Fatty acid profiles and iodine value correlations between 4 carcass fat depots from pigs fed varied combinations of ractopamine and energy

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1 Published December 4, 2014 Fatty acid profiles and iodine value correlations between 4 carcass fat depots from pigs fed varied combinations of ractopamine and B. R. Wiegand,* 1 R. B. Hinson,* 2 M. J. Ritter, S. N. Carr, and G. L. Allee* *Department of Animal Sciences, University of Missouri, Columbia 65211; and Elanco Animal Health, Greenfield, IN ABSTRACT: A total of 54 finishing barrows (initial BW = 99.8 ± 5.1 kg; PIC C22 337) reared in individual pens were allotted to 1 of 6 dietary treatments in a 2 3 factorial arrangement of treatments with 2 levels of ractopamine (0 and 7.4 mg/kg) and 3 levels of dietary (high: 3,537, medium: 3,369, and low: 3,317 kcal/kg of ME) to determine the effects of feeding ractopamine and various dietary levels on the fatty acid profile of 4 carcass fat depots (jowl, belly, subcutaneous loin, and intramuscular) and the predictive relationships of calculated iodine value (IV) between these 4 fat depots. Carcasses were sampled for fat tissues at the anterior tip of the jowl, posterior to the sternum on the belly edge, three-quarters the distance around the LM (subcutaneous fat; SC), and within the LM (intramuscular fat; IMF). Feeding ractopamine diets reduced (P < 0.05) total SFA in SC and IMF and increased (P = 0.04) total MUFA in SC. Also, feeding ractopamine diets increased (P < 0.01) the IV of IMF. Total MUFA of belly fat was reduced (P < 0.05) when the low- diet was fed compared with the high- diet. Jowl fat total MUFA was reduced (P < 0.05) and total PUFA was increased (P < 0.05) when the medium- diet was fed compared with the high- and low- diets. Iodine values, independent of treatment, were 60.97, 64.51, 55.59, and for belly, jowl, IMF, and SC fat depots, respectively. The IV correlations within fat depots were not consistent across dietary treatments because of the effect of treatments on carcass fatty acid characteristics. Feeding ractopamine diets shifted the fatty acid profile from SFA to MUFA in the SC depot. Feeding ractopamine diets did not change belly fat profiles, thus avoiding the potential negative effect of softening belly fat, which is detrimental to processing value. The IV of one fat depot may not be a good indication of IV of other fat depots because of weak correlation coefficients and the apparent influence of dietary treatment. Key words: dietary, fatty acid profile, pork, ractopamine 2011 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas INTRODUCTION Diets containing ractopamine have been shown by numerous researchers to improve ADG and feed efficiency in finishing pigs (Stites et al., 1991; Armstrong et al., 2002; See et al., 2004). Additionally, pigs fed ractopamine diets exhibit decreased subcutaneous fat (SC) and greater lean meat yield. Research has focused on the optimum dietary lysine when ractopamine is included in the last 28 to 30 d of finishing (Apple et al., 2004). This focus seems logical because Lys, if limited, would likely nullify the lean muscle advantage from feeding ractopamine diets because of the limited AA pool for protein accretion. Although some studies 1 Corresponding author: wiegandb@missouri.edu 2 Current address: JBS United, 4310 State Road 38 West, Sheridan, IN Received July 8, Accepted May 19, have evaluated the interaction of dietary and ractopamine, few have studied multiple levels of with ractopamine and the subsequent effect on fat depots other than SC. It is well documented that leaner genetic lines of pigs tend to have leaner bellies, less SC, less intramuscular fat (IMF), and deposit more unsaturated fat compared with fatter pigs (Wood et al., 1985; Correa et al., 2008). This change in degree of fat saturation is explained by a decrease in de novo synthesis of fatty acids (FA) in the leaner pigs. One might reasonably conclude that pigs with the genetic predisposition to be lean that are also fed ractopamine diets might have an added degree of unsaturation in the FA profile of their resulting pork meat products. Therefore, the objective of the current study was to evaluate varied levels of dietary with and without dietary ractopamine and the subsequent effect on FA profiles of jowl fat, belly fat, SC, and IMF in pork. Additionally, we evaluated the variation in FA profile by fat depot and estimated the correlations for iodine value (IV) be- 3580

2 tween the 4 fat depots within treatments to determine the correlation of one fat depot to another. MATERIALS AND METHODS All procedures of this project were in accordance with the guidelines of the University of Missouri Animal Care and Use Committee. Animals and Diet This experiment used carcass fat samples from pigs that were reared in a previous experiment (Hinson et al., 2011). Briefly, 54 finishing barrows (PIC C22 337) were blocked by BW and randomly allotted to treatments in a 2 3 factorial arrangement with 9 replications per treatment. The treatments included 2 levels of ractopamine (0 vs. 7.4 mg/kg; Paylean, Elanco Animal Health, Greenfield, IN) and 3 levels of dietary (average: high, 3,537; medium, 3,369; and low, 3,317 kcal of ME/kg). - diets were corn-soybean-meal based with 4% choice white grease (CWG), low- diets were corn-soybean-meal based with 0.5% CWG, and the low- diets were corn-soybean based with 0.5% CWG and 15% wheat middlings. Pigs were slaughtered after being on test for 21 d (final BW = 123 ± 5 kg) at the University of Missouri Meat Science Laboratory. Pigs were allowed to rest in lairage for a minimum of 1.5 h before being slaughtered by procedures described by Hinson et al. (2011). Fat Sample Collection Fat tissues were removed at the anterior tip of the jowl, posterior to the sternum on the belly edge, threequarters the distance around the LM (SC), and within the LM (IMF). Sample size was approximately 1 cm 2. Fat samples were collected after 24 h of carcass chill, placed in sample bags, and frozen at 20 C until they were pulverized, extracted, and prepared for FA profile determination by gas chromatography. FA Analysis Lipids were extracted from whole muscle samples using a chloroform/methanol method. One-gram muscle samples were placed in 50-mL glass tubes, and 5 ml of CHCl 3 :CH 3 OH was added (vol/vol). Samples were homogenized using a homogenizer (Tissue Tearor, Biospec Products Inc., Bartlesville, OK) on medium setting for 30 s. The probe was rinsed with CHCl 3 :CH 3 OH until 15 ml of total solution was in the glass tube. Samples were allowed to extract for 30 min. Homogenates were filtered through a sintered glass filter funnel into a 50- ml glass tube. The original sample tube was rinsed with CHCl 3 :CH 3 OH and the second tube brought to 30 ml. Eight milliliters of 0.74% KCl was added to each tube and vortexed for 1 min. After 2 h of 2 distinct Ractopamine and on fatty acid profiles phases, the top phase was removed with a glass pipette. The lower phase was transferred to a 20-mL glass tube and evaporated with N (Meyer N-Evap, Organomation Assoc. Inc., Berlin, MA). Dried samples were saponified using 1 ml of 0.5% N KOH in MeOH and heated in 70 C water bath for 10 min. Then 1 ml of 14% BF 3 in MeOH was added and samples were flushed with N 2, capped, and placed in 70 C water bath for 30 min. After cooling, 2 ml of HPLC grade hexane and 2 ml of saturated NaCl were added to each tube and vortexed for 1 min. The upper layer of sample was transferred to a 20-mL tube with 800 mg of Na 2 SO 4 to remove any moisture. Two milliliters of hexane with saturated NaCl was added to each tube and vortexed briefly. Fluid samples were pipetted into scintillation vials and evaporated completely (Meyer N-Evap, Organomation Assoc. Inc.). Samples were reconstituted with hexane to obtain 50-mg/mL samples. Samples (400 µl) were transferred to auto-sampler vials containing 1.6 ml of HPLC grade hexane. Fatty acid methyl esters were analyzed by using a gas chromatograph (Varian 430- GC, Varian, Palo Alto, CA) and a fused silica capillary column (SP-2560, 100 m 0.25 mm 0.2 µm film thickness; Supelco, Bellefonte, PA). The temperature of the injector and of the flame-ionization detector was held constant at 240 and 260 C, respectively. Helium was used as the carrier gas at a constant pressure of 2.60 kg/cm 2, and the oven was operated at 140 C for 5 min (programmed temperature to increase 2.5 C/min up to 240 C and then held constant for 16 min). Fatty acids were normalized, which means that the area of each peak was represented as a percentage of the total area. Iodine values were calculated utilizing the following equation (AOCS, 1998): IV = (0.95 C16:1) + (0.86 C18:1n-9) + (1.732 C18:2n-6) + (2.616 C18:3n-3) + (0.785 C20:1). Statistical Analysis This experiment consisted of a 2 (0 or 7.4 mg/kg of ractopamine) 3 (high, medium, and low ) factorial arrangement of treatments in a randomized complete block design, with individual carcasses serving as the experimental unit. Statistical analysis was performed for all measurements using GLM procedure (SAS Inst. Inc., Cary, NC). The model consisted of fixed effects for ractopamine level, level, replication, and ractopamine interactions. During the live phase (Hinson et al., 2011), final BW was affected by the dietary treatments. Therefore, final BW was used as a covariate in all analyses. The CORR procedure of SAS was used to estimate correlations among fat depots within each treatment for calculated IV. RESULTS 3581 Statistical analysis indicated an interactive effect between dietary level and inclusion of ractopamine

3 3582 Wiegand et al. Table 1. Interactive effects of ractopamine and program on the fatty acid (FA) composition of belly fat 1 SEM Ractopamine Energy R E 3 Total SFA Total MUFA Total PUFA Total n-3 FA Total n-6 FA n-6:n PUFA:SFA C16: C18:1n C18:2n C18:3n C20: Iodine value R E = ractopamine. for certain aspects of the FA profile of belly fat (Table 1). The total PUFA decreased in the high + ractopamine treatment compared with all other treatment groups (ractopamine, P = 0.031). Also, regarding belly samples, calculated IV was least for the high + ractopamine diet and greatest for the high without ractopamine diet with values of and 62.08, respectively (ractopamine, P = 0.047). The feeding of the ractopamine diets did not affect (P > 0.163) any of the FA concentrations in the belly fat. Additionally, calculated belly fat IV did not differ (P = 0.468) between the 0 and 7.4 mg/kg of ractopamine treatments with 61.4 and 60.8, respectively. Calculated belly fat IV were unaffected (P = 0.633) by the level of the diet. Analysis of jowl fat (Table 2) indicated a ractopamine interaction for total SFA (P = 0.036). When 0 mg/kg of ractopamine diets were fed, total SFA was reduced in the medium- diets. However, when the 7.4 mg/kg of ractopamine diets were fed, total SFA was reduced in the low- diets, whereas the medium diets remained constant. The feeding of the ractopamine diets did not affect (P = 0.054) any of the FA concentrations in the jowl fat. Additionally, calculated jowl fat IV did not differ (P = 0.990) between the 0 and 7.4 mg/kg of ractopamine treatments with 64.5 and 64.5, respectively. Total MUFA (51.5, 45.0, and 51.7 for high-, medium-, and low- diets, respectively) was reduced (P < 0.01), whereas total PUFA (15.5, 24.5, and 16.2 for high-, medium-, and low- diets, respectively), total n-3 (0.80, 1.30, and 0.87 for high-, medium-, and low- diets, respectively), and total n-6 (14.3, 21.1, and 14.6 for high-, medium-, and low diets, respectively) were increased (P < 0.05) in the medium- diets compared with the high- and low- diets regardless of ractopamine inclusion. Additionally, there was a tendency (P = 0.056) for IV values to be increased by the feeding of the medium diets, regardless of ractopamine inclusion. Subcutaneous fat (Table 3) tended to have less total SFA for the low- diets without ractopamine and decreased values for the high- + ractopamine diets (ractopamine, P = 0.055). Feeding ractopamine reduced total SFA (36.4 vs. 39.9). However, feeding ractopamine increased total MUFA (49.0 vs. 46.6; P = 0.047) when compared with the 0 mg/kg of ractopamine diets. Energy level of the diet had no effect (P > 0.053) on FA concentrations. The feeding of ractopamine did not affect (P > 0.096) total SFA, MUFA, PUFA, or IV in the IMF (Table 4). Similarly, feeding of diets with various levels had no effect (P > 0.115) on any of the FA or IV. Correlations of IV among fat depots, within treatments, indicated relatively weak associations (Table 5). Within the high- without ractopamine treatment, jowl fat was negatively correlated to belly fat ( 0.67; P = 0.05) and IMF ( 0.74; P = 0.023). Within the medium- without ractopamine treatment, IMF was positively correlated to belly fat (0.67; P = 0.047). Within the high- with 7.4 mg/kg of ractopamine treatment, SC fat was highly correlated to IMF at 0.93 (P < 0.001). DISCUSSION Feeding ractopamine diets typically results in leaner carcasses (See et al., 2004); thus, one might expect the degree of fat saturation to decrease. Leaner carcasses would be expected to have more unsaturated fat because of less de novo synthesis of SFA (Wood et al., 1985; Correa et al., 2008). However, these shifts in saturation are likely fat depot specific or fat layer specific

4 Ractopamine and on fatty acid profiles Table 2. Interactive effects of ractopamine and program on the fatty acid (FA) composition of jowl fat SEM Ractopamine Energy R E 3 Total SFA Total MUFA Total PUFA Total n-3 FA Total n-6 FA n-6:n PUFA:SFA C16: C18:1n C18:2n C18:3n C20: Iodine value R E = ractopamine. in porcine tissue (Sink et al., 1964; Apple et al., 2009). Additionally, Apple et al. (2004) showed that a high density of the diet (3.48 Mcal of ME/kg) resulted in fatter pigs when pigs were fed ractopamine diets, but the study also suggested that Lys:ME is more important to carcass leanness than density alone. If this is true, then the medium- level (3,369 kcal of ME/kg) in the current study was optimum, and it is likely that feeding the high level of (3,537 kcal/ kg of ME) did not make ractopamine more efficient as a repartitioning agent. Furthermore, the addition of CWG to increase dietary density would be expected to increase (in comparison with oils as sources) the degree of saturation in the fat profile of pork (Bee et al., 2002); however, in this study, the shift only occurred in the high- (4% added CWG) + ractopamine treatment and not in the high- (4% added CWG) without ractopamine treatment for belly fat samples. Composite fat deposition, with respect to muscle, bone, or water content, or all of those, is fairly well modeled in the pig from birth to market weight and beyond (McMeeken, 1940; Shields et al., 1983). One would expect fat to accumulate with an increasing quadratic pattern with a subsequent decreasing quadratic response to muscle mass sometime in the late grower Table 3. Interactive effects of ractopamine and program on the fatty acid (FA) composition of subcutaneous fat 1 SEM Ractopamine Energy R E 3 Total SFA Total MUFA Total PUFA Total n-3 FA Total n-6 FA n-6:n PUFA:SFA C16: C18:1n C18:2n C18:3n C20: Iodine value R E = ractopamine.

5 3584 Wiegand et al. Table 4. Interactive effects of ractopamine and program on the fatty acid (FA) composition of intramuscular fat 1 SEM Ractopamine Energy R E 3 Total SFA Total MUFA Total PUFA Total n-3 FA Total n-6 FA n-6:n PUFA:SFA C16: C18:1n C18:2n C18:3n < C20: Iodine value R E = ractopamine. Table 5. Correlations of iodine value among 4 pork fat depots within each dietary treatment combination 1 2 Belly IMF 3 Jowl SC 3 0 mg/kg of ractopamine, 4 high IMF 0.42 (0.266) 1.00 Jowl 0.67 (0.050) 0.74 (0.023) 1.00 SC 0.07 (0.859) 0.08 (0.848) 0.06 (0.869) mg/kg of ractopamine, medium IMF 0.67 (0.047) 1.00 Jowl 0.12 (0.764) 0.04 (0.915) 1.00 SC 0.08 (0.837) 0.14 (0.710) 0.07 (0.867) mg/kg of ractopamine, low IMF 0.31 (0.448) 1.00 Jowl 0.29 (0.526) 0.25 (0.549) 1.00 SC 0.44 (0.277) 0.05 (0.903) 0.06 (0.888) mg/kg of ractopamine, high IMF 0.18 (0.674) 1.00 Jowl 0.20 (0.637) 0.59 (0.123) 1.00 SC 0.08 (0.845) 0.93 (0.001) 0.46 (0.255) mg/kg of ractopamine, medium IMF 0.53 (0.139) 1.00 Jowl 0.50 (0.170) 0.24 (0.533) 1.00 SC 0.24 (0.535) 0.04 (0.915) 0.17 (0.661) mg/kg of ractopamine, low IMF 0.42 (0.256) 1.00 Jowl 0.07 (0.849) 0.24 (0.527) 1.00 SC 0.47 (0.199) 0.25 (0.509) 0.48 (0.194) Data are based on 9 samples/(fat depot treatment); value in the parentheses =. 2 Energy levels (average): high = 3,537; medium = 3,369; and low = 3,317 kcal of ME/kg. 3 IMF = intramuscular fat; SC = subcutaneous fat. 4 Ractopamine (Elanco Animal Health, Greenfield, IN).

6 to early finishing phase of the life of the pig (Shields et al., 1983). The timing of body composition shifts is driven by multiple factors related to plane of nutrition and genetic predisposition. One aspect of fat metabolism in pigs that is often overlooked is the variation contributed by early fetal programming and the subsequent growth pattern of pigs. Reports in the literature indicate that fat deposition in porcine muscle is largely influenced by birth weight of the pig and the lightest birth-weight pig in the litter will deposit more lipid in muscle tissue compared with the heaviest birth weight pig in the litter (Gondret et al., 2005; Karunaratne et al., 2005). However, more important to the current discussion on total fat deposition is the profile of that fat because this can influence processing and oxidative stability of stored pork meat. Variation in FA profiles between fat deposition sites (muscle groups) is expected in a pork carcass (Kim et al., 2008). Bragagnolo and Rodriguez-Amaya (2002) reported a greater concentration of palmitic and stearic acids in pork loin compared with fresh ham with 801 vs. 525 mg/100 g and 310 vs. 209 mg/100 g for palmitic and stearic acids, respectively. Rhee (1992) reported a PUFA:SFA of 0.30 for lean from pork, whereas Hernandez et al. (1998) reported PUFA:SFA of 0.55 and 0.56 for LM and triceps brachii, respectively. As rapid methods of fat quality evaluation are developed in the pork packing industry, it seems prudent to look at predictive relationships of various fat depots because areas that are easier to measure in a plant setting would be more advantageous. The correlation of practical significance is the relationship between jowl and belly fat. Because handheld instrumentation or incooler sampling is employed, it seems logical to sample the jowl, which is valued less and could be easily accessed or even invasively sampled at little cost. If fat profiles are similar between carcass fat depots, this in turn could predict other wholesale cuts such as pork bellies that rely heavily on determination of fat quality (Hadorn et al., 2008). However, in the current data set, the relationship between jowl and belly fat seem to be weak, regardless of dietary treatment. Our original hypothesis was that jowl and belly fat profiles would be similar, resulting in similar calculated IV and a strong correlation between the two. One possible explanation for the resulting weak relationship might be related to the varied physiological maturity of pigs at similar market weights (Gondret et al., 2005; Karunaratne et al., 2005). Hammond (1932) characterized fattening patterns of food animals to be from the distal ends and toward the visceral cavity. These patterns would indicate that finishing pigs would likely deposit fat earlier in the jowl and over the front shoulder before deposition of fat in the loin and belly region. If pigs are slaughtered at similar market weights, but differing maturities, it seems logical that the total fat content and FA profiles would differ by fat depot. Therefore, pigs that are closer to their physiological maturity at market weight Ractopamine and on fatty acid profiles could be expected to have fat profiles that are more similar when compared with pigs that are still accumulating muscle at a rapid rate vs. fat tissue. Furthermore, Berg and Walters (1983) indicated that fat distribution is likely driven by physical resistance or ease of fat accumulation. For example, they surmised that visceral fat accumulates more easily than IMF between skeletal muscles simply because of less resistance. However, Berg and Walters (1983) also pointed out that fat partitioning (type of fat deposited) is more likely controlled by genetic predisposition and environmental factors. Therefore, pigs that are lean in the loin region, by genetic predisposition or by nutritional interventions such as ractopamine (Apple et al., 2004; See et al., 2004), would be expected to have altered fat partitioning, thus altering the FA profile of specific regions within the pork carcass. Many of the examples used to describe differences between the various fat depots also help to explain why correlation values differed among dietary treatments. The dietary inclusion of ractopamine and the feeding diets with various levels affected growth performance and carcass leanness in the live portion of this trial (Hinson et al., 2011). These changes in growth and carcass composition, along with resulting changes in de novo fat synthesis, fat deposition patterns, and physiological maturity, would help to explain why IV correlations between fat depots varied among dietary treatments (Bee et al., 2002; Apple et al., 2004; Gondret et al., 2005). LITERATURE CITED 3585 AOCS Official Methods and Recommended Practices of the AOCS. 5th ed. Am. Oil Chem. Soc., Champaign, IL. Apple, J. K., C. V. Maxwell, D. C. Brown, K. G. Friesen, R. E. Musser, Z. B. Johnson, and T. A. Armstrong Effects of dietary lysine and density on performance and carcass characteristics of finishing pigs fed ractopamine. J. Anim. Sci. 82: Apple, J. K., C. V. Maxwell, D. L. Galloway, C. R. Hamilton, and J. W. S. Yancey Interactive effects of dietary fat source and slaughter weight in growing-finishing swine: II. Fatty acid composition of subcutaneous fat. J. Anim. Sci. 87: Armstrong, T. A., D. J. Ivers, J. R. Wagner, D. B. Anderson, D. J. Jones, W. C. Weldon, K. R. Maddock, and E. P. Berg The effect of ractopamine dose and duration of feeding on growth performance and carcass characteristics of finishing pigs. J. Anim. Sci. 80(Suppl. 1):219. (Abstr.) Bee, G., S. Gebert, and R. Messikommer Effect of dietary supply and fat source on the fatty acid pattern of adipose and lean tissues and lipogenesis in the pig. J. Anim. Sci. 80: Berg, R. T., and L. E. Walters The meat animal: Changes and challenges. J. Anim. Sci. 57(Suppl. 2): Bragagnolo, N., and D. B. Rodriguez-Amaya Simultaneous determination of total lipid, cholesterol and fatty acids in meat and backfat of suckling and adult pigs. Food Chem. 79: Correa, J. A., C. Gariepy, M. Marcoux, and L. Faucitano Effects of growth rate, sex and slaughter weight on fat characteristics of pork bellies. Meat Sci. 80:

7 3586 Wiegand et al. Gondret, F., L. Lefaucheur, I. Louveau, and B. Lebret The long-term influences of birth weight on muscle characteristics and eating meat quality in pigs individually reared and fed during fattening. Arch. Tierz. Dummerstorf 48: Hadorn, R., P. Eberhard, D. Guggisberg, P. Piccinali, and H. Schlich therle-cerny Effect of fat score on the quality of various meat products. Meat Sci. 80: Hammond, J Growth and Development of Mutton Qualities in the Sheep. Oliver and Boyd, Edinburgh, UK. Hernandez, P., J. L. Navarro, and F. Fodra Lipid composition and lipolytic enzyme activities in porcine skeletal muscles with different oxidative pattern. Meat Sci. 49:1 10. Hinson, R. B., B. R. Wiegand, M. J. Ritter, G. L. Allee, and S. N. Carr Impact of dietary level and ractopamine on growth performance, carcass characteristics, and meat quality of finishing pigs. J. Anim. Sci. 89: Karunaratne, J. F., C. J. Ashton, and N. C. Stickland Fetal programming of fat and collagen in porcine skeletal muscles. J. Anat. 207: Kim, J. H., P. N. Seong, S. H. Cho, B. Y. Park, K. H. Hah, L. H. Yu, D. G. Lim, I. H. Hwang, D. H. Kim, J. M. Lee, and C. N. Ahn Characterization of nutritional value for twenty-one pork muscles. Asian-australas. J. Anim. Sci. 21: McMeeken, C. P Growth and development in the pig with special reference to carcass quality characters. I, II, III. J. Agric. Sci. (Camb.) 30: Rhee, K. S Fatty acids in meats and meat products. Pages in Fatty Acids in Foods and Their Health Implications. C. K. Chow, ed. Marcel Dekkar, New York, NY. See, M. T., T. A. Armstrong, and W. C. Weldon Effect of a ractopamine feeding program on growth performance and carcass composition in finishing pigs. J. Anim. Sci. 82: Shields, R. G., Jr., D. C. Mahan, and P. L. Graham Changes in swine body composition from birth to 145 kg. J. Anim. Sci. 57: Sink, J. D., J. L. Watkins, J. H. Ziegler, and R. C. Miller Analysis of fat deposition in swine by gas-liquid chromatography. J. Anim. Sci. 23: Stites, C. R., F. K. McKeith, S. D. Singh, P. J. Bechtel, D. H. Mowrey, and D. J. Jones The effect of ractopamine hydrochloride on the carcass cutting yields of finishing swine. J. Anim. Sci. 69: Wood, J. D., R. C. D. Jones, J. A. Bayntum, and E. Dransfield Backfat quality in boars and barrows at 90 kg live weight. Anim. Prod. 40: