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RESUMO -Este experimento foi realizado para avaliar níveis de energia metabolizável (EM) (2850, 2921, 3000, 3075 e 3150 kcal/ kg) para pintos de corte, machos, de 1 a 21 dias de idade, mantidos em ambiente de conforto térmico. Quatrocentos e cinqüenta pintos, machos, com 44±0,2 g de peso inicial médio, foram distribuídos em delineamento experimental inteiramente casualizado, com cinco tratamentos, nove repetições e dez aves por unidade experimental. O nível de EM da ração influenciou o ganho de peso médio diário e o consumo de energia metabolizável, que aumentaram, e a conversão alimentar, que reduziu linearmente com o aumento do nível de energia da ração. O nível de EM da ração influenciou as taxas de deposições de proteína e gordura na carcaça e o peso de gordura abdominal, que aumentaram linearmente, enquanto o rendimento de carcaça não foi influenciado. O nível de 3075 kcal EM na ração proporcionou o melhor desempenho das aves mantidas em condição de conforto térmico, na fase de 1 a 21 dias de idade.Palavras-chave: ambiente de conforto, energia metabolizável, frangos de corte Metabolizable Energy Levels for Broilers (1 to 21 days) Maintained under a Thermoneutral EnvironmentABSTRACT -This experiment was carried out to evaluate the metabolizable energy (ME) (2850, 2921, 3000, 3075 e 3150 kcal/kg) levels for male broilers from 1 to 21 days of age, maintained in thermoneutral environment. Four hundred and fifty chicks, male, with average initial 44±0.2 g LW, were allotted to a completely randomized experimental design with five treatments, nine replicates and ten animals per experimental unit. The ME level of the diet affected the average weight gain and the ME intake, which increased, and the feed:gain ratio, that linearly decreased with the increase of the dietary energy level. The dietary energy level affected the fat and protein deposition rates of the carcass and abdominal fat weight, which linearly increased, while the carcass yield was not affected. The dietary level of 3075 kcal ME promoted the best broiler performance, from 1 to 21 days of age, maintained under a thermoneutral environment.Key Words: thermoneutral, metabolizable energy, broiler IntroduçãoAs aves, como outros animais homeotérmicos, são influenciadas pelo ambiente. Assim, para qualquer alteração do ambiente, fora da faixa de conforto térmico, os animais necessitam de ajustes, sejam de natureza anatômica, fisiológica ou comportamental, na tentativa de se adaptarem à nova condição ambiental. O ambiente influencia o processo produtivo animal, principalmente, por alterar a troca de calor e o fracionamento da energia da ração, entre o ganho de energia e a dissipação de calor.Dessa forma, proporcionar o conforto térmico para que as aves obtenham maior aproveitamento dos nutrientes da ração para o processo produtivo é meta principal a ser alcançada na avicultura moderna, uma vez que situações extremas de frio ou calor influenciam a produção dos frangos de corte, por modificar seu requerimento nutricional.Segundo TARDIN (1995), a relação entre o ...

-The aim of this experiment was to study the consequences of precise feeding on the myofibre characteristics and metabolic traits of the breast muscle (Pectoralis major, Pm) of Muscovy ducks. Twenty-four samples of breast muscle, without skin or subcutaneous fat, from two groups of ducks, control and overfed respectively, were collected at 14 weeks of age. We assayed different chemical (water content, crude proteins, total lipid ashes, total and thermosoluble collagen), biochemical (activities of the CS, LDH and β-HAD enzymes), histological (muscle fibre typing and intramuscular adipocyte measurements) and technological (drip and cooking losses, texture) determinations. At the force-feeding period, the overfed ducks weighed 6366 g and the control ducks 4606 g of body weight. In the PM muscle, some modifications of the biochemichal parameters and enzyme activities were observed but neither the shear force nor the histological characteristics of the breast muscle were affected by the fattening treatment. The overfed birds had an increased total lipids content (correlated to an increase in the intramuscular area occupied by the adipocyte) and a different fatty acid profile as the result of a higher energy feed intake. The lipids of the Pm muscle of the overfed ducks contained more C16:0, C16:1n-7 and C18:1n-9, but less C18:0, C18:2n-6 and C20:4n-6 than the control birds. These results show that in response to high energy feeding, the muscle is able to respond quickly on a metabolic basis (by increasing the activities of the oxydative enzymes) without changing its typology or morphology. Additionally, fattening was correlated to a degradation in the technological qualities of the breast muscle, especially an increase in the cooking losses. muscovy duck / force feeding / Pectoralis major / muscle typing / fatty acid Reprod. Nutr. Dev. 43 (2003) [105][106][107][108][109][110][111][112][113][114][115] 105

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