Levels of rumen degradable protein in diets for lambs

Foram conduzidos dois experimentos para avaliar o efeito de dietas com diferentes n?veis de prote?na degrad?vel no r?men (PDR) sobre o consumo, a digestibilidade aparente total dos nutrientes, o balan?o de nitrog?nio e o desempenho em cordeiros. As dietas consistiram de quatro n?veis de PDR (9,15; 9,97; 10,79 e 11,61% na MS), correspondentes a 14,25; 15,50; 16,75 e 18,00% de PB, com 40% de silagem de milho e 60% de concentrado, na base da mat?ria seca. No ensaio de digestibilidade e balan?o de nitrog?nio foram utilizados oito cordeiros machos inteiros da ra?a Santa In?s, com peso vivo m?dio de 26,9 e 24,7 kg, distribu?dos em dois quadrados latinos 4 x 4. Cada per?odo experimental teve a dura??o de 15 dias, sendo 10 para adapta??o e cinco para coletas. Os animais foram mantidos em gaiolas metab?licas individuais, usando-se sacolas para coleta total de fezes, para fins de c?lculos dos coeficientes de digestibilidade in vivo. A coleta de urina foi realizada durante 24 horas, utilizando-se baldes pl?sticos cobertos com telas, quando mediu-se o volume da quantidade excretada nesse per?odo. N?o houve efeito de n?veis crescentes de PDR sobre os consumos de nutrientes, exceto de PDR. As digestibilidades aparentes totais dos nutrientes, bem como o balan?o de nitrog?nio, tamb?m n?o foram influenciadas pelos n?veis de PDR. No ensaio de desempenho foram utilizados 31 cordeiros machos inteiros da ra?a Santa In?s, com peso vivo m?dio de 22,0 kg, distribu?dos no delineamento inteiramente casualizado, com quatro tratamentos (9,15 a 11,61% de PDR na MS), tr?s com oito repeti??es e um com sete repeti??es. Al?m desses animais, mais quatro foram abatidos no in?cio da fase experimental, representando os animais-refer?ncia na metodologia do abate comparativo. N?o houve efeito de n?veis crescentes de PDR sobre os consumos de nutrientes, exceto de PB, PDR e PNDR, bem como para o peso vivo ao abate, ganho de peso total, ganho m?dio di?rio, convers?o alimentar e caracter?sticas de carca?a (peso, ganho e rendimento). Conclui-se que os n?veis de PDR, de 9,15 a 11,61% na MS das dietas, n?o alteram o consumo de nutrientes, exceto de PB, PDR e PNDR, nem a digestibilidade aparente total dos nutrientes, o balan?o de nitrog?nio e o desempenho de cordeiros. Assim, pode-se recomendar a utiliza??o do n?vel mais baixo de PDR (9,15% na MS, com 14,25% de PB), contribuindo para a redu??o da excre??o de nitrog?nio no ambiente e de custos no sistema de produ??o.Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)Funda??o de Amparo ? Pesquisa do Estado de Minas Gerais (FAPEMIG)Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Zootecnia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2010.ABSTRACT Two experiments were conducted to evaluate the effect of diets with different levels of rumen degradable protein (RDP) on the intake, total apparent digestibility of nutrients, nitrogen balance and performance in lambs. Diets consisted of four levels of RDP (9.15, 9.97, 10.79 and 11.61% in DM), corresponding to 14.25, 15.50, 16.75 and 18.00% CP, with 40% corn silage and 60% concentrated on dry matter basis. In the digestibility trial and nitrogen balance were used eight Santa In?s lambs, with average weight of 26.9 and 24.7 kg divided into two 4 x 4 latin squares. Each experimental period lasted 15 days, considering 10 for adaptation and five for collections. The animals were kept in individual metabolic cages, using bags for total fecal collection for purposes of calculating the digestibility in vivo. The urine collection was performed during 24 hours, using plastic buckets covered with canvas, when the volume of the amount excreted in this period was measured. There was no effect of increasing levels of RDP on the nutrients intake, except for RDP. The apparent digestibilities of nutrients and nitrogen balance were also not influenced by levels of RDP. In the performance test were used 31 male Santa In?s lambs, with average weight of 22.0 kg, allotted in a completely randomized design with four treatments (9.15 to 11.61% RDP in DM), three with eight and one with seven replicates. Besides these animals, four were slaughtered in the early experimental stage, representing the reference animals in the methodology of comparative slaughter. There was no effect of increasing levels of RDP on intake of nutrients, except for CP, RDP and RUP as well as the slaughter live weight, total weight gain, average daily gain, feed conversion and carcass traits (weight, gain and yield). We conclude that levels of RDP, from 9.15 to 11.61% in DM of diets, do not alter nutrient intake, except for CP, RDP and RUP nor the total apparent digestibility of nutrients, nitrogen balance and lambs performance. Thus, we can recommend the use of the lower level of RDP (9.15% DM, with 14.25% CP), contributing to the reduction of nitrogen excretion in the environment and of costs in the production system