Peanut forage: IR = -196,589 + 12,1978 CPS + 8,3406 DMA + 1,1060 GS +17,3669 GLA (CPS – stem CP, DMA - dry matter availability, GLA - green leaves availability). Mixed pasture: IR= -7,25 + 1,15HA -0,22HI + 18,49AA -9,88GLA + 0,49HM + 1,00CPL (HA – Peanut forage height, HI – weed species height, AA - Arachis availability, GLA - green leaf availability of Marandu grass, HB – marandugrass sward height, CPL – CP of leaves of marandugrass).