Evaluation of ractopamine hydrochloride (Optaflexx) on growth performance and carcass characteristics of finishing steers across different feeding durations.

Two experiments were conducted to evaluate the effects of ractopamine hydrochloride (RAC) dose and duration on growth performance and carcass characteristics of finishing steers. In Exp. 1, 336 crossbred steers (initial BW of RAC feeding = 539 kg [SD 22]) were used in a 2 × 2 factorial arrangement of treatments with one factor being RAC dose (0 or 200 mg/steer daily) and the other factor being RAC duration (28 or 42 d prior to harvest). There were no RAC dose × duration interactions ( ≥ 0.08) for growth performance or carcass characteristics. Feeding 200 mg RAC/steer daily increased ( < 0.01) live final BW by 9.0 kg compared with steers not fed RAC. Carcass-adjusted final BW, ADG, and G:F were greater ( < 0.01) for steers fed 200 mg RAC/d compared with steers not fed RAC. Hot carcass weight was 4.7 kg heavier ( < 0.01) for steers fed 200 mg RAC/d compared with steers not fed RAC. In Exp. 2, crossbred steers ( = 576; experiment initial BW = 408 kg [SD 29]) were used in a randomized block design with a 3 × 3 factorial arrangement of treatments. Factors included RAC dose (0, 300, and 400 mg/steer daily) and RAC duration (14, 28, or 42 d prior to harvest). There was a tendency ( ≤ 0.08) for an interaction of RAC dose × duration for final live BW, DMI, and live G:F; therefore, simple effects are presented. At 28 d, live final BW for steers fed 400 mg RAC/d were heavier ( < 0.01) than for steers fed 0 mg RAC/d. There was a tendency at 28 d for increased live final BW for steers fed RAC at 300 mg/d ( = 0.08) compared with steers fed RAC at 0 mg and for steers fed 400 mg RAC/d compared with steers fed 300 mg RAC/d ( = 0.06). Live final BW was greater ( < 0.01) for steers fed RAC for 42 d at 300 and 400 mg/d compared with steers fed 0 mg; however, live final BW was similar ( = 0.48) between steers fed 300 and 400 mg RAC/d. Despite no RAC dose × duration interaction ( = 0.30) for HCW, simple effects will be presented for consistency. Hot carcass weight was greater for steers fed 300 and 400 mg RAC/d for 28 and 42 d compared with steers fed 0 mg at 28 ( ≤ 0.02) and 42 d ( < 0.01). Feeding 300 mg RAC/d for 28 or 42 d increased HCW by 5.1 and 7.6 kg, respectively, compared with steers fed 0 mg RAC. Additionally, feeding 400 mg RAC/d for 28 or 42 d resulted in increases of 8.9 and 9.4 kg, respectively, in HCW compared with steers fed 0 mg RAC. In conclusion, our results confirm that feeding RAC improves growth performance and carcass weight, with an optimal duration of feeding RAC being 28 d.

Effect of ractopamine hydrochloride (Optaflexx) dose and duration on growth performance and carcass characteristics of finishing steers.

Three experiments evaluated the effects of ractopamine hydrochloride (RAC) dose and duration on growth performance and carcass characteristics of feedlot steers. In total, 1,509 crossbred steers (530 kg initial BW [SD 22]) were used in a randomized complete block design using a 3 × 3 factorial treatment structure. Treatments consisted of RAC dose (0, 100, or 200 mg/steer daily) and duration (28, 35, or 42 d) of RAC feeding prior to harvest. Initiation of RAC dose was staggered (7 d apart) based on RAC duration, which resulted in common days on feed among treatments. Data from the 3 experiments were combined for statistical analyses. There were no RAC dose × duration interactions ( ≥ 0.85) for growth performance. Live final BW was not different ( ≥ 0.24) as RAC dose increased. Dry matter intake linearly decreased ( < 0.01) as RAC dose increased. Live ADG and G:F linearly increased ( ≤ 0.01) as RAC dose increased. Carcass-adjusted ADG and G:F linearly increased ( ≤ 0.02) as RAC dose increased. Compared with steers fed 0 mg RAC/steer daily, G:F was improved by 5.0 and 13.0% when steers were fed 100 ( = 0.31) and 200 ( = 0.01) mg RAC/steer daily, respectively. Hot carcass weight tended ( = 0.10) to linearly increase as RAC dose increased, with carcasses from steers fed 100 ( = 0.38) and 200 ( = 0.10) mg RAC/steer daily being 2.2 and 4.1 kg heavier, respectively, than carcasses from steers fed 0 mg RAC/steer daily. Increasing RAC dose linearly ( < 0.01) increased LM area and linearly ( = 0.02) decreased marbling score. Live final BW was not different ( ≥ 0.60) among RAC durations. Carcass-adjusted final BW, ADG, and G:F were not different ( ≥ 0.41) as RAC duration increased. Carcass traits did not differ ( ≥ 0.18) among RAC duration. Feeding 200 mg RAC/steer daily improved ADG, feed efficiency, and HCW. Increasing the feeding duration of RAC had no effect of growth performance or carcass characteristics. These data indicate that feeding 200 mg RAC/steer daily for 28 d improves steer growth performance.

Comparative effects of ractopamine hydrochloride and zilpaterol hydrochloride on growth performance, carcass traits, and longissimus tenderness of finishing steers.

Ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) are beta-adrenergic agonists that improve growth performance and affect carcass characteristics. The objective of this study was to evaluate the comparative effects of RAC and ZH when fed to beef steers during the last 33 d of the finishing period. Three hundred crossbred beef steers (516 +/- 8 kg) were grouped by BW, BCS, and breed type and randomly assigned to 1 of 3 treatments (10 steers per pen; 10 pens per treatment). Treatments were control (no beta-agonists added), RAC (200 mg of ractopaminexhdx(-1)d(-1), for 33 d), or ZH (75 mg of zilpaterolxanimalx(-1)d(-1), for 30 d, removed 3 d for required withdrawal period). Steers were slaughtered, carcass characteristics were evaluated, and cut-out yields were determined. Both RAC and ZH increased final BW, ADG, feed efficiency (G:F), and HCW compared with controls (P < 0.05). Compared with RAC, ZH decreased ADG, ADFI, and final BW, but increased HCW and dressing percentage (P < 0.05). Carcass yield was not affected by RAC in this experiment, whereas ZH decreased adjusted fat thickness and KPH, increased ribeye area, improved yield grade, and increased cut-out yields, when compared with controls (P < 0.05). Marbling, lean maturity, and skeletal maturity were not different between treatments (P > 0.05). Steaks from RAC steers had greater (P < 0.05) Warner-Bratzler shear force (WBSF) values than steaks from control steers at 3 and 7 d of aging, but did not differ from controls after 14 d of aging. Steaks from ZH steers had greater WBSF values (P < 0.05) than steaks from controls and RAC steaks throughout the 21-d postmortem aging period. Although both beta-adrenergic agonists were effective at improving feedlot performance, RAC showed no negative effect on WBSF after 14 d, whereas WBSF values for ZH steaks were significantly greater than controls after 21 d.

Effects of ractopamine supplementation and postmortem aging on longissimus muscle palatability of beef steers differing in biological type.

Effects of ractopamine hydrochloride (RAC) supplementation and postmortem aging on palatability of beef from steers differing in biological type were evaluated using LM samples from British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 98/type). Equal numbers of steers within each type were assigned to treatments of 0 or 200 mg.steer(-1).d(-1) of RAC fed during the final 28 d of the finishing period. Warner-Bratzler shear force (WBSF) was measured at 3, 7, 14, and 21 d postmortem, and trained sensory panel (TP) evaluation was conducted using LM samples aged for 14 d postmortem. A RAC x type interaction (P = 0.006) was detected for WBSF. Within each type, steers fed RAC produced steaks with greater (P < 0.05) WBSF values than steaks from control steers; however, the magnitude of the effect of RAC on WBSF was more pronounced among Brahman cross-breds (5.53 vs. 4.96 +/- 0.10 kg) than among Continental crossbred (4.16 vs. 3.96 +/- 0.10 kg) and British steers (4.10 vs. 3.75 +/- 0.10 kg). The effect of RAC on WBSF, though diminished slightly by aging (mean WBSF difference: 3 d = 0.49 kg; 21 d = 0.24 kg), was not completely mitigated by 21 d of postmortem storage (P(RAC x AGE) = 0.16). Steers fed RAC produced steaks that received lower (P < 0.05) TP ratings for tenderness (8.09 vs. 8.95 +/- 0.18) and juiciness (7.41 vs. 8.07 +/- 0.16 kg), along with slightly lower (P = 0.06) ratings for beef flavor (6.67 vs. 6.93 +/- 0.10 kg), compared with steaks from unsupplemented steers, regardless of biological type. Among the 3 biological types, Brahman crossbred cattle produced steaks with the greatest (P < 0.05) WBSF values at each aging period; WBSF values for steaks from British and Continental type steers did not differ (P > 0.05) at any aging time. Sensory panel ratings of tenderness, juiciness, and beef flavor were greatest (P < 0.05) for steaks from British steers, and least (P < 0.05) for steaks produced by Brahman-type steers. Results from this study suggest that RAC supplementation slightly decreases LM tenderness (WBSF and TP) of British, Continental crossbred, and Brahman cross-bred steers, and that the effect of RAC on WBSF may be more pronounced in steaks from Brahman crossbred cattle than among stenks from Continental type or British steers.

Effects of ractopamine supplementation on growth performance and carcass characteristics of feedlot steers differing in biological type.

Effects of ractopamine hydrochloride (RAC) supplementation on growth performance and carcass characteristics of feedlot steers differing in biological type were investigated using British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 420). Steers of each type were weighed at reimplantation [British, mean BW = 375 kg (SD = 38 kg); Continental crossbred, mean BW = 379 kg (SD = 42 kg); Brahman crossbred, mean BW = 340 (SD = 32 kg)] and sorted into 7 BW blocks, each block consisting of 2 pens (10 steers per pen) per type. Pens within a block x type subclass were randomly assigned to RAC treatments (0 or 200 mg x steer(-1) x d(-1) fed during the final 28 d of the finishing period). The type x RAC interaction did not affect (P > 0.05) any of the traits evaluated in this study. Feeding RAC improved (P = 0.001) ADG (1.50 vs. 1.73 +/- 0.09 kg) and G:F (0.145 vs. 0.170 +/- 0.005), but did not affect (P = 0.48) DMI of steers. Dressing percentage, adjusted fat thickness, KPH percentage, and yield grade were not affected by RAC supplementation. Carcasses of steers fed RAC had heavier (P = 0.01) HCW (359 vs. 365 +/- 4.9 kg), larger (P = 0.046) LM areas (81.7 vs. 84.0 +/- 1.1 cm(2)), and tended (P = 0.07) to have lower mean marbling scores (487 vs. 477 +/- 5.2; Slight = 400, Small = 500) than did carcasses of control steers. Among the 3 biological types, Brahman crossbred steers had the lowest DMI and produced the lightest-weight carcasses that had the lowest mean marbling score (P < 0.05). Compared with Continental crossbred and Brahman crossbred steers, British steers produced carcasses with the greatest (P = 0.001) mean marbling scores. Continental crossbred steers had the heaviest BW and greatest dressing percentages and produced the heaviest carcasses with the largest LM areas (P < 0.05) compared with British and Brahman crossbred steers. In the present study, 28 d of supplementation with RAC at a dosage rate of 200 mg x steer(-1) x d(-1) elicited consistent responses in growth performance and carcass traits among 3 diverse biological cattle types.

Effects of ractopamine supplementation on behavior of British, Continental, and Brahman crossbred steers during routine handling.

Equal numbers of British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 420) were used to examine the effects of ractopamine supplementation and biological type on behavior during routine handling. Steers were blocked by BW within type and allocated to pens, resulting in 2 pens (10 cattle per pen) representing each block x type subclass. Pens within each block x type subclass then were randomly assigned to ractopamine supplementation treatments (0 or 200 mg.steer(-1).d(-1)), which were administered during the final 28 d of the finishing period. At the time final BW were obtained (28 d after treatment initiation), a single, trained observer, blinded with respect to treatment designations, recorded subjective scores to characterize behavior of each animal. Scores included entry force score (degree of force required to load the animal into the chute); entry speed score (walk, trot, run); chute behavior score (calm, restless shifting, moderate struggling); and exit speed score (walk, trot, run). Ractopamine supplementation had no effect on entry force score, chute behavior score, or exit speed score; however, cattle supplemented with ractopamine entered the chute more rapidly than did control cattle. Biological cattle type was a significant source of variation in entry force score and exit speed score. Continental crossbreds required greater (P < 0.05) force to enter the squeeze chute than did Brahman crossbred or British steers. In addition, Continental crossbred and Brahman crossbred steers left the processing chute with the greatest speed, whereas British steers exited the processing chute most slowly. Biological cattle type did not affect scores for entry speed or behavior during restraint in the chute. No adverse effects of ractopamine supplementation on cattle behavior were observed in this study.

Effects of marbling and shear force on consumers' willingness to pay for beef strip loin steaks.

Experimental economic procedures were used to measure the effects of changes in marbling score and Warner-Bratzler shear force (WBSF) value on consumer purchasing behavior and willingness to pay for beef strip loin steaks (n = 541). Consumers were more likely to bid on a steak during the experimental auction if the steak had a high marbling score or low WBSF value. Averaging across all consumers in the study (n = 489), the predicted odds that consumers would submit a nonzero bid were favorable for steaks with a marbling score greater than Modest(50) or a WBSF value less than 3.9 kg. Bid prices for steaks were analyzed with respect to changes in steak marbling score, WBSF value, quality grade marketing category classification (Select, Low Choice, Premium Choice, and Prime), and WBSF marketing category classification (very tender, 5.40 kg). The percentage of bids that were zero was highest (P < 0.05) for Select steaks, intermediate (P < 0.05) for Low Choice steaks, and lower (P <0.05) for Premium Choice or Prime steaks. Steaks in the very tender category had the lowest (P < 0.05) percentage of zero bids, and steaks in the slightly tough and very tough categories had the highest (P < 0.05) percentage of zero bids submitted from "buyers" in the auction. Premium Choice and Prime steaks were valued higher (P < 0.05) than Select steaks by consumers. On average, Premium Choice steaks received a 0.89 dollars/kg premium, and Prime steaks received a 2.47 dollars/kg premium over the mean bid price for Select steaks. Predicted mean bid prices for steaks decreased by 1.02 dollars/kg for each 1 kg increase in WBSF value. On average, steaks in the very tender marketing category received a higher (P < 0.05) bid price than the bid price for steaks in the slightly tender, slightly tough, and very tough categories (+0.83 dollars/kg, +2.09 dollars/kg, and +2.55 dollars/kg, respectively). Mean bid prices for steaks from the slightly tough and very tough categories did not differ (P = 0.184). Compared with the mean bid price for steaks in the slightly tender category, steaks from the slightly tough and very tough categories were discounted (P < 0.05) by 1.26 dollars/kg and 1.72 dollars/kg, respectively. Results suggest that marbling score and WBSF influence both the probability that consumers will purchase and the price they are willing to pay for strip loin steaks.

Relationships of consumer sensory ratings, marbling score, and shear force value to consumer acceptance of beef strip loin steaks.

Logistic regression was used to quantify and characterize the effects of changes in marbling score, Warner-Bratzler shear force (WBSF), and consumer panel sensory ratings for tenderness, juiciness, or flavor on the probability of overall consumer acceptance of strip loin steaks from beef carcasses (n = 550). Consumers (n = 489) evaluated steaks for tenderness, juiciness, and flavor using nine-point hedonic scales (1 = like extremely and 9 = dislike extremely) and for overall steak acceptance (satisfied or not satisfied). Predicted acceptance of steaks by consumers was high (> 85%) when the mean consumer sensory rating for tenderness,juiciness, or flavor for a steak was 3 or lower on the hedonic scale. Conversely, predicted consumer acceptance of steaks was low (< or = 10%) when the mean consumer rating for tenderness, juiciness, or flavor for a steak was 5 or higher on the hedonic scale. As mean consumer sensory ratings for tenderness, juiciness, or flavor decreased from 3 to 5, the probability of acceptance of steaks by consumers diminished rapidly in a linear fashion. These results suggest that small changes in consumer sensory ratings for these sensory traits have dramatic effects on the probability of acceptance of steaks by consumers. Marbling score displayed a weak (adjusted R2 = 0.053), yet significant (P < 0.01), relationship to acceptance of steaks by consumers, and the shape of the predicted probability curve for steak acceptance was approximately linear over the entire range of marbling scores (Traces67 to Slightly Abundant97), suggesting that the likelihood of consumer acceptance of steaks increases approximately 10% for each full marbling score increase between Slight to Slightly Abundant. The predicted probability curve for consumer acceptance of steaks was sigmoidal for the WBSF model, with a steep decline in predicted probability of acceptance as WBSF values increased from 3.0 to 5.5 kg. Changes in WBSF within the high (> 5.5 kg) or low (< 3.0 kg) portions of the range of WBSF values had little effect on the probability of consumer acceptance of steaks.

Effects of repetitive use of hormonal implants on beef carcass quality, tenderness, and consumer ratings of beef palatability.

Effects of repetitive use of anabolic implants on beef carcass quality, tenderness, and consumer ratings for palatability were investigated using crossbred steer calves (n = 550). Steers from five ranches were randomly allocated to one of 10 different lifetime implant strategies or to a nonimplanted control group. Cattle were implanted at some or all of five phases of production (branding, weaning, backgrounding, feedlot entry, or reimplant time). Carcasses from the control group had higher (P < 0.05) marbling scores than carcasses from steers in all other treatment groups. Implanting steers at branding, weaning, or backgrounding vs. not implanting steers at these production stages did not affect (P > 0.05) marbling scores. Steers implanted twice during their lifetime produced carcasses with higher (P < 0.05) marbling scores than did steers receiving a total of four or five implants. Steaks obtained from carcasses in the control group had lower (P < 0.05) shear force values and were rated by consumers as more desirable (P < 0.05) for tenderness like/dislike than steaks obtained from carcasses in all other treatment groups. Implanting steers at branding or weaning production stages did not affect (P > 0.05) steak shear force values, consumer ratings for like/dislike of steak tenderness, or percentage of consumers rating overall eating quality of steaks as satisfactory. Implanting steers at backgrounding vs. not implanting steers at this production stage increased (P < 0.05) steak shear force values, but did not influence (P > 0.05) consumer ratings for like/dislike of steak tenderness or percentage of consumers rating overall eating quality of steaks as satisfactory. Steaks from nonimplanted steers were rated as more desirable (P < 0.05) for overall eating quality than steaks from steers implanted two, three, four, or five times. Use of implants increased (P < 0.05) average daily gain by 11.8 to 20.5% from weaning to harvest compared with nonimplanted controls. Implant strategies increased (P < 0.05) hot carcass weight of steers by 8.9 to 13.8% compared with the control group. Use of implants also increased (P < 0.05) longissimus muscle area and decreased (P < 0.05) estimated percentages of kidney/pelvic/heart fat, but did not affect (P > 0.05) dressing percentage or adjusted fat thickness. Our findings suggest that beef quality, palatability, and production characteristics are influenced by lifetime implant protocols.

Injection of beef strip loins with solutions containing sodium tripolyphosphate, sodium lactate, and sodium chloride to enhance palatability.

Beef strip loins (46 U.S. Choice loins and 49 U.S. Select loins) were used to evaluate the potential for enhancing beef tenderness, juiciness, and flavor by injecting fresh cuts with solutions containing sodium tripolyphosphate, sodium lactate, and sodium chloride. One half of each loin served as an untreated control, and the other half was injected with either distilled water (110% of raw weight) or a solution containing phosphate/lactate/chloride solution (107.5, 110, 112.5, or 115% of raw weight). All phosphate/lactate/chloride solutions were formulated to produce injected product concentrations of .25% sodium tripolyphosphate, .5% sodium chloride, and 2.5% sodium lactate. Ten additional U.S. Select loins were injected to 110% of raw weight with a phosphate-only solution (final product concentration of .25% sodium tripolyphosphate) for comparison with Select loins injected to 110% with phosphate/lactate/chloride and with distilled water. Steaks from each control and treated loin section were cooked to two final internal temperatures (66 degrees C and 77 degrees C) for sensory panel evaluation and shear force measurement. Injection of subprimal cuts with phosphate/lactate/chloride solutions improved tenderness (P < .05), juiciness (P < .05), and cooked beef flavor (P < .10) of strip loin steaks and was especially effective for maintaining tenderness and juiciness of steaks cooked to the higher final internal temperature. Injection of Select loins with a solution containing only sodium tripolyphosphate was not effective for improving beef tenderness or juiciness and tended to impart off-flavors characterized by sensory panelists as soapy and sour. Injection of fresh cuts with phosphate/lactate/chloride solutions could assist the beef industry's efforts to improve product quality and consistency.