J. Anim. Sci. 2005. 83:2886-2893
© 2005 American Society of Animal Science
The effects of ractopamine hydrochloride on lean carcass yields and pork quality characteristics1
S. N. Carr*,
D. J. Ivers
,
D. B. Anderson,
D. J. Jones,
D. H. Mowrey,
M. B. England*,
J. Killefer*,
P. J. Rincker* and
F. K. McKeith*,2
* Department of Animal Sciences, University of Illinois, Urbana 61801; and
and
Elanco Animal Health, A Division of Eli Lilly and Company, Greenfield, IN 46140
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Abstract
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One hundred eighty barrows were evaluated to determine the effects of ractopamine hydrochloride (RAC) on lean carcass yields and pork quality. The pens were blocked by weight (six pens per block) with starting block weights of 69.0, 70.7, 73.8, 76.6, 78.4, and 84.3 kg. Pens within a block were assigned randomly to one of three RAC treatments so each treatment in a block was replicated twice. Treatments (as-fed basis) included control diet, 10 ppm of RAC added (R10), and 20 ppm of RAC added (R20) and ranged from 25 to 41 d depending on block. Pigs were slaughtered by blocks when block average live weights were 109 kg. Gain and feed efficiency were improved (P < 0.05) with increasing dietary concentrations of RAC, but feed intake did not differ (P > 0.05). Dressing percentage was higher (P < 0.05) for RAC-treated pigs. Subjective color, firmness, marbling scores, and Minolta L* reflection of the LM were not different (P > 0.05) among treatments. Carcass weights were heavier (P < 0.05) for pigs treated with RAC compared with control pigs and were higher for R20 than for R10. The RAC-fed pigs had greater (P < 0.05) yields (actual and percentage of HCW) of the following Institutional Meat Purchase Specification (IMPS) cuts than control pigs: trimmed, boneless ham (IMPS-402C and IMPS-402G), loin (IMPS-414), sirloin, and Boston butt (IMPS-406A). Pigs treated with RAC had a greater (P < 0.05) percentage of fat-free lean trimmings (IMPS-418) than did control pigs. Pigs treated with the R20 concentration had increased (P < 0.05) water-holding capacity compared with control pigs. Purge loss decreased linearly (P < 0.05) with increasing RAC compared with control for 14-d aged, non-enhanced loins. Warner-Bratzler shear (WBS) force values measured for nonenhanced chops were greater for RAC-treated pigs than for control pigs with a low dose response (P = 0.001). Enhanced chop (salt and phosphate injection) WBS values did not differ (P > 0.05) among dietary treatments. Trained sensory evaluation panel results for tenderness decreased in a low-dose plateau response fashion for nonenhanced chops (P = 0.004). Tenderness of enhanced chops decreased linearly (P = 0.04) with increasing RAC concentrations. No differences (P > 0.05) were found in juiciness or flavor of enhanced or nonenhanced chops. Feeding RAC to late-finishing swine resulted in faster growing, more efficient animals with increased boneless subprimal yields, and it had little effect on pork juiciness and flavor.
Key Words: Carcass Yield • Pork Quality • Ractopamine • Swine
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Introduction
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Ractopamine hydrochloride (RAC; Paylean; Elanco Animal Health, Greenfield, IN) has been shown to increase carcass lean content, as well as the weight and the percentage yield of loins and hams (Stites et al., 1991
; Crome et al., 1996). Ractopamine acts to direct nutrients from fat deposition toward protein deposition.
Stites et al. (1991) reported an increase in the lean content from carcasses of pigs fed RAC, and they also observed that pigs fed RAC had ham and loin yields that were approximately 1% greater than those of the control carcasses. Watkins et al. (1990) observed that pigs fed RAC had an increased percentage of dissected lean, as well as a greater estimated fat-free lean value. Merkel (1988) reported an increase in carcass lean with no adverse effect on meat quality. This alteration produces a carcass that is more desirable in today’s market because it consists of more total pounds of edible product that is leaner and less fat. These improvements could be accomplished without changing the number of animals being produced; however, these studies were all conducted several years ago. The swine industry and genetics have evolved dramatically since these studies were conducted, and swine genetics have undergone intense selection pressure to produce leaner and more efficient animals throughout the last 20 yr.
The current study was conducted to evaluate growth performance, feed efficiency, carcass composition, cutting yields, and meat quality of contemporary finishing swine fed diets containing RAC.
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Materials and Methods
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One hundred eighty barrows (Dekalb EB or EB2 sires x Dekalb 45 or Dekalb 43 dams) were used for this experiment. The study was conducted as a randomized complete block design, with each pen (approximately 5.6 m2) of pigs representing an experimental unit. Pen means were calculated using the individual pig data. Pens of pigs were grouped into six groups; pigs within a group had similar initial BW. The six pens within a group were equally distributed between two rooms, and three RAC treatments were assigned randomly to each set of pens within a room for each weight group. All pigs within a weight group were slaughtered when the group weight averaged approximately 109 kg, and the pigs in all six pens in a block were slaughtered on the same day. The data presented in this paper include data from the six weight groups, which were fed RAC for 25, 27, 32, 34, 39, or 41 d. These weight groups had an average starting BW of approximately 84.3, 78.4, 76.6, 73.8, 70.7, and 69.0 kg, respectively, and were fed to a final weight of approximately 109 kg; thus, the weight blocks were confounded with time on test.
This study was conducted in two periods, a pretreatment acclimation period (Period 1) and the test period (Period 2). During Period 1, all pigs received an 18.5% CP, 1.13% lysine diet with 44 ppm of Tylan (as-fed basis). Before issuing the test diet in Period 2, feeders were emptied of any remaining Period 1 feed. The dietary treatments (as-fed basis) were identified as control (0 mg/kg of RAC), R10 (10 mg/kg of RAC), and R20 (20 mg/kg of RAC). The diet formulation and calculated nutrient composition for Period 2 are shown in Table 1.
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Table 1. Diet formulation and calculated nutrient composition for the ractopamine hydrochloride (RAC) feeding period (Test Period 2)a
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The pigs (individually) and feeders were weighed every 7 d at approximately 0800 during Period 2. On the day of shipping, feeders were removed from pens after pigs were weighed. The pigs were loaded and transported to the University of Illinois Meat Science Laboratory (approximately 282 km) for slaughter the following morning.
At the Meat Science Laboratory, the pigs were kept overnight in two pens with a similar number of pigs for each treatment represented in each pen. Each pen had access to water but not access to feed. At approximately 0700 on the morning after delivery to the University of Illinois, the pigs were slaughtered in random order.
Pigs were slaughtered following humane slaughter guidelines and the Institutional Animal Care and Use protocol. The pigs were weighed just before immobilization via electric stunner. After immobilization, the pigs were exsanguinated, scalded, dehaired, decapitated, eviscerated, split, and placed immediately into a 4°C cooler. The approximate time from stun to cooler was 45 min.
Following processing, HCW was recorded by weighing each side separately. One side from each carcass was used to obtain a 45-min pH with a SFK star probe (SFK Technologies, Cedar Rapids, IA) before the carcass entered the cooler. After being in the cooler for approximately 20 h, an ultimate postmortem pH measure was taken on all carcasses with the SFK star probe. The six carcasses per block were selected randomly for the more extensive pH measures at 1.5, 3.0, 4.5, and 8.0 h in addition to the 45-min and the approximate 20-h pH measures. Chops were cut from each loin, and an ultimate pH was determined by homogenizing 5 g of LM in distilled water and measuring with a bench-top pH meter (Model 720A; Orion Research, Boston, MA). Additional measures collected at approximately 20 h postmortem included typical carcass measures such as carcass length, 10th rib LM area, and 10th rib fat depth as described by the NPPC (1999); objective LM color with a Minolta Chromameter CR-300 (illuminant D65 and 0° observer; Minolta Camera Co., Japan), subjective LM color (NPPC, 1999), and objective ham semi-membranosus color with a Minolta Chromameter CR-300; and marbling (NPPC, 1999), muscle score (NPPC, 1999), muscle firmness (NPPC, 1991), and back fat measures at the first rib, last rib, and last lumbar vertebrae as described by the NPPC (1999). Analyses for moisture (AOAC, 1990), lipid (Novakofski et al., 1989), and protein (AOAC, 1990) were determined on loin chops. Belly measurements were captured 48 h postmortem. Belly flop measurements were taken by balancing the belly (lean up) at approximately the midpoint by suspending it on a rod and measuring the distance from skin to skin.
At 24 h postmortem, one side of each carcass was further processed to trimmed, boneless subprimals, and weights of intermediate cuts were collected. All primal, subprimal and trimming weights represent the weights of the respective cuts from a single side of the carcass. The number associated with the cut description shown in tables is the Institutional Meat Purchase Specification (IMPS, 1996), North American Meat Processors Association (NAMP, 1997) number of the cut most closely associated with actual cut specifications. Primal and subprimal yields expressed as a percentage of HCW were calculated using the equation: % of HCW = ([2 x actual cut weight]/HCW) x 100.
Trimmings were analyzed for lipid and water content. The Canadian back loin, IMPS-414, was weighed, vacuum-packaged, and aged for 14 d. After aging, the loin was weighed to determine percentage purge loss, and chops were collected for Warner-Bratzler shear force determination.
The ribbed side was further processed, and the Canadian back loin (IMPS-414) was collected for additional measures. A portion of the loin was injected to 110% of original weight with a solution of sodium chloride (4% by weight) and phosphate (4% by weight) to result in a finished product that contained 0.36% sodium chloride and 0.36% phosphate (by weight), vacuum-packed, and aged for 14 d (referred to as enhanced loin). After aging, the loin portion was weighed to determine percentage purge loss, and chops were collected for Warner-Bratzler shear force determination.
Additional chops were collected from aged loins (enhanced and nonenhanced) from carcasses of two selected animals per finishing pen. The animals were selected based on BW and health status at the time of slaughter. Sensory panel analysis was conducted on the chops obtained from these selected pigs using six trained panelists for each chop. A 15-cm anchored unstructured line scale was used to evaluate tenderness, juiciness, and off-flavor intensity (0 = extremely tough, extremely dry, extreme off-flavor to 15 = extremely tender, extremely juicy, no off-flavor).
Statistical analyses were conducted using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). The statistical model contained the following effects: room, block within room, treatment, and room x treatment for a total of 15 df. Each variable for sensory evaluation was tested for selected single df contrasts. The contrasts tested included 1) a linear response, 2) a low-dose plateau response in which the treated animals responded similarly but were different from control animals (a 0, +, + type of response for the 0, 10, and 20 mg/kg treatments, respectively), 3) a high dose only response, in which the control and R10-treated pigs responded similarly but were different from the R20-treated pigs (a 0, 0, + type response for 0, R10, and R20 treatments, respectively), and 4) a quadratic response. All contrasts were evaluated, but the contrast that best described the data was presented for sensory data.
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Results and Discussion
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Pig weights and feed efficiency values are presented in Table 2. Pigs fed RAC had heavier (P < 0.05) final farm weights and live slaughter weights than did pigs fed the control diet. Final farm weights and live slaughter weights also were heavier (P < 0.05) for the R20 treatment compared with the R10 treatment. Overall ADG and feed efficiency were increased (P < 0.05) with the inclusion of RAC in the diets compared with control, and for the pigs fed R20 vs. R10. Pigs fed RAC gained weight faster and more efficiently than pigs fed the control diet (P < 0.05). This finding agrees with those of Crenshaw et al. (1987), Watkins et al. (1988), and Crome et al. (1996); however, ADFI did not differ (P > 0.05) among the three treatments, which contradicts the findings of Crenshaw et al. (1987), Watkins et al. (1988), and Crome et al. (1996), who observed a decreased ADFI for pigs fed RAC.
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Table 2. Pig weights and feed efficiency as influenced by dietary ractopamine hydrochloride (RAC) concentration, as-fed basis
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Results of the postmortem pH measurements are presented in Table 3. No differences (P > 0.05) were found across treatments at any of the collection times for postmortem pH. Pigs treated with the R10 treatment had numerically greater pH values at 3, 8, and 24 h postmortem, and R20-treated pigs had numerically higher pH values at all time points. The postmortem pH decline of pigs fed RAC has not been thoroughly investigated, but Aalhus et al. (1990) investigated 40-min and 24-h postmortem pH of the LM and reported that pigs treated with 10 mg/kg of RAC had a lower (P < 0.05) 40-min pH value, and pigs treated with 20 ppm of RAC had a numerically lower 40-min pH value, than control pigs. Results from the present experiment demonstrated that R20-fed pigs had higher (P < 0.05) 45-min pH values compared with R10-fed and control pigs. The R20-fed pigs also had numerically higher pH values at 45 min and at 1.5, 3.0, 4.5, and 8 h postmortem compared with the R10-treated pigs. Ultimate pH values for RAC-treated pigs were numerically higher compared with control pigs, which agrees with the results of Aalhus et al. (1990). Dunshea et al. (1993) also showed numerically greater ultimate pH values for boars and barrows, but numerically lesser values for gilts at 20 mg/kg of RAC. Warriss et al. (1990a, b) observed that feeding the ß-agonist salbutamol produced carcasses with higher ultimate pH, but also greater shear force and fat separation. In the present study, differences (P < 0.05) were noted for loin chop pH; RAC-treated pigs had higher values (Table 3). Stites et al. (1994) reported no differences (P > 0.05), but numerically higher pH, values for loin chops from pigs treated with RAC.
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Table 3. Postmortem pH/time measurements on pork carcasses as influenced by dietary ractopamine (RAC) concentration
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The results from the loin and ham Minolta values are presented in Table 4. No differences were observed in Minolta L* values for the cut LM or for the fresh semimembranosus muscle from the ham (P > 0.05). This finding is in agreement with the results reported by Uttaro et al. (1993). Minolta a* and b* values for the cut LM were less (P < 0.05) for RAC-treated pigs than for control pigs, which also supports the results reported by Uttaro et al. (1993). Semimembranosus Minolta b* values were less (P < 0.05) for RAC-treated pigs than control pigs. Semimembranosus Minolta a* values were less (P < 0.05) for R20-treated pigs than for control pigs. The lower a* values may be due to the shift of intermediate fibers (Type IIa) to white fibers (Type IIb) (McKeith et al., 1988, 1990). Lower a* values indicate lower amounts of oxymyoglobin in the muscle. One possibility for this result could be a dilution effect caused by hypertrophy of the muscle fiber.
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Table 4. Loin and ham Minolta color values as influenced by dietary ractopamine hydrochloride (RAC) concentration
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Standard carcass measurements are presented in Table 5. Carcass muscle scores were increased (P < 0.05) with the inclusion of RAC. Loin muscle area was increased (P < 0.05) with increasing levels of RAC, which agrees with the findings of Stites et al. (1991) and was probably due to muscle fiber hypertrophy as described by Aalhus et al. (1992). There was no effect (P > 0.05) on first rib, last rib, or last lumbar fat measurements. In addition, there was no effect (P > 0.05) on 10th rib back fat, carcass length, subjective marbling score, subjective firmness score, or subjective muscle color, which agrees with the findings of Stites et al. (1991).
Analysis results for moisture, lipid, and protein of the LM are presented in Table 5
. No differences were observed in moisture in any of the treatments. Pigs treated with R10 had a lesser (P < 0.05) percentage of lipid in the LM compared with R20 pigs. Pigs treated with RAC had a greater (P < 0.05) percentage of protein in the LM than control pigs.
The quality of the belly was assessed using a "belly flop" test. No differences (P > 0.05) in the belly flop test were observed among treatments (Table 5).
Results for carcass traits are found in Table 6. The HCW and chilled carcass weights were increased (P < 0.05) with increasing levels of RAC, and dressing percentage was greater (P < 0.05) in the pigs treated with RAC compared with the control pigs. These results agree with those of Crome et al. (1996). Pigs treated with RAC at the R20 level had less cooler shrinkage and less chop drip loss than control pigs (P < 0.05). Leaf fat by weight did not differ (P > 0.05) among treatments; however, leaf fat as a percentage of HCW was less (P < 0.05) for pigs fed RAC at the 20 mg/kg concentration compared with control pigs.
Wholesale cut weights as a percentage of HCW and actual HCW are presented in Table 7. Weights of the wholesale cuts (e.g., ham [IMPS-401], shoulder [IMPS-403], loin [IMPS-410], and spareribs [IMPS-416]), were heavier (P < 0.05) for RAC-fed pigs than for control pigs. Pigs fed RAC had heavier (P < 0.05) bellies (IMPS-408) than control pigs. Pigs fed RAC also had heavier (P < 0.05) trimmed wholesale cuts (e.g., ham [IMPS-410 with collar removed], picnic [IMPS-405], Boston butt [IMPS-406], belly with skin on [IMPS-409B], and loin [IMPS-410]) compared with control pigs (Table 8). Boneless cuts were also heavier (P < 0.05) for RAC-fed pigs compared with control pigs, including boneless ham (IMPS-402C); outside ham (IMPS-402D); inside ham (IMPS-402F); knuckle, boneless picnic (IMPS-405A); picnic cushion (IMPS-405B); boneless Boston butt (IMPS-406A); Canadian back boneless loin (IMPS-414); tenderloin (IMPS-415A); and sirloin (Table 9). The following discussion with regard to cut weights will focus on differences in cut weights as a percentage of HCW.
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Table 7. Wholesale cut weights (kg) and weights as a percentage of HCW as influenced by dietary ractopamine hydrochloride (RAC) concentration
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Table 8. Trimmed wholesale cut weights (kg) and weights as a percentage of HCW as influenced by dietary racto-pamine hydrochloride (RAC) concentrations
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Table 9. Boneless (Bnls.) cut weights (kg) and weights as a percentage of HCW as influenced by dietary ractopamine hydrochloride (RAC) concentration
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The ham (IMPS-401) as percentage of HCW was greater (P < 0.05) for R20-treated pigs compared with control pigs, which agrees with the findings of Crome et al. (1996). No differences (P > 0.05) were found among any treatments with the loin (IMPS-410 skin on), belly (IMPS-408), or shoulder (IMPS-403) as a percentage of HCW or the weight (kilograms) of the neckbones, jowl, rear foot (IMPS-420), and clearplate. These results are inconsistent with those of Crome et al. (1996), who reported that wholesale cut weights generally increased with increasing doses of RAC. Uttaro et al. (1993) also reported an increase in belly weight in RAC-treated pigs.
Trimmed wholesale cut weights as a percentage of HCW are presented in Table 8. The ham (IMPS-401 with collar removed) from pigs fed the R20 treatment was greater (P < 0.001) as a percentage of HCW than the ham from pigs fed the control diet; however, no differences (P > 0.05) were observed for the ham (IMPS-401 with collar removed) as a percentage of HCW between the control and R10 inclusion or between the R10 and the R20 inclusions. These results differ somewhat from those of Stites et al. (1991), Uttaro et al. (1993), and Crome et al. (1996). These previous studies showed an increase in percentage of trimmed ham weight and trimmed loin weight as RAC concentrations increased. In the current study, no differences (P > 0.05) were found among dietary RAC concentrations with respect to the weight as a percentage of the HCW for the loin (IMPS-410), belly (IMPS-409B), or picnic (IMPS-405). Our picnic results are consistent with those of Stites et al. (1991) and Crome et al. (1996). Boston butt (IMPS-406) as a percentage of HCW was increased (P < 0.05) with the inclusion of R10 and R20 compared with the control.
Boneless wholesale cut weights as a percentage of HCW are presented in Table 9. The weight of the loin (IMPS-414) as a percentage of HCW increased (P < 0.05) with the addition of RAC to the diet compared with the control diet, which is consistent with the findings of Crome et al. (1996). Boneless picnic (IMPS-405A) weights as a percentage of the HCW increased numerically with the addition of RAC but were not significant (P > 0.05). There were also no differences (P > 0.05) among any treatments of picnic cushion (IMPS-405B) as a percentage of HCW. Weight of the boneless Boston butt (IMPS-406A) as a percentage of HCW was greater (P < 0.05) for R10 and R20 treatments compared with the control. Boneless ham (IMPS-402C) as a percentage of HCW and three-piece ham (IMPS-402G) as a percentage of HCW increased (P < 0.001) in pigs treated with RAC compared with control pigs.
The chemical analysis of the trim composition is presented in Table 10. No differences (P > 0.05) were found in the trimmings as a percentage of HCW across treatments. Moisture percentage was greater (P < 0.05) for R10 and R20 inclusions of RAC compared with the control and was numerically greater for R20 inclusion compared with R10 inclusion. Lipid percentage of the trim was less (P < 0.05) for the R10 and R20 inclusion compared with the control and was numerically lower for the R20 inclusion compared with R10-treated pigs. These results were expected because RAC-treated pigs exhibit a decrease in fat accretion and an increase in lean accretion (Watkins et al., 1990; Stites et al., 1991; Crome et al., 1996). Trimmings on a fat-free lean basis had higher calculated values (P < 0.05) for pigs fed RAC compared with control pigs.
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Table 10. Pork trim composition, percentage as influenced by dietary ractopamine hydrochloride (RAC) concentration
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Treatment with RAC at the R20 concentration resulted in improved (P < 0.05) water-holding capacity compared with the control (Table 11). Purge decreased linearly (P < 0.05) with RAC treatments for the 14-d aged, nonenhanced loins (Table 11). Aalhus et al. (1990), Dunshea et al. (1993), Uttaro et al. (1993), and Jeremiah et al. (1994) did not report any change in loin drip loss associated with RAC feeding in their experiments.
The amount (grams) of sodium chloride and phosphate solution that was injected into the loins during the enhancement process did not differ among treatments. The purge loss for the enhanced loins increased linearly (P = 0.005) with increasing RAC dose. There were no treatment differences (P > 0.05) in the cooking weight loss in either the enhanced or nonenhanced chops cooked for measuring the Warner-Bratzler shear force value (Table 11). These results agree with those of Jeremiah et al. (1994), who reported no differences in cooking loss in bacon, cured ham, shoulder roast, and loin chop; however, Uttaro et al. (1993) observed that RAC fed at the 20-mg/kg concentration decreased loin cooking loss.
Warner-Bratzler shear force values measured for the nonenhanced chops were greater for R10 and R20 than for control with a low-dose plateau response (P < 0.001). Aalhus et al. (1990) and Uttaro et al. (1993) also found greater (P < 0.05) shear force values in loins that had been treated with RAC; however, Stites et al. (1994) did not detect a difference in shear force values. Treatment means for Warner-Bratzler shear force values for the enhanced chops did not differ among the treatments, but there was a linear increase (P = 0.003) in shear force values of enhanced chops with increasing RAC concentrations. Lonergan et al. (2001) suggested that the selection for lean growth efficiency in pigs creates a decrease in postmortem proteolysis of myofibrillar protein. Decreased postmortem degradation of myofibrillar protein can create pork that is not as tender and, consequently, has increased shear force values. Apple et al. (2004) suggested that high CP levels combined with high lysine levels can lead to decreased tenderness. With this evidence in the literature, it is not surprising that pigs fed RAC tend to exhibit increasing shear force values with increasing concentrations of RAC added to the diet.
Muscle fibers can be classified into red fibers (Type I), intermediate fibers (Type IIa), and white fibers (Type IIb). Aalhus et al. (1992) suggested that pigs fed RAC have a higher percentage of white fibers (Type IIb) and a decreased percentage of intermediate fibers (Type IIa). Increases in the concentration of white fibers typically result in muscle fibers that exhibit larger diameters, which could contribute to pork that has higher shear force values with RAC feeding. Swatland (1984) showed that increased diameters in muscle fibers have been associated with decreased tenderness independent of connective tissue strength or age.
The trained sensory evaluation panel results for tenderness had results similar to the Warner-Bratzler shear force values, in which tenderness scores decreased with RAC in a low-dose plateau response fashion for nonenhanced chops (P = 0.004). The tenderness scores of enhanced chops decreased linearly (P = 0.04) with increasing RAC concentrations. The trained sensory evaluation panel detected no significant treatment differences in juiciness or flavor in either the enhanced or nonenhanced chops, which agrees with the findings of Stites et al. (1994).
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Footnotes
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1 The authors thank L. Engel for assistance in data collection. 
2 Correspondence: 205 Meat Science Lab, 1503 S. Maryland (phone: 217-333-1684; fax: 217-244-5142; e-mail: mckeith{at}uiuc.edu).
Received for publication July 7, 2003.
Accepted for publication August 18, 2005.
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Abstract
Introduction
