Effects of ractopamine and protein source on growth performance and carcass characteristics of feedlot heifers1

Abstract

An experiment was conducted to determine the relationship between feeding ractopamine and different amounts of MP on growth and carcass characteristics of feedlot heifers. Seventy-two crossbred heifers (475 kg of initial BW) were fed individually a diet based on steam-flaked corn for ad libitum intake for 29 d. Heifers were implanted with 140 mg of trenbolone acetate and 14 mg of estradiol-17beta 60 d before the experiment. Treatments were arranged as a 2 x 3 factorial and included 0 or 200 mg of ractopamine-HCl (23 ppm)/ d, and urea, solvent soybean meal, or expeller soybean meal (ESBM) as the predominant protein supplement. The amounts of MP supplied by the urea, solvent soybean meal, and ESBM diets were 688, 761, and 808 g/ d, respectively, calculated according to level 1 of the NRC model. Body weights were obtained 1 d before ractopamine feeding and at slaughter. Blood samples were obtained 1 d before starting the experiment and 13 d later. Ractopamine improved ADG, efficiency of gain, carcass-adjusted ADG, and carcass-adjusted efficiency of gain (P < 0.01). For ADG, heifers demonstrated a ractopamine x protein source interaction (P < 0.05); heifers not fed ractopamine had greater ADG when fed ESBM than when fed urea, whereas for heifers fed ractopamine there were no differences (P > or = 0.10) among protein supplements. This interaction was not observed for carcass-adjusted ADG (P = 0.60). Final live weights (P = 0.02) and carcass weights (P = 0.01) were greater with ractopamine feeding. Carcass marbling scores and yield grades were not affected by ractopamine or protein source (P > or = 0.39). Plasma total alpha-amino N and glucose concentrations decreased more from pretreatment concentrations when heifers were fed ractopamine (P < 0.05). Feeding ractopamine to heifers for 28 d before slaughter improved ADG and efficiency of gain without any large effects on carcass characteristics. The MP supply does not need to be increased from that provided by finishing diets based on steam-flaked corn with urea as the primary N supplement to allow the maximal response to ractopamine by finishing heifers.

Effects of ractopamine hydrochloride and dietary protein content on performance, carcass traits and meat quality of Nellore bulls

“…Contrary to our hypothesis, increasing dietary CP above standard requirement had no effect on body gain or feed efficiency in the present study. Our results corroborate with that of Walker et al (2006), who suggested that feeding β-agonists could enhance the efficiency with which cattle use MP, thereby leading to no change in protein requirements.…”

“…The increase in the efficiency of AA metabolism by RH supplementation can also explain the increase in plasma total protein associated with the CP120 diet. A lower muscle degradation rate, because of RH supplementation, can lead to reduced plasma urea concentration (Walker et al, 2006;Bryant et al, 2012), but this was not the case in the present study. Plasma activities of the liver enzymes AST, GGT and ALP are used as possible indicators of hepatic disturbances.…”

“…Because of the increase on muscle accretion, protein requirements may also be enhanced in ractopamine treated animals. There are few data reporting the effect of dietary CP on cattle or swine fed with ractopamine hydrochloride (RH) (Mitchell et al, 1991;Walker et al, 2006), and these reported no benefit in improving dietary CP in RH fed animals.…”

Effects of ractopamine hydrochloride are not confined to mammalian tissue: Evidence for direct effects of ractopamine hydrochloride supplementation on fermentation by ruminal microorganisms1

“…Walker and Drouillard [39] also evaluated the impact of ractopamine hydrochloride on in vitro dry matter disappearance with isonitrogenous combinations of corn and soybean meal; corn and urea; or corn, soybean meal, and urea as substrates. There was an increase in in vitro dry matter digestibility with the addition of ractopamine hydrochloride (P < 0.001), and changes in dry matter disappearance (P < 0.01) were more pronounced when ractopamine was used in conjunction with more degradable forms of nitrogen (i.e., urea This could explain results of Walker [41] and Beermann [42], in which β-adrenergic agonists elicited a greater response in ruminants fed protein sources that were more readily degraded by ruminal microbes.…”

Zilpaterol Hydrochloride on Performance and Sperm Quality of Lambs Fed Wet Brewers Grains

“…Schroeder (2004) andWalker et al (2006) reported an improvement in HCW on steers treated with the PAA ractopamine. In addition, Plascencia et al (1999) obtained 13 kg increment in carcass weight for feedlot steers fed ZH.…”