Conjugated linoleic acid improves feed efficiency, decreases subcutaneous fat, and improves certain aspects of meat quality in Stress-Genotype pigs 1

Conjugated linoleic acid improves feed efficiency, decreases subcutaneous fat, and improves certain aspects of meat quality in Stress-Genotype pigs 1 B. R. Wiegand, F. C. Parrish, Jr. 2, J. E. Swan, S. T. Larsen, and T. J. Baas 215 Meat Laboratory, Iowa State University, Ames 50011 ABSTRACT: Conjugated linoleic acid (CLA) was supplemented to crossbred growing-finishing barrows (n = 60) at 0.75% of the total diet. Pigs were randomly assigned to the CLA or control diets based on stress genotype (negative, carrier, or positive). Gain:feed was higher for CLA diet animals (350 g/kg feed) than for control diet animals (330 g/kg feed) independent of genotype (P < 0.05). No differences were observed for ADG for the diets (P = 0.71) or genotype classes (P = 0.40). Postmortem ph was lower (P < 0.01) by 3 h for CLAsupplemented pigs, with no differences in ultimate ph. No differences (P = 0.16) were observed for ultimate ph between the three genotypes. Conjugated linoleic acidsupplemented pigs exhibited less 10th rib fat depth (2.34 cm vs 2.84 cm) and last rib fat depth (2.46 cm vs 2.72 cm) than control pigs (P < 0.05). Loin muscle area (LMA) was not affected (P = 0.18) by CLA supplementation, but LMA was different (P < 0.02) for genotype; positive genotype carcasses had the largest LMA (45.02 cm 2 ) and negative carcasses had the smallest LMA (36.44 cm 2 ). Carrier carcasses were intermediate for LMA (40.76 cm 2 ). Subjective scores for color were not affected (P = 0.98) by CLA but color was different (P < 0.01), with scores of 1.50, 2.40, and 3.1 for positive, carrier, and negative genotypes, respectively. Subjective marbling scores were increased (P < 0.03) in all genotypes with CLA supplementation. Subjective firmness scores were higher (P < 0.06) for CLA-supplemented pigs and were highly correlated (0.89) to marbling scores. The L* values were higher (P < 0.01) for stress-positive pigs at 24 h postmortem. Also, L* values were higher (P < 0.01) for CLA-fed pigs over 7 d of shelf storage. Sensory characteristics were not different with CLA supplementation for tenderness (P = 0.24), juiciness (P = 0.35), or flavor intensity (P = 0.14). This study showed that LMA was increased with stress-carrier and stress-positive genotypes, but lean color was negatively affected with the presence of the stress gene. Conjugated linoleic acid supplementation improves feed efficiency, decreases backfat, and improves pork quality attributes of marbling and firmness of the longissimus muscle. Furthermore, there is seemingly no interaction between the stress-genotype status of pigs and the subsequent effect of CLA on their growth and performance. Key Words: Linoleic Acid, Meat Quality, Pigs 2001 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2001. 79:2187 2195 Introduction Currently, our research has focused on improving growth, compositional, and quality characteristics of pigs by feeding conjugated linoleic acid in the growingfinishing diet. In an effort to find a model for pork quality problems, we chose to work with a herd of known 1 Journal Paper No. J-18875 of the Iowa Agric. and Home Econ. Exp. Sta., Ames, Iowa, Project No. 3386, and supported by Hatch Act and State of Iowa funds and in part by grants from Conlinco, Inc., Detroit Lakes, MN and the National Pork Producers Council, Des Moines, IA. The authors wish to thank the Bilsland Breeding Farm, Madrid, IA and the Iowa State Univ. Meat Laboratory for their help in this research. 2 Correspondence: phone: 515 294-3280; fax: 515 294-5066; E-mail: fparrish@iastate.edu. Received June 1, 2000. Accepted April 25, 2001. stress-genotype pigs. The stress gene has been a source of pork meat quality problems for many years (Louis et al., 1993). This population of pigs, including genotypes that are negative, carriers, and positive for the stress gene, has proven to be a good source of pale, soft, and exudative (PSE) pork and has allowed us to pursue methods for understanding and possibly overcoming pork quality problems. It is true that the stress gene is being selected against in most swine operations in the United States. Pale, soft, and exudative pork, however, is a problem that occurs in stress-gene-free swine herds, and understanding methods for decreasing its incidence certainly holds merit in today s industry. Based on previous research (Park et al., 1999a; Sparks et al., 1999; Wiegand et al., 1999), we hypothesized that conjugated linoleic acid (CLA) fed at 0.75% in the diet would improve feed efficiency, decrease backfat depth, and improve pork quality characteristics of stress-genotype pigs. Consequently, our objective in this study was 2187

2188 Wiegand et al. Table 1. Diet composition and calculated chemical composition at different body weights (as-fed basis) Body weight range, kg Item 40 to 61 61 to 86 86 to 106 Ingredient, % Corn 68.76 83.47 85.01 Soybean meal 27.38 12.99 11.76 Dicalcium phosphate 1.24 0.82 0.57 Calcium carbonate 0.82 0.77 0.77 Salt 0.25 0.25 0.25 Vitamin premix a 0.20 0.20 0.20 Trace mineral premix b 0.05 0.05 0.05 Tylan 40 0.05 0.05 0.05 Lysine HCl 0.00 0.15 0.09 Oil c 1.25 1.25 1.25 Calculated chemical composition ME, kcal/kg 3,369 3,382 3,395 Lysine, % 1.00 0.73 0.65 Calcium, % 0.70 0.58 0.50 Phosphorus, % 0.60 0.47 0.42 a At 0.2% of diet contributes per kilogram of diet: 4,400 IU vitamin A, 1,100 IU vitamin D 3 ; 6.6 mg riboflavin, 17.6 mg pantothenic acid, 33 mg niacin, and 22 g vitamin B 12. b At 0.05% of the diet contributes in ppm: 75 Zn, 87.5 Fe, 30 Mn, 8.75 Cu, and 0.1 I. c Soybean oil or CLA oil in their respective treatment. to measure growth, carcass, and meat quality characteristics in stress-genotype pigs supplemented with 0.75% CLA in the growing-finishing diet. Materials and Methods All procedures of this project were in accordance with the guidelines of the Iowa State University Animal Care and Use Committee. Crossbred growing-finishing barrows (n = 60) were penned in pairs according to DNAtested stress genotypes (negative, carrier, or positive) and diet (control or 0.75% of CLA from a commercially available CLA-containing oil, CLA-60 [Conlinco, Detroit Lakes, MN]). CLA-60 contains 60% CLA isomers in the oil and therefore 1.25% oil is needed to achieve 0.75% CLA in the diet. Pigs were randomly assigned to the appropriate experimental diet, the composition of which is shown in Table 1. Pigs started the feeding trial at an average weight of 40 ± 4.6 kg and were slaughtered at an average weight of 106 ± 7.1 kg. Body weights were recorded every 2 wk to monitor ADG and to adjust protein percentage in the diet. Due to varying growth rates, pigs were slaughtered in four groups over a 30-d period at the Iowa State University Meat Laboratory. Postslaughter Carcass and Quality Measurements Temperature and ph decline in the longissimus muscle (10th and 11th rib) was monitored every hour beginning at exsanguination and continuing for 24 h postmortem. Temperature was measured with a 10-cm steel probe attached to an electro-therm TM99A digital thermometer (Middlefield, CT). A ph-star probe (SFK Technology, Cedar Rapids, IA) was used to measure ph decline. Hot carcass weights and 24-h chilled carcass weights were recorded to calculate dressing percentages and 24-h cooler shrinkage percentages. The left side was ribbed between the 10th and 11th rib and loineye area, 10th rib fat depth and color, marbling, and firmness values were recorded (NPPC, 1991). Additionally, first rib fat depth, last rib fat depth, and ham muscling score were recorded. Postfabrication Meat Quality Procedures At 24 h postmortem, carcasses were fabricated into primal cuts and the right-side bone-in loin was removed. The loin was deboned and 2.54-cm chops were removed for proximate analysis, Hunter Lab color L*, a*, and b* values (Hunter Associates, Reston, VA), and sensory panel and myoglobin determination. The remaining boneless loin section was vacuum-packaged and stored at 3 C for 21 d. At 21 d of cold storage, the loin section was sliced into 2.54-cm chops and placed on styrofoam trays with polyvinyl chloride overwrap for 1,2,3,and 7 d in a retail self-service display case at 4 C. Hunter color measurements were taken at each day of retail storage. Lipid and moisture percentages were determined using hexane extraction methods and weight differences after sample vacuum drying at 80 C, respectively (AOAC, 1990). Total myoglobin content of loin chops was determined by pulverizing a 10-g meat sample in liquid nitrogen and adding 100 ml of cold 40 mm potassium phosphate buffer (ph 6.80). The sample was blended in a Waring blender for 2 min and incubated at 4 C for 1 h. Samples were then centrifuged at 15,000 g for 30 min. The supernate was filtered through a Whatman number 1, 125-mm paper and 3 ml was transferred to a disposable cuvette. Samples were scanned from 300 to 700 nm on a Beckman DU 640 spectrophotometer (Fullerton, CA). Total myoglobin was calculated from the absorbance at 418 nm, which represents myoglobin in the oxymyoglobin state (M. E. Hunt, Kansas State Univ., personal communication). Sensory evaluation was determined by a 10-member panel. Panelists evaluated 1-cm 2 samples of loin chops that were cooked in a General Electric broiler set at 176 C. Chops were turned once when they reached an internal temperature of 35 C and cooked to a final internal temperature of 71 C. Panelists evaluated samples for tenderness, juiciness, and flavor intensity based on an 8-point descriptive scale (AMSA, 1995). Statistical Analysis Statistical analysis of the data included a completely randomized design with a 3 2 factorial arrangement of three genotypes and two diets. Analysis of variance was performed with the General Linear Model (GLM)

Conjugated linoleic acid and pork 2189 Table 2. Gain:feed (G:F) ratio and average daily gain (ADG) from three stress genotypes of pigs fed a control or conjugated linoleic acid (CLA)-supplemented diet a Genotype Item and diet Negative Carrier Positive SEM b P-value c G:F, g/kg Control 318 340 331 4.1 D < 0.05 G = 0.08 D G = 0.65 CLA 331 350 368 ADG, kg/d Control 0.88 0.94 0.87 0.06 D = 0.40 G = 0.71 D G = 0.98 CLA 0.90 0.95 0.89 a Values are for five pens with two pigs per pen. b SEM = standard error. c D = dietary effect; G = genotype effect; D G = interaction between diet and genotype. procedure of SAS (SAS Inst. Inc., Cary, NC). The following model was fitted for main effects (diet and genotype) and interactions: Y ij = + G i + D j + GD ij + e ij ; where Y ij is the dependent variable, = the overall mean, G i = the I th genotype effect, D j = the j th diet effect, GD ij = the interaction between genotypes and diet, and e ij = residual error. Data are presented as least squares means and comparisons of genotype and diet means were performed with least significant difference. Means were considered different at P < 0.05. Additionally, color, ph, and temperature data were analyzed with repeated measures over day of retail storage and hours of postmortem chilling, respectively. Results and Discussion Gain:feed ratio (G:F) and ADG data are shown in Table 2. Gain:feed ratio was higher (P < 0.05) for CLAfed animals (350 g/kg) than for control animals (330 g/ kg), independent of genotype. Chin et al. (1994) reported improvement in feed efficiency for rats fed CLA. They attributed these changes to the ability of CLA to regulate energy metabolism and nutrient partitioning. The authors speculated that if body fat were decreased by CLA supplementation, then less energy would be required to maintain animal growth, thus making them more efficient. Park et al. (1997) subsequently verified these findings in a similar mouse study. It seems possible that these same mechanisms are responsible of the feed efficiency improvement observed in pig models. No differences were observed in our study between the three stress genotypes for G:F. Furthermore, G:F was similar between controls and CLA-fed pigs at each of the three phases of the finishing diet, regardless of genotype. Also, no differences were observed for ADG in the diet or genotype classes. Similar results for G:F and ADG have been shown with CLA supplementation (Sparks et al., 1999). Figure 1 illustrates ph decline from 30 min to 24 h postmortem in the longissimus muscle at the 10th and 11th rib junction for each of the three stress genotypes (n = 60). The rate of decline was much steeper for carrier and negative genotype carcasses than for the positive genotype. At 30 min postmortem, ph was lower (P < 0.05) for the stress-positive pigs than for the carrier and negative genotypes. By 2 h postmortem, ph values for carrier and negative carcasses were higher (P < 0.01) than those for positive genotype carcasses. There were no differences (P = 0.16) between the three genotypes for ph at 24 h postmortem (ultimate ph). When the ph data were analyzed by diet (Figure 2), we found that at 3 h postmortem the carcasses from CLA-fed pigs exhibited lower (P < 0.01) ph values, but no differences Figure 1. The ph decline of loin muscle at the 10th and 11th rib for three stress genotypes. Values are means for 20 pigs per genotype. a,b Means within a time period without a common superscript letter differ (P < 0.05). c,d Means within a time period without a common superscript letter differ (P < 0.01).

2190 Wiegand et al. Figure 2. The ph decline in loin muscle at the 10th and 11th rib by experimental diet. Values are means for 30 pigs per dietary treatment. a,b Means within a time period without a common superscript letter differ (P < 0.01). (P = 0.17) were observed between diets for ultimate ph. Also, within the stress-negative genotype (Figure 3), ph values were lower (P < 0.02) at 3 h postmortem for carcasses from CLA-fed pigs thanf or control-diet carcasses. There were no differences (P = 0.18) for ultimate ph with the negative genotype. These findings suggest that the rapid ph decline in the CLA-fed pigs may have been linked to glycogen utilization. One might hypothesize that if pigs had greater feed conversion (energy utilization), then perhaps they were able to store more glycogen than the control-diet pigs. This extra glycogen presumably would have been available for postmortem muscle glycolysis (Maribo et al., 1999). This increased energy reserve could drive the production of lactic acid at a greater rate because more substrate is available. However, Dugan et al. (1999) did not show a more rapid ph decline or an accumulation of glycogen due to CLA supplementation. The differences between the Dugan et al. (1999) study and ours may be related to the genetics of the pigs, but a direct comparison of the two experiments is not possible. It is interesting to note that the correlation between 30-min ph and ultimate (24-h) ph was 0.16 (Table 3). This is a rather weak relationship, indicating that ultimate ph is a poor predictor of rate of ph decline. This becomes important in that the rate of ph decline may Figure 3. The ph decline in loin muscle at the 10th and 11th rib for stress-gene-negative pigs by experimental diet. Values are means for 10 pigs per dietary treatment. a,b Means within a time period without a common superscript letter differ (P < 0.05). be more important in pork quality prediction than ultimate ph. One might hypothesize that a fast rate of decline causing acidic conditions in combination with high muscle temperature during early postmortem may cause denaturation of proteins (Bendall, 1973), namely myoglobin, which is largely responsible for meat color (Renerre, 1999). These observations suggest that a measure of ph at 30 or 45 min and at 24 h postmortem would be useful in predicting pork quality given that a fast rate of decline and(or) a low ultimate ph can be responsible for PSE conditions (Bendall and Swatland, 1989). Initially, the significantly lower ph values resulting from CLA supplementation may be of concern with respect to their potential impact on pork quality parameters. The impact these ph data might have on loin color characteristics at 24 h postmortem are shown in Table 3. The correlation coefficient between 30-min ph and Hunter L* values was 0.50. This inverse relationship indicates a lighter loin color with declining ph. Additionally, correlation coefficients between 24-h ph and Hunter a* and b* values were 0.56 and 0.59, respectively. These results are more difficult to interpret because one would likely not expect loin color to become redder (a*) while ph values decline. Fisher et al. (2000) Table 3. Pearson correlation coefficients between ph and Hunter color values of longissimus muscle at the 10th and 11th rib interface Item 30-min ph 24-h ph L* a* b* 30-min ph 1.0 0.16 0.50 0.56 0.59 24-h ph 0.16 1.0 0.55 0.37 0.56 L* 0.50 0.55 1.0 0.56 0.86 a* 0.56 0.37 0.56 1.0 0.81 b* 0.59 0.56 0.86 0.81 1.0

Conjugated linoleic acid and pork 2191 have suggested that a* values increase because water is lost when ph values become low and meat pigment becomes more concentrated in the resulting product. These results show that further investigation into meat color is needed to understand the impact of ph on Hunter color values. Carcass data, including percentage of carcass shrink, backfat depth, and loin muscle area (LMA) are presented in Table 4. No differences were observed for percentage of carcass shrink at 24 h postmortem between any of the genotype (P = 0.63) or diet (P = 0.67) groups. Tenth rib fat depth was lower (P < 0.05) for Table 4. Carcass characteristics of three stress genotypes of pigs fed a control or conjugated linoleic acid (CLA)-supplemented diet Genotype Item and diet Negative Carrier Positive SEM a P-value b HCW, kg c Control 79 80 82 2.3 D = 0.32 G = 0.35 D G = 0.93 CLA 77 80 80 CCW, kg d Control 77 78 80 2.2 D = 0.30 G = 0.33 D G = 0.91 CLA 75 78 78 24-h shrink, % Control 2.5 2.5 2.4 0.05 D = 0.67 G = 0.63 D G = 0.74 CLA 2.5 2.5 2.5 10th rib fat, cm Control 2.97 2.71 2.87 0.13 D < 0.05 G = 0.30 D G = 0.92 CLA 3.54 2.18 2.23 Last rib fat, cm Control 2.66 2.79 2.66 0.15 D < 0.05 G = 0.99 D CLA 2.51 g 2.38 h 2.51 g LMA, cm 2e Control 35.57 g 39.80 gh 44.11 h 2.03 D = 0.18 G < 0.02 D G = 0.96 CLA 37.86 g 41.67 bh 45.85 h Color f Control 3.16 2.44 1.40 0.35 D = 0.98 G < 0.01 D G = 0.81 CLA 3.00 2.38 1.65 Marbling f Control 2.16 g 1.38 h 1.00 i 0.13 D < 0.05 G < 0.03 D G = 0.99 CLA 2.50 h 1.72 i 1.37 j Firmness f Control 2.83 g 2.05 h 1.00 i 0.24 D < 0.06 D G = 0.77 CLA 3.00 g 2.38 h 1.50 j a SEM = standard error. b D = dietary effect; G = genotype effect; D G = interaction between diet and genotype. c HCW = hot carcass weight. d CCW = chilled carcass weight. e LMA = loin muscle area. f Based on National Pork Producers Council 5-point scale. g,h,i,j Means within a row without a common superscript letter differ (P < 0.05).

2192 Wiegand et al. Table 5. Objective quality measures of loin samples from the 10th and 11th rib interface from pigs of three stress genotypes fed a control or conjugated linoleic acid (CLA)-supplemented diet a Genotype Item and diet Negative Carrier Positive SEM a P-value b Moisture, % Control 73.13 e 73.10 e 72.77 e 0.12 D < 0.04 G = 0.17 D G = 0.98 CLA 72.53 f 72.50 f 72.23 f Lipid, % Control 2.86 e 2.55 e 2.41 e 0.20 D < 0.05 G = 0.31 D G = 0.97 CLA 3.37 f 3.04 f 2.81 f L* value c Control 44.49 e 49.50 f 52.22 g 0.42 D < 0.01 G < 0.01 D G = 0.14 CLA 47.86 f 50.43 g 54.69 h a* value c Control 5.10 ef 5.48 f 5.85 g 0.26 D = 0.18 D G = 0.75 CLA 4.67 e 5.80 fg 5.73 fg b* value c Control 9.94 e 11.41 g 12.01 h 0.18 D < 0.05 D G = 0.89 CLA 10.69 f 11.59 gh 12.50 h Myoglobin, mg/g d Control 0.87 e,f 0.78 e 0.90 f 0.03 D = 0.11 G = 0.33 D CLA 0.82 e 0.79 e 0.74 e a SEM = standard error. b D = dietary effect; G = genotype effect; D G = interaction between diet and genotype. c Color values as determined by Hunter Lab Scan. d Soluble myoglobin, mg/g. e,f,g,h Means within a row without a common superscript letter differ (P < 0.05). CLA-fed pigs within each stress genotype. There was an interaction between diet and genotype that affected the last rib fat depth. Last rib fat depth was lower (P < 0.05) for CLA-fed pigs of the carrier genotype than for those of the negative and positive genotypes. These data are similar to those reported by other studies involving CLA supplementation (Dugan et al., 1997; Thiel et al., 1998; Sparks et al., 1999). Whereas Dugan et al. (1997) measured actual weights of subcutaneous fat, they reported similar linear decreases in fat with CLA feeding. Park et al. (1999b) reported a decrease in body fat after feeding the trans-10, cis-12 isomer. Pariza et al. (2000) suggested that changes in fat metabolism may be linked to enhanced β-oxidation, but definitive evidence does not yet exist to support this hypothesis. Loin muscle area at the 10th and 11th rib was not affected (P = 0.18) by CLA supplementation. Two other studies (Eggert et al., 1999; Cook et al., 1998) also reported no differences in LMA due to CLA supplementation. However, Dugan et al. (1997) reported increases in total loin muscle weight with CLA feeding. Studies in rodent models have also shown increases in wholebody protein with CLA supplementation (Park et al., 1997, 1999a). If whole-body protein increases in pigs fed CLA, these increases do not seem to be expressed as increases in longissimus muscle area. However, the possibility exists that increased muscle accretion may occur in other muscle groups. Stress-positive carcasses exhibited larger (P < 0.02) LMA than stress-negative carcasses, and stress-carrier carcasses were intermediate. Leach et al. (1996) reported similar increases for LMA in stress-genotype pigs. Subjective meat quality of the loin face at the 10th and 11th rib, including color, marbling, and firmness, are shown in Table 4. No differences were observed in color for diet effects (P = 0.98) but differences (P < 0.01) were seen for genotype effects. Marbling scores increased (P < 0.05) for CLA-fed pigs within each stress genotype. Dugan et al (1999) reported similar increases in marbling scores with CLA feeding. Increases in mar-

Conjugated linoleic acid and pork 2193 bling fat with CLA supplementation was probably due to a change in fat metabolism or the anatomical location of fat deposition, but no evidence currently exists to support this idea. The same results were observed for subjective firmness scores, which tended (P = 0.06) to increase for CLA-fed pigs within each genotype. The relationship between marbling and firmness was strong, resulting in a Pearson correlation coefficient of 0.89. This relationship suggests that by increasing marbling with CLA, one might also increase firmness of the loin face. This increase in firmness may be linked to an increase in saturated fat in pork products form CLA-fed pigs (Eggert et al., 1999). Hexane-extractable lipid analysis was used to verify subjective marbling scores (Table 5). The main effect of diet produced an increase (P < 0.05) in lipid percentage; CLA-fed pigs produced 3.07% lipid, compared with 2.61% lipid from the control-diet pigs. These increases in lipid percentages were similar to results from previous studies (Dugan et al., 1999; Wiegand et al., 1999). Proximate analysis also yielded differences in percentage of moisture of loin chops; chops from control-diet pigs had a higher (P < 0.04) percentage of moisture than chops from pigs fed CLA (73.0 vs 72.4%). These differences were evident within each genotype group, but no differences (P = 0.17) were observed for percentage of moisture among the three stress genotypes. These moisture results would likely be expected given the changes in lipid percentage in the CLA-fed pigs. Figure 4 shows Hunter L* color development of center-cut pork chops over 7 d of self-service case storage at 4 C following 21 d of whole loin vacuum storage. Hunter L* values increased sharply (P < 0.01) over storage time from d 0 to 1 and then increased slowly to 7 d. Chops from control-diet pigs initially had lower (P < 0.05) L* values than chops from CLA-fed pigs, and Figure 4. Hunter L* values of loin chops over days of retail case storage by experimental diet. Values are means for 30 pigs per dietary treatment. Figure 5. Hunter a* values of loin chops over days of retail case storage by experimental diet. Values are means for 30 pigs per dietary treatment. these differences were observed at all five time points measured. Hunter a* values (Figure 5) increased (P < 0.01) in the first 24 h of self-service storage, with a gradual decrease over 7 d of storage. No differences (P = 0.67) in a* values were observed between chops due to diet. Table 5 shows Hunter L*, a*, and b* values at 24 h postmortem for the three stress genotypes. Values for L* were higher (P < 0.01) for stress-positive pigs than for negative genotypes, whereas carrier pigs were intermediate in comparison. These results have been shown in previous studies with stress-genotype pigs (Murray et al., 1989; Fisher et al., 2000). Fisher et al. (2000) suggested that L* values were higher in stresspositive pigs because of an increased denaturation of sarcoplasmic proteins. This idea could be supported by our quantification of soluble myoglobin in the loin chop at 24 h postmortem (Table 5). Within the positive genotype, chops from the control-diet pigs had higher (P < 0.05) soluble myoglobin values than chops from CLAfed pigs (0.90 vs 0.74 mg/g). This decrease in soluble myoglobin corresponded with the increase in L* values with CLA supplementation within the positive genotype. Additionally, at 24 h postmortem we observed that positive-genotype loins exhibited higher (P < 0.01) a* values than negative-genotype loins, whereas carrier loins were intermediate for a* values. Fisher et al. (2000) suggested that the increased a* values in stresspositive pigs is the result of increased pigment concentration because of water loss in the chop. Our data do not support this explanation, because we did not observe any significant increases in soluble myoglobin among the three stress genotypes. However, within the positive genotype, we did see a decrease (P < 0.04) in moisture percentage (Table 5) in loin samples from CLA-fed pigs, which may have been linked to the lower ph during the early postmortem period. These factors in combination may have resulted in increased water loss in the stress-positive, CLA-fed pigs, which might

2194 Wiegand et al. Table 6. Sensory panel attributes of loin chops from pigs of three stress genotypes fed a control or conjugated linoleic acid (CLA)-supplemented diet Genotype Item and diet Negative Carrier Positive SEM b P-value c Tenderness Control 6.35 4.97 5.22 0.40 D = 0.24 D G = 0.25 CLA 5.53 5.16 5.09 Juiciness Control 5.76 4.56 4.22 0.38 D = 0.35 G = 0.69 D G = 0.27 CLA 5.03 4.76 3.81 Flavor intensity Control 5.41 4.92 5.01 0.20 D = 0.14 G = 0.13 D G = 0.39 CLA 5.00 4.88 4.67 Overall acceptability Control 5.36 4.88 4.22 0.18 D = 0.11 D G < 0.56 CLA 5.45 5.13 4.68 a Based on an 8-point scale with 8 being most desirable. b SEM = standard error. c D = dietary effect; G = genotype effect; D G = interaction between diet and genotype. have resulted in a loss of soluble myoglobin in this group. Sensory data are show in Table 6. The characteristics of tenderness (P = 0.24), juiciness (P = 0.35), and flavor intensity (P = 0.14) were not affected by CLA supplementation. These results verify previous studies in which no differences were observed in sensory characteristics with CLA supplementation (Dugan et al., 1999; Thiel-Cooper et al., 1999, Wiegand et al., 1999). Implications The results from this study show that supplementation with conjugated linoleic acid improves feed efficiency, decreases backfat, and improves marbling and firmness scores of loin chops. These results seem to be dependent on stress gene susceptibility for certain measures of performance and meat quality. Conjugated linoleic acid supplementation also causes a lower ph during the early postmortem period, which may have resulted in the higher Hunter L* values for loin chops. Improvements in feed efficiency and decreased backfat in combination with improvements in certain meat quality characteristics, marbling, and firmness may make pork production more profitable if the price of conjugated linoleic acid at 0.75% in the diet is nominal. Literature Cited AMSA. 1995. Research Guidelines for Cookery, Sensory Evaluation and Instrument Tenderness Measurements of Fresh Meats. National Live Stock and Meat Board, Chicago, IL. AOAC. 1990. Official Methods of Analysis. 15th ed. Association of Official Analytical Chemists, Arlington, VA. Bendall, J. R. 1973. In: G. H. Bourne (ed.) Structure and Function of Muscle. 2nd ed. vol. 2. pp 243 309. Academic Press, New York. Bendall, J. R., and H. J. Swatland. 1989. A review of the relationships of ph with physical aspects of pork quality. Meat Sci. 40:85 126. Chin, S. F., J. M. Storkson, M. E. Cook, and M. W. Pariza. 1994. Conjugated linolieic acid is a growth factor for rats as shown by enhanced weight gain and improved feed efficiency. J. Nutr. 124:2344 349. Cook, M. E., D. L. Jerome, T. D. Crenshaw, D. R. Buege, M. W. Pariza, K. J. Albright, S. P. Schmidt, J. A. Scimeca, P. A. Lofgren, and E. J. Hentges. 1998. Feeding conjugated linoleic acid improves feed efficiency and reduces carcass fat in pigs. FASEB J. 12:4843 (Abstr.). Dugan, M. E. R., J. L. Aalhus, L. E. Jeremiah, J. K. G. Kramer, and A. L. Schaefer. 1999. The effects of feeding conjugated linoleic acid on subsequent pork quality. Can. J. Anim. Sci. 79:45 51. Dugan, M. E. R., J. L. Aalhus, A. L. Schaefer, J. K. G. Kramer. 1997. The effect of conjugated linoleic acid on fat to lean repartitioning and feed conversion in pigs. Can. J. Anim. Sci. 77:723 725. Eggert, J. M., M. A. Belury, A. Kempa-Steczko, and A. P. Schinckel. 1999. Effects of conjugated linoleic acid (CLA) on growth and composition of lean gilts. J. Anim. Sci. 77(Suppl. 2):29 (Abstr.). Fisher, P., F. D. Mellett, and L. C. Hoffman. 2000. Halothane genotype and pork quality. 1. Carcass and meat quality characteristics of three halothane genotypes. Meat Sci. 54:97 105. Leach, L. M., M. Ellis, D. S. Sutton, F. K. McKeith, and E. R. Wilson. 1996. The growth performance, carcass characteristics, and meat quality of halothane carrier and negative pigs. J. Anim. Sci. 74:934 943. Louis, C. F., W. E. Rempel, and J. R. Mickelson. 1993. Porcine stress syndrome: Biochemical and genetic basis of the inherited syndrome of skeletal muscle. In: Proc. Recip. Meat Conf., Lincoln, NE. 46:89 96. Maribo, H., S. Stoier, and P. F. Jorgensen. 1999. Procedure for determination of glycolytic potential in porcine M. longissimus dorsi. Meat Sci. 51:191 193.

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