A total of 1,197 pigs (PIC 337 × 1050) were used in a 72-d study to determine the
effects of added zinc from zinc oxide (ZnO) fed in grower (d 0 to 45; initially 129.6 lb)
and finisher (d 45 to 72; initially 218.3 lb) pig diets with or without ractopamine HCl
(RAC; Paylean; Elanco Animal Health, Greenfield, IN) on growth performance and
carcass characteristics. Pens were randomly assigned to a 2 × 2 × 2 factorial arrangement
in a split-plot design. The whole plot consisted of diets with or without 75 ppm
added Zn from d 0 to 45, and the subplots were diets with or without 75 ppm added
Zn and with or without 10 ppm RAC from d 45 to 72. All diets contained 50 ppm
Zn supplied from the premix. No interactions were observed. Addition of 75 ppm Zn
during either period or both periods did not influence overall pig growth performance
or carcass characteristics. Pigs fed RAC had improved (P < 0.03) ADG, F/G, final BW,
HCW, loin depth, and fat-free lean index compared with pigs fed the control diet. In
conclusion, feeding RAC improved the performance of growing-finishing pigs, but
additional Zn did not.
