Metabolizable energy levels in diets for slow-growing chickens

Abstract In this study, we aimed to assess the impact of four levels of metabolizable energy (ME) in feed for slow-growing male and female chickens on their growth performance, carcass yield, and nutrient metabolizability. For growth performance and carcass yield analyses, 480 male and female Isa Label chicks were distributed in a completely randomized design in a 4 × 2 factorial scheme. The birds were fed experimental diets containing 4 different ME levels (2,725, 2,850, 2,975, and 3,100 kcal/kg) during two different feeding periods ranging from 1-28 and 1-56 days of age, with each treatment group consisting of 6 replicates of 10 birds each. The effects of these feeding treatments on growth performance were assessed at 28 and 56 days of age, whereas those on carcass yield were evaluated at 56 days of age. The metabolic analysis was carried out by total excreta collection from 17 to 21 days, using the same treatments as in the growth performance and carcass yield analyses and eight replicates of 10 birds, totaling 320 birds. The data were subjected to the analysis of variance and polynomial regression for ME levels. At 28 days, the chickens showed significant differences in their live weight, weight gain, and feed consumption. Moreover, a positive quadratic regression was found for live weight and weight gain, and a negative linear regression was obtained for feed conversion. At 56 days, a quadratic regression was found for feed consumption and conversion, with no effect on carcass or prime cut yields. Nitrogen balance and nitrogen metabolizability coefficient showed a quadratic regression effect. A positive linear regression was found for ether extract balance, and a quadratic regression was obtained for the metabolizability coefficient. The variables apparent ME and the ME corrected for nitrogen showed a positive linear regression effect. It can be concluded that feed containing 2,900-2,930 kcal ME/kg is recommended for broiler chickens during 1-28 days of their age, regardless of sex.