Abstract:
The effect of zilpaterol hydrochloride (ZH), a β2-adrenergic agonist, on growth, feed intake andcarcass characteristics of broilers were examined. Broilers were raised in an environmentally controlled broiler house for 35 days. A standard commercial starter and grower diet was fed until day 28 when the experimental period started. The starter diet was fed for the first 14 days, followed by the grower diet from day 15 to 28 days (14 days). The experimental diet was administered for 7 days from day 28 to day 35. A completely randomised design with a 4 x 2 factorial arrangement was used for the four experimental diets containing different levels of ZH (0 mg/kg, 5 mg/kg, 7 mg/kg and 9 mg/kg) and fed to male and female broilers reared separately. Weekly body weight (BW) and feed intake (FI) measurements were taken and data was used to calculate feed conversion ratio (FCR). Two birds per pen were selected for sampling on day 36. Carcass weights, as well as individual portion measurements were taken for breast, thighs, drumsticks, wings and abdominal fat pad. The control group had the best performance values for BW, FI and FCR (P <0.05). The highest inclusion level of 9 mg/kg ZH resulted in significantly lower performance values. By contrast, ZH had a positive effect on carcass characteristics. Supplementation of ZH at a concentration of 5 mg/kg ZH improved carcass yield in both male and female birds, whereas 7 mg/kg ZH treatment resulted in the highest thigh and breast yields (P <0.05). Zilpaterol hydrochloride reduced abdominal fat deposition in females supplemented with 5 mg/kg ZH (P <0.05), however, higher inclusion levels of ZH resulted in increased fat deposition in both males and females. A sexual dimorphic effect was observed in the study. Female birds seemed to respond better to ZH supplementation compared to males, evidenced by their higher carcass yield and lower fat deposition. Based on the results, the selected ZH inclusion rates were too high, which caused a negative response on growth performance and fat deposition. However, supplementation of ZH at a concentration of 5 mg/kg ZH improved carcass yield.
