Effects of Ractopamine in Combination with Various Hormone Implant Regimens on Growth and Carcass Attributes in Calf-Fed Holstein Steers

Abstract

The β-adrenergic agonist ractopamine (RAC) was approved for use as a feed supplement for beef cattle to increase lean muscle deposition and improve feed efficiency. The effects of several anabolic hormone implants were examined with or without RAC to determine feedlot and carcass performance of calf-fed Holstein steers. Sixteen hundred cattle were evaluated in 2 phases; cattle were divided equally into 8 treatments: 1) a nonimplanted non-RAC-fed control; 2) implanted with 20 mg estradiol benzoate plus 200 mg progesterone (EP); 3) implanted with 24 mg estradiol plus 120 mg trenbolone acetate (HT); 4) implanted with 20 mg estradiol plus 80 mg trenbolone acetate (MT); 5) nonimplanted and administered 200 mg/d RAC in the feed (R); 6) implanted with EP and administered 200 mg/d RAC (EP+R); 7) implanted with HT and administered 200 mg/d RAC (HT+R); 8) implanted with MT and administered 200 mg/d RAC (MT+R). Cattle administered RAC in both studies had increased (P < 0.05) hot carcass weight (HCW) and LM area (LMA) over cattle not fed RAC. All RAC plus implant treatments in both phases had greater (P < 0.05) HCW and LMA than the control. In addition, HCW in nearly all treatments in both phases was greater than in the R treatment group (P < 0.05). Over both phases, LMA was increased with the implant plus RAC treatments over control treatments. Ultimately, the addition of RAC in feedlot diets of Holstein steers during the last 36 d on feed increased feed efficiency and carcass lean deposition in a manner that was additive to implant effects.