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摘要
O trabalho objetivou avaliar as concentra es de ur谷ia plasm芍tica e urin芍ria; o balan o dos compostos nitrogenados e estimar as exig那ncias de prote赤na para manten a por equa es preconizadas pelos sistemas americano e britanico, em quatro bovinos e quatrobubalinos, com peso m谷dio inicial de 461,19 ㊣ 7,59 e 455,44 ㊣ 7,85 kg para os bovinos e b迆falos, respectivamente, distribu赤dos em dois quadrados latinos 4 x 4. Os tratamentos consistiram em diferentes n赤veis de concentrado (0,0; 24,0; 48,0; 72,0%) 角 base de milhomo赤do, farelo de soja e sal mineral, e feno de capim-tifton. Cada per赤odo durou 21 dias, sendo 14 de adapta o e sete para coleta. Foram coletadas amostras de fezes e urina (spot) para estimativa da produ o de mat谷ria seca fecal e volume urin芍rio. Houve intera o entre as esp谷cies para nitrog那nio (N) consumido (NC), urin芍rio (NU) g kg-0,75 e ur谷ia urin芍ria (UU); n o ocorrendo para N fecal (NF), N absorvido (NABS), NU (g d-1), balan o de N (BN) e ur谷ia plasm芍tica (UP). Independente do efeito observado entre as esp谷cies, asvari芍veis aumentaram linearmente em fun o dos n赤veis crescente de concentrado que proporcionou BN positivo. Os requerimentos de prote赤na metaboliz芍vel para manten a de bovinos e bubalinos, quando estimados por meio dos sistemas americano e britanico, s odiferentes. The work aimed to evaluate the concentrations of plasmatic and urine urea, the balance of nitrogen compounds, and to estimate the proteinrequirements for maintenance. Equations recommended by the American and British systems were used in four bovine and four bubaline steers, with initial average weight of 461.19 ㊣ 7.59 and 455.44 ㊣ 7.85 kg for cattle and buffaloes, respectively, distributed intotwo 4 x 4 Latin squares. The treatments consisted of different levels of concentrate (0.0; 24.0; 48.0; and 72.0%) composed of cracked corn, soybean meal, mineral salt, and Tiftongrass hay. Each period lasted 21 days, being 14 for adaptation and seven for collection. Samples of feces and urine (spot) were taken to estimate the production of fecal dry matter and urine volume. Interactions were observed between the species for N intake (NC), urine-N (UN) g kg-0.75 and urinary urea (UU); no interactions occurred for fecal-N (NF), absorbed-N (NABS), UN (g d-1), balance of N (BN) and plasmatic urea (UP). Regardlessof the difference observed between the species, the response variables increased linearly as functions of the growing levels of concentrate that resulted in positive BN. The estimate of metabolizable protein maintenance requirements for cattle and buffaloes differs betwee
