The effect of feeding antibiotic growth promoters on the performance of beef cattle consuming forage-based diets: A review

Abstract

Scientific literature on the use of antibiotic growth promoters (AGP) in beef cattle consuming forage-diets was reviewed. Database summarizes 136 comparisons between untreated and AGP-treated cattle from 48 bibliographic references. Performance data of cattle receiving AGP either alone or in combination with 17 β-estradiol implants was statistically analyzed. Forage quality, in terms of average daily gain (ADG), differentially influenced ( P = 0.1) the effect of AGP on beef cattle performance. As the quality of forage increased, the estimated net ADG response to monensin decreased and that to lasalocid increased. ADG increased quadratically ( P < 0.01) with increasing doses of monensin ( R 2 = 0.71) or lasalocid ( R 2 = 0.63). Ionophore-dosage level quadratically improved ( P = 0.01; R 2 = 0.52) feed conversion (FCONV) of cattle without affecting their dry matter intake (DMI; P > 0.1). A linear relationship ( P < 0.01) between ADG and dose of tetronasin ( R 2 = 0.64) or lysocellin ( R 2 = 0.52) was also observed. The combination of monensin and 17 β-estradiol implants resulted in an additive effect on ADG of grazing cattle. The experimental results reviewed show that, in beef cattle consuming forage-based diets, ionophores improve ADG and FCONV in a dose-dependent manner, with little or no effect on DMI. In addition, results suggest that forage quality influences the direction of the ADG response to AGP supplementation in cattle. Summarized data from beef cattle implanted with 17 β-estradiol and/or supplemented with monensin indicate that the combined response of these two compounds on cattle grazing high-quality pastures has no effect on ADG over that obtained by 17 β-estradiol alone.