A Meta-analysis of Zilpaterol and Ractopamine Effects on Feedlot

Abstract Text:

This study is a meta-analysis of the effects of the beta-agonists zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RAC) on feedlot performance, carcase characteristics of cattle and Warner Bratzler shear force (WBSF) of muscles. It was conducted to provide data that would be useful in considerations on the effect of these agents on meat quality in Meat Standards Australia evaluations. We conducted a comprehensive literature search and study assessment. Data were extracted from more than 50 comparisons for both agents and analyzed using a random effects meta-analysis and meta-regression using Stata (Stata 13.0). Results included forest plots, funnel plots, raw and weighted means and estimates of effects size for each of ZH or RAC, independently. There was little evidence of publication bias on evaluation of funnel plots. Both agents markedly increased final body weight as indicated by the effect size (ES) 0.45 95% confidence interval (95% CI) 0.28 to 0.62 and weighted mean difference (wmd) 8.15 kg, (95% CI 5.63 to 10.67 kg) for ZH, RAC ES 0.40 (95% CI 0.24 to 0.56) and wmd 7.67 kg (95% CI 5.58 to 9.55 kg), hot carcase weight for ZH ES 1.32 (95% CI 1.03 to 1.61) and wmd 15.18 kg (95% CI 13.62 to 16.74 kg), RAC ES 0.47 (95% CI 0.31 to 0.63) wmd 6.18 kg (95% CI 4.55 to 7.82 kg) and longissimus muscle area (ZH ES 2.30 (95% CI 1.90 to 2.71) wmd 8.01 cm² (95% CI 7.05 to 8.96 cm²), RAC ES 0.39 (95% CI 0.20 to 0.58) wmd 1.84 cm² (95% CI 1.17 to 2.52 cm²) and increased the efficiency of gain:feed ratio (ZH ES 0.88 (95% CI 0.67 to 1.11) wmd 0.15 kg (95% CI 0.11 to 0.19, RAC ES 0.77 (95% CI 0.58 to 0.96) wmd 0.018 kg (95% CI 0.014 to 0.022). These effects were particular large for ZH, however, ZH decreased fatness (by either ribfat or marbling score) with an ES of about -0.8 SD. For RAC the effects on fatness were much smaller with an ES of 0.0 and -0.1 for ribfat and marbling score, respectively. Zilpaterol also markedly increased WBSF by 1.2 standard deviations and more than 0.8 kg, while RAC increased WBSF by 0.43 standard deviations and 0.2 kg. This work has provided critically needed information on the effects of ZH and RAC on production, efficiency and meat quality.

Keywords: zilpaterol hydrochloride, ractopamine hydrochloride, meta-analysis