López-Campos, Ó., Aalhus, J. L., Okine, E. K., Baron, V. S. and Basarab, J. A. 2013. Effects of calf- and yearling-fed beef production systems and growth promotants on production and profitability. Can. J. Anim. Sci. 93: 171–184. In each of 2 yr, 112 spring-born steers were used to evaluate the effect of calf-fed vs. yearling-fed with and without growth implant and ß-adrenergic agonist on production parameters and economic potential. Steers were grouped into: (1) non-implanted feeders harvested at 11-14 mo of age, (2) growth implanted feeders harvested at 11-14 mo of age, (3) non-implanted feeders harvested at 19-23 mo of age, and (4) growth implanted feeders harvested at 19-23 mo of age. Production data were collected and economic evaluation was performed. Calf-fed steers grew slower (1.21 vs. 1.99±0.07 kg d-1) and had a poorer feed conversion ratio [5.32 vs. 4.99±0.34 kg dry matter intake (DMI) kg-1 gain] during the feedlot dietary adjustment period than yearling-fed. Calf-fed steers were more efficient than yearling-fed during the first 76-83 d (5.16 vs. 7.33±0.11 kg DMI kg-1 gain) and latter 48-79 d (5.69 vs. 14.28±1.50 kg DMI kg-1 gain) of the finishing period. Implanted steers were more efficient than non-implanted during the dietary feedlot adjustment period (4.80 vs. 5.52±0.15 kg DMI kg-1 gain), and during the first 76-83 d (6.05 vs. 6.44±0.11 kg DMI kg-1 gain) and latter 48-79 d of the finishing period (9.29 vs. 10.69±1.50 kg DMI kg-1 gain). Implanted steers grew 11.4-19.6% faster than non-implanted throughout the finishing period, while yearling-fed grew 11.1-12.9% faster during the first 76-83 d, but 49.1-64.4% slower during the last 48-79 d of the finishing period compared with calf-fed. Quality grade was improved for non-implanted steers, with 43.6% of yearling-fed and 35.7% calf-fed steers grading AAA. Adjusted net return was best for calf-fed implanted ($17.52 head-1), followed by calf-fed non-implanted ($-41.92 head-1), yearling-fed implanted ($-73.77 head-1), and yearling-fed non-implanted ($-99.65 head-1) production strategies. The results of the present study suggest that reducing age at slaughter combined with growth implant can increase profit and reduce risk, but growth implants can negatively affect the carcass quality.
valorisation des aliments