Effects of dilution of the starter diet and narrowing of the energy: Protein ratio of the finisher diet on productive performance and body composition of male broiler chicks

To minimize excessive fatness of broiler chicks, a two-stage experiment was run. During the first stage, a 75% dilution of the starter diet with oat hulls was done for 0, 7 or 10 days, starting on day 7 of age (treatments AB and C respectively). During the second stage, the energy/protein ratio (EPR) in the finisher diet (42-49 days) was manipulated to obtain either a ''normal'' (NEPR: treatments A(1)-B-1-C-1) or a ''narrow'' (NAEPR: treatment A(2)-B-2-C-2) enerpy/protein ratio. Live weight (LW) and feed intake (FI) were controlled weekly and feed conversion efficiency (FCE) was calculated. At the end of the experience, carcass characteristics and the composition of the edible part and skin were determined, and a sensory evaluation of the edible part was done. Results at 49 days of age were obtained and presented according to both factors of the factorial arrangement, as no statistical significance was found in any interaction for the different variables under study. The main results obtained during the first stage of the experiment were, for treatments A-B-C respectively: LW (kg): 2.07a, 1.87b and 1.82b; FI (kg): 4.10a; 3.83b and 3.77b; weight of the edible part (kg): 0.62a; 0.52b and 0.47b; weight of the abdominal fat (g): 38.6a; 28.6b and 25.0b; weight of the skin (g): 185.4a; 140.1b and 136.4b. The second stage of the experiment (EPR), produced the following results for treatments NEPR and NAEPR respectively: no statistical effects on LW, FI or FCE. Weight of the abdominal fat (g): 35.6a and 25.7b; weight of the skin (g): 168.8a and 139.2b; ether extract of the edible part without skin, dry basis (%): 18.3a and 15.9b; ether extract of the skin, dry basis (%): 74.6a and 71.3b. All the differences informed, were significant at least at p <0.05. The sensory evaluation showed no statistical differences among treatments. All groups were adequately accepted by the sensory panel. Finally, although the results concerning a decrease in fat content of the birds were promising, more work is needed to clearly design a feeding management system to maximize this effect with a minimum of undesirable side effects.