Abstract:

【Objective】 Two trials were conducted to investigate the effects of varying energy and protein intakes on the performance, body protein deposition and body fat deposition in broilers between 0-3 weeks and 4-6 weeks in order to identify the relationships between efficiency of protein utilization for body protein deposition (ep) and energy/protein ratio and the efficiencies of energy utilization for protein and fat deposition in broilers between 0-3 weeks and 4-6 weeks. 【Method】 The two trials with similar design were conducted during 0-3 weeks and 4-6 weeks, respectively. At 1day and 21 days of age, four hundred and thirty-two Arbor Acres (AA) broilers with similar body weight were respectively randomly arranged into 24 treatments with 3 replicates of 6 chicks by sex and diets. In each trial, broilers were fed with 95%, 80%, 65% and 50% restriction of ad libitum intake, respectively. Each day, broilers were supplied with three allowances of high-protein basal feed and appropriate amount of starch which were determined by 4 feeding levels. Thus, 12 diets with different energy/protein ratios were formed. At the beginning and the end of each trial, broilers were killed, and the body compositions were determined. 【Result】 The results showed that with the increase of energy/protein ratio, the efficiencies of protein utilization for body protein deposition in broilers between 0-3 weeks increased linearly. When the energy/protein ratio reached 69.28 MJ?kg-1, the eps of male and female broilers attained their maximum values of 0.64 and 0.63, respectively, then kept constant. With the increase of energy/protein ratio, the eps of broilers between 4-6 weeks increased linearly. When the energy/protein reached 69.28 MJ?kg-1, the eps of male and female broilers attained their maximum values of 0.58 and 0.56, respectively, then kept constant. When the energy/protein ratio was the same, the eps of male and female broilers were higher during the 0-3 weeks than during the 4-6 weeks. During the 0-3 weeks, the efficiencies of energy utilization for protein deposition in male and female broilers were 0.72 and 0.68, the efficiencies of energy utilization for fat deposition in male and female broilers were 0.59 and 0.65, 32.88 and 34.82 kJ of ME were needed for each gram of fat deposition in male and female broilers, and 66.43 and 60.12 kJ of ME were needed for each gram of protein deposition. During the 4-6 weeks, the efficiencies of energy utilization for protein deposition in male and female broilers were 0.70 and 0.65, the efficiencies of energy utilization for fat deposition in male and female broilers were 0.75 and 0.81, 34.04 and 36.38 kJ of ME were needed for each gram of fat deposition in male and female broilers, and 52.12 and 48.32 kJ of ME were needed for each gram of protein deposition. 【Conclusion】 The results above indicated that both of the efficiencies of protein utilization for body protein and the efficiencies of energy utilization for protein and fat deposition in broilers were different between 0-3 weeks and 4-6 weeks.

Key words: broiler, energy, protein, efficiency of deposition