Zilpaterol Hydrochloride Repartitions Chemical Components of the Empty Body of Holstein Steers

Abstract Text: A serial harvest from 254 to 534 days on feed (DOF) was conducted to quantify changes in growth and composition of calf-fed Holstein steers (n = 110, initial BW = 449.2 ±19.9 kg).  One-half were supplemented with the β-2 adrenergic agonist zilpaterol hydrochloride (ZH; 8.33 mg/kg 100% DM basis) with the remainder fed a control (CON) ration during the final 20 d followed by a 3 d withdrawal prior to harvest.  Cattle were randomly allocated to dietary treatment and harvest endpoint (254, 282, 310, 338, 366, 394, 422, 450, 478, 506, and 534 DOF) in a 2 x 11 factorial randomized complete block experimental design conducted in the years 2012 and 2013.  Cattle fed ZH had increased (P ≤ 0.03) empty body weight (EBW; 17.8 kg), HCW (20.7 kg), dressed yield as a percentage of shrunk BW (DYSBW; 2.1 %), dressed yield as a percentage of EBW (DYEBW; 1.3 %), and empty body moisture (EBM; 1.3 %) compared to CON steers regardless of DOF.  Concurrently, cattle fed ZH had less (P ≤ 0.02) digesta fill (6.1 kg) and empty body fat (EBF; 1.7 %) compared to CON steers.  Absolute weights of the empty body components including blood, hide, internal cavity components (ICC), and bone were not different (P > 0.20) for steers fed ZH or the CON diet.  However, cattle fed ZH had increased (P < 0.01) carcass soft tissue (CST; 20.2 kg) compared to CON cattle.  When comparing ZH and CON empty body components as a percentage of EBW, cattle fed ZH had less (P ≤ 0.02) hide (0.3 %), ICC (1.0 %), and bone (0.5 %).  Furthermore, cattle fed ZH had more (P < 0.01) CST (1.7 %) compared to CON steers with no difference (P = 0.81) in blood as a percentage of EBW.  Comparing the chemical composition of the ICC, ZH steers had less (P = 0.05) protein (0.7 %) with more (P = 0.02) ash (0.1 %) compared to CON steers.  Comparing the chemical composition of CST, cattle fed ZH had increased (P = 0.02) moisture (1.4 %) with a concurrent reduction (P< 0.01) in fat content (2.0 %) compared to CON cattle.  This investigation proposes that the increase in dressed carcass yield observed in ZH supplemented cattle may best be explained by reductions in hide, fill, and ICC.

Keywords: Beef, Zilpaterol Hydrochloride, Composition