Resumo
O objetivo deste trabalho foi avaliar os efeitos da oscilacao das concentracoes dietetica de PB sobre o desempenho e utilizacao do nitrogenio em ovinos. Foram utilizados 40 ovinos machos nao castrados, mesticos Dorper x Santa Ines, mantidos em baias individuais alimentados com duas formulacoes dieteticas: 1) R100, que atendia as exigencias diarias de PB para ovinos em crescimento, com ganho de 200 g/dia (NRC, 2007); 2) R80, que atendia apenas 80% dessa exigencia. Os tratamentos foram entao definidos de acordo com o fornecimento das dietas: 1) R100: dieta R100 fornecida durante todo o periodo experimental; 2) R100/24: um dia de dieta R100 seguida de um dia de dieta R80(i.e. R100, R80, R100, R80, ...); 3) R100/48: um dia de dieta R100 seguida de dois dias de dieta R80 (i.e. R100, R80, R80, R100, ...); 4) R100/72: um dia de dieta R100 seguida de tres dias de dieta R80 (i.e. R100, R80, R80, R80, ...) e 5) R80: reducao da proteina dietetica durante todo o periodo experimental. . O experimento teve a duracao de 64 dias e, ao final, os animais foram abatidos e suas carcacas avaliadas quanto ao peso, rendimento e espessura de gordura. Os dados foram analisados pelo pacote estatistico SAS em um delineamento inteiramente casualizado, com cinco tratamentos e oito repeticoes. O peso inicial foi utilizado como covariavel e a heterogeneidade de variancias foi testada para todas as variaveis. As medias foram comparadas atraves dos seguintes contrastes: Osc: testar o efeito da oscilacao e reducao (R100/0 versus R100/24, R100/48, R100/72 e R80); L: Efeito linear da oscilacao (0, 24, 48 e 72 horas); Q: Efeito quadratico da oscilacao (0, 24, 48 e 72 horas); e Rest: efeito da reducao (R100/0 versus R80). Significancia foi declarada a 5% de probabilidade. Nao foi observada significancia (P>0,05) de nenhum dos contrastes avaliados para consumo de materia seca (980,0 g), peso apos 30 d (33,4 kg), peso final (39,1 kg), ganho medio diario (173,6 g/dia), ganho de peso total (11,1 kg), conversao alimentar (5,9), peso de carcaca quente (16,8 kg), rendimento de carcaca quente (42,3%) e fria (42,1%) e espessura de gordura (1,4 cm). Tambem nao foi observada significancia (P>0,05) de nenhum dos contrastes avaliadospara consumo de nutrientes, exceto para o consumo de proteina e extrato etereo, o qual foi superior (P<0,05) no grupo R100. Tambem nao foi observada significancia para os metabolitos sanguineos proteinas totais e albumina, mas a ureia se apresentou superior no grupo R100 quando comparado aos demais. Os animais alimentados do grupo R100 apresentaram maior concentracao de N na urina do que os demais e maior concentracao de N retido do que os animais do grupo R80. Nao houve significancia entre os contrastes avaliados para os demais parametros relacionados ao N. Conclui-se que apesar de terem consumido menor quantidade de proteina bruta, os animais submetidos a oscilacao por ate 72 horas, apresentaram quantidade de N retido semelhante ao grupo R100/0 e menor quantidade de N excretado pela urina, o que mostra a eficiencia dessa estrategia de fornecimento dietetico para a reciclagem de nitrogenio. Especula-se que o NRC de 2007 para pequenos ruminantes superestima as exigencias de PB dietetica para ovinos 12 Dorper x Santa Ines em crescimento. Conclui-se que reducoes na concentracao dietetica de PB, com intervalos de ate 72 h, bem como o fornecimento de 80% da exigencia proteica nao comprometem o desempenho e rendimento de carcaca de ovinos.
To evaluate the effects of dietary CP oscillation on the performance and nitrogen utilization in sheep, 40 intact males lambs were used. Forty male sheep, crossbreed Dorper x Santa Ines, were kept in individual stalls. Two diets were formulated: 1) R100, which met the daily requirements of CP for growing lambs with gain of 200 g/day (NRC, 2007); 2) R80, which met only 80% of this requirement. The assays were then defined according to the diet delivery: 1) R100: R100 diet throughout the experimental period; 2) R100 / 24: one day of diet R100, followed by one day of diet R80 (ie R100, R80, R100, R80, ...); 3) R100 / 48: R80 (i.e., R100, R80, R80, R100, ...); 4) R100 / 72: a R100 diet day three-day diet R80 (ie R100, R80, R80, R80, ...) and 5) R80: reduction of dietary protein throughout the experimental period. The experiment lasted for 64 days. After that, the animals were slaughtered and their carcasses were evaluated for weight, carcass yield and fat thickness. Data were analyzed by the SAS statistical package in a completely randomized design with five treatments and eight replicates. The initial body weight was used as covariate and the variance heterogeneity was tested for all variables. The treatments were compared using the following contrasts: Osc: test the effect of oscillation and reduction (R100/0 versus R100/24, R100/48, R100/72 and R80); L: linear effect of the oscillation (0, 24, 48 and 72 hours); Q: quadratic effect of the oscillation (0, 24, 48 and 72 hours); and Rest: reduction effect (R100/0 versus R80). Significance was declared at 5% probability. No significant differences (P> 0.05) were observed for dry matter intake (980.0 g), body weight after 30 d (33.4 kg), final weight (39.1 kg), average gain (17.6 kg / day), total weight gain (11.1 kg), feed conversion (5.9), hot carcass weight (16.8 kg), hot carcass yield (42.3%), cold carcass yield (42.1%) and fat thickness (1.4 cm). There was also no significant (P> 0.05) significance of any of the contrasts evaluated for nutrient intake, except for the consumption of protein and ether extract, which was higher (P <0.05) for the R100 group. There was also no significance for total protein and albumin blood metabolites, but urea was superior in the R100 group when compared to the others. The animals fed the R100 group had higher concentration of N in the urine than the others and higher concentration of N retained than the animals of group R80. There was no significant difference between the contrasts evaluated for the other parameters related to N. We concluded that, although the animals consumed less crude protein, the ones submitted to oscillation for up to 72 hours had a similar amount of N retained than the group R100/0, and less amount of N excreted in the urine, which shows the higher efficiency of this dietary strategy for nitrogen recycling. We speculated that the NRC (2007) for small ruminants overestimates the requirements of dietary PB for crossbreed Dorper X Santa Ines growing sheep. We also concluded that reductions in the dietary concentration of CP, with intervals of up to 72 h, as well as the 80% supply of the protein requirement did not compromise the performance and carcass yield of sheep.