Selective Denervation of the Musculus pectoralis Muscle in the Chicken

Selective Denervation of the Musculus Muscle in the Chicken

pectoralis

R. J. BUHR Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication October 12, 1988)

1990 Poultry Science 69:124-132 INTRODUCTION

The rates at which post-mortem biochemical processes occur (dephosphorylarion of high-energy phosphates, glycolysis, and pH decline) as a muscle is converted to meat have been related to the ultimate quality of the cooked meat (de Fremery, 1966; Khan, 1971). Acceleration in the onset of rigor mortis, greater isometric tension, and an increased maximum state of rigor have been shown to inhibit optimal meat tenderness (de Fremery, 1966; Khan, 1974). These parameters of rigor can be influenced by preslaughter stress (de Fremery and Pool, 1960) and the reserves of muscle energy (Bate-Smith and Bendall, 1949); a profound influence is exerted by the extent of the death struggle (Khan and Nakamura, 1970; Grey et al, 1974). Postmortem processing procedures also affect: the rate at which rigor develops, meat toughness and shear-force values, i.e., the scalding temperature (Pool et al., 1959); mechanical picking (de Fremery and Pool, 1960); exhaustive electrical stimulation (Klose et al., 1972; Stewart et al., 1984); and freezing (de Fremery and Lineweaver, 1962; Klose et al., 1970).

To identify the relative importance of the factors that influence rigor, it is necessary to alter the ante- and post-mortem biochemical environment of a muscle. The methods for reducing muscle shortening post-mortem have included the use of anesthesia, neuromuscular blocking drugs, and metabolic muscle poisons (Khan, 1975). These treatments have shown that an accelerated rate of rigor mortis may not be solely responsible for toughening meat. The effects of these drug treatments are mediated throughout the body, generally delaying onset of rigor and diminishing the influences of the death struggle, and may not accurately depict the biochemical processes in the muscle postmortem. The cardiovascular system is also depressed, producing vascular stasis and edema within muscle tissue which impair the exchange of nutrients and metabolites. Investigation concerning the effects of sodium pentobarbital, iodoacetate, tubocurarine, or surgical denervation treatments on early rigor development in the Musculus (M.) pectoralis of broilers resulted in higher pH and lower lactate levels and shear values (immediately post-mortem) in sodium pentobarbital and denervated treatments than in nontreated

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ABSTRACT A surgical method for selective denervation was developed to facilitate investigations about the postmortem characteristics of denervated pectoralis muscles in chickens, Musculus (M.) pectoralis. The M. pectoralis was denervated in anesthetized chickens unilaterally or bilaterally by excising a 1-cm section of the nervus pectoralis as it branched from the N. medianoulnaris in the brachial plexus. Denervation resulted in significant (P<.01) and consistent depression in the relative weight of M. pectoralis from the wk 2 through 17 postoperative. The relative weight of the functionally antagonistic M. supracoracoideus was unaffected by ipsilateral denervation of the M. pectoralis. The M. coracobrachial^ acts in synergism with the M. pectoralis and displayed significant muscle atrophy at 4, 6, 8, and 17 wk postoperative in treatment groups where the ipsilateral M. pectoralis was denervated. Only the M. pectoralis displayed histological signs of denervation in transverse cryostat sections. Denervated tissue was characterized by atrophic and rounded muscle-fiber profiles, an increase in the endomysial and perimysial connective-tissue spaces, and leucocytes within degenerative perimysial nerves from 2 through 17 wk postoperative. Signs of denervation were distributed throughout seven zones sampled from the M. pectoralis. This study indicated that selective denervation of the M. pectoralis was achieved and that postoperative histology was necessary to accurately assess denervation. (Key words: denervation, muscle, Musculus pectoralis, chicken)

DENERVATION OF THE M. PECTORALIS MUSCLE

MATERIALS AND METHODS

Denervation Surgery. Four-wk-old, White Leghorn chicks were used in these investigations instead of 7-wk-old broilers because doing so: 1) provided easier management of the Leghorns postoperative; 2) minimized the postoperative influences of sexual maturation on growth; and 3) determined the feasibility of operating on a smaller animal at an early age. Chicks were fasted for 4 h and anesthetized with sodium pentobarbital (36 mg/kg BW

intramuscularly, M. iliofibularis); the axillary region was defeathered; and a 3-cm incision in the skin was made caudal to the coracoscapulo-humeralis joint between the dorsolateral border of the M. pectoralis and the ventral border of the M. scapulohumeral. The photographs in Figure 1 are from a 28-wk-old chicken, showing the surgery on a larger bird. The N. medianoulnaris was located on the ventral surface of the wing craniomediad to the Vena axillaris (Figure 1A, right side; IB, left side) and was followed mediad to locate the N. pectoralis in the brachial plexus (Figure 1C, right side; ID, left side). The N. radialis is also located on the ventral surface of the wing but caudomediad to the vena axillaris, is larger in diameter, and should not be confused with the N. medianoulnaris. The distance from the N. medianoulnaris at which the N. pectoralis first branched ranged from within the N. medianoulnaris (Figure 1C) to more than 1-cm-deep into the M. pectoralis. When proximal branching occurred, it was important to cut both nerve branches. The N. pectoralis was cut first at 1 cm distal to the point of branching from the N. medianoulnaris (Figure IE, right side; IF, left side). A second cut was made at the point of branching from the N. medianoulnaris; the resulting 1-cm section of the A', pectoralis was removed. Since the N. pectoralis was first cut, the M. pectoralis contracted, adducting the wing and confirming nerve identification. The incision was sutured. The chicks were returned to battery cages for 1 wk, then placed by group (to prevent intergroup competition and pecking) into floor pens covered with shavings. Processing and Muscle Sampling. Muscles from 15, unoperated, control birds of each sex were processed for histology at 4 wk of age (0 wk postoperative). Muscle weights are reported as a percentage of the adjusted carcass weight to permit observations about relative hypertrophy or atrophy for individual muscles. Adjusted carcass weight was calculated from eviscerated carcass weight minus the weight of the breast muscles (die bilateral sum of the M. pectoralis, M. supracoracoideus, and M. coracobrachialis). The postoperative birds were weighed weekly to the nearest gram; complete weight records were obtained from 75 unoperated controls, 68 unilaterally denervated (right side), and 42 bilaterally denervated. Five birds of each sex from the unoperated control group and the unilateral group as well as four

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control (McGinnis et al., 1989). However, differences did not persist at 24 h post-mortem. Waiting for 3 days postoperative before processing denervated broilers further lowered lactate levels and maintained higher pH values (immediately post mortem), compared to nontreated control and denervated broilers which were processed 1 day postoperative. Necrobiotic muscle-twitching is coordinated into motor units in excised muscle (Swatland, 1976). The importance of post-mortem neuromuscular communication and its relation to the degree of muscle contraction at the onset of rigor are known. In the absence of the nervous stimuli that occur during and after the death struggle, isolating the M. pectoralis from the nervous system before slaughter would enable muscle measurements post mortem. Investigations utilizing denervation would identify the influences of the nervous system on the parameters of rigor mortis. To enable investigations about the influences of the nervous system and a severed neuromuscular pathway on the biochemical processes of the M. pectoralis post-mortem, a simple surgical method for severing the nervus (N.) pectoralis was desired. This study was designed to confirm the selectivity of denervation to the M. pectoralis while maintaining the neuromuscular integrity of the musculi (Mm) supracoracoideus and coracobrachialis. Selective denervation of a single M. pectoralis while maintaining the post-mortem death struggle minimizes the differences between experimental and commercial processing changes post mortem in the physiological conditions, which cannot be studied by the use of general anesthesia or neuromuscular blocking agents since they have far-reaching effects through the body. In addition, the extent to which denervation had an effect throughout the M. pectoralis was examined.

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mm FIGURE 1. Surgical procedures for locating and cutting the Nervus pectoralis in a 28-wk-old chicken; right side approach A, C and E, left side approach B, D, and F. VA = Vena axillaris. NR = Nervus radialis. NMU = Nervus medianoulnaris. NP = Nervus pectoralis. MP = Musculus pectoralis.

127

DENERVATION OF THE M. PECTORALIS MUSCLE

(cb)

(sc) (p)

FIGURE 2. Sampling zones for muscle tissue from the Musculus pectoralis (p) 1-7, M supracoracoideus (sc) 8 and 9, and M. coracobrachialis (cb) 10 from a 12-wk-old, unoperated chicken. Musculus pectoralis medial surface; M. supracoracoideus, and M. coracobrachialis, lateral surfaces.

breast muscles (Mm. pectoralis, supracoracoid, and coracobrachialis) with respect to M. pectoralis denervation (RC = right side for unoperated control; LC = left side for unoperated control; RR = right side for right denervated M. pectoralis; LR = left side for right denervated M. pectoralis; RB = right side for bilateral denervated M. pectoralis; and LB = left side for bilateral denervated M. pectoralis). The sex-by-treatment interactions were not significant (P>.01) for all three muscles. Therefore, relative muscle weights for the sexes were pooled within treatment group. Duncan's multiple range test was used to compare the means of different treatment groups at each sampling period (P<.01), since there were significant treatment-by-time interactions for the M. pectoralis and M. coracobrachialis. Linear regression equations were calculated by the least squares method, using the REG procedure from the Statistical Analysis System (SAS Institute, 1987) to determine relationships among main effects. The GLM proce-

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birds of each sex from the bilateral group were sampled every 2 wk up to 8 wk of age and then again at 17 wk. The birds were fasted for 2 h, killed with chloroform (5 min in a closed container with fumes vented by a chemical hood), weighed, partially eviscerated (the gastrointestinal tract and associated organs caudal to the proventriculus and the gonads were removed). The eviscerated carcasses were weighed. The M. pectoralis was excised by making a medial cut parallel to the keel, and a cranial-lateral cut along the clavicle, then peeling off the muscle from the ribs and cutting the tendon near the point of insertion on the humerus. The M. supracoracoideus was separated from the keel, and the proximal end of the tendon of insertion was cut. The M. coracobrachialis was removed by cutting the proximal end of the tendon of insertion and then separating it from the sternum. Muscles were removed bilaterally, weighed to the nearest .01 g, placed in plastic bags, and covered with ice. Muscle Histology. After 2 h on ice, pieces of muscle (10 by 10 mm, 3 to 4 mm thick) were cut transverse to the muscle fiber's long axis, attached to water-saturated cork squares, and plunged into isopentane (-135 C for 20 s) suspended in liquid nitrogen vapor. Frozen blocks were immediately placed on dry ice, heat-sealed in plastic envelopes, and stored in a deep freezer at -58 to -68 C until sectioned. Blocks were frozen from the Mm. pectoralis, Zones 1 through 7 (Figure 2), supra-coracoideus Zones 8 and 9, and from the coracobrachialis Zone 10. Transverse sections were cut at a thickness of 12 microns (at -20 C), picked up on warm glass slides, and allowed to dry for at least 1 h. The slides were fixed in formalin; one set was stained with Harris' hematoxylin and eosinorange G (Humason, 1979); another set, with Harris' hematoxylin and Gomori's trichrome (Sheehan and Hrapchak, 1980). Both sets of stained slides were dehydrated through a graded series of ethanol and xylene and coverslipped. The slides were examined; representative samples were photographed. Statistical Analysis. Data were subjected to ANOVA using the general linear model (GLM) from the Statistical Analysis System (SAS Institute, 1987) with a model that included treatment, sex, time, and time2 as the main effects and their interactions. Six treatment groups were designated for ipsilateral

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BUHR TABLE 1. Estimates of regression parameters (± SE) and goodness of fit (R2) for log body weight (g), and Musculus pectoralis, M. supracoracoideus, and M. coracobrachialis weights as a percentage of adjusted1 carcass weight, 0 to 17 wk postoperative

Variable

Y intercept

Quadratic slope (time2)

R2

2.19 ± .01 A 2.12 ± .01 B

.094883 ± .002029A .092376 ± .001829A

-.002217 ± .0OO089A .93 -.002168 ± .000079A .93

4.302 ± .063 A 4.127 ± .084 A

.041048 ± .003398A -.049341 ± .004651 8

-.000191 ± .0000298 .42 .000499 ± .000040A .59

1.428 ± .018 A 1.443 ± .020 A

.014395 ± .000978A .015932 ± .001093A

-.000071 ± .000008A .67 -.000082 ± .000009A .67

.160 ± .002 A .160 ± .003 A

.002267 ± .000118A .000580 ± .0000558

-.000012 ± .000001 NS

.73 .58

A

" Coefficients within parameters and variables with no common superscripts are significantly different (P<.01). Adjusted carcass = eviscerated carcass - (Musculus pectoralis + M. supracoracoideus + M. coracobrachialis).

dures were used for testing the heterogeneity of the coefficients for regression equations for the six treatment groups. No significant differences (P>.01) were detected between regression coefficients within the ipsilateral muscles where the M. pectoralis was denervated (RR, RB, and LB) or within the ipsilateral muscles where the M. pectoralis was unoperated (RC, LC, and LR). Therefore, combined regression coefficients for ipsilateral muscles with regard to denervated or unoperated M. pectoralis were calculated (Table 1). Standardized anatomical nomenclature is referenced from Nomina Anatomica Avium (Baumel et al., 1979).

Nondenervated M. pectoralis, ipsilateral M. supracoracoideus in the denervated and unoperated M. pectoralis treatment groups, and ipsilateral M. coracobrachialis in the unoperated M. pectoralis treatment group all increased in relative weight with age and had significant slope coefficients, positive linear and negative quadratic (Table 1), which agrees with the literature (Holiday et al., 1972; Moran, 1977). The relative weight of the denervated M. pectoralis was significantly reduced as early as Week 2 postoperative, compared to unoperated M. pectoralis at Week 2 or to the preoperative values (Figure 4).

RESULTS AND DISCUSSION

The body weight of White Leghorn cockerels or pullets did not differ significantly between the unoperated, control group and the unilateral or the bilateral, denervated groups throughout the 17-wk postoperative period (Figure 3). Cockerels were consistently and significantly (P<.01) heavier than pullets from the time of surgery at 4 wk of age. Regression analysis revealed significantly different Yintercepts, while the slopes of the linear and quadratic coefficients were not significantly different between the sexes (Table 1). Preoperative fasting for both the unoperated and operated groups may have helped to minimize any depression between treatment groups in BW due to recovery from surgery.

COCKERELS " a Control o o Unilateral a aBilateral

PULLETS — * Contro — • Unilateral lateral 3 4 5 6 7 WEEKS POSTOPERATIVE

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FIGURE 3. Postoperative body weight (± SE).

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LogBW Males Females M. pectoralis Unoperated Denervated M. supracoracoideus (Ipsilateral M. pectoralis) Unoperated Denervated M. coracobrachialis (Ipsilateral M. pectoralis) Unoperated Denervated

Linear slope (time)

DENERVATION OF THE M. PECTORALIS MUSCLE MUSCULUS PECTORALIS Control Unilateral

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Denervated M. pectoralis showed further reduction in weight at Week 4 postoperative, 48 to 56% smaller than the values for the unoperated muscles. This exceeded the 30 to 40% atrophy reported for denervated forearm muscles in mammals at 29 days postoperative (Sunderland and Ray, 1950). The differences may be explained by the predominance of type II fibers within the chicken M. pectoralis (Chandra-Bose et al, 1964) and the fact that type II fibers are more dependent on neurotrophic influences than type I fibers and also respond to denervation by a more rapid atrophy than do type I fibers (Engel et al., 1966; Engel and Karpati, 1968). The denervated M. pectoralis displayed minimal increases in relative weight by Weeks 6 and 8 postoperative, compared to the value at 4 wk postoperative. By 17 wk postoperative, the relative weights for denervated M. pectoralis had attained values above the preoperative 4% value. Regression analysis revealed negative linear slope coefficients and positive quadratic-slope coefficients for denervated M. pectoralis that were opposite in sign to the slope coefficients for unoperated M. pectoralis (Table 1). Denervation was confirmed histologically by the presence of atrophic and rounded muscle-fiber profiles, an increase in the endomysial and perimysial connective-tissue spaces, and leucocytes within degenerative

perimysial nerves (Figure 5B, D, and F). A reduction in the diameter of the fiber provides a more accurate measure of denervation atrophy than does the weight of the muscle (Engel et al., 1966). These signs of denervation are contrasted with unoperated M. pectoralis tissue (Figure 5A, C, and E) and were present throughout the seven sampling zones from the M. pectoralis, with no signs of denervation found in tissue from the M. supracoracoideus and M. coracobrachialis. Nervous innervation of the M. supracoracoideus arises deep within the brachial plexus proximal to the origin of the N. medianoulnaris, while the innervation of the M. coracobrachialis branches for the N. medianoulnaris but is proximal to the N. pectoralis, progressing craniomediad. Both nerves are easily distinguished from the N. pectoralis and avoided. The signs of denervation just discussed varied in degree between individuals, but were common in denervated muscle from Weeks 2 through 8 postoperative. These histological signs of denervation were in agreement with those from denervated mammalian muscle (Hines and Knowlton, 1933; Sunderland and Ray, 1950). Occasionally, degeneration of an individual muscle fiber was found in both unoperated and denervated muscle tissue. Neuromuscular spindles retained their characteristic morphological appearance and were readily identifiable in denervated tissue. By 17 wk postoperative, the N. pectoralis had reinnervated the M. pectoralis in some individuals. Reinnervation by the severed N. pectoralis was assessed grossly by the contraction of the M. pectoralis when the healed nerve was cut post mortem while excising the muscle, by increases in the relative weight of M. pectoralis (80% of the unoperated value), and histologically by smaller leucocyte aggregates within the perimysial nerve trunks and the appearance of some normal (nonatrophic) muscle fibers (Figure 5F). The relative weight of the functionally antagonistic M. supracoracoideus was not different in birds that had ipsilateral denervated M. pectoralis, compared to birds where the ipsilateral M. pectoralis was not denervated (Figure 6). Regression analysis revealed comparable slope coefficients, positive linear and negative quadratic (Table 1), for the M. supracoracoideus in both treatment groups (ipsilateral, denervated M. pectoralis and ipsilateral, unoperated M. pectoralis). Histological

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FIGURE 4. Postoperative Musculus pectoralis weight as a percentage of adjusted carcass weight. Adjusted carcass = eviscerated carcass - (Musculus pectoralis + M. supracoracoideus + M. coracobrachialis). Filled symbols indicated denervated Musculus pectoralis. Values between asterisks are significantly different (P<.01) from nondenervated Musculus pectoralis values.

129

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1 0 0 pm FIGURE 5. Transverse frozen sections from Zone 2 of the Musculus pectoralis at Weeks 4 (A and B), 8 (C and D), and 17 (E and F) postoperative. Unoperatcd: A, C, and E; denervated, B, D, and F. pn = perimysial nerve, pi = perimysial leucocytes, pet = perimysial connective tissue, ect = endomysial connective tissue, af = atrophic muscle fiber, nf = normal muscle fiber.

DENERVATION OF THE M. PECTORALIS MUSCLE MUSCULUS SUPRACORACOIDEUS Left

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signs of denervation were not found in the M. supracoracoideus from either treatment group. The relative weight of the functionally synergistic M. coracobrachialis in the treatment group with ipsilateral, denervated M. pectoralis was linear and lower in slope than for the treatment group where the ipsilateral M. pectoralis was unoperated (Table 1, Figure 7). Only in the treatment group with the unilaterally denervated M. pectoralis did the ipsilateral M. coracobrachialis remain depressed in relative weight at 17 wk postoperative. There were no histological signs of denervation in all M. coracobrachialis. All these patterns of relative muscle hypertrophy and atrophy were not expected. One would expect synergistic muscles to hypertrophy and antagonistic muscles to atrophy in order to compensate for the relative change in the load imposed on the muscle groups, following the loss of a muscle by excision, denervation, or tenectomy from a muscle group. The absence of atrophy in the M. supracoracoideus where the ipsilateral M. pectoralis was denervated indicated that there may be important, alternate functions for the M. supracoracoideus other than the abduction of the wing in direct opposition to the adduction by the M. pectoralis during wingflapping. Denervated birds could not be visually detected by wing-flapping behavior in floor pens. However, when the birds were released

FIGURE 7. Postoperative Musculus coracobrachialis weight as a percentage of adjusted carcass weight. Adjusted carcass = eviscerated carcass - (Musculus pectoralis + M. supracoracoideus + M. coracobrachialis). Filled symbols indicated ipsilateral denervated Musculus pectoralis. Values between asterisks are significantly different (P<.01) from values for Musculus coracobrachialis where the ipsilateral Musculus pectoralis was not denervated.

after weighing (at a height of about 1 m), the denervated birds flapped their wings but made litde forward progress, compared to unoperated control birds. The M. supracoracoideus may contribute largely to maintaining the resting posture of the wings. A different explanation may be that the maximal growth rate of the M. supracoracoideus was restricted by the adjacent and larger M. pectoralis, and that the denervation atrophy of the M. pectoralis removed some of die restrictions or limitations. The relative muscle atrophy found in the M. coracobrachialis through 8 wk postoperative (14 to 24% smaller than M. coracobrachialis values when the ipsilateral M. pectoralis was not denervated) may be an indication of disuse atrophy resulting from a reduced frequency of contraction in the denervated, synergistic M. pectoralis. Muscle atrophy commonly follows immobilization of a limb (Helander, 1957). The degree of atrophy is less than that produced by denervation, but may exceed 20% of the contralateral, nondenervated muscle at 3 wk postimmobilization (Wells, 1969). The present study confirmed that severing the N. pectoralis at the branching point from the N. medianoulnaris resulted in selective denervation of the M. pectoralis. The M. supracoracoideus and M. coracobrachialis

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FIGURE 6. Postoperative Musculus supracoracoideus weight as a percentage of adjusted carcass weight. Adjusted carcass = eviscerated carcass - (Musculus pectoralis + M. supracoracoideus + M. coracobrachialis). Filled symbols indicated ipsilateral denervated Musculus pectoralis.

4 6 WEEKS POSTOPERATIVE

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BUHR

were not denervated and, therefore, should not be combined with M. pectoralis for samples of breast meat in investigations examining postmortem muscle physiology as influenced by denervation. ACKNOWLEDGMENTS

REFERENCES Bate-Smith, E. C , and J. R. Bendall, 1949. Factors determining the time course of rigor mortis. J. Physiol. 110: 47-65. Baumel, J. J., A. S. King, A. M. Lucas, J. E. Breazile, and H. E. Evans, ed. 1979. Nomina Anatomica Avium. Academic Press, London, England, U.K. Chandra-Bose, D. A., N. J. Chinoy, and J. C. George, 1964. Studies on the structure and physiology of the flight muscles of birds. 10. Certain biochemical differences in the cellular organization of the fowl pectoralis. Pavo 2:61-64. de Fremery, D., 1966. Relationship between chemical properties and tenderness of poultry muscle. J. Agric. Food Chem. 14:214-217. de Fremery, D., and H. Lineweaver, 1962. Early postmortem chemical and tenderness changes in poultry. Volume 1: Pages 13-21 in: Food Science and Technology. J. M. Leitch, ed. Gordon and Breach Science Publ., New York, NY. de Fremery, D., and M. F. Pool, 1960. Biochemistry of chicken muscle as related to rigor mortis and tenderization. Food Res. 25:73-87. Engel, W. K., M. H. Brooke, and P. G. Nelson, 1966. Histochemical studies of denervated or tenotomized cat muscle: Illustrating difficulties in relating experimental animal conditions to human neuromuscular diseases. Ann. N.Y. Acad. Sci. 138:160-185. Engel, W. K„ and G. Karpati, 1968. Impaired skeletal muscle maturation following neonatal neurectomy. Dev. Biol. 17:713-723. Grey, T. C , J. M. Jones, and D. S. Robinson, 1974. The influence of death struggle on the rate of glycolysis in chicken breast muscle. J. Sci. Food Agric. 25:57-66. Helander, E., 1957. On quantitative muscle protein determination: Sarcoplasm and myofibril protein content of normal and atrophic skeletal muscles. Acta Physiol. Scand. 41(Suppl. 141):77-95. Hines, H. M., and G. C. Knowlton, 1933. Changes in the

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This study was supported in part by State of Georgia and Hatch funds allocated to the Georgia Agriculture Experiment Stations of the University of Georgia. The author is grateful to Rome Ethredge for technical assistance during this project.

skeletal muscle of the rat following denervation. Am. J. Physiol. 104:379-391. Holiday, T. A., L. M. Julian, and V. S. Asmundson, 1972. Muscle growth in selected lines of muscular dystrophic chickens. Anat. Rec. 160:207-216. Humason, G. L., 1979. Hematoxylin staining. Page 118 in: Animal Tissue Techniques. A. C. Bartelett, P. C. Vapnek, and S. Weisberg, ed. W. H. Freeman Co., San Francisco, CA. Khan, A. W., 1971. Effect of temperature during postmortem glycolysis and dephosphorylation of high energy phosphates on poultry meat tenderness. J. Food Sci. 36:120-121. Khan, A. W., 1974. Relation between isometric tension, postmortem pH decline and tenderness of poultry breast meat. J. Food Sci. 39:393-395. Khan, A. W., 1975. Effect of chemical treatments causing rapid onset of rigor on tenderness of poultry breast meat. J. Agric. Food Chem. 23:449-451. Khan, A. W., and R. Nakamura, 1970. Effects of pre- and postmortem glycolysis on poultry tenderness. J. Food Sci. 35:266-267. Klose, A. A., B. J. Luyet, and L. J. Menz, 1970. Effect of contraction on tenderness of poultry muscle cooked in the prerigor state. J. Food Sci. 35:577-581. Klose, A. A., R. N. Sayre, D. De Fremery, and M. F. Pool, 1972. Effect of hot cutting and related factors in commercial broiler processing on tenderness. Poultry Sci. 51:634-638. McGinnis, J. P., D. L. Fletcher, C. M. Papa, and R. J. Buhr, 1989. Early post-mortem metabolism and muscle shortening in the pectoralis major muscle of broiler chickens. Poultry Sci. 68:386-392. Moran, E. T., 1977. Growth and meat yield in poultry. Pages 145-173 in: Growth and poultry meat production. Proc. 12th Poultry Sci. Symp. K. N. Boorman and B. J. Wilson, ed. Br. Poult. Sci. Ltd., Longman Group Limited, Harlow, Essex, U.K. Pool, M. F., A. A. Campbell and A. A. Klose, 1959. Poultry tenderness. II. Influence of processing on tenderness of chickens. Food Technol. 13:25-29. SAS Institute, 1987. SAS/STAT Guide for Personal Computers, Version 6 ed. SAS Inst. Inc., Cary, NC. Sheehan. D. G, and B. B. Hrapchak, 1980. Connective tissue and muscle fiber stains. Pages 191-192 in: Theory and Practice of Histotechnology. C. V. Mosby Co., St. Louis, MO. Stewart, M. K., D. L. Fletcher, D. Hamm, and J. E. Thomson, 1984. The influence of hot boning broiler breast muscle on pH decline and toughening. Poultry Sci. 63: 1935-1939. Sunderland, S., and L. J. Ray, 1950. Denervation changes in mammalian striated muscle. J. Neurol. Neurosurg. Psychiatr. 13:159-177. Swatland, H. J., 1976. Motor unit activity in excised prerigor beef muscle. Can. Inst. Food Sci. Technol. J. 9: 177-181. Wells, J. B., 1969. Functional integrity of rat muscle after isometric immobilization. Exp. Neurol. 24:514-522.