Abstract:
This study aimed to compare the effects of feeding 60 mg of the β-adrenergic agonist, zilpaterol
HCl (Zilmax®), per steer per day versus feeding 120 mg of the β-adrenergic agonist, R-salbutamol
(Salbutamate®10%), per steer per day for the last 30 days of the finishing period on the growth,
efficiency, and carcass characteristics of 228 typical South African feedlot steers in a completely
randomised control study. The steers were slaughtered at the same abattoir after a 3-day withdrawal
period. The growth and feedlot parameters included starting mass, slaughter mass, average daily
gain, live mass gain, and lean carcass gain. The carcass characteristics included warm (WCW) and
cold carcass mass (CCW), carcass length (CL), subcutaneous fat thickness measured over the 13th
rib (SCF), dressing percentage, carcass compactness, carcass classification score, age code, and
fat code using the South African carcass classification system. The inclusion of zilpaterol HCl as a
feed additive resulted in higher growth and efficiency, with an ADG of 1.3 kg/day (P <0.05) in steers
fed zilpaterol HCl compared to 1.1 kg/day for steers fed R-salbutamol. Steers in the zilpaterol HCl
experimental group had a 12.5 kg higher average slaughter mass, yielding ~3 kg higher calculated
lean gain than steers fed R-salbutamol. Steers fed zilpaterol HCl yielded better carcass
characteristics of 11.4 kg higher CCW and marginally longer carcasses compared to steers fed Rsalbutamol.
Therefore, the overall growth, feedlot performance, and carcass characteristics were
higher in the zilpaterol HCl-fed steers than in R-salbutamol-fed steers.
