Full Text Original

The Professional Animal Scientist 29 (2013):89–97
©2013 American Registry of Professional Animal Scientists
Theractopamine
effects of dietary
on the
performance and carcass
characteristics of late-finishing
market pigs with a previous
history of porcine circovirus type
2 associated disease (PCVAD)
R. B. Hinson,*1 G. L. Allee,* D. D. Boler,†2 M. J. Ritter,‡ C. W. Parks,§ and S. N. Carr‡
*Department of Animal Sciences, University of Missouri, Columbia 65211; †Department of Animal
Sciences, The Ohio State University, Columbus 43210; ‡Elanco Animal Health, A Division of Eli
Lilly and Company, Greenfield, IN 46140; and §Goldsboro Milling Company, Goldsboro, NC 27534
ABSTRACT
Porcine circovirus type 2 associated
disease (PCVAD) is a costly disease to
the commercial pig industry. Clinically
significant PCVAD decreases growth rate
and increases mortality in growing pigs.
Porcine circovirus type 2 can costs the
US swine industry 3 to 4 dollars per pig
and in extreme cases as much as $20
per pig because of increased mortality
rates and reduced growth performance
of infected pigs relative to pigs of higher
health. A total of 1,635 barrows and gilts
with a known history of PCVAD were
used in a randomized complete block
design with a 5 × 2 factorial arrange-
1
Current address: JBS United, 4310 State
Road 38 West, Sheridan, IN 46069.
2
Corresponding author: boler.2@osu.edu
ment of the following treatments: no
ractopamine hydrochloride (RAC), 5.0
mg/kg of RAC for 21 d, 7.4 mg/kg of
RAC for 21 d, 5.0/7.4 mg/kg step-up, or
5.0/10.0 mg/kg step-up feeding program
in barrows and gilts. Pigs assigned to
the step-up program were fed the initial
dose of 5 mg/kg of RAC for the first
14 d of the trial and then stepped-up to
the increased dose of 7.4 or 10.0 mg/
kg for the final 7 d of the feeding period.
Growth performance traits were measured weekly during the 21-d test period,
and carcass traits were measured on d 21
at the slaughter facility. Growth advantages of RAC-fed pigs over controls were
observed as early as 7 d on trial and
persisted throughout the entire live phase
of the experiment. Pigs fed RAC gained
18.6% more weight per day than did
control-fed pigs (1.02 vs. 0.86 kg/d, P
< 0.0001) during the feeding period and
were almost 21% more (P < 0.0001) efficient (G:F) than were control-fed pigs.
Loin depths of RAC-fed pigs were 0.31
cm greater (P < 0.0001) and estimated
carcass lean percentages were 0.62 percentage units greater (P < 0.0001) than
those of controls. Collectively, these data
suggest that RAC supplementation is
an effective means of improving growth
performance and carcass composition in
finishing pigs with a clinical history of
PCVAD early in the grow-finish period.
Key words: circovirus, porcine
circovirus type 2 associated disease,
pig, ractopamine hydrochloride
INTRODUCTION
Porcine circovirus was originally
considered a picornavirus-like contaminant of pig kidney cell culture
90
PK/15 (ATCC-CCL 33; Allan and
Ellis, 2000). Recently, circovirus has
been further designated into 2 distinct
categories. One strain of circovirus
associated with several conditions,
such as interstitial pneumonia in
young pigs, has been designated as
porcine circovirus type 2 (PCV2).
In clinical cases PCV2 is associated
with organ lesions and a progressive
loss of function that is described as
postweaning multisystemic wasting
syndrome and mostly affects pigs
that are 5 to 12 wk old. Other clinical
signs of postweaning multisystemic
wasting syndrome, now referred to as
porcine circovirus-associated disease
(PCVAD), are a high rate of mortality (as high as 10% in some cases),
progressive weight loss, jaundice,
and respiratory disease (Krakowka et
al., 2001). These factors can have a
tremendous negative economic effect
on vertically integrated swine production systems because finishing pigs
vaccinated against PCV2 have greater
ADG and lower mortality rates than
do pigs not vaccinated (Kristensen et
al., 2011). On average, PCV2 has cost
US swine producers 3 to 4 dollars per
pig and in extreme cases as much as
$20 per pig (Gillespie et al., 2009).
During a state of disease, such as
during PCVAD, protein metabolism
is altered; therefore, the ability of a
pig to deposit lean is reduced (Spurlock, 1997). Ractopamine hydrochloride (RAC; Paylean, Elanco Animal
Health, Greenfield, IN) is a common
feed additive in finishing diets because
RAC-fed pigs routinely perform on
average 10 to 15% better in production efficiency indicators (Apple et
al., 2007), have between 2.3 and 3.2%
heavier carcass weights (Apple et al.,
2007), and exhibit greater carcass
leanness and cutability (Kutzler et
al., 2011). There are no data available
on the effects of RAC in a population of pigs that had been previously
challenged with PCVAD. Therefore,
the objective of this experiment was
to evaluate the effects of different
ractopamine hydrochloride feeding
programs on growth performance and
carcass characteristics of finishing pigs
with a known history of PCVAD.
Hinson et al.
MATERIALS AND METHODS
Animals and Housing
Experimental procedures during
the experiment followed the guidelines stated in the Guide for the Care
and Use of Agricultural Animals in
Agricultural Research and Teaching (FASS, 1999). A total of 1,784
pigs were obtained from the on-site
nursery facility, randomized, and assigned to 1 of 80 pens. Overall pen
space was 14.12 m2 and so provided
an average floor space area of 0.69
m2 per pig. Pigs were housed in a
curtain-sided, naturally ventilated
barn. Each pen had a single cup
waterer and 4-hole single-sided box
feeder that provided approximately
122 cm of linear feed space (range of
5.30 to 6.78 cm/pig). Pigs underwent
a veterinarian-diagnosed PCVADrelated challenge within the first 3 to
6 wk after placement in the finishing
barn. Pig mortality was 2.38% during
the first 9 wk in the grower/finisher,
and there was 6.00% morbidity during
the first 9 wk in the grower/finisher.
The majority of morbid pigs eventually died after removal from the trial.
Day 0 of the trial is defined as the
day treatment diets were initiated
(21 d before slaughter). Therefore,
1,635 pigs (barrows and gilts; TR-4
sires × C-22 dams; Pig Improvement
Company, Hendersonville, TN) were
enrolled in final feeding phase of the
trial. Pigs were initially fed the same
finisher diet appropriate for the age
and BW of the pigs before initiation
of the experimental diets. Treatment
did not affect pig removal in the live
phase portion of the trial (final 21-d
feeding period). No more than 8 pigs
from any treatment were removed
during the final 21-d feeding period.
Experimental Design
At the beginning of the trial,
average initial BW was 105.1 kg.
Pigs were allotted to single-sex pens
containing between 18 and 23 pigs per
pen. Pens of pigs were then assigned
to 1 of 5 dietary treatments to fill a 5
× 2 factorial arrangement in random-
ized complete block design with 8
replicate pens per treatment.
Treatments consisted of 5 RAC
levels (0.0, 5.0, and 7.4 mg/kg or a
5.0/7.4 and 5.0/10.0 mg/kg step-up
program) and 2 sexes (barrows and
gilts). At the time of the trial (winter of 2007), only limited amounts
of PCV2 vaccine were commercially
available. Because of this, PCV2
vaccine was not an option for use in
this experiment. However, previous
research has shown no interactions
between RAC dose and PCV2 vaccinated pigs (Ritter et al., 2011).
Pigs assigned to the step-up program
were fed the initial dose of 5 mg/kg
of RAC for the first 14 d of the trial
and then stepped-up to the increased
dose of 7.4 or 10.0 mg/kg for the final
7 d of the feeding period. Diets were
corn–soybean meal based and RAC
was added to the diet at the expense
of ground corn (Table 1). Feed issued
at each feeding was recorded using the computerized Howema feed
system. Pigs were provided ad libitum
access to feed and water throughout
the entire trial. Feed weigh backs were
recorded each time pigs were weighed
to calculate interim performance.
Live Phase Data Collection
Pen weights and feed disappearance
were measured weekly throughout
the 21-d feeding period (d 0, 7, 14,
and 21). Individual pig weights were
collected at the start and conclusion of the study (d 1 and 20). Pigs
were marketed after the 21-d feeding period at an average live weight
of approximately 126 kg. Pigs were
marketed by intact pens to a federally
inspected Food Safety and Inspection
Service slaughter facility for carcass
data collection.
Slaughter Procedures
and Carcass Characteristics
A total of 1,603 pigs finished the
trial. At the end of the trial, 785 barrows and 818 gilts were removed from
their home pen, weighed by pen for
final weight determination, and tattooed with a unique number sequence
91
Ractopamine and porcine circovirus
Table 1. Dietary composition, as-fed basis
RAC inclusion, mg/kg
Item
Ingredients, %
Corn
Soybean meal, 48%
Fat, choice white grease
Monocalcium phosphate
Limestone
Salt
l-Lysine
Alimet1
l-Threonine
Vitamin premix2
Trace mineral premix
Paylean3
Copper sulfate
Calculated analysis
NRC ME, kcal/kg
Modified ME, kcal/kg
CP, %
Total lysine, %
SID lysine,4 %
Available P, %
Calcium, %
0.0
 
68.44
25.00
4.00
0.80
0.95
0.40
0.15
0.038
0.075
0.025
0.07
0.000
0.05
 
3,502
3,377
17.77
1.05
0.94
0.24
0.58
5.0
 
68.42
25.00
4.00
0.80
0.95
0.40
0.15
0.038
0.075
0.025
0.07
0.025
0.05
 
3,502
3,377
17.77
1.05
0.94
0.24
0.58
7.4
 
68.40
25.00
4.00
0.80
0.95
0.40
0.15
0.038
0.075
0.025
0.07
0.038
0.05
 
3,502
3,377
17.77
1.05
0.94
0.24
0.58
10.0
 
68.39
25.00
4.00
0.80
0.95
0.40
0.15
0.038
0.075
0.025
0.07
0.050
0.05
 
3,502
3,377
17.77
1.05
0.94
0.24
0.58
l-Met precursor HMTBA, an 88% aqueous solution of 2-hydroxy-4-(methylthio)
butanoic acid, Novus International Inc., St. Louis, MO.
2
Provided per kilogram of final diet: vitamin A, 5,512 IU; vitamin D3, 827 IU; vitamin E,
22 IU; vitamin K, 2.2 IU; riboflavin, 4 mg; vitamin B12, 0.02 mg; d-pantothenic acid, 14
mg; niacin, 25 mg; iron, 146 mg; zinc, 146 mg; manganese, 34 mg; copper, 15 mg;
iodine, 0.3 mg; selenium, 0.3 mg.
3
Provided the following inclusion of ractopamine hydrochloride (RAC; Paylean 9) per
kilogram of diet: 5, 7.4, and 10.0. Paylean is a registered trademark of Eli Lilly and
Company (Elanco Animal Health, Greenfield, IN).
4
SID = standardized ileal digestible.
1
corresponding to the pen of origin of
the pig. Pigs were loaded onto trailers
and transported approximately 295
km to a federally inspected slaughter facility. Pigs were allowed to rest
overnight with access to water for
approximately 24 h before slaughter.
Pigs were slaughtered under US Food
Safety and Inspection Service inspection via electrical immobilization and
exsanguinated, and HCW were recorded by plant personnel. Loin depth
(10th rib) and fat depth (10th rib)
were collected by plant personnel by
using an Animal Ultrasound System
(Animal Ultrasound Services and Co.
Inc., Ithaca, NY). These data were
used to calculate estimated carcass
lean percentage. Carcass yield was
calculated by dividing HCW by live
weight obtained at the farm.
Statistical Analysis
All data were analyzed with the
MIXED procedure of SAS (SAS
Institute Inc., Cary, NC). Growth
and carcass data were analyzed as a
randomized complete block design in
a 5 × 2 factorial arrangement. The
statistical model included the fixed effects of treatment, sex, and the 2-way
interaction between treatment and
sex. Block was considered a random
variable. Pen served as the experimental unit. Mean separations were
performed using the PDIFF option of
SAS. Four single–degrees of freedom
orthogonal contrasts were used to
evaluate the objectives of the experiment. They were 1) constant dose of
RAC fed at 5.0 mg/kg versus constant dose of RAC fed at 7.4 mg/kg;
2) 5.0/10.0 step-up program versus
5.0/7.4 step-up program; 3) constant
dose of RAC versus step-up RAC
feeding program; and 4) no RAC
versus the pooled effects of RAC. Assumptions of ANOVA were tested by
plotting the residuals in the Univariate procedure of SAS for normality,
and homogeneity of variances was
tested with the Levene’s test in the
GLM procedure of SAS.
Categorical pig weight gain data
were analyzed within predetermined
weight fractions by taking the average weight gain of the lightest 25%,
middle 50%, and heaviest 25% of
each pen. Data were analyzed as a
split-split plot design. Pen was the
experimental unit for the individual
weight gain data as well. The whole
plot of sex (barrow or gilt) was tested
with the interaction of block and sex.
The split plot was dietary feeding
program, and block × sex × feeding
program served as the error term.
Weight class (light 25%, middle 50%,
or heavy 25%) was the split-split plot
and was tested with block × sex ×
feeding program × weight class as the
error term. Statistical differences were
considered significant at P < 0.05
using a 2-tailed test. Three single–degrees of freedom contrast statements
were written to compare the effects of
no RAC versus the pooled effects of
RAC within a weight class.
RESULTS AND DISCUSSION
Growth Performance
There were no interactions (P
≥ 0.245) between dietary feeding
program (treatment) and sex for any
growth indicators (ADG, ADFI, or
G:F) during any part of the 21-d
evaluation period (d 7, 14, 21, the
first 14 d or the entire 21 d) during
the trial (Table 2). There were no
92
Hinson et al.
Table 2. Effects of ractopamine hydrochloride on the growth performance of late-finishing market pigs with a
previous history of PCVAD1
Dietary feeding program
Item
d 0 wt, kg
d 7 wt,2 kg
d 14 wt,2 kg
d 21 wt,2 kg
d 1–7
ADG,2,3 kg
ADFI,2 kg
G:F2
d 8–14
ADG,2 kg
ADFI, kg
G:F2
d 15–21
ADG,2,3 kg
ADFI, kg
G:F2,3
d 0–14
ADG,2 kg
ADFI, kg
G:F2,3
d 0–21
ADG,2 kg
ADFI, kg
G:F2,3
P-value
0.0
5.0
7.4
5.0/7.4
5.0/10.0
SEM
Treatment
Sex
Treatment
× sex
105.27
112.50b
119.02b
123.54b
 
1.03c
3.11
0.33b
 
0.91b
2.92
0.31b
 
0.62c
2.72
0.23c
 
0.97b
3.01
0.32b
 
0.86b
2.92
0.29b
105.05
113.92a
121.73a
126.92a
 
1.26ab
3.20
0.40a
 
1.08a
2.94
0.37a
 
0.72abc
2.66
0.27ab
 
1.18a
3.09
0.38a
 
1.02a
2.95
0.35a
105.12
114.22a
121.97a
126.76a
 
1.29a
3.22
0.40a
 
1.09a
2.88
0.38a
 
0.66bc
2.61
0.25bc
 
1.19a
3.05
0.39a
 
1.02a
2.92
0.35a
104.94
113.38ab
121.34a
126.80a
 
1.19b
3.09
0.39a
 
1.10a
2.92
0.38a
 
0.75ab
2.63
0.29ab
 
1.14a
3.00
0.38a
 
1.01a
2.88
0.35a
105.27
113.51a
121.49a
127.30a
 
1.18b
3.13
0.38a
 
1.11a
2.87
0.39a
 
0.80a
2.66
0.30a
 
1.15a
3.00
0.38a
 
1.03a
2.89
0.36a
1.233
1.280
1.375
1.237
 
0.043
0.073
0.010
 
0.042
0.074
0.010
 
0.064
0.079
0.021
 
0.033
0.066
0.007
 
0.034
0.065
0.009
0.886
0.018
<0.001
<0.0001
 
<0.0001
0.339
<0.0001
 
<0.0001
0.842
<0.0001
 
0.013
0.588
0.004
 
<0.0001
0.664
<0.0001
 
<0.0001
0.817
<0.0001
0.169
0.007
0.054
0.079
 
<0.0001
<0.0001
0.001
 
0.106
0.019
<0.0001
 
0.389
<0.0001
0.001
 
0.008
<0.0001
<0.0001
 
0.092
<0.0001
<0.0001
0.868
0.730
0.845
0.909
 
0.519
0.842
0.318
 
0.407
0.925
0.245
 
0.714
0.514
0.602
 
0.522
0.987
0.275
 
0.781
0.988
0.382
Treatment means within a row without a common superscript differ (P < 0.05).
Means calculated from 8 replicate pens/dietary treatment (18–23 pigs/pen). Growth performance was evaluated for 21 d. Trial was
conducted on PIC TR-4 × C22 pigs. PCVAD = porcine circovirus type 2 associated disease.
2
Control versus pooled dietary RAC feeding programs differ, P < 0.05.
3
Constant versus step-up RAC feeding programs differ, P < 0.05.
a–c
1
differences (P = 0.169) in starting
live BW between barrows (104.97 kg)
and gilts (105.30 kg) or between (P
= 0.547) control pigs (105.27 kg) and
RAC-fed pigs (105.10). However, by
d 7 of the feeding period, RAC pigs
(113.76 kg) were 1.26 kg heavier (P =
0.003) than were control pigs (112.50
kg). The magnitude of the difference
in BW between RAC pigs and control
pigs increased an additional 2.15 kg
(P < 0.0001), and so by d 21 of the
feeding period, RAC pigs (126.95 kg)
were 3.41 kg heavier (P < 0.0001)
than were control pigs (123.54 kg).
There were no differences in BW
among any of the RAC-fed treatment
groups on d 7, 14, or 21 of the feeding
period (Table 2). In recent studies,
pigs fed RAC have been on average
between 1.1% (Leick et al., 2010) and
3.5% (Rickard et al., 2012) heavier
than control-fed pigs. Others have reported similar ending BW advantages
for RAC (2.5%, Neill et al., 2010;
2.8%, Kutzler et al., 2010; and 3.3%,
Hinson et al., 2011) of RAC-fed pigs
over controls. Only Carr et al. (2009)
reported BW advantages of less than
1% between RAC and control pigs. In
that study, pigs were fed to a specified ending live weight as opposed to
a specified number of days. Even so,
HCW were 4% heavier in pigs fed an
amino acid–fortified diet supplemented with 5 mg/kg of RAC when compared with pigs fed the same amino
acid–fortified diet without RAC (Carr
et al., 2009). Ractopamine-fed pigs in
the current experiment were 2.75%
heavier than were controls at the end
of the feeding period. The RAC response in final BW was comparable to
other experiments using similar genetics, initial BW, ending BW, and RAC
inclusion levels. Therefore, the ending
live weight advantage of RAC-fed pigs
in this experiment when compared
with controls was expected based on
the results of previous research even
though these pigs had a clinical history of PCVAD.
Similarly, pigs fed RAC had growth
responses that were comparable
to previous research. Apple et al.
(2007) reported in a meta-analysis
of data collected before 2006 that
Ractopamine and porcine circovirus
feeding RAC between 5 and 10 mg/
kg improved ADG and feed efficiency by 11.2 and 9.6%, respectively.
More recently, Hinson et al. (2012b)
reported a ~21% improvement in
ADG and G:F when RAC was fed
at 5 mg/kg or as a 5 to 7.4 mg/
kg step-up program for 28 d. In the
current experiment, RAC improved
ADG over controls as early as 7 d on
trial and continued throughout the
entire live phase of the experiment
(Table 2). Pigs fed RAC gained 0.20
kg/d more (P < 0.0001) than did
control fed pigs during the first week
(d 7), 0.18 kg/d more (P < 0.0001)
during the second week (d 14), and
0.11 kg/d more (P < 0.001) during
the third week (d 21) of the trial.
Ractopamine-fed pigs gained 0.20
kg/d more (P < 0.0001) than did
control-fed pigs during the first 14 d
of the trial (period of time before the
step-up dose) and 0.16 kg/d more (P
< 0.0001) during the entire 21-d feeding period (Table 2). This resulted
in RAC-fed pigs (1.02 kg/d) gaining
weight 18.6% greater (P < 0.0001)
than control-fed pigs (0.86 kg/d) during the entire 21-d feed period (Table
2). Pigs fed a continuous dose of RAC
had greater (P = 0.004) ADG than
did pigs fed a step-up feeding program during the first 7 d of the feeding trial. During this portion of the
trial pigs fed the step-up programs
were only being fed 5.0 mg/kg, which
is the same dietary inclusion level
as one of the continuous treatment
groups. The likely difference was attributed to the treatment group fed a
continuous dose of 7.4 mg/kg having
a greater ADG than either of the
step-up program treatment groups
(Table 2). However, during the last 7
d of the feeding trial (d 15–21), the
step-up RAC feeding program treatment groups had greater (P = 0.031)
ADG than did the continuous dose
treatment groups. During this portion
of the trial, the step-up treatment
groups were receiving 7.4 and 10.0
mg/kg of RAC, whereas the continuous dose treatment groups were
receiving 5.0 and 7.4 mg/kg of RAC,
respectively.
Feed efficiency (G:F) of RAC-fed
pigs was 18.2% greater (P < 0.0001)
than that of controls at d 7 of the
feeding trial, 22.6% greater (P <
0.0001) at d 14 of the feeding trial,
and 21.7% greater (P < 0.01) at d
21 of the feeding trial (Table 2). This
resulted in overall feed efficiency
improvements of 18.8% (P < 0.0001)
during the first 14 d of the trial
and almost 21% improvement (P <
0.0001) in RAC-fed pigs (0.35 kg/kg)
when compared with controls (0.29
kg/kg) for the entire 21-d feeding
period (Table 2).
Similar to most previously published
data, there were no differences (P ≥
0.14) in ADFI between RAC-fed pigs
and control-fed pigs during any of the
3 evaluated time periods (d 0–7, 7–14,
or 14–21) nor during d 0 to 14 or d 0
to 21 of the study (Table 2).
Two previous experiments (Armstrong et al., 2004; Hinson et al.,
2012a) that evaluated the effects of
RAC dose and duration reported
similar findings to the current experiment. Armstrong et al. (2004)
reported greater (P < 0.05) ADG
values in RAC-fed pigs (1.12 kg/d)
when compared with control-fed pigs
(0.85 kg/d) as early as 6 d after RAC
initiation, and Hinson et al. (2012a)
reported a linear increase (P = 0.002)
in the response to RAC for ADG during a 35-d finishing period. Growth
data from this experiment also indicated advantages in performance as
early as 7 d on the treatment diets.
Pig Performance by Beginning
Weight Category
Because of the high level of variation in BW of finishing pigs at the
time of marketing, it is common
industry practice to market pigs over
a period of several weeks to allow
slower-growing pigs to reach the
desired market weight (DeDecker et
al., 2005). In cases such as the current experiment, where all pigs are
marketed at one time, a large amount
of variation in ending BW would be
expected within the study population.
Therefore, it is of interest to know if
93
the heaviest- and lightest-weight pigs
within a population at the beginning
of the feeding period respond similarly
to RAC. Table 3 illustrates the overall
growth of categories of pigs within
a population (single finishing barn)
when they were separated into 1 of 3
BW categories at the time of allocation to pen. There were no interactions between sex and category (P ≥
0.069) for any production indicator.
There were, however, interactions between diet and category for total gain
(P = 0.003) and ADG (P = 0.003).
Starting trial weights were not different among any of the treatments
groups within weight classification
(Table 3). However, RAC-fed pigs
were heavier (P < 0.05) at the end
of the 21-d feeding trial in both the
middle fraction of the pen and the
heavy fraction of the pen (Table 3).
In the middle and heavy categories,
RAC-fed pigs had at least 3.0 kg
heavier BW than did control-fed pigs.
Ractopamine-fed pigs in the middle
category (126.57 kg) were 3.5 kg
heavier (P < 0.0001) than control-fed
pigs (123.07 kg), and RAC-fed pigs in
the heavy category (138.52 kg) were
3.33 kg heavier (P < 0.0001) than
heavy-weight control-fed pigs (135.19
kg). Though not statistically different (P = 0.134), RAC-fed pigs in the
light category (112.06 kg) tended to
be 1.19 kg heavier than control-fed
pigs (110.87 kg) at the end of the
feeding period. The lack of statistical
difference in the light-weight fraction
may be related to the control-fed pigs
being 0.47 kg heavier than the RACfed pigs at the start of the feeding
period. The improvement in ending
BW is a result of RAC-fed pigs having a greater ADG in the light (P
= 0.002), middle (P < 0.001), and
heavy (P < 0.001) fractions of the
pen (Table 3). Therefore total gain of
RAC-fed pigs was greater in each of
the 3 weight categories. Ractopaminefed pigs in the light-weight group
gained 1.68 kg more (P = 0.002) than
controls. Ractopamine-fed pigs in
the middle-weight group gained 3.14
kg more (P < 0.0001) than controls.
Ractopamine-fed pigs in the heavy-
 
 
 
 
 
94.00
110.87
16.86b
0.80b
 
106.39
123.07b
16.68b
0.80b
 
117.56
135.19b
17.63c
0.84a
0.0
 
 
 
 
 
93.54
112.16
18.63a
0.89a
 
106.49
126.31a
19.82a
0.94a
 
116.66
138.12a
21.46ab
1.02bc
5.0
 
 
 
 
 
93.82
112.29
18.48a
0.88a
 
107.35
126.68a
19.33a
0.92a
 
117.60
138.75a
21.15b
1.01b
7.4
 
 
 
 
 
1
a–c
Treatment means within a row without a common superscript differ (P < 0.05).
PCVAD = porcine circovirus type 2 associated disease.
2
Main and interactive probability values of pen fractions based on weight category.
3
Control versus pooled dietary RAC feeding programs differ, P < 0.01.
Start weight,2 kg
End weight,2 kg
Total gain,2 kg
ADG,2 kg/d
Light 25% fraction of pen
Start weight, kg
End weight, kg
Total gain,3 kg
ADG,3 kg/d
Middle 50% fraction of pen
Start weight, kg
End weight,3 kg
Total gain,3 kg
ADG,3 kg/d
Heavy 25% fraction of pen
Start weight, kg
End weight,3 kg
Total gain,3 kg
ADG,3 kg/d
Item
92.79
111.86
19.07a
0.91a
 
106.95
126.94a
20.00a
0.95a
 
116.86
138.25a
21.39ab
1.02bc
5.0/7.4
Dietary feeding program
 
 
 
 
 
93.97
111.93
17.96ab
0.86ab
 
106.23
126.36a
20.13a
0.96a
 
116.49
138.94a
22.44a
1.07c
5.0/10.0
 
 
 
 
 
1.284
1.287
0.461
0.022
 
1.284
1.287
0.461
0.022
 
1.284
1.287
0.461
0.022
SEM
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
<0.0001
<0.0001
<0.0001
<0.0001
Pen fraction
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
0.532
0.625
0.069
0.072
Fraction
× sex
P-value
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
0.867
0.424
0.003
0.003
Fraction
× treatment
Table 3. Effects of ractopamine hydrochloride (RAC) on pig performance of late-finishing market pigs with a previous history of PCVAD1 when
segregated by weight class within a pen
94
Hinson et al.
95
Treatment means within a row without a common superscript differ (P < 0.05).
Means calculated from 8 replicate pens/dietary treatment (18–23 pigs/pen). Growth performance was evaluated for 21 d. Trial was conducted on PIC TR-4 × C22 pigs.
PCVAD = porcine circovirus type 2 associated disease.
2
Pooled standard error of treatment × sex.
3
Control versus pooled dietary RAC feeding programs differ, P < 0.05.
1
a,b
0.800
0.598
0.655
0.262
0.817
0.122
<0.0001
0.016
<0.0001
0.181
<0.0001
0.415
<0.0001
<0.0001
0.327
1.120
0.036
0.066
0.137
0.420
95.68a
1.57
7.23a
56.44a
76.71
95.89a
1.55
7.22a
56.48a
77.13
95.84a
1.58
7.20a
56.36a
77.01
95.23a
1.55
7.18a
56.40a
76.97
Treatment
× sex
Sex
SEM2
Treatment
P-value
5.0/10.0
5.0/7.4
7.4
5.0
0.0
91.99b
1.60
6.90b
55.80b
76.49
Carcass weight,3 kg
Backfat, cm
Loin depth,3 cm
Estimated carcass lean,3 %
Carcass yield, %
The RAC responses for carcass
traits in the current experiment were
expected and are similar to results
that have been reported by other
authors (Kutzler et al., 2011; Hinson
et al., 2012a). Perhaps more importantly is that pigs in this experiment
responded to RAC similarly to the
meta-analysis of data conducted by
Apple et al. (2007). Pigs fed RAC
(95.66 kg) had 3.67 kg (4.0%) heavier
(P < 0.0001) HCW than controlfed (91.99 kg) pigs (Table 4). Hot
carcass weights of RAC-fed pigs fed
Item
Carcass Characteristics
Dietary feeding program
weight group gained 3.98 kg more
(P < 0.0001) than controls (Table
3). Because pigs were categorized at
the time of allocation based on live
weight, it is no surprise there are
differences among the categories for
ending live weight. Even so, RAC pigs
gained more (P < 0.01) weight during
the feeding trial than control pigs
regardless of the weight category. On
average, RAC-fed pigs gained 2.93 kg
(range of 1.68 to 3.98 kg) more weight
over the 21-d feeding period than the
control-fed pigs. As stated, RAC-fed
pigs gained more weight per day than
did the control-fed pigs regardless of
weight classification (Table 3). Pigs
fed RAC in the light category gained
0.08 kg more weight per day than
did control pigs in the light category,
RAC pigs in the middle category
gained 0.14 kg more weight per day
than did controls in the middle
category, and RAC pigs in the heavy
group category gained 0.19 kg more
weight per day than did control pigs
in the heavy category. Collectively,
these data show that RAC is effective
at improving ADG and total weight
gain in pigs classified as light, middle,
or heavy even in conditions of previous disease challenge. Based on initial
BW of the pigs, RAC significantly
improved the rate of gain in all 3
weight classes, indicating RAC can
improve the growth rate of not only
the average pig, but also the lightest
and heaviest pig even with a history
of PCVAD.
Table 4. Effects of ractopamine hydrochloride (RAC) on the carcass characteristics of late-finishing market pigs with a previous history of PCVAD1
Ractopamine and porcine circovirus
96
at least 7.4 mg/kg are consistently
higher than are those of control-fed
pigs (Fernández-Dueñas et al., 2008;
Kutzler et al., 2010; Hinson et al.,
2011). The effects of RAC on HCW
at 5 mg/kg are less consistent. Some
researchers have reported an advantage in HCW of pigs fed RAC at 5
mg/kg (Fernández-Dueñas et al.,
2008; Rincker et al., 2009), whereas
others have not (Leick et al., 2010).
Even so, the consensus of the historical literature indicates dietary
RAC inclusion will improve HCW by
2.3% (5 mg/kg) to 3.1% (10 mg/kg)
(Apple et al., 2007). So the 4.0% improvement in HCW observed in this
study should have been anticipated.
Pigs in this experiment fed RAC had
carcass yields that tended to be 0.47
percentage units greater (P = 0.081)
than those of pigs not fed RAC. The
meta-analysis of data reported a
0.2 percentage unit improvement in
carcass yield of pigs fed 5.0 mg/kg of
RAC and a 0.6 percentage unit improvement in carcass yield when pigs
were fed 10.0 mg/kg when compared
with pigs not fed RAC (Apple et
al., 2007). There were no differences
(P = 0.096) in backfat thickness in
RAC pigs (1.56 cm) when compared
with control pigs (1.60 cm), but the
loin depths of RAC pigs were 0.31
cm (4.5%) greater (P < 0.0001) than
those of control pigs. This led to
estimated carcass lean of the RAC
pigs (56.42%) being 0.62 percentage
units greater (P < 0.0001) than the
estimated carcass lean values of the
control pigs (55.80%; Table 4). These
carcass measurements were also comparable to the differences reported in
the Apple et al. (2007) meta-analysis.
In that analysis, feeding 5.0 mg/kg of
RAC to finishing pigs reduced 10thrib backfat thickness by 0.04 cm, and
feeding RAC at 10.0 mg/kg reduced
backfat thickness by 0.14 cm. Likewise, feeding 5.0 mg/kg of RAC to
finishing pigs increased loin depth by
3.7%, and inclusion rates of 10.0 mg/
kg increased loin depth by 9.5% when
compared with pigs not fed RAC.
Estimated carcass lean was increased
between 0.9 and 1.3 percentage units
Hinson et al.
in the meta-analysis of pigs fed between 5.0 and 10 mg/kg.
IMPLICATIONS
There were no significant treatmentrelated differences for any response
variables among the 4 initial RAC
feeding programs. Feeding RAC to
finishing pigs for 21 d before slaughter improved ADG by19%, G:F by
21%, HCW by 3.59 kg, and estimated
carcass lean by 0.62 percentage units
when compared with the control-fed
pigs. The pig’s previous known history of PCVAD in this trial did not
prevent them from responding to the
RAC treatment similarly to pigs of
other trials. Collectively, these data
suggest that RAC supplementation
is an effective means of improving
growth performance and carcass composition subsequent to PCV2 health
challenges.
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