Zilpaterol-HCl (Zilmax; Intervet/Schering-Plough Animal Health, Millsboro; DE)
is an orally active β2-adrenergic agonist that is approved for use in feedlot cattle at the
rate of 7.56 g/ton of diet dry matter for the final 20 to 40 days on feed. The minimum
withdrawal time for Zilmax is 3 days. Zilmax increases hot carcass weight and dressing
percentage, primarily as a result of increasing lean muscle mass and decreasing body
fat. Zilmax also decreases marbling and increases shear-force values (i.e., less tender) of
steaks. This study was conducted to determine whether the benefits of Zilmax would be
retained with longer withdrawal times while overcoming undesirable effects on shear
force and marbling.
