Live BW and carcass traits of steer calves were evaluated after feeding Optaflexx (200mg/day) for 35 days on an intermittent basis or continuously. The negative control consisted of 63 days on the same diet without Optaflexx, whereas the positive control consisted of Optaflexx supplemented daily during the last 35 days prior to harvest. The four-day intermittent treatment consisted of feeding Optaflexx for seven days, followed by four days of no Optaflexx, while the seven-day intermittent treatment consisted of seven days on Optaflexx, followed by seven days off. In both the four-day and seven-day intermittent treatments, cattle received Optaflexx for a total of 35 days. Regardless of the delivery pattern, feeding Optaflexx increased ADG, DMI, and live BW. Feeding 200 mg per steer daily of Optaflexx for a total of 35 days in either four-day or seven-day intermittent patterns was as effective but no more so as continuous feeding for a 35-day period

Benton, Joshua R, Benton

Choat, W. Travis

Dib, Marco G.

Erickson, Galen

Griffin, William A

Klopfenstein, Terry

Sindt, Justin J.

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Beef Cattle Reports Animal Science Department 2011 Feeding Strategies of Optaflexx on Growth Performance and Carcass Characteristics of Feedlot Steers Marco G. Dib University of Nebraska-Lincoln William A. Griffin University of Nebraska-Lincoln, wgriffin2@unl.edu Joshua R. Benton Benton University of Nebraska-Lincoln, jbenton2@unl.edu Galen Erickson University of Nebraska-Lincoln, gerickson4@unl.edu Terry Klopfenstein Universitiy of Nebraska-Lincoln, tklopfenstein1@unl.edu See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr  Part of the Animal Sciences Commons Dib, Marco G.; Griffin, William A.; Benton, Joshua R. Benton; Erickson, Galen; Klopfenstein, Terry; Sindt, Justin J.; and Choat, W. Travis, "Feeding Strategies of Optaflexx on Growth Performance and Carcass Characteristics of Feedlot Steers" (2011). Nebraska Beef Cattle Reports. 606. https://digitalcommons.unl.edu/animalscinbcr/606 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. Authors Marco G. Dib, William A. Griffin, Joshua R. Benton Benton, Galen Erickson, Terry Klopfenstein, Justin J. Sindt, and W. Travis Choat This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/animalscinbcr/606 Page 74 — 2011 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.Feeding Strategies of Optaflexx on Growth Performance and Carcass Characteristics of Feedlot SteersMarco G. DibWilliam A. GriffinJosh R. BentonGalen E. EricksonTerry J. KlopfensteinJustin J. SindtW. Travis Choat1SummaryLive BW and carcass traits of steer calves were evaluated after feeding Optaflexx (200mg/day) for 35 days on an intermittent basis or continuously. The negative control consisted of 63 days on the same diet without Optaflexx, whereas the positive control consisted of Optaflexx supplemented daily during the last 35 days prior to harvest. The four-day intermittent treatment consist-ed of feeding Optaflexx for seven days, followed by four days of no Optaflexx, while the seven-day intermittent treat-ment consisted of seven days on Opta-flexx, followed by seven days off. In both the four-day and seven-day intermittent treatments, cattle received Optaflexx for a total of 35 days. Regardless of the delivery pattern, feeding Optaflexx in-creased ADG, DMI, and live BW. Feed-ing 200 mg per steer daily of Optaflexx for a total of 35 days in either four-day or seven-day intermittent patterns was as effective but no more so as continuous feeding for a 35-day period.IntroductionRactopamine hydrochloride (Opta-flexx; Elanco Animal Health, India-napolis, Ind.) increases live weight gain and gain efficiency. Optaflexx is approved for continuous feeding to feedlot cattle during the last 28 to 42 days prior to harvest at a dose ranging from 70 to 430 mg per steer daily or 9.1 to 27.3 g/ton of DM. Continuous feeding of Optaflexx for 42, 35, and 28 days prior to harvest at doses up to 200 mg per steer increased live BW by 16.4, 18.1, and 18.8 lb, respectively, compared with a control diet, and improved ADG by 0.53 lb/day in feed-lot steers. In addition, LM area also was larger for treated animals, with no effect on fat depth. Additionally, about 87% of the live weight response has been observed in the first 28 days compared to 42 days when Optaflexx was fed at 200 mg/steer daily (2006 Nebraska Beef Cattle Report, pp. 72-74, 2007 Nebraska Beef Cattle Report, pp. 65 - 67). Studies in pigs indicate that intermittent use of Optaflexx increases ADG, F:G, and BW. Our objective was to evaluate the effects of intermittent use of Optaflexx on growth and carcass characteristics of feedlot steers.ProcedureCrossbred steer calves (BW = 1057 + 26 lb) were assigned to two blocks based on reimplant BW. The heavy block consisted of 1 replication of 40 steers, and the light block con-sisted of 7 replications of 280 steers. Steers were assigned randomly to a pen within block and pens assigned randomly to 1 of the 4 treatments (8 pens/treatment; 10 steers/pen). The treatments consisted of no delivery of Optaflexx (NONE), continuously feeding of Optaflexx throughout the last 35 days prior to harvest (CON-TIN), intermittent seven day feeding Optaflexx followed by four days of withdrawal (4-dINT) and intermit-tent seven days feeding Optaflexx followed by seven days of withdrawal (7-dINT). The three treatments with Optaflexx resulted in a total of 35 days of feeding Optaflexx but on different days. Steers were managed during the pre-trial phase (102 days) in the actual experiment pens after being assigned within a block (4 pens for the heavy block and 28 pens for the light block). Three animals were removed from three different pens prior to Optaflexx feeding due to death or health rea-sons. Before the start of the trial, each steer was weighed on two consecutive days after feed restriction (decrease of 2 lb/day of DM during three days). Pens of animals were weighed weekly, with a 4% shrink factor applied to the BW, throughout the 63 days of the Optaflexx treatment period and prior to harvest.Steers were implanted with Compo-nent TE-IS initially and re-implanted with Component TE-S 98 days prior to harvest. Steers were fed once per day at approximately 0830 hour, and the Optaflexx supplement was top dressed in a supplement at a rate of 0.5 lb per steer to ensure that steers received the amount of 200 mg of Optaflexx per day. The carrier used was fine ground corn. Steers received 0.5 lb of fine ground corn when not on Optaflexx or for the negative control treatment. Diets were formulated to meet or exceed NRC (1996) requirements for metabolizable protein, Ca, P, and K. High-moisture corn was fed at 50% of diet DM, wet corn gluten feed (Sweet Bran®, Cargill, Blair, Neb.) at 40% of DM and ground wheat straw at 5% of DM (Table 1). Diets were prepared by loading the HMC, WCGF, ground wheat straw, and then by adding dry supplement in the mixer/delivery box (Roto-Mix® model 420, Roto-Mix, Dodge City, Kan.). Rumensin and Tylan were fed to all steers, with consump-tions of 348 and 90 mg/head/daily, respectively. Feeds and feeding proce-dures remained the same throughout Table 1.  Diet composition and analyzed nutrient analysis for diets fed.Ingredient % of DMHigh-moisture Corn 50.0Wet Corn Gluten Feed 40.0Ground Wheat Straw 5.0Dry Supplement 5.0Analyzed Nutrient Analysis, % DMDM 66.3CP 14.3Ether Extract 4.3Calcium 0.66Phosphorus 0.54Potassium 0.74© The Board of Regents of the University of Nebraska.  All rights reserved. 2011 Nebraska Beef Cattle Report  — Page 75 ResultsResults for feedlot performance and carcass characteristics are pre-sented in Table 2 and Table 3, respec-tively. Dry matter intake was affected (P = 0.05) by Optaflexx 7-dINT treat-ment with steers consuming slightly more DM than all other treatments.Live BW increased (P < 0.04) for all Optaflexx treatments compared to NONE. Optaflexx 7-dINT was also significantly different from the CONTIN and 4-dINT. The CONTIN was 14 lb heavier than the NONE, the 4-dINT was 13 lb (no difference when compared with the CONTIN) and the 7-dINT was 33 lb heavier than the NONE, and approximately 19 lb heavier than the CONTIN and 4-dINT treatments. Live ADG was also affected positively by the Optaflexx treatments compared to NONE, providing an in-crease of approximately 0.29 lb/day.On a carcass basis, treatments were not different when compared to NONE, except for the calculated yield grade trait that decreased for the 4-dINT treatment when compared to all other treatments due to differ-ences in KPH scores. Positive trends for carcass adjusted final BW, HCW, and LM area were observed mainly for the 7-dINT treatment when compared to the others. Efficiency analyses show that steers on Optaflexx treat-ments had numerically lower F:G than NONE (values numerically lower and P values less than 0.20).Results from this experiment indicate that 200 mg/steer daily of Optaflexx fed intermittently increases DMI, ADG, and Live BW. Tendencies for a larger LM area on the positive control and better F:G on all Opta-flexx treatments were also observed.In conclusion, withdrawing Opta-flexx for seven or four days then re-feeding, when compared to continu-ous, had no effect on live ADG or F:G. 1Marco G. Dib, graduate student; William A. Griffin, research technician; Josh R. Benton, research technician; Galen E. Erickson, associate professor; Terry J. Klopfenstein, professor; University of Nebraska–Lincoln Department of Animal Science. Justin J. Sindt and W. Travis Choat, Elanco Animal Health, Indianapolis, Ind.Table 2. Growth performance of steers fed Optaflexx in continuous vs. intermittent patterns.Treatments NONE1 CONTIN2 4-dINT3 7-dINT4 SEM P-valueLive PerformanceInitial BW, lb 1077 1076 1074 1090 8.7 0.28Live Final BW, lb 1352a 1366b 1365b 1385c 10.7 0.04DMI, lb/day 22.3a 22.0a 22.3a 22.9b 0.31 0.05ADG, lb 4.36a 4.61b 4.61b 4.68b 0.09 <0.01F:G5 5.33 5.14 5.21 5.22  0.09Carcass Adjusted PerformanceFBW, lb 1347 1356 1351 1371 11.5 0.19ADG, lb 4.36 4.45 4.40 4.47 0.12 0.40F:G5 5.32 5.12 5.24 5.23  0.521NONE: treatment did not receive Optaflexx.2CONTIN: treatment received Optaflexx for 35 days continuously.34-dINT: treatment received intermittent seven day feeding Optaflexx followed by four days of with-drawal.47-dINT: treatment received intermittent seven day feeding Optaflexx followed by seven days of with-drawal.5Analyzed as G:F, reported as F:G.Table 3. Carcass characteristics of steers fed Optaflexx in continuous vs. intermittent patterns.Treatments NONE1 CONTIN2 4-dINT3 7-dINT4 SEM P-valueCarcass Characteristics      HCW, lb 848 854 851 864 7.3 0.18Dressing, %a 62.8 62.5 62.4 62.4 0.22 0.2512th rib fat, in 0.5 0.48 0.49 0.52 0.03 0.51Marbling scoreb 507 485 506 505 14 0.37LM area, in2 14.6 15.1 14.5 14.6 0.2 0.09USDA yield gradec 2.73a 2.76a 2.45b 2.78a 0.1 <0.011NONE: treatment did not receive Optaflexx.2CONTIN: treatment received Optaflexx for 35 days continuously.34-dINT: treatment received intermittent seven day feeding Optaflexx followed by four days of with-drawal.47-dINT: treatment received intermittent 7 day feeding Optaflexx followed by seven days of withdrawal.aDressing percentage = carcass weight / average live weight (4% shrink).bUSDA marbling score where 450 = slight50, 500 = small0, and 550 = small50cUSDA calculated yield grade = 2.50 + (2.5*FT, in) – (0.32*LM area, in2) + (0.2*KPH, %) + (0.0038*HCW).the pre-trial and trial phases, except for the use of the top dressing with or without Optaflexx that occurred only during the last 63 days prior to harvest.Feed samples were collected from each load and each supplement (with or without Optaflexx) every other week, during the mixer discharge in the beginning, middle, and end of each load. Optaflexx supplements were sam-pled from supplement bags. Samples were processed and analyzed for DM content, CP, Ca, P, K, and ether extract.All steers were harvested on the same day after 165 days on feed, and 63 days of Optaflexx treatment pe-riod. At harvest, HCW were collected, and after approximately a 48-hour chill, LM area and fat thickness were measured. Bone score, lean score, and KPH were subjectively assigned by a University of Nebraska–Lincoln research technician, and marbling score was assigned by a USDA grader. Yield grade was calculated using the equation (YG= 2.50 + (2.5*FT, in) – (0.32*LM area, in2) + (0.2*KPH, %) + (0.0038*HCW, lb)).Growth performance was evalu-ated on a 4% shrunk weight basis, across and within the Optaflexx treatment period. Data from the ran-domized complete block design were analyzed using a mixed model analy-sis (Proc Mixed, SAS), with treatment and block included in the model as fixed variables. Pen was the experi-mental unit. Data were analyzed using a protected F-test and means sepa-rated using a bonfevroni t-test when the F-test variable was significant (i.e., alpha = 0.05).

Feeding Strategies of Optaflexx on Growth Performance and Carcass Characteristics of Feedlot Steers

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Nebraska Beef Cattle Reports Animal Science Department 
2011 
Feeding Strategies of Optaflexx on Growth Performance and 
Carcass Characteristics of Feedlot Steers 
Marco G. Dib 
University of Nebraska-Lincoln 
William A. Griffin 
University of Nebraska-Lincoln, wgriffin2@unl.edu 
Joshua R. Benton Benton 
University of Nebraska-Lincoln, jbenton2@unl.edu 
Galen Erickson 
University of Nebraska-Lincoln, gerickson4@unl.edu 
Terry Klopfenstein 
Universitiy of Nebraska-Lincoln, tklopfenstein1@unl.edu 
See next page for additional authors 
Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr 
 Part of the Animal Sciences Commons 
Dib, Marco G.; Griffin, William A.; Benton, Joshua R. Benton; Erickson, Galen; Klopfenstein, Terry; Sindt, 
Justin J.; and Choat, W. Travis, "Feeding Strategies of Optaflexx on Growth Performance and Carcass 
Characteristics of Feedlot Steers" (2011). Nebraska Beef Cattle Reports. 606. 
https://digitalcommons.unl.edu/animalscinbcr/606 
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. 
Authors 
Marco G. Dib, William A. Griffin, Joshua R. Benton Benton, Galen Erickson, Terry Klopfenstein, Justin J. 
Sindt, and W. Travis Choat 
This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/
animalscinbcr/606 
Page 74 — 2011 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.
Feeding Strategies of Optaflexx on Growth Performance 
and Carcass Characteristics of Feedlot Steers
Marco G. Dib
William A. Griffin
Josh R. Benton
Galen E. Erickson
Terry J. Klopfenstein
Justin J. Sindt
W. Travis Choat1
Summary
Live BW and carcass traits of steer 
calves were evaluated after feeding 
Optaflexx (200mg/day) for 35 days on 
an intermittent basis or continuously. 
The negative control consisted of 63 days 
on the same diet without Optaflexx, 
whereas the positive control consisted of 
Optaflexx supplemented daily during 
the last 35 days prior to harvest. The 
four-day intermittent treatment consist-
ed of feeding Optaflexx for seven days, 
followed by four days of no Optaflexx, 
while the seven-day intermittent treat-
ment consisted of seven days on Opta-
flexx, followed by seven days off. In both 
the four-day and seven-day intermittent 
treatments, cattle received Optaflexx 
for a total of 35 days. Regardless of the 
delivery pattern, feeding Optaflexx in-
creased ADG, DMI, and live BW. Feed-
ing 200 mg per steer daily of Optaflexx 
for a total of 35 days in either four-day 
or seven-day intermittent patterns was 
as effective but no more so as continuous 
feeding for a 35-day period.
Introduction
Ractopamine hydrochloride (Opta-
flexx; Elanco Animal Health, India-
napolis, Ind.) increases live weight 
gain and gain efficiency. Optaflexx is 
approved for continuous feeding to 
feedlot cattle during the last 28 to 42 
days prior to harvest at a dose ranging 
from 70 to 430 mg per steer daily or 
9.1 to 27.3 g/ton of DM. Continuous 
feeding of Optaflexx for 42, 35, and 
28 days prior to harvest at doses up 
to 200 mg per steer increased live BW 
by 16.4, 18.1, and 18.8 lb, respectively, 
compared with a control diet, and 
improved ADG by 0.53 lb/day in feed-
lot steers. In addition, LM area also 
was larger for treated animals, with 
no effect on fat depth. Additionally, 
about 87% of the live weight response 
has been observed in the first 28 days 
compared to 42 days when Optaflexx 
was fed at 200 mg/steer daily (2006 
Nebraska Beef Cattle Report, pp. 72-
74, 2007 Nebraska Beef Cattle Report, 
pp. 65 - 67). Studies in pigs indicate 
that intermittent use of Optaflexx 
increases ADG, F:G, and BW. Our 
objective was to evaluate the effects 
of intermittent use of Optaflexx on 
growth and carcass characteristics of 
feedlot steers.
Procedure
Crossbred steer calves (BW = 1057 
+ 26 lb) were assigned to two blocks 
based on reimplant BW. The heavy 
block consisted of 1 replication of 
40 steers, and the light block con-
sisted of 7 replications of 280 steers. 
Steers were assigned randomly to a 
pen within block and pens assigned 
randomly to 1 of the 4 treatments (8 
pens/treatment; 10 steers/pen). The 
treatments consisted of no delivery 
of Optaflexx (NONE), continuously 
feeding of Optaflexx throughout the 
last 35 days prior to harvest (CON-
TIN), intermittent seven day feeding 
Optaflexx followed by four days of 
withdrawal (4-dINT) and intermit-
tent seven days feeding Optaflexx 
followed by seven days of withdrawal 
(7-dINT). The three treatments with 
Optaflexx resulted in a total of 35 days 
of feeding Optaflexx but on different 
days. Steers were managed during the 
pre-trial phase (102 days) in the actual 
experiment pens after being assigned 
within a block (4 pens for the heavy 
block and 28 pens for the light block). 
Three animals were removed from 
three different pens prior to Optaflexx 
feeding due to death or health rea-
sons. Before the start of the trial, each 
steer was weighed on two consecutive 
days after feed restriction (decrease 
of 2 lb/day of DM during three days). 
Pens of animals were weighed weekly, 
with a 4% shrink factor applied to the 
BW, throughout the 63 days of the 
Optaflexx treatment period and prior 
to harvest.
Steers were implanted with Compo-
nent TE-IS initially and re-implanted 
with Component TE-S 98 days prior to 
harvest. Steers were fed once per day 
at approximately 0830 hour, and the 
Optaflexx supplement was top dressed 
in a supplement at a rate of 0.5 lb per 
steer to ensure that steers received the 
amount of 200 mg of Optaflexx per 
day. The carrier used was fine ground 
corn. Steers received 0.5 lb of fine 
ground corn when not on Optaflexx 
or for the negative control treatment. 
Diets were formulated to meet or 
exceed NRC (1996) requirements for 
metabolizable protein, Ca, P, and K. 
High-moisture corn was fed at 50% of 
diet DM, wet corn gluten feed (Sweet 
Bran®, Cargill, Blair, Neb.) at 40% of 
DM and ground wheat straw at 5% 
of DM (Table 1). Diets were prepared 
by loading the HMC, WCGF, ground 
wheat straw, and then by adding dry 
supplement in the mixer/delivery box 
(Roto-Mix® model 420, Roto-Mix, 
Dodge City, Kan.). Rumensin and Tylan 
were fed to all steers, with consump-
tions of 348 and 90 mg/head/daily, 
respectively. Feeds and feeding proce-
dures remained the same throughout 
Table 1.  Diet composition and analyzed nutrient 
analysis for diets fed.
Ingredient % of DM
High-moisture Corn 50.0
Wet Corn Gluten Feed 40.0
Ground Wheat Straw 5.0
Dry Supplement 5.0
Analyzed Nutrient Analysis, % DM
DM 66.3
CP 14.3
Ether Extract 4.3
Calcium 0.66
Phosphorus 0.54
Potassium 0.74
© The Board of Regents of the University of Nebraska.  All rights reserved. 2011 Nebraska Beef Cattle Report  — Page 75 
Results
Results for feedlot performance 
and carcass characteristics are pre-
sented in Table 2 and Table 3, respec-
tively. Dry matter intake was affected 
(P = 0.05) by Optaflexx 7-dINT treat-
ment with steers consuming slightly 
more DM than all other treatments.
Live BW increased (P < 0.04) for 
all Optaflexx treatments compared 
to NONE. Optaflexx 7-dINT was 
also significantly different from the 
CONTIN and 4-dINT. The CONTIN 
was 14 lb heavier than the NONE, 
the 4-dINT was 13 lb (no difference 
when compared with the CONTIN) 
and the 7-dINT was 33 lb heavier than 
the NONE, and approximately 19 lb 
heavier than the CONTIN and 4-dINT 
treatments. Live ADG was also affected 
positively by the Optaflexx treatments 
compared to NONE, providing an in-
crease of approximately 0.29 lb/day.
On a carcass basis, treatments 
were not different when compared 
to NONE, except for the calculated 
yield grade trait that decreased for the 
4-dINT treatment when compared 
to all other treatments due to differ-
ences in KPH scores. Positive trends 
for carcass adjusted final BW, HCW, 
and LM area were observed mainly for 
the 7-dINT treatment when compared 
to the others. Efficiency analyses 
show that steers on Optaflexx treat-
ments had numerically lower F:G than 
NONE (values numerically lower and 
P values less than 0.20).
Results from this experiment 
indicate that 200 mg/steer daily of 
Optaflexx fed intermittently increases 
DMI, ADG, and Live BW. Tendencies 
for a larger LM area on the positive 
control and better F:G on all Opta-
flexx treatments were also observed.
In conclusion, withdrawing Opta-
flexx for seven or four days then 
re-feeding, when compared to continu-
ous, had no effect on live ADG or F:G. 
1Marco G. Dib, graduate student; William 
A. Griffin, research technician; Josh R. Benton, 
research technician; Galen E. Erickson, associate 
professor; Terry J. Klopfenstein, professor; 
University of Nebraska–Lincoln Department 
of Animal Science. Justin J. Sindt and W. Travis 
Choat, Elanco Animal Health, Indianapolis, Ind.
Table 2. Growth performance of steers fed Optaflexx in continuous vs. intermittent patterns.
Treatments NONE1 CONTIN2 4-dINT3 7-dINT4 SEM P-value
Live Performance
Initial BW, lb 1077 1076 1074 1090 8.7 0.28
Live Final BW, lb 1352a 1366b 1365b 1385c 10.7 0.04
DMI, lb/day 22.3a 22.0a 22.3a 22.9b 0.31 0.05
ADG, lb 4.36a 4.61b 4.61b 4.68b 0.09 <0.01
F:G5 5.33 5.14 5.21 5.22  0.09
Carcass Adjusted Performance
FBW, lb 1347 1356 1351 1371 11.5 0.19
ADG, lb 4.36 4.45 4.40 4.47 0.12 0.40
F:G5 5.32 5.12 5.24 5.23  0.52
1NONE: treatment did not receive Optaflexx.
2CONTIN: treatment received Optaflexx for 35 days continuously.
34-dINT: treatment received intermittent seven day feeding Optaflexx followed by four days of with-
drawal.
47-dINT: treatment received intermittent seven day feeding Optaflexx followed by seven days of with-
drawal.
5Analyzed as G:F, reported as F:G.
Table 3. Carcass characteristics of steers fed Optaflexx in continuous vs. intermittent patterns.
Treatments NONE1 CONTIN2 4-dINT3 7-dINT4 SEM P-value
Carcass Characteristics      
HCW, lb 848 854 851 864 7.3 0.18
Dressing, %a 62.8 62.5 62.4 62.4 0.22 0.25
12th rib fat, in 0.5 0.48 0.49 0.52 0.03 0.51
Marbling scoreb 507 485 506 505 14 0.37
LM area, in2 14.6 15.1 14.5 14.6 0.2 0.09
USDA yield gradec 2.73a 2.76a 2.45b 2.78a 0.1 <0.01
1NONE: treatment did not receive Optaflexx.
2CONTIN: treatment received Optaflexx for 35 days continuously.
34-dINT: treatment received intermittent seven day feeding Optaflexx followed by four days of with-
drawal.
47-dINT: treatment received intermittent 7 day feeding Optaflexx followed by seven days of withdrawal.
aDressing percentage = carcass weight / average live weight (4% shrink).
bUSDA marbling score where 450 = slight50, 500 = small0, and 550 = small50
cUSDA calculated yield grade = 2.50 + (2.5*FT, in) – (0.32*LM area, in2) + (0.2*KPH, %) + 
(0.0038*HCW).
the pre-trial and trial phases, except 
for the use of the top dressing with or 
without Optaflexx that occurred only 
during the last 63 days prior to harvest.
Feed samples were collected from 
each load and each supplement (with 
or without Optaflexx) every other 
week, during the mixer discharge in 
the beginning, middle, and end of each 
load. Optaflexx supplements were sam-
pled from supplement bags. Samples 
were processed and analyzed for DM 
content, CP, Ca, P, K, and ether extract.
All steers were harvested on the 
same day after 165 days on feed, and 
63 days of Optaflexx treatment pe-
riod. At harvest, HCW were collected, 
and after approximately a 48-hour 
chill, LM area and fat thickness were 
measured. Bone score, lean score, 
and KPH were subjectively assigned 
by a University of Nebraska–Lincoln 
research technician, and marbling 
score was assigned by a USDA grader. 
Yield grade was calculated using the 
equation (YG= 2.50 + (2.5*FT, in) – 
(0.32*LM area, in2) + (0.2*KPH, %) + 
(0.0038*HCW, lb)).
Growth performance was evalu-
ated on a 4% shrunk weight basis, 
across and within the Optaflexx 
treatment period. Data from the ran-
domized complete block design were 
analyzed using a mixed model analy-
sis (Proc Mixed, SAS), with treatment 
and block included in the model as 
fixed variables. Pen was the experi-
mental unit. Data were analyzed using 
a protected F-test and means sepa-
rated using a bonfevroni t-test when 
the F-test variable was significant (i.e., 
alpha = 0.05).


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Feeding Strategies of Optaflexx on Growth Performance and Carcass Characteristics of Feedlot Steers

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