T he effects of dietary

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1 The Professional Animal Scientist 29 (2013): American Registry of Professional Animal Scientists T he effects of dietary ractopamine 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 ABSTRACT 1 Current address: JBS United, 4310 State Road 38 West, Sheridan, IN Corresponding author: boler.2@osu.edu 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 arrangement 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 kg/d, P < ) during the feeding period and were almost 21% more (P < ) efficient (G:F) than were control-fed pigs. Loin depths of RAC-fed pigs were 0.31 cm greater (P < ) and estimated carcass lean percentages were 0.62 percentage units greater (P < ) 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

2 90 Hinson et al. 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. 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 m 2 and so provided an average floor space area of 0.69 m 2 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 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 randomized 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

3 Ractopamine and porcine circovirus 91 Table 1. Dietary composition, as-fed basis Item 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 RAC inclusion, mg/kg Ingredients, % Corn Soybean meal, 48% Fat, choice white grease Monocalcium phosphate Limestone Salt l-lysine Alimet l-threonine Vitamin premix Trace mineral premix Paylean Copper sulfate Calculated analysis NRC ME, kcal/kg 3,502 3,502 3,502 3,502 Modified ME, kcal/kg 3,377 3,377 3,377 3,377 CP, % Total lysine, % SID lysine, 4 % Available P, % Calcium, % 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 D 3, 827 IU; vitamin E, 22 IU; vitamin K, 2.2 IU; riboflavin, 4 mg; vitamin B 12, 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 Paylean is a registered trademark of Eli Lilly and Company (Elanco Animal Health, Greenfield, IN). 4 SID = standardized ileal digestible. 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

4 92 Hinson et al. Table 2. Effects of ractopamine hydrochloride on the growth performance of late-finishing market pigs with a previous history of PCVAD 1 Dietary feeding program P-value Item / /10.0 SEM Treatment Sex Treatment sex d 0 wt, kg d 7 wt, 2 kg b a a ab a d 14 wt, 2 kg b a a a a < d 21 wt, 2 kg b a a a a < d 1 7 ADG, 2,3 kg 1.03 c 1.26 ab 1.29 a 1.19 b 1.18 b < < ADFI, 2 kg < G:F b 0.40 a 0.40 a 0.39 a 0.38 a < d 8 14 ADG, 2 kg 0.91 b 1.08 a 1.09 a 1.10 a 1.11 a < ADFI, kg G:F b 0.37 a 0.38 a 0.38 a 0.39 a < < d ADG, 2,3 kg 0.62 c 0.72 abc 0.66 bc 0.75 ab 0.80 a ADFI, kg < G:F 2, c 0.27 ab 0.25 bc 0.29 ab 0.30 a d 0 14 ADG, 2 kg 0.97 b 1.18 a 1.19 a 1.14 a 1.15 a < ADFI, kg < G:F 2, b 0.38 a 0.39 a 0.38 a 0.38 a < < d 0 21 ADG, 2 kg 0.86 b 1.02 a 1.02 a 1.01 a 1.03 a < ADFI, kg < G:F 2, b 0.35 a 0.35 a 0.35 a 0.36 a < < a c Treatment means within a row without a common superscript differ (P < 0.05). 1 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 < Constant versus step-up RAC feeding programs differ, P < differences (P = 0.169) in starting live BW between barrows ( kg) and gilts ( kg) or between (P = 0.547) control pigs ( kg) and RAC-fed pigs (105.10). However, by d 7 of the feeding period, RAC pigs ( kg) were 1.26 kg heavier (P = 0.003) than were control pigs ( kg). The magnitude of the difference in BW between RAC pigs and control pigs increased an additional 2.15 kg (P < ), and so by d 21 of the feeding period, RAC pigs ( kg) were 3.41 kg heavier (P < ) than were control pigs ( 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

5 Ractopamine and porcine circovirus 93 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 < ) than did control fed pigs during the first week (d 7), 0.18 kg/d more (P < ) 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 < ) 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 < ) 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 < ) 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 < ) than that of controls at d 7 of the feeding trial, 22.6% greater (P < ) 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 < ) during the first 14 d of the trial and almost 21% improvement (P < ) 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 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 ( kg) were 3.5 kg heavier (P < ) than control-fed pigs ( kg), and RAC-fed pigs in the heavy category ( kg) were 3.33 kg heavier (P < ) than heavy-weight control-fed pigs ( kg). Though not statistically different (P = 0.134), RAC-fed pigs in the light category ( kg) tended to be 1.19 kg heavier than control-fed pigs ( 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 < ) than controls. Ractopamine-fed pigs in the heavy-

6 94 Hinson et al. Table 3. Effects of ractopamine hydrochloride (RAC) on pig performance of late-finishing market pigs with a previous history of PCVAD 1 when segregated by weight class within a pen Dietary feeding program P-value Item / /10.0 SEM Pen fraction Fraction sex Fraction treatment 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 b a a a ab ADG, 3 kg/d 0.80 b 0.89 a 0.88 a 0.91 a 0.86 ab Middle 50% fraction of pen Start weight, kg End weight, 3 kg b a a a a Total gain, 3 kg b a a a a ADG, 3 kg/d 0.80 b 0.94 a 0.92 a 0.95 a 0.96 a Heavy 25% fraction of pen Start weight, kg End weight, 3 kg b a a a a Total gain, 3 kg c ab b ab a ADG, 3 kg/d 0.84 a 1.02 bc 1.01 b 1.02 bc 1.07 c a c Treatment means within a row without a common superscript differ (P < 0.05). 1 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.

7 Ractopamine and porcine circovirus 95 weight group gained 3.98 kg more (P < ) 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. Carcass Characteristics 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 < ) HCW than controlfed (91.99 kg) pigs (Table 4). Hot carcass weights of RAC-fed pigs fed Table 4. Effects of ractopamine hydrochloride (RAC) on the carcass characteristics of late-finishing market pigs with a previous history of PCVAD 1 P-value Dietary feeding program Treatment sex / /10.0 SEM 2 Treatment Sex Item Carcass weight, 3 kg b a a a a < Backfat, cm < Loin depth, 3 cm 6.90 b 7.18 a 7.20 a 7.22 a 7.23 a < Estimated carcass lean, 3 % b a a a a < < Carcass yield, % a,b Treatment means within a row without a common superscript differ (P < 0.05). 1 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.

8 96 Hinson et al. 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 < ) than those of control pigs. This led to estimated carcass lean of the RAC pigs (56.42%) being 0.62 percentage units greater (P < ) 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 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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Killefer Comparison of varying doses and durations of ractopamine hydrochloride on late finishing-pig carcass characteristics and meat quality. J. Anim. Sci. 89: Kutzler, L. W., C. M. Peterson, M. Ellis, S. N. Carr, M. J. Ritter, T. A. Armstrong, F. K. McKeith, and J. Killefer Ractopamine (Paylean) response in heavy-weight finishing pigs. Prof. Anim. Sci. 26: Leick, C. M., C. L. Puls, M. Ellis, J. Killefer, T. R. Carr, S. M. Scramlin, M. B. England, A. M. Gaines, B. F. Wolter, S. N. Carr, and F. K. McKeith Effect of distillers dried grains with solubles and ractopamine (Paylean) on quality and shelf-life of fresh pork and bacon. J. Anim. Sci. 88: Neill, C. R., R. D. Goodband, M. D. Tokach, J. L. Nelssen, S. S. Dritz, J. M. DeRouchey, C. N. Groesbeck, and K. R. Brown Ef-

9 Ractopamine and porcine circovirus 97 fects of intermittent ractopamine hydrochloride use on pig growth performance in late finishing. Prof. Anim. Sci. 26: Rickard, J. W., B. R. Wiegand, D. Pompeu, R. B. Hinson, G. D. Gerlemann, R. Disselhorst, M. E. Briscoe, H. L. Evans, and G. L. Allee The effect of corn distillers dried grains with solubles, ractopamine, and conjugated linoleic acid on the carcass performance, meat quality, and shelf-life characteristics of fresh pork following three different storage methods. Meat Sci. 90: Rincker, P. J., J. Killefer, P. D. Matzat, S. N. Carr, and F. K. McKeith The effect of ractopamine and intramuscular fat content on sensory attributes of pork from pigs of similar genetics. J. Muscle Foods 20: Ritter, M. J., K. Cera, N. Paton, and S. N. Carr Effects of ractopamine dose on growth performance traits of finishing pigs raised and marketed under U.S. commercial conditions. J. Anim. Sci. 89(E-suppl.):260. (Abstr.) Spurlock, M. E Regulation of metabolism and growth during immune challenge: An overview of cytokine function. J. Anim. Sci. 75: