Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Objetivou-se avaliar o efeito da restriÃÃo alimentar quantitativa e da classe sexual no balanÃo de nitrogÃnio, sÃntese e eficiÃncia de proteÃna microbiana, por meio dos derivados de purina urinÃrios, e perfil de Ãcidos graxos na carne de ovinos Santa InÃs. Foram utilizados 30 ovinos machos com peso mÃdio inicial de 13,00  1,49 kg, em delineamento inteiramente casualizado, em esquema fatorial 3x2, sendo trÃs nÃveis alimentares (0, 30 e 60%) e duas classes sexuais (castrados e nÃo castrados). Foi utilizado uma dieta Ãnica de relaÃÃo volumoso:concentrado 60:40, utilizando feno de Tiffton-85 (Cynodon sp.) como volumoso. NÃo foram observados efeito de classe sexual e interaÃÃes entre nÃveis de restriÃÃo alimentar e classe sexual. Constatou-se balanÃo de nitrogÃnio positivo em todos os nÃveis de restriÃÃo e menores relaÃÃes N retido/N consumido e N retido/N absorvido no nÃvel de 60%. Os derivados de purina, purinas totais e absorvidas, produÃÃo e eficiÃncia de sÃntese de nitrogÃnio e proteÃna microbiana expressas em g/kgNDT, foram responsivas (P<0,05) aos nÃveis de restriÃÃo alimentar. Os nÃveis de restriÃÃo alimentar nÃo alteram (P>0,05) as variÃveis de Ãcido Ãrico (mg/kg0,75dia e mmol/kg0,75dia), as eficiÃncias de nitrogÃnio e proteÃna microbiana (g/kgCHOT e g/kgMO), e as concentraÃÃes (mg/100g) dos Ãcidos graxos C15:0, C18:3n6, C18:2c12t10, C22:1n9, C24:1, alÃm das relaÃÃes AGPI:AGS, &#969;6:&#969;3, (C18:0+ C18:1): C16:0, o Ãndice de trombogenicidade e atividade da &#8710;9-desaturase C16:0. Os lipÃdeos totais e os Ãcidos graxos C14:0, C16:0, C16:1n9c, C17:0, C17:1, C18:0, C18:1n9t, C18:1n9c, C18:2n6c, C18:3n3, C18:2c9t11 foram influenciados (P<0,05) pelos nÃveis de restriÃÃo alimentar, assim como as relaÃÃes AGPI:AGMI, AGMI:AGS e a atividade da &#8710;9-desaturase C18:0. ConcluÃ-se que a avaliaÃÃo nutricional de ovinos Santa InÃs em restriÃÃo alimentar, atravÃs do balanÃo de nitrogÃnio e da eficiÃncia de sÃntese de proteÃna microbiana, indica melhor utilizaÃÃo de nutrientes, em especial no nÃvel de 60%, e que a classe sexual nÃo influencia nenhum dos parÃmetros avaliados. Animais em restriÃÃo alimentar apresentam caracterÃsticas desejÃveis na qualidade de carne. Entretanto, a relaÃÃo &#969;6:&#969;3 apresenta-se como fator indicativo para novos estudos que se objetivem elevar as concentraÃÃes de Ãcidos graxos &#969;3 em carnes de cordeiros Santa InÃs em crescimento, para melhor valor nutricional dos produtos cÃrneos. / To evaluate the effect of quantitative and sexual class food restriction on nitrogen balance, microbial protein synthesis and efficiency. This evaluation was made by purine urinary derivates and fat acid profile on Santa InÃs sheep meat. 30 male ovine was used. They had an average initial weight of 13,00  1,49 kg. Every animal was submited to a completely randomized design in a factorial 3x2, there were three dietary levels (0, 30 and 60%) and two sexual classes (castrated and not castrated). There was only one diet with forage:concentration 60:40, Tiffton-85 (Cynodon sp) hay was used as a forage. Any effect of sexual class or interaction between levels of food restriction and sexual class was observed. Was found a positive nitrogen balance on all levels of food restriction, a lower relation between N retained/N consumed and N retained/N absorbed on level of 60%. Those purine derivate, total purine, absorbed purine, production and efficiency of nitrogen synthesis and microbial protein expressed in g/kgNDT, were responsive (p<0,05) on levels of food restriction. There were no alteration on levels of food restriction (p>0,05) those variables uric acid (mg / mmol kg0,75dia and / kg0,75dia), nitrogen efficiencies and microbial protein (g/ g kg CHOT / gMO), and the concentrations (mg / 100g ) of fatty acids C15: 0, C18: 3n6, C18: 2c12t10, C22: 1n9, C24: 1, in addition to the PUFAs relationships: SFA &#969;6: &#969;3 (C18: 0+ C18: 1) C16: 0, thrombogenicity index and activity of &#916;9-desaturase C16: 0. The total lipids and C14 fatty acids: 0, C16: 0, C16: 1n9c, C17: 0, C17: 1, C18: 0, C18: 1n9t, C18: 1n9c, C18: 2n6c, C18: 3n3, C18: 2c9t11 were influenced (P <0.05) by dietary restriction levels, as well as relations PUFA: MUFA, MUFA: SFA and the activity of &#916;9-desaturase C18: 0. In conclusion, the nutritional evaluation of Santa InÃs ovine in food restriction, based on nitrogen balance and efficiency of microbial protein synthesis, show that are a better utilization of nutrients specially on level of 60%, and the sexual class has no influence on every single evaluated parameter. Animals that are in food restriction have desirable characteristics on meat quality. However, the relation &#969;6: &#969;3 appears as indicative factor for further studies to objectify raise &#969;3 fatty acid concentrations in meat lambs Santa InÃs growing, for better nutritional value of meat products.