Abstract
A Box-Behnken designed study was completed to predict growth performance, carcass characteristics and plasma hormone and metabolite levels as influenced by dietary energy, amino acid densities and starch to lipid ratios in male broiler chickens. The design comprised three dietary energy densities (11.25, 12.375 and 13.5 MJ/kg), three digestible lysine concentrations (9.2, 10.65 and 12.1 g/kg) and three starch to lipid ratios (4.5, 12.25 and 20.0) in broiler diets based on maize and soybean meal. Each of thirteen dietary treatments was offered to 10 replicates of 15 birds per replicate floor pen or a total of 1,950 Ross 308 male broiler chickens from 21 to 35 days post-hatch. Increasing dietary energy decreased feed intake with a quadratic relationship between feed intake and dietary standardised ileal digestible (SID) Lys concentrations, where increasing SID Lys initially increased and then depressed feed intake. Increasing dietary amino acid density increased body weight gain and carcass weight; however, dietary energy did not influence body weight gain, carcass and breast meat weight. Feed efficiency was positively influenced by energy and amino acid densities but negatively influenced by starch to lipid ratios and energy and amino acids had more pronounced impacts than starch to lipid ratios. This study indicated that both energy and amino acid densities regulate feed intakes in broiler chickens. Body weight gain of modern broiler chickens is more responsive to amino acid densities; nevertheless, dietary energy density continues to play an important role in protein utilisation, as reflected in significantly reduced plasma uric acid levels.
Highlights
Satisfactory muscle protein deposition requires both glucose and amino acids because glucose is the primary energy source to promote the incorporation of amino acids into protein [1]
The influence of dietary treatments on weight gain, feed intake and feed conversion ratio (FCR) from 21–35 days post-hatch is shown in Table 5 (S1 Table)
The interactions between dietary energy densities, amino acid and the energy source in respect of feed intake indicate that regulation of feed intake involves all three factors
Summary
Satisfactory muscle protein deposition requires both glucose and amino acids because glucose is the primary energy source to promote the incorporation of amino acids into protein [1]. Modern broiler chickens are selected for optimal growth rate, feed conversion efficiency and breast meat yield and are very responsive to both energy and amino acid dietary densities [3,4,5]. This emphasises the importance of energy and amino acid densities in the formulation of practical broiler chicken diets where these densities are usually considered in tandem. Our recent study [6] considered the former approach where broiler chickens were offered diets containing consistent digestible lysine to metabolisable energy ratios and the influence of starch to lipid ratios and dietary energy densities on growth performance was investigated. There is a lack of recent studies investigating the interactive influence of energy and amino acids in broiler chickens when energy and amino acids are manipulated separately
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