A Repartitioning Agent to Improve Performance and Carcass Composition of Broilers

Abstract

Clenbuterol [benzyl alcohol, 4-amino-α-(t-butylamino)methyl-3,5-dichloro] was tested in the finisher ration of broilers in three series of experiments for its effects on performance and carcass characteristics. In Experiment 1, administration of clenbuterol at feed levels of .25, .5, 1, 2, and 4 ppm from 28 to 49 days of age resulted in significant sex combined weight gain improvements at all levels except 4 ppm and significant feed efficiency improvements at all levels tested. Uneviscerated body composition analysis indicated that clenbuterol treatment significantly increased body protein and water content and decreased body fat in female birds. In males, body fat was significantly reduced by 1, 2, and 4 ppm clenbuterol. From these results the 1 ppm level was selected for further testing. In Experiments 2 and 3, clenbuterol fed from 28 to 49 days of age significantly improved sex combined weight gain and feed efficiency and both male and female 49-day weights. Carcass yield was significantly increased in males and females by 1.11 and 1.91 percentage points, respectively. Abdominal fat was significantly reduced by clenbuterol feeding only in females. Carcass analysis indicated that clenbuterol-fed birds had a significantly lower carcass fat content. In Experiments 4 to 7, clenbuterol was administered at 1 ppm in the finishing feed but was withdrawn 3 to 5 days prior to terminal performance and carcass evaluations. Clenbuterol significantly improved sex combined weight gain and feed efficiency, and 49-day weights for both sexes. Carcass yield was significantly increased in males and females by .54 and .98 percentage points, respectively. Clenbuterol reduced abdominal fat only in female birds. Carcass fat content was significantly lower in both males and females fed clenbuterol while carcass protein was increased in females. These experiments demonstrate that clenbuterol causes a repartitioning of energy in the broiler resulting in improved performance, carcass yield, and carcass lean tissue content and reduced carcass fat. This repartitioning effect was more pronounced in females which also had reduced abdominal fat. These improvements were maintained in birds subjected to a 3- to 5-day withdrawal of clenbuterol.