Impact of ractopamine hydrochloride on growth, efficiency, and carcass traits of finishing pigs in a three-phase marketing strategy

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1 Published November 24, 2014 Impact of ractopamine hydrochloride on growth, efficiency, and carcass traits of finishing pigs in a three-phase marketing strategy G. D. Gerlemann,* G. L. Allee,* P. J. Rincker, M. J. Ritter, D. D. Boler, 1 and S. N. Carr *Department of Animal Sciences, University of Missouri, Columbia 65211; Elanco Animal Health, A Division of Eli Lilly and Company, Greenfield, IN, 46140; and Department of Animal Sciences, University of Illinois, Urbana ABSTRACT: The objectives were to determine the effects of ractopamine hydrochloride (RAC) in a 3-phase marketing strategy. One thousand seven hundred forty pigs were used in 80 single-sex pens in 2 blocks. Each pen housed approximately 22 pigs. Sixteen percent of the total population of pigs was sold during the first marketing period, 18% was sold during the second marketing period, and the remaining 66% was sold during the third marketing period. Data were analyzed as a randomized complete block design of 2 treatments. Pigs in the second marketing group had greater growth performance indicators than pigs in the first marketing group. Over the entire feeding period, pigs fed RAC were 2.73 kg heavier (P < ), had 0.11 kg/d greater (P < ) ADG, and had 0.04 greater (P < ) G:F than pigs not fed RAC. Hot carcass weights were 3.3% greater (P < ), carcass yields were 0.68 (% units) greater (P < ), fat depth was 7.2% less (P < ), loin depth was 5.6% greater (P < ), and estimated carcass lean was 0.97% units greater (P < ) in RAC-fed pigs when compared with pigs not fed RAC. By the end of the first marketing period carcasses from pigs fed RAC (89.73 kg) were 2.1% heavier (P = 0.04) and gained 0.19 kg/d more (P = 0.03) carcass weight than carcasses from pigs not fed RAC (87.89 kg). By the end of the second marketing period carcasses from pigs fed RAC (99.00 kg) were 3.1% heavier (P < 0.001) and gained 0.14 kg/d more (P < 0.001) carcass weight than carcasses from pigs not fed RAC (96.02 kg). By the end of the third marketing period carcasses from pigs fed RAC ( kg) were 3.7% heavier (P < ) and gained 0.10 kg/d more (P < ) carcass weight than carcasses from pigs not fed RAC (99.06 kg). Although carcass gain per day decreased with extended RAC feeding duration, HCW advantages continued to increase as feeding duration was increased from 7 d to 35 d. Growth benefits were evident during the initial marketing period, but as duration increased differences diminished. Therefore, RAC can provide the expected growth performance benefits when included in the diet for up to 21 d, but HCW advantages continue to increase throughout the entire 35 d feeding period. Even though carcass benefits were not as evident in pigs sold during the first marketing period, advantages (particularly HCW) continued to increase with each marketing period. Key words: three-phase marketing, Paylean, pig, ractopamine hydrochloride 2014 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas INTRODUCTION The majority of finishing pigs in the United States are sold and marketed on a matrix that offers premiums and discounts on the basis of carcass weight and the percentage of lean meat (Meyer, 2005). This payment structure rewards swine producers for 1) selling their pigs at nondiscounted carcass weight ranges, 2) 1 Corresponding author: dboler2@illinois.edu Received April 3, Accepted January 6, minimizing variation in carcass weights, and 3) increasing the percentage of lean meat. Therefore, most U.S. producers sell multiple marketing groups (range: 2 to 6) from a barn, which are spread out over a 2- to 6-wk total time period (DeDecker et al., 2007; Patience et al., 2009; Hinson et al., 2012b). The percentage of pigs sold within each marketing group varies by producer, but on average 50 to 60% of the total pigs are sold in the final marketing group (DeDecker, 2002, 2006; Gerlemann et al., 2013). This marketing approach not only reduces variation in carcass weight but also improves the performance (ADG by 11%, ADFI by 6%, and feed-to-gain

2 Ractopamine with three-phase marketing 1201 ratio by 6%) of the pigs remaining in the barn through increased floor space and feeder space when compared to whole-house marketing, which empties the entire barn on 1 d (DeDecker et al., 2007). Ractopamine hydrochloride (RAC; Paylean; Elanco Animal Health, Greenfield, IN) is a feed ingredient that is commonly added to the diet 7 d before the first group of pigs is marketed from a barn because it improves ADG, feed-to-gain ratio, and carcass leanness in finishing swine when fed with a 16% CP diet (FDA, 1999, 2006). This allows producers to manage live weights, allocated space per pig, and carcass composition as well as input costs. However, to meet the aforementioned label claims, RAC has to be fed such that the average pig in the population gains at least 20.4 kg of BW from the time RAC is initiated until the end of the feeding period. Pigs marketed at an initial 7-d feeding period (approximately 20% of the population) will not meet these requirements, and therefore it is also important to understand the effects of RAC in the second (approximately 20% of the population) and third (approximately 60% of the population) marketing groups, which may be marketed approximately 14 and 28 d later, respectively. Despite all of the available literature on RAC in finishing pigs (Apple et al., 2007), only 3 studies have evaluated the effects of RAC on growth and carcass traits of finishing pigs marketed over multiple groups and selling dates (Patience et al., 2009; Hinson et al., 2012a; Gerlemann et al., 2013). However, there are no published studies on the effects of feeding RAC in a 3-phase marketing strategy under U.S. commercial conditions. Therefore, the objectives of this trial were to compare the effects of feeding an industry representative control diet versus a diet containing 7.4 mg/kg RAC and added nutrition (per label requirement) on performance and carcass traits of finishing pigs marketed under U.S. commercial conditions in a 3-phase marketing strategy (20% sold at 7 d, 20% sold at 21 d, and 60% sold 35 d after RAC initiation). Materials and methods The procedures used in this experiment followed the guidelines stated in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 2010). Animals and Housing Approximately 1,740 pigs (barrows and gilts; PIC 337 sires C22 dams; Pig Improvement Company, Hendersonville, TN) were used in a randomized complete block experimental design. A total of 80 single sex pens stratified over 2 blocks were used in the experiment. Each pen initially housed 22 pigs per pen. Block was defined Table 1. Dietary composition, as-fed basis Ractopamine inclusion, mg/kg Ingredient, % Corn Soybean Meal 48% Fat, Choice White Grease Monocalcium Limestone Salt l-lysine Alimet l-threonine Paylean Vitamin premix with phytase Mineral premix Calculated analysis NRC ME, Mcal/kg Modified ME, Mcal/kg CP, % Total lysine, % SID 3 lysine, % Total P (%) Available P (%) Ca (%) g SID lysine/mcal NRC ME g SID lysine/mcal Modified ME SID Met:Lys SID Met+Cys:Lys SID Thr:Lys SID Trp:Lys SID Ile:Lys SID Val:Lys l-met precursor HMTBA, an 88% aqueous solution of 2-hydrox- 4-(methylthio) butanic acid (Novus International Inc., St. Louis, MO). 2 Provided either 0.0 or 7.4 mg of ractopamine hydrochloride (Paylean 9) per kilogram of diet. Paylean is a registered trademark of Eli Lilly and Company (Elanco Animal Health), Greenfield, IN. 3 SID = Standardized ileal digestible. as the date treatment diets were initiated. The experiment had 2 treatments (NRC formulated control diet with 0 or 7.4 mg/kg RAC and increased lysine for the 35 d duration of the feeding trial; Table 1) and each treatment was replicated 40 times. Kutzler et al. (2011) reported a 0.45 kg cutability advantage in pigs fed 17.77% CP and 0.94% total ileal digestible (TID) lysine when compared with pigs fed 13.13% CP and 0.64% TID lysine. Additionally, they reported a 1.58 kg advantage in cutability in pigs fed either 5.0 or 7.4 mg/kg RAC in a 17.77% CP/0.94% TID lysine diet when compared with pigs not fed RAC but 17.77% CP and 0.94% TID lysine. Therefore, RAC increases cutability in finishing pigs even when diets differ in CP and lysine. So, different basal diets were used in this experiment to more closely represent industry use. Overall pen size was m 2, which resulted in 0.64 m 2 of

3 1202 Gerlemann et al. Table 2. Summary of housing conditions and marketing strategy of pigs fed ractopamine hydrochloride and sold in a 3-phase marketing system Housing conditions n = 80 First marketing period Days on feed 7 Feeder space, cm 5.55 Floor space, m Approximate % of pigs sold/pen 1 16 Second marketing period Days on feed 21 Feeder space, cm 6.59 Floor space, m Approximate % of pigs sold/pen 18 Third marketing period Days on feed 35 Feeder space, cm 8.41 Floor space, m Approximate % of pigs sold/pen pigs were marketed in block 1 and 3 pigs were marketed in block pigs were marketed in block 1 and 15 pigs were marketed in block 2. floor space per pig. Each pen had a single cup waterer and 4-hole single-sided box feeder that initially provided a total of 122 cm of linear feeder space (5.55 cm/pig). Pigs were housed in a curtain-sided, naturally ventilated barn and were provided ad libitum access to feed and water throughout the 35 d feeding trial. Treatment diets were initiated when the mean population BW was kg and continued for 35 d for an average BW gain of 26.8 kg (entire population mean BW gain was between 20.4 and 40.9 kg during the entire feeding phase). Pig weights were recorded 2 wk before treatment initiation, at treatment initiation (d 0), and at d 7, 21, and 35 (termination) of the feeding trial. Individual pig weights were collected in block 1 while pen weights were taken in block 2. Pigs in block 1 were identified with a unique individual ear tag number for each pig. All pigs were evaluated by the investigators and considered sound and healthy before enrollment onto the trial. Marketing Strategy The pigs used in this experiment were sold over 3 different marketing periods (Table 2). Approximately, 16% of the pigs were sold on d 7 (marketing period 1), approximately 18% were sold on d 21 (marketing period 2), and the remaining approximately 66% of the pigs were sold on d 35 of the feeding period (marketing period 3). Below is a detailed description of how market weight pigs were selected for each marketing group. First Marketing Period. The heaviest pigs in a pen (1 to 4 depending on the number of pigs remaining per pen; adjustments were made to account for morbidity and mortality loss) were marketed after 7 d on the feeding trial. Individual pigs were weighed in each of the 40 pens representing block 1 and the truly heaviest 3 to 4 pigs per pen were selected for marketing. The heaviest 1 to 3 pigs from each of the 40 pens representing block 2 were selected for slaughter based on visual appraisal by the production sites normal marketing personnel. Pigs selected for marketing, regardless of block, were tattooed, loaded on a truck, and transported for slaughter. The remaining pigs in each pen were weighed (as individuals in block 1 and as a pen in block 2) and put back in their original pens. Each pen contained 18 (block 1; 0.78 m 2 floor space/pig) or 19 (block 2; 0.74 m 2 floor space/pig) pigs per pen (average floor space of 0.76 m 2 ; Table 2) after the first marketing period. Second Marketing Period. The 4 heaviest remaining pigs in a pen were marketed after 21 d on the feeding trial for the second marketing group. Individual pigs were weighed in each of the 40 pens representing block 1 and the truly heaviest 4 pigs per pen were selected for marketing. The heaviest 4 pigs from each of the 40 pens representing block 2 were selected for slaughter based on visual appraisal by the production sites normal marketing personnel. Pigs selected for marketing, regardless of block, were tattooed, loaded on a truck, and transported for slaughter. The remaining pigs in each pen were weighed (as individuals in block 1 and as a pen in block 2) and put back in their original pens. Each pen contained 14 (block 1: 1.01 m 2 floor space/pig) or 15 (block two 0.94 m 2 floor space/ pig) pigs per pen (average floor space of 0.97 m 2 ; Table 2) after the second marketing period. Third Marketing Period. On d 35 of the feeding trial all remaining pigs were marketed for slaughter. Pigs in block 1 were weighed as individuals and pigs in block 2 were weighed as a pen. All pigs were tattooed, loaded on a truck, and transported for slaughter. Harvest Procedures and Carcass Characteristics During each marketing period designated pigs were transported approximately 250 km to a federally inspected harvest facility. Pigs were harvested via carbon dioxide immobilization and exsanguination. Hot carcass weights were collected at the time of slaughter along with back fat depth, loin depth, and estimated carcass lean. Carcass measurements were collected using a Fat-O-Meater system (Fat-O-Meater measurements; SFK Technology Fat-O-Meater, Herlev, Denmark). Carcass yield (dressing percentage) was calculated by dividing the HCW by the ending live weight collected at the farm. Estimated carcass lean was provided using a calculated plant proprietary equation.

4 Ractopamine with three-phase marketing 1203 Statistical Analyses Data were analyzed as a randomized complete block arrangement of 2 treatments. Pen served as the experimental unit for all response parameters and the final model included the fixed effects of treatment. Block and replicate nested within block were included in the model as random variables. Sex was not included in the model; however, the variation due to sex was accounted for by including replicate in the model. Least square means and SE were calculated with the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Mean separation was conducted using the PDIFF option in the MIXED procedure of SAS. Statistical differences were considered significant at P < 0.05 using a 2-tailed test. RESULTS AND DISCUSSION Overall Growth Performance There were no differences (P = 0.52) in starting BW between pigs not fed RAC ( kg) and pigs fed RAC ( kg; Table 3). Overall growth performance of pigs fed RAC in this trial were greater than pigs not fed RAC and were similar to historical data. Over the entire feeding period, pigs fed RAC were 2.73 kg (2.1%) heavier (P < ), had 0.11 kg/d (10.9%) greater (P < ) ADG, and had 0.04 (12.9%) greater (P < ) G:F than pigs not fed RAC. The improvement in overall growth performance (greater ADG, less ADFI, and greater G:F) resulted in RAC-fed pigs (28.07 kg) gaining 2.48 kg (9.7% improvement) more total gain than control-fed pigs (25.59 kg; Table 3). Growth Performance by Marketing Period Pigs in the second marketing group had greater growth performance indicators than pigs in the first marketing group. Among the contributors to these improvements may be increased allotted floor space and feeder space as pigs were removed from each pen as well as changes to social competition. First Marketing Period (Day Zero to Seven of Ractopamine Feeding). At the end of the first marketing period, pigs fed RAC tended (P = 0.10) to be 1.19 kg heavier after 7 d on feed than pigs not fed RAC. Ractopamine-fed pigs gained 0.16 kg/d more (P < 0.01) weight and had a 0.05 greater (P = 0.01) G:F than control pigs (Table 3). There were no differences (P = 0.62) in ADFI between RAC fed pigs and control-fed pigs during the first marketing period. The heaviest 16% of the pigs were removed and marketed on d 7 (marketing group 1). Second Marketing Period (Day Eight to Twenty- One of Ractopamine Feeding). The performance parameters measured in the second marketing period (d Table 3. Effects of ractopamine hydrochloride (RAC) on pig performance when pigs are sold in a 3-phase marketing strategy Treatment Control RAC SEM P-value Pens, n Start weight, kg d (first feeding period) 1 End of period live wt, kg ADG (0 7 d of RAC feeding), kg/d <0.01 ADFI (0 7 d of RAC feeding), kg/d G:F (0 7 d of RAC feeding) F:G 2 (0 7 d of RAC feeding) Total gain (0 7 d of RAC feeding), kg d (second feeding period) 2 End of period live wt, kg < ADG (8 21 d of RAC feeding), kg/d < ADFI (8 21 d of RAC feeding), kg/d <0.01 G:F (8 21 d of RAC feeding) < F:G (8 21 d of RAC feeding) < Total gain (8 21 d of RAC feeding), kg d (third feeding period) 3 End of period live wt, kg < ADG (22 35 d of RAC feeding), kg/d ADFI (22 35 d of RAC feeding), kg/d <0.01 G:F (22 35 d of RAC feeding) F:G (22 35 d of RAC feeding) Total gain (22 35 d of RAC feeding), kg Entire feeding period 4 Live wt, kg < ADG (0 35 d of RAC feeding), kg/d < ADFI (0 35 d of RAC feeding), kg/d <0.001 G:F (0 35 d of RAC feeding) < F:G (0 35 d of RAC feeding) < Total gain (0 35 d of RAC feeding), kg Pens contained 22 pigs per pen in block 1 and 2. 2 Pens contained 18 pigs per pen in block 1 and 19 pigs per pen in block 2. 3 Pens contained 14 pigs per pen in block 1 and 15 pigs per pen in block 2. 4 Weighted average of growth performance for the entire 35 d feeding period. 8 to 21) are based on the 84% of the pigs remaining in the barn. Pigs that were fed RAC ( kg) and marketed in the second marketing group on d 21 were 3.26 kg heavier (P < ) than pigs not fed RAC ( kg) at the end of the marketing period. Ractopaminefed pigs had improved performance indicators when compared to pigs not fed RAC during the second marketing period. Pigs fed RAC gained 0.14 kg/d more (P < ) weight, consumed 0.19 kg/d less (P < 0.01) feed, and had G:F that were 0.07 units greater (P < ) than pigs not fed RAC (Table 3). This resulted in RAC-fed pigs gaining 1.42 kg more BW during the additional 2 wk of the second marketing period than pigs not fed RAC. Increased floor space and decreased feeder competition is known to improve pig performance (DeDecker

5 1204 Gerlemann et al. et al., 2005). More recently, Gerlemann et al. (2013) demonstrated that as pigs are removed from a pen and floor space per pig increases performance also increases. In that study a nearly 30% increase in floor space and feeder space (removing the heaviest 20% of the pigs in a pen) resulted in a 5.4% improvement in ADG regardless of dietary treatment. In the current study, 16% of the pigs in each pen were sold during the first marketing period. Average daily gain, regardless of dietary treatment, increased nearly 20%. The inclusion of RAC and increased floor and feeder space increased ADG 17.3% from the first marketing group to the second marketing group, but ADG improved 22.8% in control pigs from the first marketing group to the second (Table 3). Even so, feed efficiency (G:F) improved 15.5% in RAC-fed pigs but only improved 9.7% in control-fed pigs. At the same time ADFI increased in control-fed pigs by 0.29 kg/d. After the second marketing group was sold on d 21, only 66% of the pigs remained. Third Marketing Period (Day Twenty-Two to Thirty-Five of Ractopamine Feeding). Therefore, the performance parameters measured in the third marketing period (d 22 to 35) are based on the 66% of the pigs remaining in the barn. By the end of the third marketing period only marginal increases in growth performance parameters were observed from d 22 to 35, but overall responses due to RAC persisted. Pigs fed RAC ( kg) were 3.34 kg (2.5%) heavier (P < ) than pigs not fed RAC ( kg), but there were no differences (P = 0.35) in ADG from d 22 to 35 between the 2 treatments. Pigs not fed RAC consumed (P < 0.01) 0.14 kg more feed per day than pigs fed RAC. So, the advantage in gain to feed demonstrated by RACfed pigs over pigs not fed RAC in previous marketing periods decreased in the third marketing period relative to the marginal difference observed in the second. Pigs fed RAC (0.31) had greater (P = 0.02) feed efficiency (G:F) when compared with pigs not fed RAC (0.29; Table 3). During the final 14 d of the third marketing period, only 66% (14 or 15 pigs/pen depending on block) of the original population remained. This meant floor space per pig was increased and feeder space competition was decreased by 27.6% from the second marketing period. Even so, overall growth performance in the final marketing period, regardless of treatment, was not as good as pigs in the second marketing period. Average daily gains of pigs in the third marketing group were 6.7% less and G:F were 21.4% less than those sold during the second marketing group. So, increasing floor space after the greater performing pigs are removed (pigs sold in the first 2 marketing periods) did not further improve growth performance, but RAC-fed pigs maintained their advantage in live weight when compared with controls. Carcass Characteristics Main effect differences of carcass characteristics were expected and similar to previous reports. Hot carcass weights were 3.1% greater (P < ), carcass yield was 0.68 % units greater (P < ), fat depth was 7.2% less (P < ), and loin depth was 5.6% greater (P < ) in RAC-fed pigs when compared to pigs not fed RAC. This resulted in estimated carcass lean values being 0.97% units greater in RAC-fed pigs than pigs not fed RAC. Recent studies evaluating RAC with different dietary ingredients, doses, durations, and production systems have reported an advantage in estimated carcass lean between 0.41 to 1.12% units (Webster et al., 2007; Leick et al., 2010; Kutzler et al., 2011; Tavárez et al., 2012). First Marketing Period. Hot carcass weights of pigs fed RAC for 7 d tended (P = 0.12) to be 1% (0.92 kg) greater than HCW of pigs not fed RAC (Table 4). There were no differences (P = 0.75) in carcass yield between RAC-fed pigs (73.23%) and control-fed pigs (73.18%). This resulted in RAC-fed pigs (51.86%) tending to have a 0.47% unit greater (P = 0.06) estimated carcass lean value than pigs not fed RAC (51.39). Second Marketing Period. Changes in carcass characteristics due to feeding RAC generally take longer durations or greater doses than required to change performance characteristics (Armstrong et al., 2004; Kutzler et al., 2011; Hinson et al., 2012a). These changes become more evident during the second marketing period (21 d on RAC). Pigs fed RAC had 3.27 kg heavier (P < ; 3.45% increase) HCW than pigs not fed RAC. Pigs fed RAC also had 0.66% units greater (P < 0.001) carcass yields, 1.28 mm less (P < 0.01) 10th rib fat thickness, and 2.48 mm greater (P < 0.01) loin depths when compared with pigs not fed RAC (Table 4). This equated to a 0.73% unit increase (P < 0.01) in estimated carcass leanness of RAC-fed pigs (51.96%) when compared with pigs not fed RAC (51.23%). Third Marketing Period. The magnitude of differences in carcass characteristics between RAC-fed pigs and pig not fed RAC increased for each evaluated characteristic for pigs sold during the third marketing period. Pigs fed RAC had 3.57 kg heavier (P < ; 3.62% increase) HCW than pigs not fed RAC. Pigs fed RAC also had 0.82% units greater (P < ) carcass yields, 1.99 mm less (P < ) 10th rib fat thickness, and 3.96 mm greater (P < ) loin depths when compared with pigs not fed RAC (Table 4). This equated to a 1.16% unit increase (P < ) in estimated carcass leanness of RAC-fed pigs (52.14%) when compared with pigs not fed RAC (50.98%). Carcass Daily Gain. Pigs in block 1 were weighed individually during each weigh period to monitor carcass daily gain. A standardized HCW was determined for each pig by regressing carcass yield from pigs not fed RAC in

6 Ractopamine with three-phase marketing 1205 Table 4. Effects of ractopamine hydrochloride (RAC) on carcass characteristics when pigs were sold in a 3-phase marketing strategy Treatment Control RAC SEM P-value Pens, n d of RAC feeding (first marketing group) 1 HCW, kg Carcass yield, % Fat depth, mm Loin depth, mm Estimated carcass lean, % d of RAC feeding (second marketing group) 2 HCW, kg < Carcass yield, % <0.001 Fat depth, mm <0.01 Loin depth, mm <0.01 Estimated carcass lean, % < d of RAC feeding (third marketing group) 3 HCW, kg < Carcass yield, % < Fat depth, mm < Loin depth, mm < Estimated carcass lean, % < All 3 marketing groups 4 HCW, kg < Carcass yield, % < Fat depth, mm < Loin depth, mm < Estimated carcass lean, % < Four pigs per pen were sold in block 1 and 3 pigs per pen were sold in block 2; pen served as the experimental unit. 2 Four pigs per pen were sold in block 1 and block 2; pen served as the experimental unit. 3 All remaining pigs were sold in the third marketing group (14 pigs in block 1 and 15 pigs in block 2); pen served as the experimental unit. 4 Weighted average of carcass characteristics from each of the 3 marketing groups. this study in a similar manner as that reported by Pompeu et al. (2013). It was determined carcasses would yield 72.8% at the time of dietary treatment initiation. Therefore, a standardized initial HCW was determined for each individual pig by multiplying initial live BW by This allows for calculation of carcass ADG, which is economically more important than live BW ADG because it accounts for yield and payment based on carcass weight. Initial standardized HCW were not different between treatments for marketing period 1 (P = 0.45), 2 (P = 0.89), or 3 (P = 0.82; Table 5). Carcasses from pigs in the first marketing period of block 1 fed RAC (89.73 kg) were 2.1% heavier (P = 0.04) and gained 28.6% (0.19 kg/d) more (P = 0.03) carcass weight than carcasses from pigs not fed RAC (87.89 kg). By the end of the second marketing period the magnitude of difference between treatments for HCW had increased from the first marketing period. Table 5. Effects of ractopamine hydrochloride (RAC) on carcass characteristics of pigs sold in a 3-phase marketing strategy from block 1 that were individually weighed 1 Treatment Control RAC n = 20 n = 20 SEM P-value 7 d of RAC feeding 2 Pigs, no Days on feed (RAC), no. 7 7 Standardized initial HCW, 3 kg HCW, kg Carcass yield, % Fat depth, mm Loin depth, mm Estimated carcass lean, % Carcass ADG, kg/d d of RAC feeding 4 Pigs, no Days on feed (RAC), no Standardized initial HCW, 3 kg HCW, kg <0.001 Carcass yield, % Fat depth, mm Loin depth, mm Estimated carcass lean, % Carcass ADG, kg/d < d of RAC feeding 5 Pigs, no Days on feed (RAC), no Standardized initial HCW, 3 kg HCW, kg < Carcass yield, % < Fat depth, mm < Loin depth, mm < Estimated carcass lean, % < Carcass ADG, kg/d < Pen was considered the experimental unit. 2 Data are based on pigs that were marketed on Day 7 (excludes removals and Day 21 and 35 pigs). 3 Standarized initial HCW = initial BW 73% standard carcass yield. 4 Data are based on pigs that were marketed on Day 21 (excludes removals and Day 7 and 35 pigs). 5 Data are based on pigs that were marketed on Day 35 (excludes removals and Day 7 and 21 pigs). By the end of the second marketing period carcasses from pigs fed RAC (99.00 kg) were 3.1% heavier (P < 0.001) and gained 18.9% (0.14 kg/d) more (P < 0.001) carcass weight than carcasses from pigs not fed RAC (96.02 kg). Hot carcass weight advantages of RAC-fed pigs continued to increase during the third marketing period. By the end of the third marketing period carcasses from pigs fed RAC ( kg) were 3.7% heavier (P < ) and gained 14.7% (0.10 kg/d) more (P < ) carcass weight than carcasses from pigs not fed RAC (99.06 kg; Table 5). Although the RAC percent improvement in carcass weight

7 1206 Gerlemann et al. Figure 1. Differences in body weight and carcass weight using average pen weight data from both blocks of pigs between ractopamine hydrochloride (RAC)-fed pigs and control (Con)-fed pigs (RAC Con) at each of the 3 marketing periods. gain per day decreased over the 3 marketing periods, HCW advantages continued to increase as feeding duration was increased from 7 d to 21 d and even out to 35 d. The reduction in magnitude of differences for carcass gain per day is likely a reflection of the desensitization of the β-receptor and reflective of the decreased advantage in BW ADG (Spurlock et al., 1994). Body Weight versus Carcass Weight Advantage It has become common knowledge that pigs fed RAC and marketed in an equal time on feed (short-on-space marketing) approach will be heavier than their control counterparts. Hinson et al. (2011) reported a 4.08 kg BW advantage of barrows individually fed 7.4 mg/kg RAC for 21 d when compared with individually housed barrows not fed RAC. In a more commercially applicable study, Gerlemann et al. (2013) reported a 2.43 kg BW advantage of pigs fed 7.4 mg/kg RAC for 17 d when compared to pigs not fed RAC. That BW advantage increased to 4.47 kg when floor space was increased and pigs were provided an additional 14 d on trial (Gerlemann et al., 2013). It is also common knowledge that RAC-fed pigs will reach a desired market weight in fewer days on feed when pigs are marketed at equal BW (long-on-space marketing approach). Hinson et al. (2012b) reported a greater percentage of RAC-fed pigs were marketed during the first 3 marketing periods of an equal marketing weight scheme experiment when compared with pigs not fed RAC. Additionally, Hinson et al. (2012b) reported a lower percentage of RAC-fed pigs failed to meet the desired HCW requirements for marketing when compared with the percentage of pigs not fed RAC that failed to meet the HCW requirements for marketing. It is also clear from historical literature that feeding between 5.0 and 10.0 mg/kg RAC to finishing pigs increases HCW 2.3 to 3.2%, respectively, over pigs not fed RAC (Apple et al., 2007). What is not clear is the effect on the change in the magnitude of difference between BW and HCW at extended RAC feeding durations. Data from this trial illustrates an increasing magnitude of difference in HCW as RAC duration increases (Fig. 1). Pigs fed RAC in this trial had 1.19 kg heavier BW and 0.93 kg heavier HCW than pigs not fed RAC after the first marketing period (Fig. 1). Those advantages increased to 3.26 kg in live weight and 3.27 kg of HCW by the end of the second marketing period. What is most interesting, however, is that during the period of time between the second and third marketing period the advantage in live weight was relatively stagnant with only a 0.08 kg increase in the advantage of live weight between RAC-fed pigs and pigs not fed RAC. Spurlock et al. (1994) reported that long term exposure to a β-agonist, such as ractopamine, leads to desensitization of the β-receptor and an overall reduction of the effect. Recently, Hinson et al. (2013) demonstrated this desensitization phenomenon when pigs fed 7.4 mg/kg RAC for 21 d experienced a reducing advantage in ADG from 0.26 kg/d after 7 d on test to 0.18 kg/d after 14 d on test and finally to only 0.04 kg/d by 21d on test. What is interesting, in the current study, is the magnitude of differences between pigs fed and not fed RAC for HCW increased 0.30 kg between the second and third marketing period. Today most packers determine the value of a pork carcass by using a combination of estimated carcass leanness and HCW rather than live weight. Therefore, previous experiments reporting reduced marginal benefit to live weight in long duration feeding programs may actually be underestimating the total benefit of feeding RAC. In this trial there was increased advantage in HCW by feeding pigs RAC for up to 35 d (Fig. 1). The increased advantage in live weight by feeding RAC appeared to plateau by d 21. These data provide justification for feeding finishing pigs RAC for longer than 21 or 28 d to market the final cut at the desire weight. Conclusion Results from this experiment shows RAC can provide the expected growth performance benefits when included in the diet for up to 21 d, but HCW advantages continued to increase all the way through the entire 35 d feeding. The growth benefits were evident in the early phases, but as duration increased the benefits began to diminish. Even so, RAC-fed pigs gained 0.11 kg/d more than pigs not fed RAC for a total BW advantage of 2.72 kg (2.48 kg of total gain) throughout the entire feeding period. Even though carcass benefits were not as noticeable in pigs sold during the first marketing period, carcass characteristic advantages (particularly HCW) continued to increase with each marketing period. These data suggest that a RAC feeding programs can be beneficial in a commercial production type setting where RAC is fed for up to 35 d and multiple marketing periods are used.

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