Effects of conventional and nonconventional growth-enhancing technologies for finishing feedlot beef steers

Two experiments were conducted to evaluate conventional (tylosin, monensin, steroidal hormone growth implants, and β-adrenergic agonist) and nonconventional [direct-fed microbial (DFM), fibrolytic enzyme (ENZ), and flavoring agent (OLEO)] growth-enhancing technologies on the performance of finishing beef feedlot steers. In Exp. 1, 384 crossbred beef steers (499 ± 28.6 kg of BW) were randomly assigned to 8 feedlot pens equipped with a system for measurement of individual feed intake. Steers were assigned to 1 of 8 diets with or without hormonal implants in a completely randomized 8 × 2 factorial treatment structure, with diet and implant as main factors (24 implanted steers and 24 nonimplanted steers per pen). The diet treatments were (1) nonmedicated diet (NMD); (2) NMD+DFM; (3) NMD+ENZ; (4) NMD+OLEO; (5) NMD+DFM+ENZ+OLEO; (6) medicated diet containing monensin, tylosin, and β-adrenergic agonist (CVD); (7) CVD+DFM+ENZ, and (8) CVD+DFM+ENZ+OLEO. In Exp. 2, 960 crossbred beef steers (426 ± 39.9 kg of BW) were randomly allocated to 1 of 4 treatments (12 pens per treatment): (1) natural (no antibiotics, ionophores, growth implants, or β-adrenergic agonists; NAT); (2) NAT+OLEO; (3) medicated diet containing ionophore and tylosin (CONV); and (4) CONV with hormonal implant and β-adrenergic agonist (CONV+HI/BA). Improvement (P < 0.05) in the performance of finishing feedlot steers with the use of conventional growth-enhancing technologies was confirmed. The nonconventional technologies evaluated did not result in any improvement (P > 0.10) in growth performance. Eliminating conventional growth-enhancing technologies reduced feed efficiency and growth performance, consequently undermining the sustainability of beef production systems.