Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / To evaluate the responses of canarana grass erecta lisa (Echinochloa pyramidalis Lam.) grazed by dairy heifers, this study was conduct. Was used a factorial arrangement 2.0 x 2.0 (two frequencies and two defoliation intensity) in completely plots randomized design with five replicates (paddocks). The defoliation frequencies corresponded to interception from 85 and 95% of active photosynthetic radiation and the defoliation intensity corresponded the residual leaf area index 1.0 and 2.0. Were evaluated the growth in regrowth by morphogenesis method, the gas exchange and biomass flow. Were analyzed the growth characteristic: crop growth rate (CGR), relative growth rate (RGR), net assimilate rate (NAR), leaf area ratio (LAR), specific leaf area (SLA), and leaf weight ratio (LWR), also were evaluates: total dry mass forage (TDMF), fresh dry mass forage (FDMF), fresh dry mass leaf (FDML), fresh dry mass stem (FDMS), leaf/stem ratio (L/S). The exchange gas trial were made following measurements: transpiration (E), stomatal conductance (gs), photosynthesis (A), internal CO2/reference CO2 ratio (Ci/CR), efficient use of water (EUW), intrinsic use of water (IUW) and relative index of the chlorophyll (RIC). The variable belonging to biomass flow were: leaf elongation rate (LER), and stem (SER), the elongation rate of the leaf 1/ elongation rate of the leaf 2 (ERL1/ERL2), leaf previous senescence rate (LPVSR), leaf posterior senescence rate (LPOSR) and leaf total senescence rate (LTSR), leafs live number (LLN) and total leafs number (TLN), life leaf time (LLT), leaf appearance rate (LAR) and crop accumulation rate (CAR). The TDMF, FDMF, FDMS and FDML presented increasing values based on age, The L/S ratio showed x. Were obtained increasing values to CGR, and decreasing values RGR, NAR. The values of SFA were increased to 20 days, after showed decreasing values. On the exchange gas trial, there wasnât difference between management strategies (P>0.05), however on post-grazing the variables EUW and IUW showed lower average (P<0.05), to 85% IAPR. About to cycles of the grazing the evaluates of pre-grazing, the E was lower to 95% IAPR management x intensity 2.0 (P<0.05) The EUW showed lower values to 95% IAPR x intensity 1and higher to 95% x intensity 2 (P<0.05). Evaluates made on post-grazing there was difference to the content of the chlorophyll that showed lower average to intensity 1.0 (P<0.05). On the biomass flow trial, the PVSR, LLN and ALR presented lower values to the less defoliation frequencies (P<0.05), the LPOSR showed lower values to defoliation frequencies. The physiologic characteristic were changed by differences defoliation frequencies and intensity. The growth index of canopy RGR, NAR were committed with the age, but the same not occur to the CGR. The canarana grass should be handled frequently defoliation of 95% interception of photosynthetically active radiation associated whit a residual leaf index 2.0. / Objetivou-se avaliar as respostas do capim-canarana erecta lisa (Echinochloa pyramidalis Lam.) ao pastejo por novilhas leiteiras num arranjo fatorial 2,0 x 2,0 (duas frequÃncias e duas intensidades de desfolhaÃÃo) num delineamento em blocos completos casualizados com cinco repetiÃÃes (piquetes). As frequÃncias de desfolhaÃÃo corresponderam à intercepÃÃo de 85 e 95% da radiaÃÃo fotossinteticamente ativa e as intensidades de desfolhaÃÃo corresponderam aos Ãndices de Ãrea foliar residual de 1,0 e 2,0. Foram avaliados: o crescimento em rebrotaÃÃo pelo mÃtodo da morfogÃnese, as trocas gasosas e o fluxo de biomassa. Das caracterÃsticas de crescimento foram analisadas: a taxa de crescimento da cultura (TCC), a taxa de crescimento relativo (TCR), a taxa de assimilaÃÃo lÃquida (TAL), a razÃo de Ãrea foliar (RAF), a Ãrea foliar especÃfica (AFE) e a razÃo de peso foliar (RPF). TambÃm foram avaliadas: a massa seca de forragem total (MSFT), a massa seca de forragem verde (MSFV), a massa seca de lÃminas foliares verdes (MSLV), a massa seca de colmos verdes (MSCV), a relaÃÃo folha/colmo (F/C). Para o ensaio de trocas gasosas, foram feitas mediÃÃes das seguintes variÃveis: transpiraÃÃo (E), condutÃncia estomÃtica (gs), fotossÃntese (A), relaÃÃo CO2 interno/CO2 de referÃncia (Ci/CR), uso eficiente da Ãgua (UEA), uso intrÃnseco da Ãgua (UIA) e Ãndice relativo de clorofila (IRC). As caracterÃsticas do fluxo de biomassa incluÃram: as taxas de alongamento foliar (TAlF) e das hastes (TAlH), a razÃo entre a taxa de alongamento da folha 1 e da folha 2 (TAlF1/TAlF2), a taxa de senescÃncia foliar anterior (TSFA), a taxa de senescÃncia posterior (TSFP) e a taxa de senescÃncia foliar total (TSFT), o nÃmero de folhas vivas (NFV), o nÃmero de folhas totais (NFT); o tempo de vida da folha (TVF); a taxa de aparecimento da folha (TApF) e a taxa de acÃmulo da cultura (TAC). A MSFT, MSFV, MSCV e MSLV apresentaram valores crescentes em funÃÃo da idade, a relaÃÃo F/C apresentou valores decrescentes. Obtiveram-se valores crescentes para TCC, para TCR, TAL os valores foram decrescentes. Os valores de AFE foram crescentes atà aos 20 dias, seguido de valores decrescentes. No ensaio de trocas gasosas, prÃ-pastejo, nÃo houve diferenÃa para as estratÃgias de manejo (P>0,05). Entretanto, no pÃs-pastejo as variÃveis UEA, A e UIA apresentaram mÃdias menores (P<0,05), para 85% IRFA. Com relaÃÃo aos ciclos de pastejo para leituras de prÃ, a E foi menor para o manejo 95% IRFA x intensidade 2 (P<0,05). A UEA apresentou valores inferiores em 95% IRFA x intensidade 1 e superiores para 95% IRFA x intensidade 2 (P<0,05). Para leitura no pÃs-pastejo, houve diferenÃa para o conteÃdo de clorofila, que apresentou valores inferiores para intensidade 1,0 (P<0,05). No ensaio de fluxo de biomassa A TSFA, NFV e TApF apresentaram valores menores para as menores frequÃncias de desfolhaÃÃo (P<0,05), a TSFP apresentou menores valores para maiores frequÃncias de desfolhaÃÃo. As caracterÃsticas fisiolÃgicas foram alteradas pelas diferentes frequÃncias e intensidade de desfolhaÃÃo. Os Ãndices de crescimento do dossel TCR, TAL foram comprometidos com o aumento da idade, mas o mesmo nÃo ocorreu para o e TCC. O capim-canarana deve ser manejado com frequÃncia de desfolhaÃÃo de 95% de interceptaÃÃo da radiaÃÃo fotossinteticamente ativa associada a um Ãndice de Ãrea foliar residual de 2,0.