396 Effect of zinc amino acid complexes on growth performance and carcass characteristics of finishing beef steers fed with or without ractopamine hydrochloride- a nine study pooled analysis

Abstract

Abstract A nine-study retrospective pooled analysis was conducted to evaluate supplemental Zn provided as an amino acid complex (ZnAA) on growth performance, carcass quality and yield in finishing beef steers fed with or without ractopamine hydrochloride (RAC) prior to slaughter. Data from nine well-controlled studies conducted at university and commercial feedlot research facilities in AB, IA, KS, OK and TX were evaluated using 249 pens ranging from 6 to 275 steers /pen (Total number=14,096 animals.; initial BW = 340± 6.2 kg). Treatments evaluated were: (1) Control (CON) =basal diet with 0 to 11 mg-1·kg-1 DM ZnAA and no RAC; (2) RAC = 200 to 320 mg RAC ∙hd-1∙d-1 fed 28 to 42 d prior to slaughter; (3) ZnAA only =30 to 120 mg-1·kg-1 DM fed throughout finishing period; (4) ZnAA + RAC. Main effects of feeding RAC, ZnAA and RAC × ZnAA interaction were determined for growth performance and carcass data with pen as experimental unit and initial BW as covariate. Combined analyses indicated no RAC × ZnAA interactions (P ≥ 0.23). RAC main effect improved carcass-adjusted growth performance and increased HCW and ribeye area (P ≤ 0.01). Main effect ZnAA increased carcass-adjusted final BW, ADG, and HCW (P ≤ 0.01); improved carcass-adjusted Gain: DM feed ratio (P = 0.06), dressing percentage (P = 0.02), and increased calculated yield grade, backfat thickness and percentage of carcass internal fat (P ≤ 0.10). A RAC × ZnAA interaction (P ≤ 0.10) was observed for USDA quality and yield grade distribution of carcasses. Incidence and severity of liver abscesses were reduced (P ≤ 0.05) by feeding either ZnAA or RAC. Feeding ZnAA and RAC to finishing cattle separately or in combination were additive for producing incremental improvements in production and carcass traits of economic importance.