The effects of grade, gender, and postmortem treatment on beef. I. Composition, cutability, and meat quality

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1 The effects of grade, gender, and postmortem treatment on beef. I. Composition, cutability, and meat quality L. E. Jeremiah, J. L. Aalhus, W. M. Robertson, and L. L. Gibson Meat Research Section, Agriculture Canada Research Centre, Lacombe, Alberta, Canada T4L 1W1. Scientific Paper no. 797, received 2 December 1994, accpeted 27 October Jeremiah, L. E., Aalhus, J. L., Robertson, W. M. and Gibson, L. L The effects of grade, gender, and postmortem treatment on beef. I. Composition, cutability, and meat quality. Can. J. Anim. Sci. 77: A total of 195 beef carcasses of two genders (steers and heifers) and four Canadian carcass grades (A1, A2, B1, and B2) were evaluated to examine the effects of carcass grade, gender, and postmortem electrical stimulation on carcass composition, cutability (yield of specific primal cuts), and meat quality traits (traits related to appearance, palatability, yield, and consumer appeal). Cutability was not influenced by either grade or gender. Increased fatness appeared to be distributed equally in all portions (segments) of the carcass. Canadian beef carcass grades effectively segregated carcasses according to grade definitions for both composition and quality. Gender differences in quality generally reflected compositional differences observed between steers and heifers. High voltage electrical stimulation reduced shear force values, but exerted a greater influence on steer than heifer carcasses. Key words: Beef, composition, cutability, quality, grades, gender, electrical stimulation Jeremiah, L. E., Aalhus, J. L., Robertson, W. M. et Gibson, L. L Effets du classement, du genre de l animal et des interventions post mortem sur la viande bovine. I. Composition, rendement boucher et qualité de la viande. Can. J. Anim. Sci. 77: Cent quatre-vingt quinze carcasses de deux types sexuels : bouvillons et génisses et de quatre niveaux de classement, A1, A2, B1 et B2 ont été évalués quant aux effets de la catégorie de la carcasse, de l état sexuel et de la stimulation électrique sur la composition de la carcasse, sur le rendement boucher (rendement de morceaux de particuliers) ainsi que sur la qualité de la viande : aspect, appétabilité, rendement et attrait pour le consommateur. Le rendement boucher n était influencé ni par le niveau de classement ni par l état sexuel. Le surcroît de graisse paraissait également réparti entre tous les segments de la carcasse. Le système canadien de classement des carcasses se révélait donc efficace pour séparer les carcasses selon les critères acceptés quant à la composition et à la qualité de la viande. Les différences qualitatives relevées entre bouvillons et génisses tenaient généralement à la composition de la viande des deux types sexuels. La stimulation électrique à haute tension abaissait les valeurs de force de cisaillement de la viande particulièrement pour les carcasses de génisses. Mots clés: Boeuf, composition, rendement boucher, qualité, catégorie au classement, type sexuel, stimulation électrique To remain competitive with alternate protein sources, major changes will be required in both the production and processing of beef. One of the greatest potentials to increase beef production efficiency (input cost/kilogram of edible lean product produced) relates to the fatness endpoint at which cattle are marketed. Substantial improvements in such efficiency can be made by slaughtering cattle with less carcass fat. In addition, consumer demand has largely shifted to foods lower in fat content. However, the minimum level of fatness that cattle may be finished, to attain an acceptable level of eating satisfaction has not been determined, to date (Jeremiah et al. 1992). A recent Canadian consumer survey revealed that with increased levels of marbling a progressive decrease in acceptability of striploin steaks occurred at the point of purchase or visual assessment. However, contrasting results were observed during consumption (Jeremiah et al. 1992). Another Canadian consumer survey revealed variation in beef eating quality, particularly tenderness, to be a major concern among consumers (McDonell 1990). Although lack 33 of consumer education in the selection and preparation of beef cuts may be a contributing factor to this variation in eating quality, production of beef with less fat has increased substantially. The proportion of A1 carcasses within the Canadian A grade has increased from 40% in 1972 to more than 70% in 1990 (Aalhus et al. 1992). In addition, the advent of more rapid commercial chilling methods for beef carcasses may be a contributing factor through the production of cold-induced toughening (Jeremiah 1978). The hotel, restaurant, and institutions trade has found 25 to 30% of the beef it receives to be unacceptable in eating quality, particularly tenderness (McDonell, C., personal communication). Jones et al. (1991) reported 24 to 39% of the steaks in their study were unacceptable in eating quality depending on marbling level, and Jeremiah et al. (1992) found 18 to 32% of the steaks in their consumer survey to be unacceptable at the point of consumption, depending on Abbreviations: LT, longissimus thoracis

2 34 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 1. Numbers of carcasses evaluated for each carcass grade and gender Carcass grade Gender A1 A2 B1 B2 Heifers Steers marbling level. Aalhus et al. (1992) indicated 20% of the steaks in their study were unacceptable to consumers in tenderness when time on feed and postmortem aging simulated Canadian production practices. The proportion of unacceptable steaks could be reduced to approximately 10%, by including high voltage electrical stimulation, as a means of quality control. The present study was designed and undertaken to evaluate the effects of Canadian carcass grade (which reflects relative carcass fatness), and gender, and potential interactive effects of electrical stimulation with these factors on the composition, cutability (proportion of saleable cuts), and quality of beef. The Canadian beef carcass grading regulations were instituted to facilitate orderly marketing of beef, based upon meeting specific standards for certain grades. At the time the present study was conducted, grade requirements for the four carcass grades being evaluated were as follows (Agriculture Canada ): Canada A1 a) Not less than 4 nor more than 10 mm of subcutaneous fat. b) Soft, red, porous bones when split; evidence of cartilage tips on the lumbar vertebrae; no more than slight ossification in the spinous processes caps of the thoracic vertebrae; and a sternum with distinct divisions. c) Firm, bright red longissimus (loin-eye) muscles, 10 min after knife ribbing. d) A firm, white or slightly reddish or amber tinged fat cover, which extends over the exterior carcass surface, but which may be somewhat lacking over the hips and shoulders. e) Freedom from narrowness through the loins and ribs, marked angularity of muscling, and depressions in the hips and shoulders. Canada A2 Standards equivalent to A1 but with not less than 10 mm nor more than 15 mm of subcutaneous fat. Canada B1 Bone structure, muscling, muscle color and firmness, and fat cover equivalent to A but not less than 2 mm nor not more than 4 mm of subcutaneous fat. Canada B2 a) Bone structure equivalent to Al. b) Moderately firm and darkened longissimus muscles 10 min after knife ribbing. Table 2. Least squares mean proportions (g 100 g 1 ) of body cavity fat from different carcass grades and genders Grade Gender Mean SE A1 Heifer 2.2b 0.06 Steer 2.2bc 0.04 A2 Heifer 3.2a 0.19 Steer 2.1bcd 0.22 B1 Heifer 2.5abcd 0.38 Steer 1.9d 0.06 B2 Heifer 2.5b 0.19 Steer 1.8cd 0.22 a d Means in the same column followed by a common letter do not differ significantly (P > 0.05). c) Subcutaneous fat cover of at least 1 mm thickness. d) A firm or slightly soft fat cover, ranging from white to pale yellow in color, which extends over most of the exterior carcass surface, but which may be somewhat lacking over the hips and shoulders. e) At least medium muscling with some deficiencies. MATERIALS AND METHODS A total of 196 beef carcasses of two genders (heifers and steers) and four Canadian beef carcass grades were utilized (Table 1). The majority of these carcasses (176) came from two experiments previously described (Aalhus et al. 1992). To increase the number of B1 carcasses, 20 steer carcasses of unknown origin and management, and without postmortem electrical stimulation were subsequently obtained from a commercial packing plant. Production, slaughter, and postmortem treatment of the majority of the animals were as previously described (Aalhus et al. 1992). After splitting and prior to postmortem treatment (45 min post-slaughter) warm carcass weights were recorded, and loin lean depth was measured between the 11th and 12th ribs, 8 cm from the midline using the Hennessey beef grading probe (Jones et al. 1989). Alternate carcass sides were electrically stimulated with a Koch-Britton stimulator [Kansas City, MO; 470 V, 1.5 A, 60 Hz, 20 pulses min 1 for 1 min (Aalhus et al. 1992)]. All sides were then washed, shrouded, and chilled for 24 h at 1 C. After chilling both left and right sides were weighed and then ribbed between the 12th and 13th ribs. Canadian grades and carcass traits (muscle color and marbling) were assessed on both sides of the carcass by an Agriculture Canada meat grader. Subjective color scores were assessed using a three-point scale (1 = bright; 2 = moderately dark; 3 = dark). Subjective marbling scores were determined using United States Department of Agriculture Grade Standards (10 point scale; 1 = very abundant; 10 = devoid). All unstimulated sides were broken into primal cuts. The primal cuts were then separated into fat (subcutaneous, intermuscular, and body cavity), lean and bone according to procedures described by Rahnefeld et al. (1983). Prior to physical separation of the loin, a 20-mm-thick steak was cut from the anterior end (13th rib area) of each loin. The

3 JEREMIAH ET AL. GRADE, GENDER, AND STIMULATION EFFECTS ON BEEF COMPOSITION AND QUALITY 35 Table 3. Least squares mean proportions (g 100 g 1 ) of carcass components from different carcass grades A1 A2 B1 B2 Component Mean SE Mean SE Mean SE Mean SE Hindquarter Forequarter Round Sirloin Loin Rib Chuck Brisket Shank Plate Flank Rib, loin, and sirloin Lean 59.0b c a ab 1.22 Bone 16.4b c a ab 0.50 Total dissectable fat 24.4b a c b 1.89 Subcutaneous fat 7.9b a c b 0.50 Intermuscular fat 14.3b a c bc 0.71 longissimus thoracis (LT) muscle was traced and then measured with an electronic planimeter. Subcutaneous fat thickness was measured with a ruler at the minimum point of thickness in the fourth quarter of the longitudinal axis of the LT muscle from the vertebra and perpendicular to the exterior surface of the fat (Agriculture Canada ). Ultimate ph was measured with a Corning model 4 ph-temperature meter (Corning Glass Works, Medfield, MA) equipped with an Ingold spear-type electrode (Ingold Messtechnik AG, Undorf, Switzerland). Hunter Lab color values were also determined using a Macbeth Series 1500 Color Measuring System (Newburg, NY). This steak was then physically separated with the remainder of the loin. Loin-eye (LT muscle) area, subcutaneous fat thickness, ultimate ph, and Hunter Lab values were also measured on a comparable steak from the stimulated side. LT muscle samples from both carcass sides were ground separately three times through a 3-mm grinding plate. Expressible juice was determined on 20 g if ground sample centrifuged for 60 min at g (Aalhus et al. 1992). Moisture content was determined as the proportion of weight lost after heating at 105 C for 24 h. Intramuscular fat content was measured as total fat extracted from 4 g of dried muscle during a 10-min extraction at 105 C in petroleum ether. Compositional and cutability data were analyzed using the general linear model (GLM) of the SAS Institute, Inc. (1990) and a 4 2 factorial model with carcass grade, gender, and their interaction as main effects. Meat quality data were analyzed using the same GLM and a split-plot model with carcass grade, gender, and their interaction in the main plot and postmortem treatment (electrical stimulation) and its interactions in the split-plot. When significant interactions were observed (P < 0.05) mean separation of interaction means were by Bonferroni t-tests, to control the alpha level for type-1 errors. When significant interactions were not observed (P > 0.05) and when significant main effects Grade a c Means in the same row without a letter or followed by a common letter do not differ significantly (P > 0.05). Table 4. Least squares mean proportions (g 100 g 1 ) of carcass components from different genders Gender Heifer Steer Component Mean SE Mean SE Hindquarter Forequarter Round Sirloin Loin Rib Chuck Brisket Shank Plate Flank Rib, loin, and sirloin Lean Bone 16.2b a 0.27 Total dissectable fat 25.6a b 1.04 Subcutaneous fat 8.3a b 0.27 Intermuscular fat a,bmeans in the same row without a superscript do not differ significantly (P > 0.05). (P < 0.05) were observed, Bonferroni t-tests were utilized to separate main effect means. RESULTS AND DISCUSSION Composition and Cutability The only significant (P < 0.05) grade/gender two-way interaction was for proportion of body cavity fat (Table 2). This interaction arose as a result of heifers having more body cavity fat in the A2 and B2 grades (P < 0.05), but not in the A1 and B1 grades (P > 0.05). A2 heifer carcasses had more body cavity fat than A1 and B2 heifer carcasses and all steer carcasses and A1 and B2 heifer carcasses had more body cavity fat than B1 and B2 steer carcasses.

4 36 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 5. Least squares means and standard errors for meat quality properties of carcasses of different grades Grade A1 A2 B1 B2 Trait Mean SE Mean SE Mean SE Mean SE Hunter L 36.19a a b c 0.52 Marbling score z 7.02bc c a b 0.10 Intramuscular fat (g 100 g 1 ) 10.16b a c b 0.68 Moisture (g 100 g 1 ) 73.56b d a c 0.20 z Marbling score is in a 10-point scale: 1 = very abundant; 10 = devoid. a d Means in the same row without a letter or followed by a common letter do not differ significantly (P > 0.05). Differences among carcass grades in the proportion of the carcass represented by hindquarter, forequarter, high priced cuts (rib, loin, and sirloin), and individual primal cuts were not observed (P > 0.05). However, differences in the individual tissue components (dissectible lean, fat partitioning, and carcass bone) were detected (P < 0.05) (Table 3). B1 carcasses had the highest proportions of lean and bone (62.8 and 18.0, respectively), and A2 carcasses had the lowest (54.8 and 15.1, respectively). A1 carcasses also had higher proportions of lean and bone (59.0 and 16.4, respectively) than A2 carcasses (54.8 and 15.1, respectively) (P < 0.05). A2 carcasses had the highest proportions of total dissectible, subcutaneous, and intermuscular fat (30.1, 10.4, and 17.1, respectively), and B1 carcasses had the lowest (15.1, 5.2, and 11.8, respectively). Heifer carcasses had higher proportions of total dissectible and subcutaneous fat (25.6 and 8.3, respectively) and a lower proportion of bone (16.2) (P < 0.05) than steer carcasses, (21.0, 7.3, and 17.3, respectively) (Table 4). The proportions of carcass lean, hindquarter, forequarter, highpriced cuts (rib, loin, and sirloin), and individual primal cuts did not differ (P > 0.05) between steers and heifers. As previously mentioned, the Canadian grading system assigns youthful carcasses into the B1 and A grades on the basis of subcutaneous fat thickness, with B1 carcasses having 2 to 4 mm, A1 carcasses having 4 to 10 mm, and A2 carcasses having 10 to 15 mm. The B2 grade is for dark cutting carcasses. Therefore, it is not surprising that differences in individual tissue components were observed among carcass grades, with B1 carcasses having the highest proportions of lean and bone, and A2 carcasses having the highest proportions of total dissectible, subcutaneous, intermuscular, and body cavity fat. The lean contents of both A1 and A2 carcasses were within the ranges reported by Jones et al. (1987), but the mean lean content of carcasses in both grades were substantially lower than previously reported values. The proportions represented by hindquater, forequarter, high-priced cuts (rib, loin and sirloin), and individual primal cuts did not differ among carcass grades, suggesting increases in fatness were evenly distributed throughout the carcass. Table 6. Least squares means and standard errors for meat quality properties of carcasses of different genders Gender Heifer Steer Trait Mean SE Mean SE Hunter L Marbling score z 6.97b a 0.06 Intramuscular fat (g 100g 1 ) Moisture (g 100g 1 ) z Marbling score is on a 10-point scale: 1 = very abundant; 10 = devoid. a,bmeans in the same row without a letter or followed by a common letter do not differ significantly (P > 0.05). Meat Quality Significant (P < 0.05) grade gender interactions were detected in all meat quality traits, except Hunter L values, graders marbling scores, and the proportions of intramuscular fat and moisture. A1 and A2 LT muscle had the highest Hunter L values (36.19 and 37.58, respectively), and therefore, the lightest colored lean, and B2 LT muscles had the lowest L values (32.16), and therefore, the darkest colored lean (Table 5). B1 LT muscles also had higher L values (34.85) and lighter colored lean than B2 LT muscles (P < 0.05). B1 LT muscles had the least visible marbling and the highest marbling scores (7.44), and B2 LT muscles had less visible marbling and higher marbling scores (7.10) than A2 LT muscles (6.81) (P < 0.05). A2 LT muscles had the most chemically determined intramuscular fat (13.26), and B1 LT muscles contained the least (6.73) (P < 0.05). A2 LT muscles contained the least moisture (72.50) and B1 LT muscles contained the most (74.29) (P < 0.05). A1 LT muscles also contained more moisture (73.56) than B2 LT muscles (73.05). Differences attributable to gender were not detected in Hunter L values, or the proportions of intramuscular fat and moisture in LT muscles (P > 0.05) (Table 6). However, heifer LT muscles exhibited more visible marbling and had lower marbling scores (6.97) than steer LT muscles (7.21) (P < 0.05). B2 heifer and steer carcasses received the highest subjective color scores (2.00) (Table 7) A2 heifer and A1 and B1 steer LT muscles had lower ultimate ph values (5.62, 5.62, and 5.63, respectively) than all other LT muscles, except those from A2 steer carcasses (5.62). B2 heifer LT muscles had the highest ultimate ph values (6.11). Al heifer LT muscles also had lower ultimate ph values (5.68) than B1 and B2 steer LT muscles (5.86 and 5.82, respectively). In addition, A2 heifer and A1 steer LT muscles had lower shear force values (6.10 and 6.66 kg, respectively) than all other LT muscles, except A2 steer LT muscles (6.24 kg) (P < 0.05), and A1 heifer and A2 steer LT muscles had lower

5 JEREMIAH ET AL. GRADE, GENDER, AND STIMULATION EFFECTS ON BEEF COMPOSITION AND QUALITY 37 shear force values (7.06 and 6.24 kg, respectively) than B1 steer LT muscles (7.97 kg). Consequently, present results are consistent with and support a previous report that the majority of tough carcasses have moderately dark lean color and ultimate ph values between 5.8 and 6.2 (Jeremiah et al. 1991). In addition, the fact B1 carcasses generally yielded the highest shear force values and A2 carcasses generally yielded the lowest supports the negative relationships between fatness and shear force values observed by various workers (Jeremiah 1978). A1 heifer and A2 steer LT muscles had the highest Hunter a values (20.00 and 19.74, respectively), and therefore, the reddest lean color, and B1 and B2 heifer LT muscles had the lowest Hunter a values (15.16 and 13.56, respectively) and the least red lean color (Table 7). In addition, A1 steer LT muscles had higher Hunter a values (18.65) and redder lean color than B2 steer LT muscles (17.53). A1 and A2 steer LT muscles had higher Hunter b values (14.73 and 15.48, respectively) and more yellow lean color than all other LT muscles, except B1 steer LT muscles (14.48), and B2 heifer LT muscles had the lowest Hunter b values (8.79) and the least yellow lean color (P < 0.05). In addition, B1 steer LT muscles had higher Hunter b values (14.48) than A1 and B1 heifer (13.83 and 11.03, respectively) and B2 steer (12.53) LT muscles (P < 0.05), and A1 heifer LT muscles had higher Hunter b: values (13.83) than B1 heifer (11.03) and B2 steer (12.53) LT muscles. B2 heifer LT muscles contained the least expressible juice (15.91), and A1 and A2 heifer and A1, and A2 and B1 steer LT muscles contained more expressible juice (24.72, 24.48, 24.77, 25.53, and 24.73, respectively) than B2 steer LT muscles (21.58). B1 heifer and B1 and B2 steer carcasses had the least subcutaneous fat thickness (3.00, 2.68, and 3.96 mm, respectively) and A2 heifer and steer carcasses had the most (12.34 and mm, respectively). In addition, A1 heifer carcasses had more subcutaneous fat thickness (7.19 mm) than A1 steer carcasses (6.55 mm), probably indicating heifers begin to deposit fat at an earlier age than steers. Although differences in LT (loin-eye) area were not detected among carcass grades or genders (P > 0.05), A2 steer carcasses had greater 11th/12th rib lean depth, measured on the warm carcass with the Hennessey grading probe (81.47) than all other carcasses except A2 and B2 heifer carcasses (72.64 and mm, respectively), and B2 steer carcasses had less 11th/12th rib lean depth (54.93 mm) than all other carcasses, except B1 heifer and steer carcasses (60.00 and mm, respectively) (P < 0.05) (Table 7). The fact heifer carcasses contained greater proportions of total dissectible, subcutaneous, and body cavity fat than steer carcasses, but similar proportions of hindquarter, forequarter, high-priced cuts, and individual primal cuts provides further evidence that increased fatness is distributed equally throughout the carcass, and supports reports that heifers are generally fatter than steers at a given age and/or liveweight (Jeremiah 1978). As expected, A2 carcasses contained the most subcutaneous fat at the 12th rib, marbling, and chemically deter- Table 7. Meat quality properties of LT from different carcass grades and genders z Grade A1 A2 B1 B2 Heifer Steer Heifer Steer Heifer Steer Heifer Steer Trait Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Subjective color score y 1.00b b b b b b a a 0.00 Hunter a 20.00a b bc a d bc d c 0.53 b 13.83c a bcd a e ab f de 0.59 Ultimate ph 5.68c d d cd b d b 0.03 Shear force value (kg) 7.06c d d cd a b bc bcd 0.57 Expressible juice (g 100 g 1 ) 24.72ab ab ab a bc ab d c 0.76 Subcutaneous fat (mm) 7.19b c a a d d bc d 0.60 Loin-eye area (cm 2 ) th 12th rib lean depth (mm) x 69.18b b ab a bc bc ab c 5.27 Subcutaneous fat (mm) 7.19b c a a d d bc d 0.60 z Gender includes heifers and steers. y Color score on a 3-point scale: 1 = bright; 2 = moderately dark; 3 = dark. x Measured on the hot carcass with the Hennessey grading probe. a fmeans in the same row without a letter or followed by a common letter do not differ significantly (P > 0.05).

6 38 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 8. Meat quality properties of LT muscle from carcasses with different grades with and without electrical stimulation Grade A1 A2 B1 B2 Control Stimulated Control Stimulated Control Stimulated Control Stimulated Trait Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Hunter L 36.42b a ab a bc c d d 0.79 a 17.73b a a a bc bc cd d 0.49 b 13.63bc a ab a bc c d d 0.55 Ultimate ph 5.68dc f f f cd c b a 0.03 Expressible Juice (g 100 g 1 ) 24.17bc a abc ab abc c d de 0.71 a f Means in the same row without a letter or followed by a common letter do not differ significantly (P > 0.05). mined intramuscular fat, and B1 carcasses contained the least. Moreover, as expected, B2 carcasses had the highest ultimate ph, the lowest amount of expressible juice, and the darkest lean color. Therefore, the Canadian beef carcass grading system was effectively segregating carcasses according to grade definitions. Interaction Effects of Electrical Stimulation on Quality Significant (P < 0.05) grade treatment interactions were observed for ultimate ph, expressible juice, and Hunter L, a, and b values and significant (P < 0.05) gender treatment interactions were observed for subcutaneous fat thickness and shear force values. Electrically stimulated B2 LT muscles had the highest ultimate ph (6.03), and electrically stimulated A1 and A2 LT muscles had lower ultimate ph values (5.62 and 5.61, respectively) than all other LT muscles, except A2 control LT muscles (5.64) (P < 0.05) (Table 8). In addition, control B2 LT muscles had higher ultimate ph values (5.90) than control A1, A2, and B1 and stimulated B1 LT muscles (5.68, 5.64, 5.73, and 5.75, respectively). Stimulated B2 LT muscles contained the least expressible juice (17.65), and control B2 LT muscles contained less expressible juice (19.84) than all other LT muscles, except stimulated B2 LT muscles. In addition, stimulated B1 LT muscles contained less expressible juice (23.57) than stimulated A1 and A2 LT muscles (25.32 and 25.49, respectively). Stimulated A1 and A2 LT muscles had higher Hunter L and b values (37.95 and and 14.93, and 15.18, respectively) and lighter and more yellow lean color than all other LT muscles, except control A2 LT muscles (36.76 and 13.63, respectively), and control and stimulated B2 LT muscles had the lowest Hunter L and b values (32.78 and and and 10.21, respectively) and the darkest and least yellow lean color (P < 0.05). Control A1 LT muscles had higher Hunter L and b values (36.42 and 13.63, respectively) and lighter and more yellow lean color than stimulated B1 LT muscles (34.71 and 12.63, respectively). Stimulated A1 and stimulated and control A2 LT muscles also had the highest Hunter a values (18.92, 18.65, and 19.30, respectively) and the reddest lean color, while stimulated B2 LT muscles had lower Hunter a values (15.14) and less red lean color than all other LT muscles, except control B2 LT muscles (15.94). Control A1 LT muscles also had higher Hunter a values (17.73) and redder lean color than control B2 LT muscles (15.94). Gender treatment interactions in subcutaneous fat thickness and shear force values occurred because controls had more subcutaneous fat cover (7.62 mm) than treated heifer carcasses (7.14 mm), while treated steer carcasses had more subcutaneous fat cover (6.51 mm) than controls (6.20 mm), and because electrical stimulation elicited a greater response in shear force values (2.58 kg) in steer LT muscles than in heifer LT muscles (1.85 kg) (Table 9). In the present study electrical stimulation exerted essentially no influence on meat quality traits, except for shear force values. Shear force values were reduced by over 2 kg on the average in the present study, representing a 25%

7 JEREMIAH ET AL. GRADE, GENDER, AND STIMULATION EFFECTS ON BEEF COMPOSITION AND QUALITY 39 Table 9. Meat quality properties of LT muscle from carcasses with different genders with and without electrical stimulation Heifer Control Stimulated Control Stimulated Trait Mean SE Mean SE Mean SE Mean SE Shear force value (kg) 9.18a c b d 0.28 Subcutaneous fat (mm) 7.62a ab c bc 0.29 a d Means in the same row without a letter or followed by a common letter do not differ significantly (P > 0.05). Steer reduction. Such a reduction in shear force supports the findings reported by various other workers (Savell et al. 1977; McKeith et al. 1979, 1981; Bidner et al. 1981; Cole et al. 1981; McIntyre and Ryan 1984; Aalhus et al. 1992). However, the magnitude of the reduction in shear force values observed in the present study from high voltage electrical stimulation is greater than that observed by most other workers (Pearson and Dutson 1985), and it should be noted some workers have failed to observe influences of electrical stimulation on shear values (Dutson et al. 1982; Riley et al. 1982; Wood and Froehlich 1983), and others have observed increases in shear values from electrical stimulation (Riley et al. 1982). It is not surprising such diversity in results has been observed, due to the variation in application techniques and study conditions. In the studies in which a response to electrical stimulation was not observed, the animals had likely undergone some degree of preslaughter stress, which may have depleted muscle glycogen and resulted in only a limited contraction in response to the electrical stimulation treatment. The general lack of response in ultimate ph, lean color, and marbling differences due to electrical stimulation in the present study is contrary to previous reports of reduced ultimate ph, increases in brightness and redness of lean color, and greater perception of marbling (Savell et al. 1978), but supports previous observations that electrical stimulation did not influence any measures of initial retail acceptability (Jeremiah and Martin 1982). Gender grade interactions largely reflected the influence of fatness on meat quality traits observed for different grades and genders. Electrical stimulation appeared to magnify certain meat quality differences observed among grades, as evidenced by the significant grade treatment interactions observed. The significant gender treatment interaction observed in shear force values indicated electrical stimulation exerted a greater influence upon the reduction of shear force values in steer carcasses than in heifer carcasses. CONCLUSIONS Canadian beef carcass grades effectively segregated carcasses according to grade definitions for both composition and quality. Gender differences in quality generally reflected the compositional differences observed between steers and heifers. High-voltage electrical stimulation reduced shear force values by over 2 kg on average (approximately 25%), but exerted a greater influence on steer than heifer carcasses. ACKNOWLEDGMENTS The authors are grateful to the Meat Research Center staff for their assistance in slaughter and carcass cut-out, to Alan Tong for his statistical guidance, and to Loree Verquin for typing the manuscript. Aalhus, J. L., Jones, S. D. M., Tong, A. K. W., Jeremiah, L. E., Robertson, W. M. and Gibson, L. L The combined effects of time on feed, electrical stimulation and aging on beef quality. Can. J. Anim. 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9 This article has been cited by: 1. I. Galli, G. Teira, F. Perlo, P. Bonato, O. Tisocco, A. Monje, S. Vittone Animal performance and meat quality in cull cows with early weaned calves in Argentina. Meat Science 79:3, [Crossref]