The effects of ractopamine hydrochloride (Optaflexx®) dosage (0, 300, and 400 mg/head/day) and duration (14, 28, or 42 days) on growth performance were evaluated in feedlot finishing diets. Feeding 300 mg of Optaflexx for 28 or 42 days increased live final BW by 13 and 29 lb, while feeding Optaflexx at 400 mg resulted in 27 or 24 lb increases relative to 0 mg steers, respectively. Feeding 300 mg of Optaflexx for 28 or 42 days would suggest 11.1 or 16.6 lb improvements in HCW, while feeding 400 mg of Optaflexx would suggest 19.7 or 20.7 lb heavier carcasses compared to steers fed 0 mg Optaflexx, respectively

Bittner, Curtis J.

Burken, Dirk B.

Erickson, Galen E.

MacDonald, James C.

Pyatt, Nathan A.

Shreck, Adam L., Shreck

English

UNL | Libraries

University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Nebraska Beef Cattle Reports Animal Science Department
2015
Effect of 300 or 400 mg Daily of Ractopamine
Hydrochloride on Growth Performance and
Carcass Characteristics of Finishing Steers During
the Last 14, 28, or 42 Days
Curtis J. Bittner
University of Nebraska-Lincoln
Dirk B. Burken
University of Nebraska-Lincoln
Adam L. Shreck Shreck
University of Nebraska-Lincoln
James C. MacDonald
University of Nebraska-Lincoln, jmacdonald2@unl.edu
Galen E. Erickson
University of Nebraska-Lincoln, gerickson4@unl.edu
See next page for additional authorsFollow this and additional works at: http://digitalcommons.unl.edu/animalscinbcr
Part of the Large or Food Animal and Equine Medicine Commons, Meat Science Commons, and
the Veterinary Preventive Medicine, Epidemiology, and Public Health Commons
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.
Bittner, Curtis J.; Burken, Dirk B.; Shreck, Adam L. Shreck; MacDonald, James C.; Erickson, Galen E.; and Pyatt, Nathan A., "Effect of
300 or 400 mg Daily of Ractopamine Hydrochloride on Growth Performance and Carcass Characteristics of Finishing Steers During
the Last 14, 28, or 42 Days" (2015). Nebraska Beef Cattle Reports. 854.
http://digitalcommons.unl.edu/animalscinbcr/854
Authors
Curtis J. Bittner, Dirk B. Burken, Adam L. Shreck Shreck, James C. MacDonald, Galen E. Erickson, and
Nathan A. Pyatt
This article is available at DigitalCommons@University of Nebraska - Lincoln: http://digitalcommons.unl.edu/animalscinbcr/854
Page 90 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.
Effect of 300 or 400 mg Daily of Ractopamine Hydrochloride 
on Growth Performance and Carcass Characteristics of  
Finishing Steers During the Last 14, 28, or 42 Days
Curtis J. Bittner
Dirk B. Burken
Adam L. Shreck
James C. MacDonald
Galen E. Erickson
Nathan A. Pyatt1
Summary
The effects of ractopamine hydrochlo-
ride (Optaflexx®) dosage (0, 300, and 
400 mg/head/day) and duration (14, 
28, or 42 days) on growth performance 
were evaluated in feedlot finishing diets. 
Feeding 300 mg of Optaflexx for 28 or 
42 days increased live final BW by 13 
and 29 lb, while feeding Optaflexx at 
400 mg resulted in 27 or 24 lb increases 
relative to 0 mg steers, respectively. 
Feeding 300 mg of Optaflexx for 28 or 
42 days would suggest 11.1 or 16.6 lb 
improvements in HCW, while feeding 
400 mg of Optaflexx would suggest 19.7 
or 20.7 lb heavier carcasses compared to 
steers fed 0 mg Optaflexx, respectively.
Introduction
ß-adrenergic agonists have been 
shown to increase protein accretion 
and decrease fat accretion in animal 
growth (Journal of Animal Science, 
1998, 76:160). Ractopamine hydro-
chloride (trade name Optaflexx; 
Elanco Animal Health, Greenfield, 
Ind.) is a ß-1 adrenergic agonists and 
is approved for feeding the last 28 to 
42 days at the label dose of 70-430 
mg/head/day to finishing cattle before 
harvest. When fed to finishing cattle, 
Optaflexx improves feed efficiency, 
final BW, and HCW when fed the last 
28 to 42 days of the finishing period. 
However, few data exist evaluating 
the effects of feeding Optaflexx to 
yearling steers for less than 28 days 
due to FDA restrictions. Therefore, 
Table 1. Basal diet and supplement.
Ingredient % of diet DM
High-moisture corn
Dry-rolled corn
Modified distillers grains plus solubles
Sweet Bran
Wheat straw
28.0
18.0
25.0
20.0
5.0
Dry supplement1
 Fine ground corn
 Limestone
 Salt
 Tallow
 Beef trace mineral
 Vitamin A-D-E
 Rumensin-90
 Tylan-40
1.5118
1.9980
0.3000
0.1000
0.0500
0.0150
0.0165
0.0087
1Supplement formulated to be fed at 4% of diet DM and formulated for 30 g/ton Rumensin and 90 
mg/daily of Tylan.
the objective of this experiment was 
to evaluate the effects of Optaflexx 
dose and duration (14-42 days) on 
animal growth performance of year-
ling steers.
Procedure
Crossbred yearling steers  
(n = 576; BW = 899 ± 64 lb) were uti-
lized in a randomized block design  
(n = 4 BW blocks) with a 3 x 3 facto-
rial treatment design to study the 
effects of Optaflexx dosage and dura-
tion on growth performance. Factors 
included Optaflexx feeding duration 
(14, 28, or 42 days prior to harvest) 
and Optaflexx dosage (0, 300, and 400 
mg/head/day). Steers were received 
at the University of Nebraska’s Agri-
cultural Research and Development 
Center (ARDC) near Mead, Neb., in 
the fall of 2012. Prior to initiation of 
trial, steers were limit-fed at 2% BW 
for 5 days a diet consisting of 50% 
Sweet Bran® and 50% alfalfa hay (DM 
basis) to minimize variation in gas-
trointestinal fill. Steers were weighed 
two consecutive days (day 0 and 1) 
to establish initial BW. Steers were 
blocked by day 0 BW, stratified by 
BW, and assigned randomly within 
strata to pens. Pens were assigned 
randomly to treatments. The study 
consisted of eight pens per treatment 
with eight steers per pen. Cattle were 
adapted to a common finishing diet 
(Table 1) over a 19-day period con-
sisting of four adaptation diets. The 
amount of modified distillers grains 
plus solubles (MDGS), Sweet Bran, 
wheat straw, and supplement included 
in each adaptation diet was held con-
stant at 25, 20, 5, and 4% (DM basis), 
respectively. The amount of corn was 
gradually introduced in the diet while 
replacing alfalfa hay. The supplement 
was formulated for 30 g/ton Rumen-
sin® and to provide 90 mg/steer daily 
of Tylan®. Cattle were fed once daily 
between 0700 and 0900 hours. 
Optaflexx was initiated when 
steers were within 14 to 42 days of 
their projected endpoints. Two weeks 
prior to treatment initiation and ev-
ery seven days thereafter, steers were 
removed from their pens (approxi-
mately 0700 hours) and pen weights 
were collected using a pen scale. On 
the morning of treatment initiation, 
each pen was removed and weighed. 
All residual feed remaining in the 
© The Board of Regents of the University of Nebraska.  All rights reserved. 2015 Nebraska Beef Cattle Report  — Page 91 
procedure of SAS. Treatment differ-
ences were declared significant at  
P ≤ 0.05.
Results
The interaction of dose x duration 
was observed for final live BW and 
F:G (P < 0.05; Table 2); therefore, sim-
ple effects will be presented. Intake 
was 0.9 lb/day greater (P = 0.02) for 
steers fed 0 mg Optaflexx compared 
to 300 and 400 for 28 days. Live final 
BW was not different (P > 0.35) for 
steers fed 0, 300, or 400 mg Optaflexx 
for 14 days. At 28 days, live final BW 
was 27 lb heavier (P < 0.01) for steers 
fed Optaflexx at 400 mg than steers 
receiving 0 mg Optaflexx. At 28 days, 
steers fed Optaflexx at 300 mg tended 
(P =0.07) to be 13 lb heavier than 
steers receiving 0 mg. Feeding 400 mg 
Optaflexx for 28 days increased  
(P = 0.05) live final BW 14 lb com-
pared to 300 mg. Live final BW was 
29 and 24 lb greater (P <0.01) for 
steers fed Optaflexx for 42 days at 300 
and 400 mg compared to 0 mg. Live 
final BW were not different (P = 0.51) 
between steers receiving Optaflexx at 
300 and 400 mg for 42 days. Weekly 
live BW response over 0 mg fed steers 
is presented in Figure 1. Feeding 300 
mg of Optaflexx would provide 23.4, 
26.7, and 28.9 lb of added live BW, 
(Continued on next page)
bunk was removed and weighed. Pen 
weights (4% pencil shrink applied) 
were collected every seven days to 
evaluate animal performance over the 
Optaflexx treatment phase. Optaflexx 
was delivered daily during the treat-
ment phase via top-dress at either 
300 or 400 mg/head/day, depending 
on treatment, with fine ground corn 
used as the carrier. Three top-dress 
supplements were used during the 
treatment phase, one that contained 
no Optaflexx (1 lb/head/day of fine 
ground corn), one that contained 300 
mg of Optaflexx (1 lb/head/day of a 
600 g/t Optaflexx medicated supple-
ment), and one that contained 400 mg 
of Optaflexx (1.11 lb/head/day of a 720 
g/t Optaflexx medicated supplement). 
Steers that were fed 0 mg/head/day of 
Optaflexx were top-dressed daily with 
fine ground corn during the treatment 
phase. 
One hundred days prior to the 
target marketing date for steers on 
the 28 day treatment, all steers were 
implanted with Component TE-S 
with Tylan®. The terminal implant 
window ranged from 86 to 114 days, 
depending on treatment duration. 
On day of shipping, cattle were fed 
50% of the previous days feed call 
and then in the afternoon all cattle to 
be shipped were removed from their 
pens, pen weighed, and loaded onto 
the truck. All steers were harvested at 
Greater Omaha Packing Co. (Omaha, 
Neb.) the following morning. Hot 
carcass weight was obtained on day of 
harvest. After a 48 hour chill, USDA 
marbling score, 12th rib fat depth, and 
LM area were recorded. Yield grade 
was calculated from the following for-
mula: 2.50 + (2.50*fat thickness, in) 
+ (0.2* 2.5 [KPH]) + (0.0038*HCW, 
lb) – (0.32*LM area, in2). Final live 
BW were pencil shrunk 4% to calcu-
late dressing percent and live animal 
performance. A common dressing 
percentage of 63% was used to calcu-
late carcass-adjusted performance to 
determine final BW, ADG, and F:G. 
Animal performance and carcass 
characteristics were analyzed as a 3 x 
3 factorial using the MIXED proce-
dure of SAS (SAS Institute, Inc., Cary, 
N.C.), with pen being the experi-
mental unit and animals that were 
removed during the experiment not 
included in the analysis. The model 
included the effects of dose, duration, 
and dose x duration interaction. Block 
was treated as a fixed effect. Due to a 
significant difference in BW among 
steers when Optaflexx was initiated, 
Optaflexx initial BW was used as 
a covariate in the model. The sig-
nificance of the linear and quadratic 
coefficients were tested for Optaflexx 
dose when looking at final live BW 
and HCW change over Optaflexx 
feeding duration using the MIXED 
Table 2.  Animal performance of steers fed 0, 300, and 400 mg/head/day of Optaflexx for 14, 28, or 42 days at the end of the finishing period.
Duration: 14 day 28 day 42 day
SEM Int. Dose DurDosage: 0 300 400 0 300 400 0 300 400
Live Performance
 Initial BW, lb
 Live final BW, lb1
 Over Control, lb
 DMI, lb/day
 ADG, lb2
 Feed:Gain3
892
1385e
—
26.4ab
4.02ab
6.54abc
890
1390e
5
26.4ab
4.09a
6.45ab
889
1391e
6
26.4ab
4.10a
6.41ab
886
1414d
—
27.0a
3.88c
6.94d
890
1427cd
13
26.1b
3.94bc
6.58bc
891
1441c
27
26.1b
4.04ab
6.41a
891
1473b
—
26.5ab
3.88c
6.80cd
891
1502a
29
26.8ab
4.06a
6.59ab
888
1497a
24
27.1a
4.06a
6.66abcd
2
6
0.4
0.13
0.006
0.54
0.03
0.07
0.15
0.04
0.57
0.01
 0.69
<0.01
<0.01
0.50
<0.01
0.59
0.08
0.24
Carcass-Adjusted Performance
 Final BW, lb4
 ADG, lb5
 Feed:Gain
1339e
3.65e
7.25d
1346e
3.73de
7.09cd
1353e
3.77cd
6.99bcd
1399d
3.78cd
7.14d
1417c
3.85bc
6.76ab
1424c
3.89abc
6.67a
1454b
3.73de
7.04cd
1480a
3.90ab
6.80abc
1486a
3.97ab
6.76ab
9
0.10
0.005
0.30
0.51
0.63
<0.01
<0.01
 0.01
<0.01
<0.01
0.03
a-eMeans with different superscripts differ (P < 0.05).
1Live final BW measured by weighing cattle on pen scale day of shipping and applying a 4% pencil shrink.
2Calculated using live final BW.
3Analyzed as G:F, the reciprocal of F:G.
4Calculated from HCW divided by a common dressing percent (63%).
5Calculated using carcass-adjusted final BW.
Page 92 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.
300 400
35
30
25
20
15
10
5
0
Li
ve
 B
W
 C
h
an
ge
 O
ve
r 
0 
m
g,
 lb
O400 = -0.0179x2 + 1.3132x (Quad. P < 0.01)
R2 = 0.9904
O300 = -0.0107x2 + 1.137x (Quad. P < 0.01)
R2 = 0.9105
 0 7 14 21 28 35 42 49
Optaflexx Feeding Duration, Days
Figure 1.  Live BW change when feeding 300 and 400 mg Optaflexx over 0 mg of Optaflexxab.
aGrowth performance is calculated on a shrunk basis (4%).
bDay 7-14 has 24 Optaflexx 300 mg pens averaged together and 24 Optaflexx 400 mg pens averaged 
together, days 21-28 has 16 pens for 300 mg and 16 for 400 mg, and days 35-42 has 8 pens for 300 mg 
and 8 for 400 mg.
Table 3.  Carcass characteristics of steers fed 0, 300, and 400 mg/head/day of Optaflexx for 14, 28, or 42 days at the end of the finishing period.
Duration: 14 day 28 day 42 day SEM Int. Dose Dur
Dosage: 0 300 400 0 300 400 0 300 400
Carcass Characteristics
 HCW, lb
 Over Control, lb
 Dressing, %1
 Marbling2
 LM area, in
 12th rib fat, in
 Calculated YG
843.4e
—
60.9b
440cd
13.3cd
0.48c
3.1cd
848.1e
4.7
61.0b
430d
13.1d
0.50bc
3.3bc
852.3e
8.9
61.2b
432d
13.1d
0.50bc
3.3abc
881.7d
—
62.4a
465abc
13.4bcd
0.59a
3.5ab
892.8c
11.1
62.6a
452bcd
13.8abc
0.55ab
3.3abc
901.4c
19.7
62.4a
467abc
13.6abc
0.57a
3.4ab
915.7b
—
62.3a
484a
13.8abc
0.58a
3.5a
932.3a
16.6
62.2a
485a
13.9ab
0.59a
3.5a
936.4a
20.7
62.7a
475ab
14.0a
0.59a
3.5a
5
0.4
11
0.2
0.02
0.1
0.30
0.73
0.86
0.18
0.72
0.46
<0.01
0.53
0.71
0.83
0.93
0.86
<0.01
0.01
<0.01
0.83
<0.01
0.04
a-eMeans with different superscripts differ (P < 0.05).
1DP = Dressing Percent; calculated from HCW divided by live final BW, with a 4% pencil shrink applied.
2Marbling Score: 300 = Slight, 400 = Small, 500 = Modest, etc.
while feeding 400 mg would provide 
22.7, 24.0, and 23.6 lb of added live 
BW over 0 mg fed steers for a 28, 35, 
and 42 feeding duration, respectively. 
Carcass-adjusted ADG was not 
different (P = 0.19; 3.65 vs. 3.73 lb) 
between steers fed Optaflexx at 0 
mg and 300 mg for 14 days. Carcass-
adjusted ADG was greater (P = 0.05) 
for steers fed Optaflexx at 400 mg 
(3.77 lb) compared to 0 mg (3.65); 
however, carcass-adjusted ADG was 
not different (P = 0.47) between 
steers receiving 300 and 400 mg of 
Optaflexx for 14 days. At 28 days, car-
cass-adjusted ADG was not different 
(P > 0.20) among cattle fed Optaflexx 
at 0 or 300 mg and 300 or 400 mg. 
Feeding 400 mg of Optaflexx tended 
to increase (P = 0.06; 3.89 vs. 3.78 lb) 
carcass-adjusted ADG compared to 
0 mg for 28 days. Carcass-adjusted 
ADG was greater (P < 0.01) for steers 
fed Optaflexx for 42 days at 300 (3.90 
lb) and 400 mg (3.97 lb) compared to 
0 mg (3.73 lb). There was a tendency 
(P = 0.10) for an improvement in 
carcass-adjusted feed conversion (F:G) 
when steers were fed Optaflexx at 400 
compared to 0 mg for 14 days. Car-
cass-adjusted feed conversion was not 
different (P = 0.35) between steers fed 
0 and 300 mg of Optaflexx for 14 days. 
No difference (P = 0.48) in carcass-
adjusted F:G was observed when feed-
ing Optaflexx for 14 days at 300 or 400 
mg. Compared to 0 mg of Optaflexx, 
carcass-adjusted F:G was improved  
(P < 0.01) by 5.3 and 7.0% when steers 
were fed 300 or 400 mg of Optaflexx 
for 28 days, but were not different 
(P = 0.43) between 300 and 400 mg 
for 28 days. There was a tendency 
(P = 0.10) for 3.4% improvement in 
carcass-adjusted F:G when steers were 
fed 300 mg of Optaflexx compared 
to 0 mg for 42 days. Feeding 400 mg 
of Optaflexx for 42 days resulted in 
a 4.0% improvement (P = 0.03) in 
carcass-adjusted F:G compared to 0 
mg; however, carcass-adjusted F:G 
was not different (P = 0.64) between 
steers receiving 300 and 400 mg of 
Optaflexx. 
There were no significant (P > 0.17; 
Table 3) dose x duration interaction 
for carcass data; however, the simple 
effects will be presented. Hot carcass 
weight was not different (P = 0.33; 
843.4 vs. 848.1 lb) between yearlings 
fed Optaflexx at 0 and 300 mg for 14 
days, but tended (P = 0.07) to be 8.9 
lb heavier for steers fed 400 mg of 
Optaflexx compared to 0 mg. Hot car-
cass weight was 11.1 and 19.7 lb great-
er (P < 0.02) for steers fed 300 and 400 
mg of Optaflexx for 28 days compared 
to 0 mg (881.7 lb). Carcasses from 
yearlings fed Optaflexx for 42 days at 
300 and 400 mg were 16.6 and 20.7 lb 
heavier (P < 0.01) than 0 mg (915.7 lb) 
fed steers. Hot carcass weight change 
over 0 mg fed steers is presented in 
Figure 2. Feeding 300 mg of Optaflexx 
would provide 11.0, 13.7, and 16.4 lb 
of added HCW, while feeding 400 mg 
would provide 15.8, 19.7, and 23.6 lb 
© The Board of Regents of the University of Nebraska.  All rights reserved. 2015 Nebraska Beef Cattle Report  — Page 93 
both live BW and HCW change. A 
feeding duration of 14 days is not 
approved for Optaflexx; therefore, 
conclusions are based on 28 and 42 
days of feeding Optaflexx. Feeding 
300 mg of Optaflexx to yearling steers 
for 28 or 42 days increased live final 
BW (13 and 29 lb) and HCW (11.1 
and 16.6 lb) compared to cattle fed 
0 mg of Optaflexx. Feeding 400 mg 
of Optaflexx the last 28 or 42 days to 
yearling steers improved live final BW 
(27 and 24 lb) and HCW (19.7 and 
20.7 lb) relative to 0 mg fed cattle. In 
yearling steers, Optaflexx improves 
F:G, final live BW, and HCW when fed 
at 300 or 400 mg for the last 28 or 42 
days of the finishing period. 
1Curtis J. Bittner, research technician; 
Dirk B. Burken, research technician; Adam L. 
Shreck, graduate student; James C. MacDonald, 
assistant professor; Galen E. Erickson, professor, 
University of Nebraska–Lincoln Department of 
Animal Science, Lincoln Neb.; Nathan A. Pyatt, 
Elanco Animal Health, Greenfield Ind.
300 400
30
25
20
15
10
5
0
H
C
W
 C
h
an
ge
 O
ve
r 
0 
m
g,
 lb
 0 7 14 21 28 35 42 49
Optaflexx Feeding Duration, Days
O400 = -0.5626x (Linear P < 0.01)
R2 = 0.6953
O300 = -0.3913x (Linear P < 0.01)
R2 = 0.9897
Figure 2.  Hot carcass weight change when feeding 300 and 400 mg Optaflexx over 0 mg of 
Optaflexxab.
aDay 7-14 has 24 Optaflexx 300 mg pens averaged together and 24 Optaflexx 400 mg pens averaged 
together, days 21-28 has 16 pens for 300 mg and 16 for 400 mg, and days 35-42 has 8 pens for 300 mg 
and 8 for 400 mg.
of added HCW over 0 mg fed steers 
for a 28, 35, and 42 feeding duration, 
respectively. No other treatment dif-
ferences (P > 0.05) were observed for 
LM area, dressing percent, marbling 
score, fat thickness, or calculated yield 
grade. 
In this study, yearling steers were 
fed Optaflexx for 14 days in order 
to develop the response curves for 


Effect of 300 or 400 mg Daily of Ractopamine Hydrochloride on Growth Performance and Carcass Characteristics of
Finishing Steers During the Last 14, 28, or 42 Days

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Beef Cattle Reports Animal Science Department 2015 Effect of 300 or 400 mg Daily of Ractopamine Hydrochloride on Growth Performance and Carcass Characteristics of Finishing Steers During the Last 14, 28, or 42 Days Curtis J. Bittner University of Nebraska-Lincoln Dirk B. Burken University of Nebraska-Lincoln Adam L. Shreck Shreck University of Nebraska-Lincoln James C. MacDonald University of Nebraska-Lincoln, jmacdonald2@unl.edu Galen E. Erickson University of Nebraska-Lincoln, gerickson4@unl.edu See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr  Part of the Large or Food Animal and Equine Medicine Commons, Meat Science Commons, and the Veterinary Preventive Medicine, Epidemiology, and Public Health Commons Bittner, Curtis J.; Burken, Dirk B.; Shreck, Adam L. Shreck; MacDonald, James C.; Erickson, Galen E.; and Pyatt, Nathan A., "Effect of 300 or 400 mg Daily of Ractopamine Hydrochloride on Growth Performance and Carcass Characteristics of Finishing Steers During the Last 14, 28, or 42 Days" (2015). Nebraska Beef Cattle Reports. 854. https://digitalcommons.unl.edu/animalscinbcr/854 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 Curtis J. Bittner, Dirk B. Burken, Adam L. Shreck Shreck, James C. MacDonald, Galen E. Erickson, and Nathan A. Pyatt This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/animalscinbcr/854 Page 90 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.Effect of 300 or 400 mg Daily of Ractopamine Hydrochloride on Growth Performance and Carcass Characteristics of  Finishing Steers During the Last 14, 28, or 42 DaysCurtis J. BittnerDirk B. BurkenAdam L. ShreckJames C. MacDonaldGalen E. EricksonNathan A. Pyatt1SummaryThe effects of ractopamine hydrochlo-ride (Optaflexx®) dosage (0, 300, and 400 mg/head/day) and duration (14, 28, or 42 days) on growth performance were evaluated in feedlot finishing diets. Feeding 300 mg of Optaflexx for 28 or 42 days increased live final BW by 13 and 29 lb, while feeding Optaflexx at 400 mg resulted in 27 or 24 lb increases relative to 0 mg steers, respectively. Feeding 300 mg of Optaflexx for 28 or 42 days would suggest 11.1 or 16.6 lb improvements in HCW, while feeding 400 mg of Optaflexx would suggest 19.7 or 20.7 lb heavier carcasses compared to steers fed 0 mg Optaflexx, respectively.Introductionß-adrenergic agonists have been shown to increase protein accretion and decrease fat accretion in animal growth (Journal of Animal Science, 1998, 76:160). Ractopamine hydro-chloride (trade name Optaflexx; Elanco Animal Health, Greenfield, Ind.) is a ß-1 adrenergic agonists and is approved for feeding the last 28 to 42 days at the label dose of 70-430 mg/head/day to finishing cattle before harvest. When fed to finishing cattle, Optaflexx improves feed efficiency, final BW, and HCW when fed the last 28 to 42 days of the finishing period. However, few data exist evaluating the effects of feeding Optaflexx to yearling steers for less than 28 days due to FDA restrictions. Therefore, Table 1. Basal diet and supplement.Ingredient % of diet DMHigh-moisture cornDry-rolled cornModified distillers grains plus solublesSweet BranWheat straw28.018.025.020.05.0Dry supplement1 Fine ground corn Limestone Salt Tallow Beef trace mineral Vitamin A-D-E Rumensin-90 Tylan-401.51181.99800.30000.10000.05000.01500.01650.00871Supplement formulated to be fed at 4% of diet DM and formulated for 30 g/ton Rumensin and 90 mg/daily of Tylan.the objective of this experiment was to evaluate the effects of Optaflexx dose and duration (14-42 days) on animal growth performance of year-ling steers.ProcedureCrossbred yearling steers  (n = 576; BW = 899 ± 64 lb) were uti-lized in a randomized block design  (n = 4 BW blocks) with a 3 x 3 facto-rial treatment design to study the effects of Optaflexx dosage and dura-tion on growth performance. Factors included Optaflexx feeding duration (14, 28, or 42 days prior to harvest) and Optaflexx dosage (0, 300, and 400 mg/head/day). Steers were received at the University of Nebraska’s Agri-cultural Research and Development Center (ARDC) near Mead, Neb., in the fall of 2012. Prior to initiation of trial, steers were limit-fed at 2% BW for 5 days a diet consisting of 50% Sweet Bran® and 50% alfalfa hay (DM basis) to minimize variation in gas-trointestinal fill. Steers were weighed two consecutive days (day 0 and 1) to establish initial BW. Steers were blocked by day 0 BW, stratified by BW, and assigned randomly within strata to pens. Pens were assigned randomly to treatments. The study consisted of eight pens per treatment with eight steers per pen. Cattle were adapted to a common finishing diet (Table 1) over a 19-day period con-sisting of four adaptation diets. The amount of modified distillers grains plus solubles (MDGS), Sweet Bran, wheat straw, and supplement included in each adaptation diet was held con-stant at 25, 20, 5, and 4% (DM basis), respectively. The amount of corn was gradually introduced in the diet while replacing alfalfa hay. The supplement was formulated for 30 g/ton Rumen-sin® and to provide 90 mg/steer daily of Tylan®. Cattle were fed once daily between 0700 and 0900 hours. Optaflexx was initiated when steers were within 14 to 42 days of their projected endpoints. Two weeks prior to treatment initiation and ev-ery seven days thereafter, steers were removed from their pens (approxi-mately 0700 hours) and pen weights were collected using a pen scale. On the morning of treatment initiation, each pen was removed and weighed. All residual feed remaining in the © The Board of Regents of the University of Nebraska.  All rights reserved. 2015 Nebraska Beef Cattle Report  — Page 91 procedure of SAS. Treatment differ-ences were declared significant at  P ≤ 0.05.ResultsThe interaction of dose x duration was observed for final live BW and F:G (P < 0.05; Table 2); therefore, sim-ple effects will be presented. Intake was 0.9 lb/day greater (P = 0.02) for steers fed 0 mg Optaflexx compared to 300 and 400 for 28 days. Live final BW was not different (P > 0.35) for steers fed 0, 300, or 400 mg Optaflexx for 14 days. At 28 days, live final BW was 27 lb heavier (P < 0.01) for steers fed Optaflexx at 400 mg than steers receiving 0 mg Optaflexx. At 28 days, steers fed Optaflexx at 300 mg tended (P =0.07) to be 13 lb heavier than steers receiving 0 mg. Feeding 400 mg Optaflexx for 28 days increased  (P = 0.05) live final BW 14 lb com-pared to 300 mg. Live final BW was 29 and 24 lb greater (P <0.01) for steers fed Optaflexx for 42 days at 300 and 400 mg compared to 0 mg. Live final BW were not different (P = 0.51) between steers receiving Optaflexx at 300 and 400 mg for 42 days. Weekly live BW response over 0 mg fed steers is presented in Figure 1. Feeding 300 mg of Optaflexx would provide 23.4, 26.7, and 28.9 lb of added live BW, (Continued on next page)bunk was removed and weighed. Pen weights (4% pencil shrink applied) were collected every seven days to evaluate animal performance over the Optaflexx treatment phase. Optaflexx was delivered daily during the treat-ment phase via top-dress at either 300 or 400 mg/head/day, depending on treatment, with fine ground corn used as the carrier. Three top-dress supplements were used during the treatment phase, one that contained no Optaflexx (1 lb/head/day of fine ground corn), one that contained 300 mg of Optaflexx (1 lb/head/day of a 600 g/t Optaflexx medicated supple-ment), and one that contained 400 mg of Optaflexx (1.11 lb/head/day of a 720 g/t Optaflexx medicated supplement). Steers that were fed 0 mg/head/day of Optaflexx were top-dressed daily with fine ground corn during the treatment phase. One hundred days prior to the target marketing date for steers on the 28 day treatment, all steers were implanted with Component TE-S with Tylan®. The terminal implant window ranged from 86 to 114 days, depending on treatment duration. On day of shipping, cattle were fed 50% of the previous days feed call and then in the afternoon all cattle to be shipped were removed from their pens, pen weighed, and loaded onto the truck. All steers were harvested at Greater Omaha Packing Co. (Omaha, Neb.) the following morning. Hot carcass weight was obtained on day of harvest. After a 48 hour chill, USDA marbling score, 12th rib fat depth, and LM area were recorded. Yield grade was calculated from the following for-mula: 2.50 + (2.50*fat thickness, in) + (0.2* 2.5 [KPH]) + (0.0038*HCW, lb) – (0.32*LM area, in2). Final live BW were pencil shrunk 4% to calcu-late dressing percent and live animal performance. A common dressing percentage of 63% was used to calcu-late carcass-adjusted performance to determine final BW, ADG, and F:G. Animal performance and carcass characteristics were analyzed as a 3 x 3 factorial using the MIXED proce-dure of SAS (SAS Institute, Inc., Cary, N.C.), with pen being the experi-mental unit and animals that were removed during the experiment not included in the analysis. The model included the effects of dose, duration, and dose x duration interaction. Block was treated as a fixed effect. Due to a significant difference in BW among steers when Optaflexx was initiated, Optaflexx initial BW was used as a covariate in the model. The sig-nificance of the linear and quadratic coefficients were tested for Optaflexx dose when looking at final live BW and HCW change over Optaflexx feeding duration using the MIXED Table 2.  Animal performance of steers fed 0, 300, and 400 mg/head/day of Optaflexx for 14, 28, or 42 days at the end of the finishing period.Duration: 14 day 28 day 42 daySEM Int. Dose DurDosage: 0 300 400 0 300 400 0 300 400Live Performance Initial BW, lb Live final BW, lb1 Over Control, lb DMI, lb/day ADG, lb2 Feed:Gain38921385e—26.4ab4.02ab6.54abc8901390e526.4ab4.09a6.45ab8891391e626.4ab4.10a6.41ab8861414d—27.0a3.88c6.94d8901427cd1326.1b3.94bc6.58bc8911441c2726.1b4.04ab6.41a8911473b—26.5ab3.88c6.80cd8911502a2926.8ab4.06a6.59ab8881497a2427.1a4.06a6.66abcd260.40.130.0060.540.030.070.150.040.570.01 0.69<0.01<0.010.50<0.010.590.080.24Carcass-Adjusted Performance Final BW, lb4 ADG, lb5 Feed:Gain1339e3.65e7.25d1346e3.73de7.09cd1353e3.77cd6.99bcd1399d3.78cd7.14d1417c3.85bc6.76ab1424c3.89abc6.67a1454b3.73de7.04cd1480a3.90ab6.80abc1486a3.97ab6.76ab90.100.0050.300.510.63<0.01<0.01 0.01<0.01<0.010.03a-eMeans with different superscripts differ (P < 0.05).1Live final BW measured by weighing cattle on pen scale day of shipping and applying a 4% pencil shrink.2Calculated using live final BW.3Analyzed as G:F, the reciprocal of F:G.4Calculated from HCW divided by a common dressing percent (63%).5Calculated using carcass-adjusted final BW.Page 92 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.300 40035302520151050Live BW Change Over 0 mg, lbO400 = -0.0179x2 + 1.3132x (Quad. P < 0.01)R2 = 0.9904O300 = -0.0107x2 + 1.137x (Quad. P < 0.01)R2 = 0.9105 0 7 14 21 28 35 42 49Optaflexx Feeding Duration, DaysFigure 1.  Live BW change when feeding 300 and 400 mg Optaflexx over 0 mg of Optaflexxab.aGrowth performance is calculated on a shrunk basis (4%).bDay 7-14 has 24 Optaflexx 300 mg pens averaged together and 24 Optaflexx 400 mg pens averaged together, days 21-28 has 16 pens for 300 mg and 16 for 400 mg, and days 35-42 has 8 pens for 300 mg and 8 for 400 mg.Table 3.  Carcass characteristics of steers fed 0, 300, and 400 mg/head/day of Optaflexx for 14, 28, or 42 days at the end of the finishing period.Duration: 14 day 28 day 42 day SEM Int. Dose DurDosage: 0 300 400 0 300 400 0 300 400Carcass Characteristics HCW, lb Over Control, lb Dressing, %1 Marbling2 LM area, in 12th rib fat, in Calculated YG843.4e—60.9b440cd13.3cd0.48c3.1cd848.1e4.761.0b430d13.1d0.50bc3.3bc852.3e8.961.2b432d13.1d0.50bc3.3abc881.7d—62.4a465abc13.4bcd0.59a3.5ab892.8c11.162.6a452bcd13.8abc0.55ab3.3abc901.4c19.762.4a467abc13.6abc0.57a3.4ab915.7b—62.3a484a13.8abc0.58a3.5a932.3a16.662.2a485a13.9ab0.59a3.5a936.4a20.762.7a475ab14.0a0.59a3.5a50.4110.20.020.10.300.730.860.180.720.46<0.010.530.710.830.930.86<0.010.01<0.010.83<0.010.04a-eMeans with different superscripts differ (P < 0.05).1DP = Dressing Percent; calculated from HCW divided by live final BW, with a 4% pencil shrink applied.2Marbling Score: 300 = Slight, 400 = Small, 500 = Modest, etc.while feeding 400 mg would provide 22.7, 24.0, and 23.6 lb of added live BW over 0 mg fed steers for a 28, 35, and 42 feeding duration, respectively. Carcass-adjusted ADG was not different (P = 0.19; 3.65 vs. 3.73 lb) between steers fed Optaflexx at 0 mg and 300 mg for 14 days. Carcass-adjusted ADG was greater (P = 0.05) for steers fed Optaflexx at 400 mg (3.77 lb) compared to 0 mg (3.65); however, carcass-adjusted ADG was not different (P = 0.47) between steers receiving 300 and 400 mg of Optaflexx for 14 days. At 28 days, car-cass-adjusted ADG was not different (P > 0.20) among cattle fed Optaflexx at 0 or 300 mg and 300 or 400 mg. Feeding 400 mg of Optaflexx tended to increase (P = 0.06; 3.89 vs. 3.78 lb) carcass-adjusted ADG compared to 0 mg for 28 days. Carcass-adjusted ADG was greater (P < 0.01) for steers fed Optaflexx for 42 days at 300 (3.90 lb) and 400 mg (3.97 lb) compared to 0 mg (3.73 lb). There was a tendency (P = 0.10) for an improvement in carcass-adjusted feed conversion (F:G) when steers were fed Optaflexx at 400 compared to 0 mg for 14 days. Car-cass-adjusted feed conversion was not different (P = 0.35) between steers fed 0 and 300 mg of Optaflexx for 14 days. No difference (P = 0.48) in carcass-adjusted F:G was observed when feed-ing Optaflexx for 14 days at 300 or 400 mg. Compared to 0 mg of Optaflexx, carcass-adjusted F:G was improved  (P < 0.01) by 5.3 and 7.0% when steers were fed 300 or 400 mg of Optaflexx for 28 days, but were not different (P = 0.43) between 300 and 400 mg for 28 days. There was a tendency (P = 0.10) for 3.4% improvement in carcass-adjusted F:G when steers were fed 300 mg of Optaflexx compared to 0 mg for 42 days. Feeding 400 mg of Optaflexx for 42 days resulted in a 4.0% improvement (P = 0.03) in carcass-adjusted F:G compared to 0 mg; however, carcass-adjusted F:G was not different (P = 0.64) between steers receiving 300 and 400 mg of Optaflexx. There were no significant (P > 0.17; Table 3) dose x duration interaction for carcass data; however, the simple effects will be presented. Hot carcass weight was not different (P = 0.33; 843.4 vs. 848.1 lb) between yearlings fed Optaflexx at 0 and 300 mg for 14 days, but tended (P = 0.07) to be 8.9 lb heavier for steers fed 400 mg of Optaflexx compared to 0 mg. Hot car-cass weight was 11.1 and 19.7 lb great-er (P < 0.02) for steers fed 300 and 400 mg of Optaflexx for 28 days compared to 0 mg (881.7 lb). Carcasses from yearlings fed Optaflexx for 42 days at 300 and 400 mg were 16.6 and 20.7 lb heavier (P < 0.01) than 0 mg (915.7 lb) fed steers. Hot carcass weight change over 0 mg fed steers is presented in Figure 2. Feeding 300 mg of Optaflexx would provide 11.0, 13.7, and 16.4 lb of added HCW, while feeding 400 mg would provide 15.8, 19.7, and 23.6 lb © The Board of Regents of the University of Nebraska.  All rights reserved. 2015 Nebraska Beef Cattle Report  — Page 93 both live BW and HCW change. A feeding duration of 14 days is not approved for Optaflexx; therefore, conclusions are based on 28 and 42 days of feeding Optaflexx. Feeding 300 mg of Optaflexx to yearling steers for 28 or 42 days increased live final BW (13 and 29 lb) and HCW (11.1 and 16.6 lb) compared to cattle fed 0 mg of Optaflexx. Feeding 400 mg of Optaflexx the last 28 or 42 days to yearling steers improved live final BW (27 and 24 lb) and HCW (19.7 and 20.7 lb) relative to 0 mg fed cattle. In yearling steers, Optaflexx improves F:G, final live BW, and HCW when fed at 300 or 400 mg for the last 28 or 42 days of the finishing period. 1Curtis J. Bittner, research technician; Dirk B. Burken, research technician; Adam L. Shreck, graduate student; James C. MacDonald, assistant professor; Galen E. Erickson, professor, University of Nebraska–Lincoln Department of Animal Science, Lincoln Neb.; Nathan A. Pyatt, Elanco Animal Health, Greenfield Ind.300 400302520151050HCW Change Over 0 mg, lb 0 7 14 21 28 35 42 49Optaflexx Feeding Duration, DaysO400 = -0.5626x (Linear P < 0.01)R2 = 0.6953O300 = -0.3913x (Linear P < 0.01)R2 = 0.9897Figure 2.  Hot carcass weight change when feeding 300 and 400 mg Optaflexx over 0 mg of Optaflexxab.aDay 7-14 has 24 Optaflexx 300 mg pens averaged together and 24 Optaflexx 400 mg pens averaged together, days 21-28 has 16 pens for 300 mg and 16 for 400 mg, and days 35-42 has 8 pens for 300 mg and 8 for 400 mg.of added HCW over 0 mg fed steers for a 28, 35, and 42 feeding duration, respectively. No other treatment dif-ferences (P > 0.05) were observed for LM area, dressing percent, marbling score, fat thickness, or calculated yield grade. In this study, yearling steers were fed Optaflexx for 14 days in order to develop the response curves for 

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Effect of 300 or 400 mg Daily of Ractopamine Hydrochloride on Growth Performance and Carcass Characteristics of Finishing Steers During the Last 14, 28, or 42 Days

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