Excessive Levels of Dietary Protein and Energy Induce Lack of Growth Promoting Effects of Clenbuterol in Broilers

  • Hamano, Y. (Department of Animal Science, Akita Prefectural College of Agriculture) ;
  • Yamazaki, S. (Department of Animal Science, Kitasato University) ;
  • Kume, K. (Department of Animal Science, Kitasato University) ;
  • Kobayashi, S. (Department of Animal Science, Kitasato University) ;
  • Terashima, Y. (Department of Animal Science, Kitasato University)
  • Received : 1998.01.31
  • Accepted : 1998.04.06
  • Published : 1998.10.01


The present study examined the effects of excessive dietary protein and energy on growth response to clenbuterol in broilers. The chicks were allocated into 6 groups at 14d old, and used for a $3{\times}2$ factorial experiment. Birds were fed six diets, the control diet containing 21% crude protein (CP) and 3,100 kcal of metabolizable energy ME/kg, a high protein (30% CP) or a high energy (3,500 kcal/ ME/kg) diet, with or without 1 ppm clenbuterol, for 18 d. Clenbuterol feeding markedly decreased (p < 0.05) body weight gain by 23% in the high energy group. Feed intake was also decreased (p < 0.05) by clenbuterol administration across diet treatments. Abdominal fat weight was reduced (p < 0.05) by clenbuterol only when chickens were fed the high energy diet. Clenbuterol increased (p < 0.05) leg muscle weight in the control diet group, but decreased (p < 0.05) it in the high energy group. Muscle protein concentration was increased by 11 % in leg muscle only of the birds at the high energy level. In leg muscle, clenbuterol enhanced the protein/DNA ratio by 18%, except for the high protein group. These results indicate that feeding a diet containing excessive amounts of protein and more energy than normal did not necessarily improve growth response to clenbuterol.