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There has been extensive research on feeding broilers low-CP (LCP) diets to reduce nitrogen (N) excretion in the environment. It is well established that broilers fed LCP diets exhibit improvements in N efficiency, but this is coupled with inferior growth performance and poor carcass quality. Therefore, 2 experiments were undertaken to explore energy and N balance and performance in birds fed LCP diets to determine bird responses to dietary energy content. Both experiments used isoenergetic grower–finisher diets formulated to reduced- or high-CP (HCP) level. Measurements of AME, net energy, and N balance were conducted in a calorimetry system (experiment 1), and bird performance was measured in a floor pen feeding study (experiment 2). In experiment 1, birds fed the LCP diet had a comparatively higher ratio of energy (AME and net energy) intake to N retained, higher N efficiency (N retained/N intake), and higher ratio of energy retained as fat to total energy retention. In experiment 2, the LCP-fed birds had a comparatively higher feed conversion ratio at day 14 to 35 and a higher relative fat pad weight on day 35. Abdominal fat pad was positively correlated with the energy (AME and net energy) intake–to–weight gain ratio, suggesting that energy in excess was deposited as fat. These results present more highly efficient use of N in broilers reared on LCP diets. However, these birds also consumed excess energy relative to N retained, which was deposited as body fat accretion, thereby increasing the feed conversion ratio. |
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