Response of Young Broilers to Graded Levels of Dietary Protein and Amino Acids
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Date
2005-06-27
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Abstract
Previous research suggested that broiler body weight responds in a linear manner to increasing concentrations of dietary crude protein (CP) containing an ideal profile of amino acids. Three studies were conducted to determine the effects of CP and amino acid balance on the response of young broilers to graded levels of CP and lysine. Experiments 1 and 2 utilized a series of 12 diets that were formulated to contain CP levels of 21.8, 23.5, 25.2, and 26.9% at each of three levels of ME (3000 kCal/kg, 3100 kCal/kg, and 3200 kCal/kg). In all formulations the percentage of dietary ME supplied by added oil was kept constant and dietary CP was set at 5.5% of total lysine resulting in total lysine concentrations 1.20%, 1.29% 1.38% and 1.47%. Experiment 1 utilized 1,152 Cobb x Cobb broilers reared in 72 floor pens with 8 male and 8 female birds per pen while the same experimental diets were applied to 640 male and female broilers with six replicate pens of five male and five female broilers in Experiment 2. Weekly body weight gain (BWG), feed intake and mortality were recorded. All data were subjected to multiple regression analyses and orthogonal contrasts were used to describe the nature of the response obtained. Results showed 21 d broiler BWG to respond in a linear manner to increasing levels of lysine balanced to maintain the same ratios of CP and essential amino acids to the highest total lysine level of 1.47% (27% CP). Increasing dietary ME from 3,000 to 3,100 kCal/kg improved BWG with no further improvement when the ME was increased to 3,200 kCal/kg. There was no effect of dietary ME concentration on feed intake resulting in no interaction between dietary ME and CP on BWG.
Experiment 3 further evaluated the response in broiler BWG to increasing concentrations of lysine incorporated in the diet either alone or in a balanced manner to dietary CP. Two lysine deficient basal diets were formulated to contain either 22.0% Protein (LOW CP) or 27.2% (High CP) while the other essential amino acids were fixed in proportion to the respective dietary CP content and met or exceeded NRC (1994) recommendations. The basal diets were each supplemented with Lysine-HCL to create eight diets containing 0.85%, 1.08%, 1.19%, and 1.30%, or 1.12%, 1.22%, and 1.45% digestible lysine for the Low CP and High CP diet series, respectively. A third series of diets (Balanced CP) was created by blending one intermediate diet of each of the High CP and Low CP diet series in the required proportions resulting in a series of diets containing graded CP levels of 22.0, 23.9, 25.6 and 27.2% while all contained the same ratio of lysine to CP and a fixed ideal ratio of indispensable amino acids to lysine. Treatments were applied to 800 Ross 308 male broiler chicks, distributed across 80 floor pens. Results showed the 20 d BWG of birds on the Low CP diet series to be best described by a quadratic function with the total lysine requirement estimated at 1.22%. In contrast, the response in BWG to both the High CP and Balanced CP diet series was only linear in nature with the absence of a plateau in the response to lysine allowing no estimate of the lysine requirements over the range of CP evaluated. These data suggests that broilers can respond to higher levels of dietary lysine than has previously been reported in the literature, provided that essential and non-essential amino acid levels were also increased proportionately.
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Keywords
Broiler, protein, amino acids, ideal amino acid profile, lysine
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Degree
MS
Discipline
Poultry Science
