An experiment evaluated the live BW response of steers being fed Optaflexx for various durations. The design consisted of two Optaflexx levels (0 vs. 200 mg per steer daily) and two Optaflexx feeding durations (28 or 42 days immediately prior to slaughter). However, Optaflexx was started on the same day (day 151 of the feeding period). Feeding 200 mg/steer daily of Optaflexx significantly (P\u3c0.01) improved final BW, ADG, and F:G compared to controls. Feeding 200 mg /steer daily of Optaflexx provided 16.4 and 18.8 lb of added BW above controls for the 28 and 42 feeding duration, respectively, but most (approximately 87%) of this weight gain was within the first 28 days of the time that Optaflexx was fed

Erickson, Galen E.

Greenquist, Matthew A.

Platter, William J.

Van Koevering, Michael T.

Vander Pol, Kyle J.

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Beef Cattle Reports Animal Science Department January 2007 Performance Profile and Carcass Characteristics of Steers Fed Optaflexx Matthew A. Greenquist University of Nebraska-Lincoln, mgreenquist2@unl.edu Kyle J. Vander Pol University of Nebraska-Lincoln Galen E. Erickson University of Nebraska-Lincoln, gerickson4@unl.edu William J. Platter Elanco Animal Health, Indianapolis, Ind. Michael T. Van Koevering Elanco Animal Health, Indianapolis, Ind. Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr  Part of the Animal Sciences Commons Greenquist, Matthew A.; Vander Pol, Kyle J.; Erickson, Galen E.; Platter, William J.; and Van Koevering, Michael T., "Performance Profile and Carcass Characteristics of Steers Fed Optaflexx" (2007). Nebraska Beef Cattle Reports. 77. https://digitalcommons.unl.edu/animalscinbcr/77 This Article is brought to you for free and open access by the Animal Science Department at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Nebraska Beef Cattle Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. © The Board of Regents of the University of Nebraska.  All rights reserved. 2007 Nebraska Beef Report  — Page 65 Performance Profile and Carcass Characteristicsof Steers Fed OptaflexxMatthew A. GreenquistKyle J. Vander PolGalen. E. Erickson Terry J. KlopfensteinWilliam J. PlatterMichael T. Van Koevering1SummaryAn experiment evaluated the live BW response of steers being fed Optaflexx for various durations. The design consisted of two Optaflexx levels (0 vs. 200 mg per steer daily) and two Optaflexx feeding durations (28 or 42 days immediately prior to slaughter). However, Optaflexx was started on the same day (day 151 of the feeding period). Feeding 200 mg/steer daily of Optaflexx significantly (P<0.01) improved final BW, ADG, and F:G compared to controls. Feeding 200 mg /steer daily of Optaflexx provided 16.4 and 18.8 lb of added BW above controls for the 28 and 42 feeding dura-tion, respectively, but most (approxi-mately 87%) of this weight gain was within the first 28 days of the time that Optaflexx was fed. Introduction Optaflexx (ractopamine hydro-chloride) is a growth promoting feed additive approved for use with feedlot cattle the last 28 to 42 days immediately prior to slaughter. The expected increase in final BW of feed-ing 200 mg/steer daily of Optaflexx from Elanco’s post approval studies is 14.8 to 17.6 lb. Market shifts and environmental factors such as weather make optimal slaughter dates chal-lenging to predict prior to the start of feeding Optaflexx. The ability to predict performance changes dur-ing the late part of finishing period is important to justify making feeding and management changes to improve performance and carcass character-istics. Currently, there are limited data to evaluate the effects of feeding Optaflexx over time, or to evaluate the effects of Optaflexx when cattle are fed past their projected slaughter date. The objectives of our study were to evaluate 0 and 200 mg/steer daily of Optaflexx fed to steers for the last 28 or 42 days immediately prior to slaughter, and to evaluate how feeding Optaflexx can affect feedlot perfor-mance past projected finishing dates.ProcedureCrossbred steer calves (BW = 1189 lb) were used in a 2 by 2 factorial design (n=1; 28 pens). The treat-ments consisted of two Optaflexx levels (0 vs. 200 mg/steer daily) fed for two durations (28 or 42 days imme-diately prior to slaughter). However, Optaflexx feeding was started on the same day (day 151 of the feed-ing period). Steers were managed for a pre-trial phase (8 days) in pens of 20 head. At reimplant time cattle were weighed for two consecutive days. First day weights were used for stratification and steers were assigned to weight block (three blocks) and randomly allocated to treatment. Pens were assigned randomly to the four treatments. During weights on day 2, cattle were sorted into their respective pens with similar numbers of animals in each pen (12 steers/pen) and com-parable bunk (>18 inches/head) space for each animal.All steers were fed twice daily (070 and 120) with Optaflexx treatments being applied in a meal supplement fed at 4% of the diet DM. Metabolizable protein, Ca, P, and K requirements were formulated to meet or exceed NRC (1996) require-ments. High-moisture corn was fed at 58.5% of DM, wet corn gluten feed at 0% of DM, and alfalfa hay at 7.5% of DM (Table 1). Diets were prepared by loading the HMC first and then by adding the supplement while the mixer/delivery box (Roto-Mix® model 420, Roto-Mix®, Dodge City, Kan.) was running at idle. Gluten feed and alfalfa hay were subsequently added and diets were mixed continuously for 12 revolutions (approximately three minutes) at 1,500 rpm. Feeds and feeding procedures remained the same throughout the pre-trial and trial phase, except for the use of the new supplements formulated to pro-vide 0 and 200 mg/head of Optaflexx daily in the 28 or 42 days prior to slaughter. Two feed samples (approximately .5 lb) were retrieved from each batch of feed prepared for the morning feed deliveries (070) in the first and last week of the experiment. Samples were collected at the mixer discharge from the beginning, middle, and end of each treatment load. Samples were processed and analyzed for CP, ether extract, TDN, ADF, Ca, P, and mois-ture.Individual BW were collected on days -14, 0, and 28 or 42 of the exper-iment. Pen weights were taken on days -14, -7, 0, 7, 14, 21, 28, 5, and 42. A list of study events is presented in Table 2. All residual feed remaining at the time the steers were removed from their pen was weighed.Table 1. Diet composition and analyzed nutrient analysis.Ingredient, % of DMHigh-moisture corn 58.5Wet Corn Gluten Feed 0.0Alfalfa hay 7.5Dry supplement a 4.0Analyzed Nutrient AnalysisMoisture 67.89CP, % 14.05TDN, % 77.90ADF, % 7.84Calcium, % 0.66Phosphorus, % 0.50Ether Extract, % 4.0aDry supplement supplied 24.8 g/ton (DM basis) of Rumensin®, 90 mg/hd of Tylan®, and either 0 g/ton or 17.4 g/ton 100% DM of ractopamine to the experimental diets.(Continued on next page)Page 66 — 2007 Nebraska Beef Report  © The Board of Regents of the University of Nebraska.  All rights reserved.On day 28, steers being fed Optaflexx for 28 days were transported to Excel, Schuyler, Neb., and randomly presented for slaughter. Steers being fed Optaflexx for 42 days were fed for an additional 14 days (past day 28) to determine the effects of Optaflexx on performance and carcass characteris-tics when steers are fed past their pro-jected finishing date (179 DOF). At slaughter, hot carcass weights were collected and carcasses were chilled for approximately 6 hours, after which LM area and fat thick-ness were measured and marbling score called by a trained USDA grader. Yield grade was calculated using the equation (YG = 2.50 + (2.5*FT, in) - (0.2*LM area, in2) + (0.2*KPH, %) + (0.008*HCW, lb)).Data were analyzed using a mixed model analysis (Proc Mixed, SAS) with treatment (dose and duration) included in the model as fixed vari-ables and block as a random effect. Day 0 weight was used as a covariate in the analysis. Pen constituted the experimental unit with probabilities less than or equal to α (0.05) being considered significant.ResultsGrowth was evaluated on a 4% shrunk basis, across and within Optaflexx feeding durations. There were no Optaflexx dose (0 or 200 mg/steer daily) by Optaflexx feeding duration (28 or 42 days) interactions observed for growth performance traits in this study. The main effects of feeding 200 mg/steer daily of Optaflexx to steers for either 28 or 42 days immediately prior to slaughter increased (P<0.01) final live BW and ADG by 0.5 lb/day (14.4%) compared to controls (Table ). Using regression analysis (Figure 1) to calculate point-in-time estimates for Optaflexx response, the quadratic equation (R2 = 0.97; P = .02; (y = -0.0095x2 + 0.8x + 0.5)) would pre-dict that feeding 200 mg/steer daily of Optaflexx would provide 16.4, 18.1, and 18.8 lb of added live BW above controls for a 28, 5 and 42 feeding duration, respectively.Table 2.  List of study events.  Individual Weights Pens Weights Slaughter Optaflexx Feeding Optaflexx Feeding Optaflexx Feeding Durationa Durationa Durationa Study Day Date 28 days 42 days 28 days 42 days 28 days 42 days -14 /29/05 X X X X -7 4/05/05   X X 0 4/12/05 X X X X 7 4/19/05   X X 14 4/26/05   X X 21 5/0/05   X X 28 5/10/05 X  X X X 5 5/17/05    X 42 5/24/05  X  X  Xa Optaflexx was fed the final 28 or 42 days immediately prior to slaughter.Table 3. Main effects of growth and carcass characteristics of steers fed Optaflexx for an average of 35da.Optaflexx mg/head/day 0 200Pens, n 14 14Steers, n 168 16 INT b  DOSE c Performance, individual weightsInitial BW, lb d 1189 1189 — —Final BW , lb 118 16 0.69 <0.01DMI, lb/d 2.59 2.72 0.66 0.66ADG, lb .68 4.21 0.44 <0.01F:G 6.46 5.68 0.85 <0.01Carcass CharacteristicsHCW, lb 844 854 0.74 <0.01Dress, % e 64.08 64.01 0.7 0.6012th rib fat, in 0.66 0.64 0.99 0.28LM area, in2 14.07 14.21 0.42 0.4Marbling score f  517 517 0.50 0.99Yield grade, calculated g .0 .24 0.6 0.52aSteers were fed Optaflexx for 28 and 42 days and presented in the table as an average of 5 days. Growth performance calculated on a shrunk basis (4%), LS means.bINT = Observed significance level for Optaflexx Dose by Duration treatment interaction.cDOSE = Observed significance level for main effect of Optaflexx Dose. dInitial weights were used as a covariate. eDressing percentage = carcass weight / average live weight (4% shrink).fUSDA marbling score where 450=slight50, 500=small0, and 550=small50.gWhere yield grade = 2.50 + (2.5*FT, in) - (0.2*LM area, in2) + (0.2*KPH, %) + (0.008*HCW, lb).2520151050Live Weight Response over Controls, lbFigure 1. Growth performance profile for steers fed Optaflexx for 28 or 42ab.aGrowth performance is calculated on a shrunk basis (4%), LS means.bDay 7 – 28 has 28 Optaflexx pens averaged together (28 days and 42 days Optaflexx treatments), days 5-42 have only 14 pens (42 days Optaflexx treatments).0 7 14 21 28 5 42Optaflexx Feeding Duration, Daysy = -0.0095x2 + 0.8 + 0.5R2 = 0.97; P=0.02© The Board of Regents of the University of Nebraska.  All rights reserved. 2007 Nebraska Beef Report  — Page 67 There were no Optaflexx dose (0 or 200 mg/steer daily) by Optaflexx feeding duration (28 or 42 days) interactions observed for carcass characteristics in this study. The main effects of feeding 200 mg/steer daily of Optaflexx to steers for either 28 or 42 days immediately prior to slaughter, increased (P<0.01) hot carcass weights by 10.5 lb. Feeding 200 mg/steer daily of Optaflexx to steers had no effect on dressing percentage, 12th rib fat thickness, LM area, marbling scores, or calculated yield grade (Table ).Results from this experiment indi-cate feeding 200 mg/steer daily of Optaflexx for the last 28 or 42 days prior to slaughter increases BW, but most of this BW advantage (87%) is within the first 28 days of the feeding period. Steers fed Optaflexx past their projected slaughter date maintained their performance advantage over the controls.1Matthew A. Greenquist, research techni-cian; Kyle J. Vander Pol, research technician; Galen E. Erickson, associate professor; and Terry J. Klopfenstein, professor, Animal Science, Lincoln. William J. Platter and Michael T. Van Koevering, Elanco Animal Health, Indianapolis, Ind.Table 4. Growth and carcass characteristics of steers fed Optaflexx for 28 or 42aOaflexx Feeding Duration 28 42Optaflexx mg/head/day  0 200 0 200Pens, n 7 7 7 7Steers, n 84 84 82 81 DOSE b  DURA c PerformanceInitial BW, lb d 1189 1189 1189 1189 — —Final BW , lb 1294 110 142 161 <0.01 <0.01DMI, lb/d 2.16 2.42 24.01 24.01 0.6 0.02ADG, lb .7 4.2 .64 4.09 <0.01 0.07Feed:gain 6.26 5.46 6.66 5.90 <0.01 <0.01Carcass CharacteristicsHCW, lb  826 87 862 872 <0.01 <0.01Dress, % e 6.88 6.9 64.29 64.10 0.64 0.0612th rib fat, in 0.62 0.60 0.71 0.68 0.25 <0.01LM area, in2 1.59 1.86 14.55 14.57 0.7 <0.01Marbling score f 517 512 517 522 0.96 0.42Yield grade, calculated g .26 .16 .4 . 0.47 0.11aGrowth characteristics calculated on a shrunk basis (4%), LS means.bDOSE = Observed significance level for main effect of Optaflexx Dose. cDURA = Observed significance level for main effect of Optaflexx Duration. dInitial weights were used as a covariate and are also represented as arithmetic means.eDressing percentage = carcass weight / average live weight (4% shrink).fUSDA marbling score where 450=slight50, 500=small0, and 550=small50.gWhere yield grade = 2.50 + (2.5*FT, in) - (0.2*LM area, in2) + (0.2*KPH, %) + (0.008*HCW, lb).Feeding 200 mg/steer daily of Optaflexx to steers had no effect on DMI, thus, the added BW from feeding Optaflexx resulted in an improvement (P<0.01) in feed con-version (12.1%) over controls. Body weight, DMI and ADG were increased (P<0.04) with duration of feeding (Table 4). Pen weights were taken on a weekly basis to monitor the growth of steers (Table 2). Steers fed 200 mg/steer daily of Optaflexx had significant (P<0.01) increases in BW and ADG during all weekly weight intervals (7, 14, 21, 28, 5 and 42 days). There were no differences in DMI during any of the weekly mea-surements, resulting in significant (P<0.0) improvements in F:G during all weekly intervals.

Performance Profile and Carcass Characteristics of Steers Fed Optaflexx

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Nebraska Beef Cattle Reports Animal Science Department 
January 2007 
Performance Profile and Carcass Characteristics of Steers Fed 
Optaflexx 
Matthew A. Greenquist 
University of Nebraska-Lincoln, mgreenquist2@unl.edu 
Kyle J. Vander Pol 
University of Nebraska-Lincoln 
Galen E. Erickson 
University of Nebraska-Lincoln, gerickson4@unl.edu 
William J. Platter 
Elanco Animal Health, Indianapolis, Ind. 
Michael T. Van Koevering 
Elanco Animal Health, Indianapolis, Ind. 
Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr 
 Part of the Animal Sciences Commons 
Greenquist, Matthew A.; Vander Pol, Kyle J.; Erickson, Galen E.; Platter, William J.; and Van Koevering, 
Michael T., "Performance Profile and Carcass Characteristics of Steers Fed Optaflexx" (2007). Nebraska 
Beef Cattle Reports. 77. 
https://digitalcommons.unl.edu/animalscinbcr/77 
This Article is brought to you for free and open access by the Animal Science Department at 
DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Nebraska Beef Cattle 
Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 
© The Board of Regents of the University of Nebraska.  All rights reserved. 2007 Nebraska Beef Report  — Page 65 
Performance Profile and Carcass Characteristics
of Steers Fed Optaflexx
Matthew A. Greenquist
Kyle J. Vander Pol
Galen. E. Erickson 
Terry J. Klopfenstein
William J. Platter
Michael T. Van Koevering1
Summary
An experiment evaluated the live BW 
response of steers being fed Optaflexx for 
various durations. The design consisted 
of two Optaflexx levels (0 vs. 200 mg per 
steer daily) and two Optaflexx feeding 
durations (28 or 42 days immediately 
prior to slaughter). However, Optaflexx 
was started on the same day (day 151 
of the feeding period). Feeding 200 
mg/steer daily of Optaflexx significantly 
(P<0.01) improved final BW, ADG, and 
F:G compared to controls. Feeding 200 
mg /steer daily of Optaflexx provided 
16.4 and 18.8 lb of added BW above 
controls for the 28 and 42 feeding dura-
tion, respectively, but most (approxi-
mately 87%) of this weight gain was 
within the first 28 days of the time that 
Optaflexx was fed. 
Introduction 
Optaflexx (ractopamine hydro-
chloride) is a growth promoting 
feed additive approved for use with 
feedlot cattle the last 28 to 42 days 
immediately prior to slaughter. The 
expected increase in final BW of feed-
ing 200 mg/steer daily of Optaflexx 
from Elanco’s post approval studies 
is 14.8 to 17.6 lb. Market shifts and 
environmental factors such as weather 
make optimal slaughter dates chal-
lenging to predict prior to the start 
of feeding Optaflexx. The ability to 
predict performance changes dur-
ing the late part of finishing period is 
important to justify making feeding 
and management changes to improve 
performance and carcass character-
istics. Currently, there are limited 
data to evaluate the effects of feeding 
Optaflexx over time, or to evaluate the 
effects of Optaflexx when cattle are 
fed past their projected slaughter date. 
The objectives of our study were 
to evaluate 0 and 200 mg/steer daily 
of Optaflexx fed to steers for the last 
28 or 42 days immediately prior to 
slaughter, and to evaluate how feeding 
Optaflexx can affect feedlot perfor-
mance past projected finishing dates.
Procedure
Crossbred steer calves (BW = 1189 
lb) were used in a 2 by 2 factorial 
design (n=1; 28 pens). The treat-
ments consisted of two Optaflexx 
levels (0 vs. 200 mg/steer daily) fed for 
two durations (28 or 42 days imme-
diately prior to slaughter). However, 
Optaflexx feeding was started on 
the same day (day 151 of the feed-
ing period). Steers were managed for 
a pre-trial phase (8 days) in pens 
of 20 head. At reimplant time cattle 
were weighed for two consecutive 
days. First day weights were used for 
stratification and steers were assigned 
to weight block (three blocks) and 
randomly allocated to treatment. Pens 
were assigned randomly to the four 
treatments. During weights on day 2, 
cattle were sorted into their respective 
pens with similar numbers of animals 
in each pen (12 steers/pen) and com-
parable bunk (>18 inches/head) space 
for each animal.
All steers were fed twice daily 
(070 and 120) with Optaflexx 
treatments being applied in a meal 
supplement fed at 4% of the diet DM. 
Metabolizable protein, Ca, P, and 
K requirements were formulated to 
meet or exceed NRC (1996) require-
ments. High-moisture corn was fed 
at 58.5% of DM, wet corn gluten feed 
at 0% of DM, and alfalfa hay at 7.5% 
of DM (Table 1). Diets were prepared 
by loading the HMC first and then 
by adding the supplement while the 
mixer/delivery box (Roto-Mix® model 
420, Roto-Mix®, Dodge City, Kan.) 
was running at idle. Gluten feed and 
alfalfa hay were subsequently added 
and diets were mixed continuously 
for 12 revolutions (approximately 
three minutes) at 1,500 rpm. Feeds 
and feeding procedures remained the 
same throughout the pre-trial and 
trial phase, except for the use of the 
new supplements formulated to pro-
vide 0 and 200 mg/head of Optaflexx 
daily in the 28 or 42 days prior to 
slaughter. 
Two feed samples (approximately 
.5 lb) were retrieved from each batch 
of feed prepared for the morning 
feed deliveries (070) in the first and 
last week of the experiment. Samples 
were collected at the mixer discharge 
from the beginning, middle, and end 
of each treatment load. Samples were 
processed and analyzed for CP, ether 
extract, TDN, ADF, Ca, P, and mois-
ture.
Individual BW were collected on 
days -14, 0, and 28 or 42 of the exper-
iment. Pen weights were taken on 
days -14, -7, 0, 7, 14, 21, 28, 5, and 42. 
A list of study events is presented in 
Table 2. All residual feed remaining at 
the time the steers were removed from 
their pen was weighed.
Table 1. Diet composition and analyzed nutrient 
analysis.
Ingredient, % of DM
High-moisture corn 58.5
Wet Corn Gluten Feed 0.0
Alfalfa hay 7.5
Dry supplement a 4.0
Analyzed Nutrient Analysis
Moisture 67.89
CP, % 14.05
TDN, % 77.90
ADF, % 7.84
Calcium, % 0.66
Phosphorus, % 0.50
Ether Extract, % 4.0
aDry supplement supplied 24.8 g/ton (DM basis) 
of Rumensin®, 90 mg/hd of Tylan®, and either 0 
g/ton or 17.4 g/ton 100% DM of ractopamine to 
the experimental diets.
(Continued on next page)
Page 66 — 2007 Nebraska Beef Report  © The Board of Regents of the University of Nebraska.  All rights reserved.
On day 28, steers being fed 
Optaflexx for 28 days were transported 
to Excel, Schuyler, Neb., and randomly 
presented for slaughter. Steers being 
fed Optaflexx for 42 days were fed for 
an additional 14 days (past day 28) to 
determine the effects of Optaflexx on 
performance and carcass characteris-
tics when steers are fed past their pro-
jected finishing date (179 DOF). 
At slaughter, hot carcass weights 
were collected and carcasses were 
chilled for approximately 6 hours, 
after which LM area and fat thick-
ness were measured and marbling 
score called by a trained USDA grader. 
Yield grade was calculated using the 
equation (YG = 2.50 + (2.5*FT, in) - 
(0.2*LM area, in2) + (0.2*KPH, %) + 
(0.008*HCW, lb)).
Data were analyzed using a mixed 
model analysis (Proc Mixed, SAS) 
with treatment (dose and duration) 
included in the model as fixed vari-
ables and block as a random effect. 
Day 0 weight was used as a covariate 
in the analysis. Pen constituted the 
experimental unit with probabilities 
less than or equal to α (0.05) being 
considered significant.
Results
Growth was evaluated on a 4% 
shrunk basis, across and within 
Optaflexx feeding durations. There 
were no Optaflexx dose (0 or 200 
mg/steer daily) by Optaflexx feeding 
duration (28 or 42 days) interactions 
observed for growth performance 
traits in this study. 
The main effects of feeding 200 
mg/steer daily of Optaflexx to steers 
for either 28 or 42 days immediately 
prior to slaughter increased (P<0.01) 
final live BW and ADG by 0.5 lb/day 
(14.4%) compared to controls (Table 
). Using regression analysis (Figure 
1) to calculate point-in-time estimates 
for Optaflexx response, the quadratic 
equation (R2 = 0.97; P = .02; (y = 
-0.0095x2 + 0.8x + 0.5)) would pre-
dict that feeding 200 mg/steer daily 
of Optaflexx would provide 16.4, 18.1, 
and 18.8 lb of added live BW above 
controls for a 28, 5 and 42 feeding 
duration, respectively.
Table 2.  List of study events. 
 Individual Weights Pens Weights Slaughter
 Optaflexx Feeding Optaflexx Feeding Optaflexx Feeding
 Durationa Durationa Durationa
 Study Day Date 28 days 42 days 28 days 42 days 28 days 42 days
 -14 /29/05 X X X X
 -7 4/05/05   X X
 0 4/12/05 X X X X
 7 4/19/05   X X
 14 4/26/05   X X
 21 5/0/05   X X
 28 5/10/05 X  X X X
 5 5/17/05    X
 42 5/24/05  X  X  X
a Optaflexx was fed the final 28 or 42 days immediately prior to slaughter.
Table 3. Main effects of growth and carcass characteristics of steers fed Optaflexx for an average of 
35da.
Optaflexx mg/head/day 0 200
Pens, n 14 14
Steers, n 168 16 INT b  DOSE c 
Performance, individual weights
Initial BW, lb d 1189 1189 — —
Final BW , lb 118 16 0.69 <0.01
DMI, lb/d 2.59 2.72 0.66 0.66
ADG, lb .68 4.21 0.44 <0.01
F:G 6.46 5.68 0.85 <0.01
Carcass Characteristics
HCW, lb 844 854 0.74 <0.01
Dress, % e 64.08 64.01 0.7 0.60
12th rib fat, in 0.66 0.64 0.99 0.28
LM area, in2 14.07 14.21 0.42 0.4
Marbling score f  517 517 0.50 0.99
Yield grade, calculated g .0 .24 0.6 0.52
aSteers were fed Optaflexx for 28 and 42 days and presented in the table as an average of 5 days. 
Growth performance calculated on a shrunk basis (4%), LS means.
bINT = Observed significance level for Optaflexx Dose by Duration treatment interaction.
cDOSE = Observed significance level for main effect of Optaflexx Dose. 
dInitial weights were used as a covariate. 
eDressing percentage = carcass weight / average live weight (4% shrink).
fUSDA marbling score where 450=slight50, 500=small0, and 550=small50.
gWhere yield grade = 2.50 + (2.5*FT, in) - (0.2*LM area, in2) + (0.2*KPH, %) + (0.008*HCW, lb).
25
20
15
10
5
0
Li
ve
 W
ei
gh
t R
es
po
n
se
 o
ve
r 
C
on
tr
ol
s,
 lb
Figure 1. Growth performance profile for steers fed Optaflexx for 28 or 42ab.
aGrowth performance is calculated on a shrunk basis (4%), LS means.
bDay 7 – 28 has 28 Optaflexx pens averaged together (28 days and 42 days Optaflexx treatments), days 
5-42 have only 14 pens (42 days Optaflexx treatments).
0 7 14 21 28 5 42
Optaflexx Feeding Duration, Days
y = -0.0095x2 + 0.8 + 0.5
R2 = 0.97; P=0.02
© The Board of Regents of the University of Nebraska.  All rights reserved. 2007 Nebraska Beef Report  — Page 67 
There were no Optaflexx dose (0 
or 200 mg/steer daily) by Optaflexx 
feeding duration (28 or 42 days) 
interactions observed for carcass 
characteristics in this study. The main 
effects of feeding 200 mg/steer daily of 
Optaflexx to steers for either 28 or 42 
days immediately prior to slaughter, 
increased (P<0.01) hot carcass weights 
by 10.5 lb. Feeding 200 mg/steer daily 
of Optaflexx to steers had no effect 
on dressing percentage, 12th rib fat 
thickness, LM area, marbling scores, 
or calculated yield grade (Table ).
Results from this experiment indi-
cate feeding 200 mg/steer daily of 
Optaflexx for the last 28 or 42 days 
prior to slaughter increases BW, but 
most of this BW advantage (87%) is 
within the first 28 days of the feeding 
period. Steers fed Optaflexx past their 
projected slaughter date maintained 
their performance advantage over the 
controls.
1Matthew A. Greenquist, research techni-
cian; Kyle J. Vander Pol, research technician; 
Galen E. Erickson, associate professor; and 
Terry J. Klopfenstein, professor, Animal Science, 
Lincoln. William J. Platter and Michael T. Van 
Koevering, Elanco Animal Health, Indianapolis, 
Ind.
Table 4. Growth and carcass characteristics of steers fed Optaflexx for 28 or 42a
Oaflexx Feeding Duration 28 42
Optaflexx mg/head/day  0 200 0 200
Pens, n 7 7 7 7
Steers, n 84 84 82 81 DOSE b  DURA c 
Performance
Initial BW, lb d 1189 1189 1189 1189 — —
Final BW , lb 1294 110 142 161 <0.01 <0.01
DMI, lb/d 2.16 2.42 24.01 24.01 0.6 0.02
ADG, lb .7 4.2 .64 4.09 <0.01 0.07
Feed:gain 6.26 5.46 6.66 5.90 <0.01 <0.01
Carcass Characteristics
HCW, lb  826 87 862 872 <0.01 <0.01
Dress, % e 6.88 6.9 64.29 64.10 0.64 0.06
12th rib fat, in 0.62 0.60 0.71 0.68 0.25 <0.01
LM area, in2 1.59 1.86 14.55 14.57 0.7 <0.01
Marbling score f 517 512 517 522 0.96 0.42
Yield grade, calculated g .26 .16 .4 . 0.47 0.11
aGrowth characteristics calculated on a shrunk basis (4%), LS means.
bDOSE = Observed significance level for main effect of Optaflexx Dose. 
cDURA = Observed significance level for main effect of Optaflexx Duration. 
dInitial weights were used as a covariate and are also represented as arithmetic means.
eDressing percentage = carcass weight / average live weight (4% shrink).
fUSDA marbling score where 450=slight50, 500=small0, and 550=small50.
gWhere yield grade = 2.50 + (2.5*FT, in) - (0.2*LM area, in2) + (0.2*KPH, %) + (0.008*HCW, lb).
Feeding 200 mg/steer daily of 
Optaflexx to steers had no effect 
on DMI, thus, the added BW from 
feeding Optaflexx resulted in an 
improvement (P<0.01) in feed con-
version (12.1%) over controls. Body 
weight, DMI and ADG were increased 
(P<0.04) with duration of feeding 
(Table 4). Pen weights were taken 
on a weekly basis to monitor the 
growth of steers (Table 2). Steers fed 
200 mg/steer daily of Optaflexx had 
significant (P<0.01) increases in BW 
and ADG during all weekly weight 
intervals (7, 14, 21, 28, 5 and 42 
days). There were no differences in 
DMI during any of the weekly mea-
surements, resulting in significant 
(P<0.0) improvements in F:G during 
all weekly intervals.


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Performance Profile and Carcass Characteristics of Steers Fed Optaflexx

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