Introduction
The compounds known as B-adrenergic agonists(B-AA) are organic molecules that have the ability to bind to B-adrenergic receptors(B-AR) and start biochemical reactions that will result in increased rate of weight gain and carcass leanness through enhanced accretion of skeletal muscle and reduction in accretion of fat(Mersmann, 1998: Mersmann, 1998). Zilpaterol hydrochloride(ZH) is an orally active members of a B-AA. which have gener- ally been shown to improve average daily gain(ADG), gain: feed(G:F), carcass weight gain, dressing percentage, and longissimus dorsi(LD) muscle in beef cattle(Avendano-Reyes et al.. 2006) and