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Comparative effects of zilpaterol hydrochloride and ractopamine hydrochloride on growth performance, carcass characteristics, and longissimus tenderness of feedlot heifers fed barley-based diets
The Professional Animal Scientist 27 (2011):116–121
©2011 American Registry of Professional Animal Scientists
Comparative effects of zilpaterol hydrochloride and
ractopamine hydrochloride on growth performance, carcass characteristics, and longissimus tenderness of feedlot heifers fed barley-based diets J. Van Donkersgoed,*1 G. Royan,†2 J. Berg,†2 J. Hutcheson,‡ PAS, and M. Brown,§ PAS *Alberta Beef Health Solutions, Box 307, Picture Butte, Alberta, Canada T0K 1V0; †Intervet/ Schering-Plough Animal Health, 18750 Route Transcanadienne, Kirkland, Quebec, Canada H9H 4M7; ‡Intervet/Schering-Plough Animal Health, 35500 West 91st Street, De Soto, KS 66018; and §West Texas A&M University, Canyon 79016
ABSTRACT A randomized complete block design trial was conducted with 3,444 beef heifers housed in 10 pens per treatment and fed barley-based diets to evaluate the effects of ractopamine (Optaflexx, Elanco Animal Health, Greenfield, IN) and zilpaterol (Zilmax, Intervet/ScheringPlough Animal Health, De Soto, KS) on health, performance, carcass traits, and longissimus muscle tenderness in a commercial feedlot in western Canada. Treatments consisted of feeding Optaflexx at 20 mg/kg (100% DM basis) for 29 d at the end of the feeding period or Zilmax at 8.3 mg/kg (100% DM basis) for 20 d
Corresponding author: [email protected] Research supported by Intervet/ScheringPlough Animal Health. 1 2
at the end of the feeding period, followed by a 4-d withdrawal period before slaughter. No differences (P > 0.05) were detected in morbidity, mortality, number of salvaged animals, ADG, feed efficiency, or final BW between heifers fed Zilmax or Optaflexx. Dry matter intake was reduced (P < 0.008) when heifers were fed Zilmax compared with when heifers were fed Optaflexx. Heifers fed Zilmax had heavier (P = 0.0001) HCW (9.7 kg), greater dressing percent (1.66 percentage units), greater percentage of YG 1 carcasses (6 percentage units), a lower percentage of YG 3 carcasses (8 percentage units), and a lower percentage of Canadian AAA carcasses (9 percentage units) compared with heifers fed Optaflexx. No differences (P = 0.98) were detected in tenderness between heifers fed Zilmax or those fed Optaflexx. Based on the grid on which these feedlot heifers
were sold, the additional economic value of Zilmax to Optaflexx was $20.35 (Canadian) per heifer. Feeding Zilmax for 20 d to British-influenced finishing heifers resulted in leaner carcasses and greater carcass weight without compromising tenderness when compared with feeding Optaflexx. Key words: beta-agonist, ractopamine, zilpaterol, performance, tenderness
INTRODUCTION Feeding β-adrenergic agonists typically results in an increase in ADG accompanied by a slight decrease in feed intake, resulting in an improvement in feed efficiency (Mersmann, 2002). In addition to improvements in animal performance, β-adrenergic ago-
Economic value of feeding zilpaterol and ractopamine
nists also increase carcass weight and leanness (Montgomery et al., 2009). Optaflexx (ractopamine hydrochloride, Elanco Animal Health, Greenfield, IN) is a β-agonist approved for use in the United States and Canada in steers and heifers fed in confinement during the last 28 to 42 d before slaughter. There are limited and inconsistent data on the effect of Optaflexx in feedlot heifers on improving performance and carcass characteristics (Walker et al., 2006; Sissom et al., 2007; Quinn et al., 2008; Griffin et al., 2009; Bryant et al., 2010). Zilmax (zilpaterol hydrochloride, Intervet/Schering-Plough Animal Health, De Soto, KS) is a β-agonist approved for use in the United States and Canada in cattle fed in confinement during the last 20 to 40 d before slaughter. Previous research conducted in the United States has shown that Zilmax increases BW gain, feed efficiency, and HCW but reduces average YG and QG in feedlot heifers (Montgomery et al., 2009). RoblesEstrada et al. (2009) evaluated the effects of Zilmax in feedlot heifers fed in Mexico and demonstrated an increase in carcass-adjusted ADG, carcass weight, dressing percent, and ribeye area and improved F:G with no effect on marbling score when compared with controls. Zilmax was recently approved in Canada (2009), but it has been used in cattle production since 2007 in the United States and since the 1990s in South Africa and Mexico. Optaflexx has been used in cattle production since 2008 in Canada and in the United States since 2003. No data have been reported from experiments conducted under large-scale commercial conditions, which are typical of most Canadian feedlots, evaluating the effectiveness of Zilmax in comparison with Optaflexx in finishing heifers. The objectives of the present study were to evaluate growth performance, carcass characteristics, and beef shear force in heifers fed either Zilmax or Optaflexx in a large commercial feedlot in western Canada.
MATERIALS AND METHODS Animals and Management Animals were handled in compliance with applicable local regulations and in accordance with the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999). Yearling heifers (n = 3,444) from one feedlot in southern Alberta were used during the fall and winter of 2009–2010. For the entire experiment, all heifers received the same basal diet consisting on a DM basis of barley silage (10.68%), barley grain (65.03%), dry corn distillers grains (20.06%), and a base supplement (4.24%) containing minerals, vitamins, and monensin. The diets were formulated to meet or exceed NRC (2000) requirements. Separate supplements containing Zilmax and Optaflexx were prepared by a commercial feed mill. The supplements were identical in composition except for the β-agonist medication. All diets were manufactured immediately before feeding with on-site mixer feed trucks (Roto-Mix, Dodge City, KS). Feed was delivered 3 times daily and offered in sufficient quantities to allow for ad libitum intake. Feed bunks were emptied before placing animals into trial pens. Dry matter intake was recorded by pen at the time of feed delivery in a computerized data management system (DG Pro, Computer Aid, Okotoks, Alberta, Canada). Samples of the supplements were collected by the commercial feed mill when they were manufactured, and samples of the medicated feed (TMR) were collected at the beginning of study and once every 14 d during the trial. Samples were submitted to commercial laboratories for analysis of zilpaterol hydrochloride concentrations (Intervet Analytical Laboratory, Lawrence, KS) and ractopamine hydrochloride concentrations (Eurofins AvTech Laboratories, Portage, MI). In all but one zilpaterol feed sample, medication levels were within the targeted range of 80 to 120% of label claim at 8.3 mg/kg on a 100% DM basis. Trace back of this single feed
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sample could not determine why zilpaterol medication levels were only within 62% of target levels. Physical inventory of the amount of supplement added to batches was confirmed to be correct.
Experimental Design The eligible pool of cattle included pens of feedlot heifers with the same days on feed, average BW, and terminal trenbolone acetate implant and that were approximately 40 to 50 d from slaughter. Heifers from these pens were combined and weighed individually. Heifers that weighed >614 kg or that had the appearance of a high percentage of exotic breeding (e.g., Charolais, Simmental, Saler, Maine-Anjou) were not eligible for the trial. The chute scale was checked with standardized weights before the start of the study, and the scale was tared to zero after every 10 to 20 animals through the chute. Scale resolution was set to 2.2 kg. Single animals were assigned randomly to 1 of 2 matched pens (block) through the processing chute. Pens were randomly assigned to treatment within a block. This process was repeated until all 10 blocks (20 pens) were complete. Both pens within a block contained either 144 heifers or 192 heifers to represent either 3 or 4 livestock truck loads for shipment to slaughter. Day 0 occurred approximately 10 d after individual animals were randomized to treatment pens and approximately 29 d before slaughter. At this time, each pen within a block was weighed on a government-certified group scale that had a scale resolution of 4.5 kg. This group pen weight served as the start weight for the study.
Treatments There were 2 treatments in this study: 1) Zilmax, 8.3 mg/kg zilpaterol hydrochloride (100% DM basis), and 2) Optaflexx, 20 mg/kg ractopamine hydrochloride (100% DM basis). Treatments began with the first feeding on d 1. Optaflexx was fed on d 1
118 and continued for a minimum of 28 d until slaughter. For heifers receiving Zilmax, the feeding period was divided into 3 phases: a non-Zilmax supplement was fed the first 4 d, then the Zilmax supplement was fed for 20 d, and then the non-Zilmax supplement was fed for the last 4 d to ensure a 4-d withdrawal.
Data Collection Normal health monitoring occurred. Cattle were examined daily by an experienced animal health crew for signs of clinical disease. Animals requiring treatment for any cause were treated according to a standardized treatment protocol developed and monitored by the feedlot veterinarian. Complete treatment records were kept in a chute-side computerized animal health program (DG Pro, Computer Aid). Animals that died were subjected to a postmortem examination by the feedlot veterinarian, and the cause of death was recorded. Any animals that were sold for salvage were recorded. On approximately d 29, blocks of cattle were shipped for slaughter to Lakeside Packers in Brooks, Alberta, Canada. Final BW at shipment were measured by pen using a governmentcertified truck scale. Additional shipping documents were provided to identify trial cattle, and arrangements were made with the processor to ensure that cattle were kept segregated by pen on livestock trucks, in holding pens at the plant, and during processing at the plant so that carcass data were provided back accurately for each pen. Livestock manifests were separate for each matched pen and identified the specific feedlot and pen within the feedlot. In addition, to ensure identification of carcass data by pen, the number of animals shipped from pens within a block differed by one animal. The packing plant was blind to the treatment status of pens. Carcass weights and standard Canadian carcass grading parameters including quality and yield grades and dressing percent were obtained by pen from the processor.
Van Donkersgoed et al.
Shear Force Loins were collected from carcasses from both treatment groups on 4 different processing dates and sent by the packer to Agri-Food Discovery Place, Edmonton, Alberta, Canada. A total of 50 beef strip loins were received, with 25 strip loins from each β-agonist treatment. Within each treatment, strip loins were removed from carcasses that graded grade AAA with a YG of A1 or A2. Only AAA loins were selected because Mehaffey et al. (2009) showed differences from controls in shear force only in Choice steaks aged 14 d. Loins from the Optaflexx group were matched to the Zilmax group for marbling, estimated red meat yield, and carcass weight. Within each strip loin, there were 4 further aging treatments, with steaks from each strip loin aged for 7, 14, 21, and 28 d postmortem. Four, 2.54-cm (1-inch) thick steaks were removed from the loin end of each strip loin (steaks 1, 2, 3, and 4) after that end was faced (the immediate surface removed). Steaks were cut using a cutting guide and a ruler to ensure uniformity and consistency of steak thickness. Steaks 1, 2, 3, and 4 were assigned to 7, 14, 21, and 28 d of aging so that aging treatments were balanced for anatomical location. Individually packaged frozen steaks were thawed at 0 to 4°C for 24 h before cooking. Steaks were weighed before cooking, and color was measured using a Minolta spectrometer (Minolta CR400, Konica-Minolta, Nanshan, China). Steaks were cooked on a General Electric “4 in 1” grill preheated to 177°C to an internal temperature of 71°C. Cooking time and yield were recorded for each steak. Temperature was monitored using calibrated temperature probes (Fisher Scientific Company, Ottawa, Ontario, Canada). The identification of each steak was maintained throughout. Cooked steaks were placed on trays, covered with plastic film, and stored overnight at 0 to 4°C until peak shear force analysis. Six, 1.27-cm-diameter cores were removed from each steak, with
2 cores each from the lateral, medial, and middle areas of each steak. Meat cores containing large pockets of connective tissue or fat were not used unless most cores from a steak or an area of a steak (medial, middle, or lateral) contained large pockets of connective tissue or fat. In this case, a core or cores were used that had large pockets of connective tissue or fat because they were deemed representative of the steak structure. Cores with large pockets of connective tissue or fat were identified during recording of data. Each core was sheared once using a 3-mm-thick triangular blade fitted to a material testing machine (LRX Plus, Digital Measurement Metrology, Brampton, Ontario, Canada) fitted with a 1,000-N load cell, and the peak force was recorded. The material testing machine used was calibrated by the manufacturer. The peak force of each steak was the mean of the 6 cores.
Statistical Analyses Performance and Carcass Data. Performance data were calculated using total start BW for the pen, total final BW for the pen, total DMI for the pen, and total animal days for the pen. Final BW included the weight of cattle shipped to slaughter and those animals removed at shipping due to livestock truck over-weights (i.e., insufficient space for all study cattle) but excluded weights of salvaged and dead cattle and feed consumed by these removed cattle. Initial and final BW were shrunk 4%. Outcome measures included DMI, ADG, feed efficiency, carcass weight, and carcass yield and quality characteristics. Average daily gain and feed efficiency outcome measures did not include the weight of dead animals. Additional outcome measures included morbidity, mortality, and number of salvaged cattle. Data were analyzed as a randomized complete block design, and pen served as the experimental unit for all analyses. Growth performance, HCW, and dressing percent data were analyzed using MIXED procedures of SAS (ver-
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Economic value of feeding zilpaterol and ractopamine
sion 9.2, SAS Inst. Inc., Cary, NC). The model included the fixed effect of treatment, and block served as a random effect. Initial weight was different by treatment; therefore, initial weight was used as a covariate for final shrunk BW, HCW, and dressing percentage because the absolute change in carcass weight is an important response criterion for the treatments under consideration. Carcass QG and YG distributions were analyzed using GLIMMIX procedures of SAS for binomial data with the same model as described previously. Shear Force Data. The treatment structure included loins from cattle that had been fed Optaflexx or Zilmax. The design structure was a completely randomized design. Loin was the experimental unit. Data were analyzed using the MIXED procedure of SAS to account for both fixed and random effects. Fixed effects included feed additive treatment and aging time, whereas random effects included day of cooking, total cooking time, maximum internal steak temperature, and total cooking losses. Aging time within loin was a repeated measure and was analyzed using an unstructured covariance model. Treatment means were generated using the LSMEANS option and separated when significant (P < 0.05) using the PDIFF option. Economic Data. The grid on which cattle are sold will determine the economic value of feeding Zilmax compared with Optaflexx in finishing feedlot heifers. The following grid was used by the feedlot owner to determine the economic value of Zilmax based on outcomes that were statistically significant at P < 0.05. Zilmax was priced at $1.09 per heifer per day, and Optaflexx was priced at $0.29 per heifer per day. Over 20 d of feeding, the Zilmax cost was $21.80, and over 29 d of feeding, the Optaflexx cost was $8.41, resulting in a $13.39 per heifer difference in drug cost. Feed costs were $1.75/heifer daily. Heifers fed Zilmax ate 10.5 kg (23 lb, as-fed basis) less feed than did heifers fed Optaflexx, which was valued at $1.49 lower feed cost over
29 d. Hot carcass weight was valued at $0.68/kg ($1.50/lb). The additional 9.55 kg (21 lb) of carcass weight for heifers fed Zilmax was worth an additional $31.50. Canadian AAA carcasses were valued at an additional $5 per carcass based on the Choice/ Select spread at the time the study was completed ($5 × 0.09 = $0.45). A base level of Canadian YG 3 carcasses was allowed at 20%. Above that level, the discount was $15 per carcass ($15 × 0.08 = $1.20).
RESULTS AND DISCUSSION Morbidity, Mortality, and Removals There were no differences (P > 0.05) in morbidity, mortality, or removals between treatments (data not shown). Ten animals were removed from the study between allocation and the start of the feeding study, 8 animals for Optaflexx and 2 animals for Zilmax. Of the 10 animals removed, 6 were treated and removed and 4 died. In the Optaflexx group, treatment removals included 2 injuries, 1 foot rot, and 1 interstitial pneumonia, whereas death removals included 1 interstitial pneumonia, 1 cellulitis, and 1 congestive heart failure. In the Zilmax group, treatment removals included 1 foot rot and 1 hairy heel warts, and 1 animal died from unknown causes.
There was no difference (P = 0.14) in morbidity rates between treatments. Morbidity rates averaged 3% in each treatment group, and the most common cause of morbidity was foot rot. Fifteen heifers were salvaged before slaughter, 6 in the Optaflexx treatment and 9 in the Zilmax treatment. Five animals died during the trial feeding period. The causes of death for the 3 heifers fed Optaflexx included gas bloat, interstitial pneumonia, and chronic pneumonia. The causes of death for the 2 heifers fed Zilmax were broncho-interstitial pneumonia and pulmonary edema. None of these deaths were attributed to treatment. There was no difference (P > 0.05) in mortality between the 2 treatment groups during the trial feeding period.
Performance and Carcass Characteristics Although ADG and feed efficiency were not altered by treatment (P > 0.05, Table 1), heifers receiving Zilmax consumed less feed (0.3 kg/d) than did heifers fed Optaflexx (P = 0.008). Similar to the present results, Scramlin et al. (2010) observed a reduction in feed intake between Zilmax and Optaflexx in finishing steers. Montgomery et al. (2009) noted a reduction in feed intake (0.5 kg/d)
Table 1. Effects of β-agonists1 on growth performance and health of feedlot heifers fed barley-based diets Item Pens Cattle Days on feed Initial shrunk BW, kg Final shrunk BW, kg Covariate-adjusted final BW,2 kg DMI, kg/d ADG, live basis, kg/d Feed efficiency, live basis
Zilmax
Optaflexx
SE
P-value
10 1,725 29 568.7 602.9 601.6 9.38 1.12 8.52
10 1,719 29 565.5 599.9 601.3 9.68 1.14 8.53
— — — 7.9 7.7 1.2 0.15 0.04 0.33
— — — 0.02 0.07 0.69 0.008 0.53 0.98
Zilmax, Intervet/Schering-Plough Animal Health, De Soto, KS; Optaflexx, Elanco Animal Health, Greenfield, IN.
1
2
Raw data were adjusted using initial BW as a covariate (P < 0.10) in the model.
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Van Donkersgoed et al.
Table 2. Effects of β-agonists1 on carcass characteristics of feedlot heifers fed barley-based diets Item
Zilmax
Optaflexx
SE
HCW, kg Covariate-adjusted hot weight,2 kg Dressing percent (DP) Covariate-adjusted DP3 Prime, % AAA, % AA, % A, % B4, % D4,3 % YG 1, % YG 2, % YG 3, % Other grade, %
372.8 371.9 61.84 61.86 0.8 62.1 34.6 0.6 1.9 0 24.7 52.9 20.3 2.1
361.2 362.2 60.22 60.20 1.7 70.8 24.5 0.2 2.7 0.1 19.0 49.9 28.3 2.8
4.4 1.3 0.15 0.13 — — — — — — — — — —
P-value 0.0001 0.0001 0.0001 0.0001 0.05 0.0001 0.0001 0.05 0.15 NA4 0.0008 0.06 0.0001 0.19
Zilmax, Intervet/Schering-Plough Animal Health, De Soto, KS; Optaflexx, Elanco Animal Health, Greenfield, IN.
1
2
Raw data were adjusted using initial BW as a covariate (P < 0.10) in the model.
3
Model did not converge due to insufficient nonzero data.
4
NA = not available.
by heifers fed Zilmax compared with negative controls. Final BW did not differ (P > 0.05) between treatments (Table 1). However, heifers fed Zilmax had a 9.7-kg-heavier HCW than did heifers fed Optaflexx (P < 0.0001, Table 2). The increase in HCW for heifers fed Zilmax was attributed in part to an increase in dressing percent of 1.66 percentage units. Avendaño-Reyes et al. (2006) and Scramlin et al. (2010) demonstrated in steers an increase in carcass weight of 7.7 kg with Zilmax compared with Optaflexx. Increased carcass weight and dressing percent have been a consistent effect of Zilmax over Optaflexx in feedlot steers. The current study is the first work to demonstrate an increase in carcass weight for Zilmax over Optaflexx in feedlot heifers. Heifers fed Zilmax produced more Canadian YG 1 carcasses (P = 0.0008; 6 percentage units) and fewer Canadian YG 3 carcasses (P = 0.0001; 8 percentage units) than did heifers fed Optaflexx. The effect of Zilmax in increasing carcass leanness as reflected by an increase in YG 1 and a decrease in YG 3 carcasses is
similar to the effects seen for steers fed Zilmax or Optaflexx (AvendañoReyes et al., 2006; Scramlin et al., 2010). There were fewer (P < 0.05) Prime and AAA carcasses and more (P < 0.05) AA and A carcasses from heifers fed Zilmax than from those fed Optaflexx. Montgomery et al. (2009) demonstrated that finishing heifers fed Zilmax had a similar QG distribution when compared with controls. In contrast to the present results in heifers, Scramlin et al. (2010) observed no differences in marbling score between Zilmax and Optaflexx in steers.
Shear Force There were no (P > 0.95) differences in Warner-Bratzler shear force measurements between Zilmax and Optaflexx (3.51 and 3.51 ± 0.20 kg, respectively). Increased postmortem aging decreased (P < 0.001) WarnerBratzler shear force of steaks from heifers fed either Zilmax or Optaflexx. Postmortem aging from 7 to 28 d decreased Warner-Bratzler shear force values by 15.1, 6.8, and 1.4%. The lack (P = 0.58) of an interaction
indicates tenderness of steaks from heifers fed either Zilmax or Optaflexx improved with aging, and the magnitude of change over time was similar for Zilmax and Optaflexx. Platter and Choat (2008) observed an increase in shear force in heifers and steers fed Optaflexx when compared with controls. Brooks et al. (2009) observed an increase in shear force in steers and heifers fed Zilmax for 20 versus 30 versus 40 d before slaughter when compared with controls. However, O’Neill (2001) found no differences in shear force values for meat from steers treated, or not treated, with zilpaterol hydrochloride and concluded that zilpaterol hydrochloride did not reduce tenderness of beef. Scramlin et al. (2010) demonstrated that when Zilmax was fed for 30 d, there was an increase in shear force compared with Optaflexx in finishing steers. In contrast, Avendaño-Reyes et al. (2006) demonstrated that there were no differences in shear force between steers fed Zilmax for 30 d and those fed Optaflexx. Brooks et al. (2009) demonstrated that feeding Zilmax for 30 and 40 d resulted in greater shear force than when cattle were fed Zilmax for 20 d. Zilmax fed for 20 d before slaughter is recommended in both the United States and Canada to mitigate the negative effects on shear force seen at 30 and 40 d of zilpaterol feeding. These data suggest there is no difference in shear force between Zilmax fed for 20 d and Optaflexx fed for 29 d in heifers.
Economics When all the economic values were added together [$31.50 (from carcass weight) − $0.45 (from carcass quality) + $1.20 (from YG 3 premium) + $1.49 (less feed) − $13.39 (difference in feed additive costs)], the value of feeding Zilmax over Optaflexx in these British-based heifers was $20.35 per heifer.
IMPLICATIONS Heifers fed Zilmax had heavier HCW, higher dressing percent, and
Economic value of feeding zilpaterol and ractopamine
fewer YG 3 carcasses, but fewer Prime and AAA carcasses, than did heifers fed Optaflexx. No differences were detected between Zilmax and Optaflexx for Warner-Bratzler shear force. The economic value of Zilmax compared with Optaflexx in feedlot heifers was improved by $20.35/ animal. Zilmax can be fed for 20 d to British-influenced finishing heifers with the expectations of increased carcass weight and leanness with no difference in tenderness compared with heifers fed Optaflexx.
ACKNOWLEDGMENTS We would like to thank the participating feedlot owner and staff, as well as research technicians Darren Malchow and Lynn Usenik (both with Alberta Beef Health Solutions, Picture Butte, Alberta, Canada), for their participation in this study.
LITERATURE CITED Avendaño-Reyes, L., V. Torres-Rodríguez, F. J. Meraz-Murillo, C. Pérez-Linares, F. Figueroa-Saavedra, and P. H. Robinson. 2006. Effects of two β-adrenergic agonists on finishing performance, carcass characteristics, and meat quality of feedlot steers. J. Anim. Sci. 84:3259. Brooks, J. C., H. C. Claus, M. E. Dikeman, J. Shook, G. G. Hilton, T. E. Lawrence, J. M. Mehaffey, B. J. Johnson, D. M. Allen, M. N. Streeter, W. T. Nichols, J. P. Hutcheson, D. A. Yates, and M. F. Miller. 2009. Effects of
zilpaterol hydrochloride feeding duration and postmortem aging on Warner-Bratzler shear force of three muscles from beef steers and heifers. J. Anim. Sci. 87:3764. Bryant, T. C., T. Engle, M. Galyean, J. Wagner, J. Tatum, R. Anthony, and S. Laudert. 2010. Effects of ractopamine and trenbolone acetate implants with or without estradiol on growth performance, carcass characteristics, adipogenic enzyme activity, and blood metabolites in feedlot steers and heifers. J. Anim. Sci. 88:4102. FASS (Federation of Animal Science Societies). 1999. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. FASS, Champaign, IL. Griffin, W. A., G. Erickson, B. Dicke, T. Klopfenstein, R. Cooper, D. Jordon, R. Swingle, W. Moseley, G. Sides, and D. Weigel. 2009. Effects of ractopamine (Optaflexx) fed in combination with melengestrol acetate on feedlot heifer performance. Prof. Anim. Sci. 25:33. Mehaffey, J. M., J. Brooks, R. Rathmann, E. Alsup, J. Hutcheson, W. Nichols, M. Streeter, D. Yates, J. Johnson, and M. Miller. 2009. Effects of feeding zilpaterol hydrochloride to beef and calf-fed Holstein cattle on consumer palatability ratings. J. Anim. Sci. 87:3712. Mersmann, H. J. 2002. Beta adrenergic receptor modulation of adipocyte metabolism and growth. J. Anim. Sci. 80(Suppl. 1):E24. Montgomery, J. L., C. Krehbiel, J. Cranston, D. Yates, J. Hutcheson, W. Nichols, M. Streeter, D. Bechtol, E. Johnson, T. TerHune, and T. Montgomery. 2009. Dietary zilpaterol hydrochloride. I. Feedlot performance and carcass traits of steers and heifers. J. Anim. Sci. 87:1374. NRC. 2000. Nutrient Requirements of Beef Cattle. National Academy Press, Washington, DC.
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O’Neill, H. A. 2001. The effect of zilpaterol hydrochloride on dietary N-requirements and the quality and nutritional value of meat components. MS Thesis. University of Pretoria, Pretoria, South Africa. Platter, W. J., and W. T. Choat. 2008. Balancing beef quality and red meat yield with ractopamine hydrochloride. Pages 1–6 in Proc. Reciprocal Meat Conf., Gainesville, FL. Quinn, M. F., C. Reinhardt, E. Loe, B. Dependbusch, M. Corrigan, M. May, and J. Drouillard. 2008. The effects of ractopaminehydrogen chloride (Optaflexx) on performance, carcass characteristics, and meat quality in feedlot heifers. J. Anim. Sci. 86:902. Robles-Estrada, J. C., A. A. Arrizon, A. Barreras, J. F. Calderon, F. Figueroa-Saavedra, N. Torrentera, A. Plascencia, and R. A. Zinn. 2009. Effects of preslaughter withdrawal period on response of feedlot heifers to zilpaterol hydrochloride supplementation: Growth performance and carcass characteristics. J. Anim. Sci. 87:1759. Scramlin, S. M., W. J. Platter, R. A. Gomez, W. T. Choat, F. K. McKeith, and J. Killefer. 2010. Comparative effects of ractopamine hydrochloride and zilpaterol chloride on growth performance, carcass traits and longissimus tenderness of finishing steers. J. Anim. Sci. 88:1823. Sissom, E. K., C. Reinhardt, J. Hutcheson, W. Nichols, D. Yates, R. Swingle, and B. Johnson. 2007. Response to ractopamine-HCl in heifers is altered by implant strategy across days on feed. J. Anim. Sci. 85:2125. Walker, D. K., E. Titgemeyer, J. Drouillard, E. Loe, B. Depenbusch, and A. Webb. 2006. Effects or ractopamine and protein source on growth performance and carcass characteristics of feedlot heifers. J. Anim. Sci. 84:2795.
©2011 American Registry of Professional Animal Scientists
Comparative effects of zilpaterol hydrochloride and
ractopamine hydrochloride on growth performance, carcass characteristics, and longissimus tenderness of feedlot heifers fed barley-based diets J. Van Donkersgoed,*1 G. Royan,†2 J. Berg,†2 J. Hutcheson,‡ PAS, and M. Brown,§ PAS *Alberta Beef Health Solutions, Box 307, Picture Butte, Alberta, Canada T0K 1V0; †Intervet/ Schering-Plough Animal Health, 18750 Route Transcanadienne, Kirkland, Quebec, Canada H9H 4M7; ‡Intervet/Schering-Plough Animal Health, 35500 West 91st Street, De Soto, KS 66018; and §West Texas A&M University, Canyon 79016
ABSTRACT A randomized complete block design trial was conducted with 3,444 beef heifers housed in 10 pens per treatment and fed barley-based diets to evaluate the effects of ractopamine (Optaflexx, Elanco Animal Health, Greenfield, IN) and zilpaterol (Zilmax, Intervet/ScheringPlough Animal Health, De Soto, KS) on health, performance, carcass traits, and longissimus muscle tenderness in a commercial feedlot in western Canada. Treatments consisted of feeding Optaflexx at 20 mg/kg (100% DM basis) for 29 d at the end of the feeding period or Zilmax at 8.3 mg/kg (100% DM basis) for 20 d
Corresponding author: [email protected] Research supported by Intervet/ScheringPlough Animal Health. 1 2
at the end of the feeding period, followed by a 4-d withdrawal period before slaughter. No differences (P > 0.05) were detected in morbidity, mortality, number of salvaged animals, ADG, feed efficiency, or final BW between heifers fed Zilmax or Optaflexx. Dry matter intake was reduced (P < 0.008) when heifers were fed Zilmax compared with when heifers were fed Optaflexx. Heifers fed Zilmax had heavier (P = 0.0001) HCW (9.7 kg), greater dressing percent (1.66 percentage units), greater percentage of YG 1 carcasses (6 percentage units), a lower percentage of YG 3 carcasses (8 percentage units), and a lower percentage of Canadian AAA carcasses (9 percentage units) compared with heifers fed Optaflexx. No differences (P = 0.98) were detected in tenderness between heifers fed Zilmax or those fed Optaflexx. Based on the grid on which these feedlot heifers
were sold, the additional economic value of Zilmax to Optaflexx was $20.35 (Canadian) per heifer. Feeding Zilmax for 20 d to British-influenced finishing heifers resulted in leaner carcasses and greater carcass weight without compromising tenderness when compared with feeding Optaflexx. Key words: beta-agonist, ractopamine, zilpaterol, performance, tenderness
INTRODUCTION Feeding β-adrenergic agonists typically results in an increase in ADG accompanied by a slight decrease in feed intake, resulting in an improvement in feed efficiency (Mersmann, 2002). In addition to improvements in animal performance, β-adrenergic ago-
Economic value of feeding zilpaterol and ractopamine
nists also increase carcass weight and leanness (Montgomery et al., 2009). Optaflexx (ractopamine hydrochloride, Elanco Animal Health, Greenfield, IN) is a β-agonist approved for use in the United States and Canada in steers and heifers fed in confinement during the last 28 to 42 d before slaughter. There are limited and inconsistent data on the effect of Optaflexx in feedlot heifers on improving performance and carcass characteristics (Walker et al., 2006; Sissom et al., 2007; Quinn et al., 2008; Griffin et al., 2009; Bryant et al., 2010). Zilmax (zilpaterol hydrochloride, Intervet/Schering-Plough Animal Health, De Soto, KS) is a β-agonist approved for use in the United States and Canada in cattle fed in confinement during the last 20 to 40 d before slaughter. Previous research conducted in the United States has shown that Zilmax increases BW gain, feed efficiency, and HCW but reduces average YG and QG in feedlot heifers (Montgomery et al., 2009). RoblesEstrada et al. (2009) evaluated the effects of Zilmax in feedlot heifers fed in Mexico and demonstrated an increase in carcass-adjusted ADG, carcass weight, dressing percent, and ribeye area and improved F:G with no effect on marbling score when compared with controls. Zilmax was recently approved in Canada (2009), but it has been used in cattle production since 2007 in the United States and since the 1990s in South Africa and Mexico. Optaflexx has been used in cattle production since 2008 in Canada and in the United States since 2003. No data have been reported from experiments conducted under large-scale commercial conditions, which are typical of most Canadian feedlots, evaluating the effectiveness of Zilmax in comparison with Optaflexx in finishing heifers. The objectives of the present study were to evaluate growth performance, carcass characteristics, and beef shear force in heifers fed either Zilmax or Optaflexx in a large commercial feedlot in western Canada.
MATERIALS AND METHODS Animals and Management Animals were handled in compliance with applicable local regulations and in accordance with the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999). Yearling heifers (n = 3,444) from one feedlot in southern Alberta were used during the fall and winter of 2009–2010. For the entire experiment, all heifers received the same basal diet consisting on a DM basis of barley silage (10.68%), barley grain (65.03%), dry corn distillers grains (20.06%), and a base supplement (4.24%) containing minerals, vitamins, and monensin. The diets were formulated to meet or exceed NRC (2000) requirements. Separate supplements containing Zilmax and Optaflexx were prepared by a commercial feed mill. The supplements were identical in composition except for the β-agonist medication. All diets were manufactured immediately before feeding with on-site mixer feed trucks (Roto-Mix, Dodge City, KS). Feed was delivered 3 times daily and offered in sufficient quantities to allow for ad libitum intake. Feed bunks were emptied before placing animals into trial pens. Dry matter intake was recorded by pen at the time of feed delivery in a computerized data management system (DG Pro, Computer Aid, Okotoks, Alberta, Canada). Samples of the supplements were collected by the commercial feed mill when they were manufactured, and samples of the medicated feed (TMR) were collected at the beginning of study and once every 14 d during the trial. Samples were submitted to commercial laboratories for analysis of zilpaterol hydrochloride concentrations (Intervet Analytical Laboratory, Lawrence, KS) and ractopamine hydrochloride concentrations (Eurofins AvTech Laboratories, Portage, MI). In all but one zilpaterol feed sample, medication levels were within the targeted range of 80 to 120% of label claim at 8.3 mg/kg on a 100% DM basis. Trace back of this single feed
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sample could not determine why zilpaterol medication levels were only within 62% of target levels. Physical inventory of the amount of supplement added to batches was confirmed to be correct.
Experimental Design The eligible pool of cattle included pens of feedlot heifers with the same days on feed, average BW, and terminal trenbolone acetate implant and that were approximately 40 to 50 d from slaughter. Heifers from these pens were combined and weighed individually. Heifers that weighed >614 kg or that had the appearance of a high percentage of exotic breeding (e.g., Charolais, Simmental, Saler, Maine-Anjou) were not eligible for the trial. The chute scale was checked with standardized weights before the start of the study, and the scale was tared to zero after every 10 to 20 animals through the chute. Scale resolution was set to 2.2 kg. Single animals were assigned randomly to 1 of 2 matched pens (block) through the processing chute. Pens were randomly assigned to treatment within a block. This process was repeated until all 10 blocks (20 pens) were complete. Both pens within a block contained either 144 heifers or 192 heifers to represent either 3 or 4 livestock truck loads for shipment to slaughter. Day 0 occurred approximately 10 d after individual animals were randomized to treatment pens and approximately 29 d before slaughter. At this time, each pen within a block was weighed on a government-certified group scale that had a scale resolution of 4.5 kg. This group pen weight served as the start weight for the study.
Treatments There were 2 treatments in this study: 1) Zilmax, 8.3 mg/kg zilpaterol hydrochloride (100% DM basis), and 2) Optaflexx, 20 mg/kg ractopamine hydrochloride (100% DM basis). Treatments began with the first feeding on d 1. Optaflexx was fed on d 1
118 and continued for a minimum of 28 d until slaughter. For heifers receiving Zilmax, the feeding period was divided into 3 phases: a non-Zilmax supplement was fed the first 4 d, then the Zilmax supplement was fed for 20 d, and then the non-Zilmax supplement was fed for the last 4 d to ensure a 4-d withdrawal.
Data Collection Normal health monitoring occurred. Cattle were examined daily by an experienced animal health crew for signs of clinical disease. Animals requiring treatment for any cause were treated according to a standardized treatment protocol developed and monitored by the feedlot veterinarian. Complete treatment records were kept in a chute-side computerized animal health program (DG Pro, Computer Aid). Animals that died were subjected to a postmortem examination by the feedlot veterinarian, and the cause of death was recorded. Any animals that were sold for salvage were recorded. On approximately d 29, blocks of cattle were shipped for slaughter to Lakeside Packers in Brooks, Alberta, Canada. Final BW at shipment were measured by pen using a governmentcertified truck scale. Additional shipping documents were provided to identify trial cattle, and arrangements were made with the processor to ensure that cattle were kept segregated by pen on livestock trucks, in holding pens at the plant, and during processing at the plant so that carcass data were provided back accurately for each pen. Livestock manifests were separate for each matched pen and identified the specific feedlot and pen within the feedlot. In addition, to ensure identification of carcass data by pen, the number of animals shipped from pens within a block differed by one animal. The packing plant was blind to the treatment status of pens. Carcass weights and standard Canadian carcass grading parameters including quality and yield grades and dressing percent were obtained by pen from the processor.
Van Donkersgoed et al.
Shear Force Loins were collected from carcasses from both treatment groups on 4 different processing dates and sent by the packer to Agri-Food Discovery Place, Edmonton, Alberta, Canada. A total of 50 beef strip loins were received, with 25 strip loins from each β-agonist treatment. Within each treatment, strip loins were removed from carcasses that graded grade AAA with a YG of A1 or A2. Only AAA loins were selected because Mehaffey et al. (2009) showed differences from controls in shear force only in Choice steaks aged 14 d. Loins from the Optaflexx group were matched to the Zilmax group for marbling, estimated red meat yield, and carcass weight. Within each strip loin, there were 4 further aging treatments, with steaks from each strip loin aged for 7, 14, 21, and 28 d postmortem. Four, 2.54-cm (1-inch) thick steaks were removed from the loin end of each strip loin (steaks 1, 2, 3, and 4) after that end was faced (the immediate surface removed). Steaks were cut using a cutting guide and a ruler to ensure uniformity and consistency of steak thickness. Steaks 1, 2, 3, and 4 were assigned to 7, 14, 21, and 28 d of aging so that aging treatments were balanced for anatomical location. Individually packaged frozen steaks were thawed at 0 to 4°C for 24 h before cooking. Steaks were weighed before cooking, and color was measured using a Minolta spectrometer (Minolta CR400, Konica-Minolta, Nanshan, China). Steaks were cooked on a General Electric “4 in 1” grill preheated to 177°C to an internal temperature of 71°C. Cooking time and yield were recorded for each steak. Temperature was monitored using calibrated temperature probes (Fisher Scientific Company, Ottawa, Ontario, Canada). The identification of each steak was maintained throughout. Cooked steaks were placed on trays, covered with plastic film, and stored overnight at 0 to 4°C until peak shear force analysis. Six, 1.27-cm-diameter cores were removed from each steak, with
2 cores each from the lateral, medial, and middle areas of each steak. Meat cores containing large pockets of connective tissue or fat were not used unless most cores from a steak or an area of a steak (medial, middle, or lateral) contained large pockets of connective tissue or fat. In this case, a core or cores were used that had large pockets of connective tissue or fat because they were deemed representative of the steak structure. Cores with large pockets of connective tissue or fat were identified during recording of data. Each core was sheared once using a 3-mm-thick triangular blade fitted to a material testing machine (LRX Plus, Digital Measurement Metrology, Brampton, Ontario, Canada) fitted with a 1,000-N load cell, and the peak force was recorded. The material testing machine used was calibrated by the manufacturer. The peak force of each steak was the mean of the 6 cores.
Statistical Analyses Performance and Carcass Data. Performance data were calculated using total start BW for the pen, total final BW for the pen, total DMI for the pen, and total animal days for the pen. Final BW included the weight of cattle shipped to slaughter and those animals removed at shipping due to livestock truck over-weights (i.e., insufficient space for all study cattle) but excluded weights of salvaged and dead cattle and feed consumed by these removed cattle. Initial and final BW were shrunk 4%. Outcome measures included DMI, ADG, feed efficiency, carcass weight, and carcass yield and quality characteristics. Average daily gain and feed efficiency outcome measures did not include the weight of dead animals. Additional outcome measures included morbidity, mortality, and number of salvaged cattle. Data were analyzed as a randomized complete block design, and pen served as the experimental unit for all analyses. Growth performance, HCW, and dressing percent data were analyzed using MIXED procedures of SAS (ver-
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Economic value of feeding zilpaterol and ractopamine
sion 9.2, SAS Inst. Inc., Cary, NC). The model included the fixed effect of treatment, and block served as a random effect. Initial weight was different by treatment; therefore, initial weight was used as a covariate for final shrunk BW, HCW, and dressing percentage because the absolute change in carcass weight is an important response criterion for the treatments under consideration. Carcass QG and YG distributions were analyzed using GLIMMIX procedures of SAS for binomial data with the same model as described previously. Shear Force Data. The treatment structure included loins from cattle that had been fed Optaflexx or Zilmax. The design structure was a completely randomized design. Loin was the experimental unit. Data were analyzed using the MIXED procedure of SAS to account for both fixed and random effects. Fixed effects included feed additive treatment and aging time, whereas random effects included day of cooking, total cooking time, maximum internal steak temperature, and total cooking losses. Aging time within loin was a repeated measure and was analyzed using an unstructured covariance model. Treatment means were generated using the LSMEANS option and separated when significant (P < 0.05) using the PDIFF option. Economic Data. The grid on which cattle are sold will determine the economic value of feeding Zilmax compared with Optaflexx in finishing feedlot heifers. The following grid was used by the feedlot owner to determine the economic value of Zilmax based on outcomes that were statistically significant at P < 0.05. Zilmax was priced at $1.09 per heifer per day, and Optaflexx was priced at $0.29 per heifer per day. Over 20 d of feeding, the Zilmax cost was $21.80, and over 29 d of feeding, the Optaflexx cost was $8.41, resulting in a $13.39 per heifer difference in drug cost. Feed costs were $1.75/heifer daily. Heifers fed Zilmax ate 10.5 kg (23 lb, as-fed basis) less feed than did heifers fed Optaflexx, which was valued at $1.49 lower feed cost over
29 d. Hot carcass weight was valued at $0.68/kg ($1.50/lb). The additional 9.55 kg (21 lb) of carcass weight for heifers fed Zilmax was worth an additional $31.50. Canadian AAA carcasses were valued at an additional $5 per carcass based on the Choice/ Select spread at the time the study was completed ($5 × 0.09 = $0.45). A base level of Canadian YG 3 carcasses was allowed at 20%. Above that level, the discount was $15 per carcass ($15 × 0.08 = $1.20).
RESULTS AND DISCUSSION Morbidity, Mortality, and Removals There were no differences (P > 0.05) in morbidity, mortality, or removals between treatments (data not shown). Ten animals were removed from the study between allocation and the start of the feeding study, 8 animals for Optaflexx and 2 animals for Zilmax. Of the 10 animals removed, 6 were treated and removed and 4 died. In the Optaflexx group, treatment removals included 2 injuries, 1 foot rot, and 1 interstitial pneumonia, whereas death removals included 1 interstitial pneumonia, 1 cellulitis, and 1 congestive heart failure. In the Zilmax group, treatment removals included 1 foot rot and 1 hairy heel warts, and 1 animal died from unknown causes.
There was no difference (P = 0.14) in morbidity rates between treatments. Morbidity rates averaged 3% in each treatment group, and the most common cause of morbidity was foot rot. Fifteen heifers were salvaged before slaughter, 6 in the Optaflexx treatment and 9 in the Zilmax treatment. Five animals died during the trial feeding period. The causes of death for the 3 heifers fed Optaflexx included gas bloat, interstitial pneumonia, and chronic pneumonia. The causes of death for the 2 heifers fed Zilmax were broncho-interstitial pneumonia and pulmonary edema. None of these deaths were attributed to treatment. There was no difference (P > 0.05) in mortality between the 2 treatment groups during the trial feeding period.
Performance and Carcass Characteristics Although ADG and feed efficiency were not altered by treatment (P > 0.05, Table 1), heifers receiving Zilmax consumed less feed (0.3 kg/d) than did heifers fed Optaflexx (P = 0.008). Similar to the present results, Scramlin et al. (2010) observed a reduction in feed intake between Zilmax and Optaflexx in finishing steers. Montgomery et al. (2009) noted a reduction in feed intake (0.5 kg/d)
Table 1. Effects of β-agonists1 on growth performance and health of feedlot heifers fed barley-based diets Item Pens Cattle Days on feed Initial shrunk BW, kg Final shrunk BW, kg Covariate-adjusted final BW,2 kg DMI, kg/d ADG, live basis, kg/d Feed efficiency, live basis
Zilmax
Optaflexx
SE
P-value
10 1,725 29 568.7 602.9 601.6 9.38 1.12 8.52
10 1,719 29 565.5 599.9 601.3 9.68 1.14 8.53
— — — 7.9 7.7 1.2 0.15 0.04 0.33
— — — 0.02 0.07 0.69 0.008 0.53 0.98
Zilmax, Intervet/Schering-Plough Animal Health, De Soto, KS; Optaflexx, Elanco Animal Health, Greenfield, IN.
1
2
Raw data were adjusted using initial BW as a covariate (P < 0.10) in the model.
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Van Donkersgoed et al.
Table 2. Effects of β-agonists1 on carcass characteristics of feedlot heifers fed barley-based diets Item
Zilmax
Optaflexx
SE
HCW, kg Covariate-adjusted hot weight,2 kg Dressing percent (DP) Covariate-adjusted DP3 Prime, % AAA, % AA, % A, % B4, % D4,3 % YG 1, % YG 2, % YG 3, % Other grade, %
372.8 371.9 61.84 61.86 0.8 62.1 34.6 0.6 1.9 0 24.7 52.9 20.3 2.1
361.2 362.2 60.22 60.20 1.7 70.8 24.5 0.2 2.7 0.1 19.0 49.9 28.3 2.8
4.4 1.3 0.15 0.13 — — — — — — — — — —
P-value 0.0001 0.0001 0.0001 0.0001 0.05 0.0001 0.0001 0.05 0.15 NA4 0.0008 0.06 0.0001 0.19
Zilmax, Intervet/Schering-Plough Animal Health, De Soto, KS; Optaflexx, Elanco Animal Health, Greenfield, IN.
1
2
Raw data were adjusted using initial BW as a covariate (P < 0.10) in the model.
3
Model did not converge due to insufficient nonzero data.
4
NA = not available.
by heifers fed Zilmax compared with negative controls. Final BW did not differ (P > 0.05) between treatments (Table 1). However, heifers fed Zilmax had a 9.7-kg-heavier HCW than did heifers fed Optaflexx (P < 0.0001, Table 2). The increase in HCW for heifers fed Zilmax was attributed in part to an increase in dressing percent of 1.66 percentage units. Avendaño-Reyes et al. (2006) and Scramlin et al. (2010) demonstrated in steers an increase in carcass weight of 7.7 kg with Zilmax compared with Optaflexx. Increased carcass weight and dressing percent have been a consistent effect of Zilmax over Optaflexx in feedlot steers. The current study is the first work to demonstrate an increase in carcass weight for Zilmax over Optaflexx in feedlot heifers. Heifers fed Zilmax produced more Canadian YG 1 carcasses (P = 0.0008; 6 percentage units) and fewer Canadian YG 3 carcasses (P = 0.0001; 8 percentage units) than did heifers fed Optaflexx. The effect of Zilmax in increasing carcass leanness as reflected by an increase in YG 1 and a decrease in YG 3 carcasses is
similar to the effects seen for steers fed Zilmax or Optaflexx (AvendañoReyes et al., 2006; Scramlin et al., 2010). There were fewer (P < 0.05) Prime and AAA carcasses and more (P < 0.05) AA and A carcasses from heifers fed Zilmax than from those fed Optaflexx. Montgomery et al. (2009) demonstrated that finishing heifers fed Zilmax had a similar QG distribution when compared with controls. In contrast to the present results in heifers, Scramlin et al. (2010) observed no differences in marbling score between Zilmax and Optaflexx in steers.
Shear Force There were no (P > 0.95) differences in Warner-Bratzler shear force measurements between Zilmax and Optaflexx (3.51 and 3.51 ± 0.20 kg, respectively). Increased postmortem aging decreased (P < 0.001) WarnerBratzler shear force of steaks from heifers fed either Zilmax or Optaflexx. Postmortem aging from 7 to 28 d decreased Warner-Bratzler shear force values by 15.1, 6.8, and 1.4%. The lack (P = 0.58) of an interaction
indicates tenderness of steaks from heifers fed either Zilmax or Optaflexx improved with aging, and the magnitude of change over time was similar for Zilmax and Optaflexx. Platter and Choat (2008) observed an increase in shear force in heifers and steers fed Optaflexx when compared with controls. Brooks et al. (2009) observed an increase in shear force in steers and heifers fed Zilmax for 20 versus 30 versus 40 d before slaughter when compared with controls. However, O’Neill (2001) found no differences in shear force values for meat from steers treated, or not treated, with zilpaterol hydrochloride and concluded that zilpaterol hydrochloride did not reduce tenderness of beef. Scramlin et al. (2010) demonstrated that when Zilmax was fed for 30 d, there was an increase in shear force compared with Optaflexx in finishing steers. In contrast, Avendaño-Reyes et al. (2006) demonstrated that there were no differences in shear force between steers fed Zilmax for 30 d and those fed Optaflexx. Brooks et al. (2009) demonstrated that feeding Zilmax for 30 and 40 d resulted in greater shear force than when cattle were fed Zilmax for 20 d. Zilmax fed for 20 d before slaughter is recommended in both the United States and Canada to mitigate the negative effects on shear force seen at 30 and 40 d of zilpaterol feeding. These data suggest there is no difference in shear force between Zilmax fed for 20 d and Optaflexx fed for 29 d in heifers.
Economics When all the economic values were added together [$31.50 (from carcass weight) − $0.45 (from carcass quality) + $1.20 (from YG 3 premium) + $1.49 (less feed) − $13.39 (difference in feed additive costs)], the value of feeding Zilmax over Optaflexx in these British-based heifers was $20.35 per heifer.
IMPLICATIONS Heifers fed Zilmax had heavier HCW, higher dressing percent, and
Economic value of feeding zilpaterol and ractopamine
fewer YG 3 carcasses, but fewer Prime and AAA carcasses, than did heifers fed Optaflexx. No differences were detected between Zilmax and Optaflexx for Warner-Bratzler shear force. The economic value of Zilmax compared with Optaflexx in feedlot heifers was improved by $20.35/ animal. Zilmax can be fed for 20 d to British-influenced finishing heifers with the expectations of increased carcass weight and leanness with no difference in tenderness compared with heifers fed Optaflexx.
ACKNOWLEDGMENTS We would like to thank the participating feedlot owner and staff, as well as research technicians Darren Malchow and Lynn Usenik (both with Alberta Beef Health Solutions, Picture Butte, Alberta, Canada), for their participation in this study.
LITERATURE CITED Avendaño-Reyes, L., V. Torres-Rodríguez, F. J. Meraz-Murillo, C. Pérez-Linares, F. Figueroa-Saavedra, and P. H. Robinson. 2006. Effects of two β-adrenergic agonists on finishing performance, carcass characteristics, and meat quality of feedlot steers. J. Anim. Sci. 84:3259. Brooks, J. C., H. C. Claus, M. E. Dikeman, J. Shook, G. G. Hilton, T. E. Lawrence, J. M. Mehaffey, B. J. Johnson, D. M. Allen, M. N. Streeter, W. T. Nichols, J. P. Hutcheson, D. A. Yates, and M. F. Miller. 2009. Effects of
zilpaterol hydrochloride feeding duration and postmortem aging on Warner-Bratzler shear force of three muscles from beef steers and heifers. J. Anim. Sci. 87:3764. Bryant, T. C., T. Engle, M. Galyean, J. Wagner, J. Tatum, R. Anthony, and S. Laudert. 2010. Effects of ractopamine and trenbolone acetate implants with or without estradiol on growth performance, carcass characteristics, adipogenic enzyme activity, and blood metabolites in feedlot steers and heifers. J. Anim. Sci. 88:4102. FASS (Federation of Animal Science Societies). 1999. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. FASS, Champaign, IL. Griffin, W. A., G. Erickson, B. Dicke, T. Klopfenstein, R. Cooper, D. Jordon, R. Swingle, W. Moseley, G. Sides, and D. Weigel. 2009. Effects of ractopamine (Optaflexx) fed in combination with melengestrol acetate on feedlot heifer performance. Prof. Anim. Sci. 25:33. Mehaffey, J. M., J. Brooks, R. Rathmann, E. Alsup, J. Hutcheson, W. Nichols, M. Streeter, D. Yates, J. Johnson, and M. Miller. 2009. Effects of feeding zilpaterol hydrochloride to beef and calf-fed Holstein cattle on consumer palatability ratings. J. Anim. Sci. 87:3712. Mersmann, H. J. 2002. Beta adrenergic receptor modulation of adipocyte metabolism and growth. J. Anim. Sci. 80(Suppl. 1):E24. Montgomery, J. L., C. Krehbiel, J. Cranston, D. Yates, J. Hutcheson, W. Nichols, M. Streeter, D. Bechtol, E. Johnson, T. TerHune, and T. Montgomery. 2009. Dietary zilpaterol hydrochloride. I. Feedlot performance and carcass traits of steers and heifers. J. Anim. Sci. 87:1374. NRC. 2000. Nutrient Requirements of Beef Cattle. National Academy Press, Washington, DC.
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O’Neill, H. A. 2001. The effect of zilpaterol hydrochloride on dietary N-requirements and the quality and nutritional value of meat components. MS Thesis. University of Pretoria, Pretoria, South Africa. Platter, W. J., and W. T. Choat. 2008. Balancing beef quality and red meat yield with ractopamine hydrochloride. Pages 1–6 in Proc. Reciprocal Meat Conf., Gainesville, FL. Quinn, M. F., C. Reinhardt, E. Loe, B. Dependbusch, M. Corrigan, M. May, and J. Drouillard. 2008. The effects of ractopaminehydrogen chloride (Optaflexx) on performance, carcass characteristics, and meat quality in feedlot heifers. J. Anim. Sci. 86:902. Robles-Estrada, J. C., A. A. Arrizon, A. Barreras, J. F. Calderon, F. Figueroa-Saavedra, N. Torrentera, A. Plascencia, and R. A. Zinn. 2009. Effects of preslaughter withdrawal period on response of feedlot heifers to zilpaterol hydrochloride supplementation: Growth performance and carcass characteristics. J. Anim. Sci. 87:1759. Scramlin, S. M., W. J. Platter, R. A. Gomez, W. T. Choat, F. K. McKeith, and J. Killefer. 2010. Comparative effects of ractopamine hydrochloride and zilpaterol chloride on growth performance, carcass traits and longissimus tenderness of finishing steers. J. Anim. Sci. 88:1823. Sissom, E. K., C. Reinhardt, J. Hutcheson, W. Nichols, D. Yates, R. Swingle, and B. Johnson. 2007. Response to ractopamine-HCl in heifers is altered by implant strategy across days on feed. J. Anim. Sci. 85:2125. Walker, D. K., E. Titgemeyer, J. Drouillard, E. Loe, B. Depenbusch, and A. Webb. 2006. Effects or ractopamine and protein source on growth performance and carcass characteristics of feedlot heifers. J. Anim. Sci. 84:2795.