Effect of grain inclusion rates in diets provided to early-weaned calves and steroidal implants utilization on growth performance and carcass characteristics of beef steers.

One hundred and twenty-one Angus × SimAngus-crossbred steers (body weight ( BW ) = 159 ± 22 kg) were used to evaluate the effects of different grain inclusion ( GI ) rates in diets provided to early-weaned calves and steroidal implants ( SI ) utilization on growth performance and carcass characteristics, particularly intramuscular fat deposition, of beef steers. The experiment was conducted as a randomized complete block design with a 2 × 2 factorial arrangement of treatments, consisting of two GI rates (35% vs. 58%, dry matter ( DM ) basis), each one associated or not to steroidal implant utilization (no implants vs. 80 mg trenbolone acetate ( TA ) + 16 mg estradiol followed by 120 mg TA + 24 mg of estradiol). After being early-weaned (124 ± 14 d of age), steers were offered an average of 4.5 kg/d (DM basis) of a concentrate-based diet with a greater or lesser GI rate for 60 d. After being fed a concentrate-based diet with different GI rates for 60 d, steers were fed a common backgrounding diet for 56 d and subsequently fed a common high-grain diet until harvested at a constant final BW (620 kg). Steers were not implanted until the beginning of the backgrounding phase and then re-implanted when initiating the finishing phase. Data were analyzed using PROC MIXED in SAS. There were no GI × SI interactions ( P  ≥ 0.62) for any of the growth performance parameters throughout the experimental period. Implanted steers tended to have a greater average daily gain ( P  = 0.10) during the finishing phase than nonimplanted steers. For the 12th rib fat thickness and yield grade ( YG ), a GI × SI interaction ( P  = 0.03) and a tendency for a GI × SI interaction ( P  = 0.10) was detected, respectively. Nonimplanted steers fed diets with greater GI rates presented the greatest 12th rib fat thickness and tended to have the greatest YG among treatments. No other interactions ( P  ≥ 0.33) were observed for the hot carcass weight, Longissimus muscle ( LM ) area, quality grade, marbling score, and kidney-pelvic-heart fat content. Steers fed diets with lesser GI rates tended to have a greater LM area than steers fed diets with greater GI rates ( P  = 0.10). Results from this experiment indicate that varying GI rates in diets provided to early-weaned calves and subsequent implantation with steroidal hormones did not affect marbling deposition.