Effects of zilpaterol hydrochloride and zinc methionine on growth performance and carcass characteristics of beef bulls

Sixty beef bulls with a body weight (BW) of 314.7 +/- 16.2 kg were used to evaluate the effects of zilpaterol hydrochloride (ZH) and zinc methionine (ZM) on growth performance and carcass characteristics. The experimental design was a randomized complete block, with a factorial 2 x 2 arrangement of treatments (ZH: 0 and 0.15 mg kg(-1) BW; ZM: 0 and 80 mg kg(-1) dry matter). The ZH increased (P<0.05) the final BW, average daily gain, feed conversion, carcass yield and longissimus dorsi area. Bulls fed ZH plus ZM had less (P<0.01) backfat thickness and intramuscular fat (IMF) compared with those fed ZH or ZM alone. The ZH increased (P<0.02) the meat crude protein content and cooking loss. It is therefore concluded that ZH increases growth performance, carcass yield, longissimus dorsi area, and meat crude protein. The interaction of ZM and ZH did not present additional advantages. The reason for the reduction in backfat thickness and IMF by ZH plus ZM is unclear, and implies that our knowledge of beta-agonistic adrenergic substances and their interactions with minerals is incomplete.