Comparative effects of monensin and alternative feed additives on productive performance and rumen fermentation in...

Zebu cattle predominate in tropical beef systems, but no meta-analysis has compared monensin with alternative additives specifically in Zebu cattle. This meta-analysis aimed to compare the effects of monensin and alternative feed additives on productive performance and rumen fermentation in Zebu beef cattle. Forty-seven studies (408 comparisons) were included. We performed a random-effects meta-analysis to estimate mean differences (MD) with 95% confidence intervals and explored heterogeneity using subgroup analyses and meta-regression. Average daily gain (ADG) was greater in animals receiving natural additives (+5.01%; MD = 0.063; CI: 0.048 to 0.078) or probiotics (+5.03%; MD = 0.083; CI: 0.021 to 0.145) than in those receiving monensin. In contrast, ADG was lower in animals treated with virginiamycin (-3.42%; MD = -0.042; CI: -0.073 to -0.010) or lasalocid (-14.5%; MD = -0.076; CI: -0.081 to -0.072). These increases in ADG with natural additives and probiotics could potentially shorten finishing time under typical feedlot conditions. Dry matter intake (DMI) was higher in animals receiving monensin plus virginiamycin, natural additives, virginiamycin, monensin plus narasin, probiotics, narasin, and monensin plus probiotics compared with monensin alone. Feed efficiency (FE) was higher in animals supplemented with monensin plus virginiamycin (+2.05%; MD = 0.003; CI: 0.0003 to 0.006) but lower in those receiving virginiamycin alone (-9.90%; MD = -0.014; CI: -0.016 to -0.011) compared with monensin. Methane emissions did not differ among treatments, indicating similar effects on enteric methane production. Natural additives and probiotics increased ADG, but the diversity of compounds and inclusion levels limits identifying which specific components drive the response. Overall, monensin remains a consistent additive for improving FE in Zebu cattle, whereas combining it with virginiamycin resulted in even greater FE and may represent a useful strategy.