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Chicken Breast Muscle Fiber Type and Diameter as Influenced by Age and Intramuscular Location
Chicken Breast Muscle Fiber Type and Diameter as Influenced by Age and Intramuscular Location D. P. SMITH and D. L. FLETCHER1 Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication September 28, 1987)
1988 Poultry Science 67:908-913 INTRODUCTION
A number of factors such as age, sex, and strain have been shown to affect meat tenderness. These factors have also been shown to affect muscle fiber type and diameter. However, few studies have established a direct cause and effect relationship between muscle fiber type and diameter to subsequent meat tenderness. Older birds have been shown to yield tougher meat than younger birds (Lowe, 1948; Shrimpton and Miller, 1960; May et al., 1962; Stadelman et al., 1966). Guhne (1970) stated age was a more important influence on breast meat tenderness than sex or body weight. Goodwin et al. (1969) reported that female broiler breast meat was tougher than male broiler breast meat. May et al. (1962) found that meat from 72-wk-old laying hens was significantly tougher than meat from 10-wk-old broilers. A positive relationship between muscle fiber diameter and meat toughness has been reported in red meat species (Hiner etal., 1953; Herring et al., 1965; Tuma et al., 1962). Fiber diameter has been shown to be affected by body weight, age and sex (Joubert, 1956; Varadarajulu and Cunning-
'To whom correspondence should be addressed.
908
ham, 1971). Thus, it is well established that as an animal ages, the muscle fiber diameter increases and the meat becomes tougher. Tuma et al. (1962) reported that the relationship between fiber diameter and shear force became variable when adjusted for age, indicating that age was more important than fiber diameter in meat tenderness. Age is also important for fiber type, as intermediate fibers change to white fibers (Ashmore and Doerr, 1971). Differences in muscle fiber diameter within specific muscles have been reported in bovine longissimus dorsi (Tuma et al., 1962), several muscles of the rat (Romanul, 1964; Gauthier, 1970) and chick sartorius and adductor muscles (Ashmore and Doerr, 1971). Papa and Fletcher (1988) reported that the post-mortem rate and degree of shortening were affected by location within the broiler pectoralis major muscle. Rate and degree of shortening have also been shown to influence subsequent meat texture. The purpose of this study was to determine if the locational differences reported by Papa and Fletcher (1988) could in part be explained by differences in muscle fiber type or diameter. Specific objectives included: 1) to determine muscle fiber type and diameter by location within the pectoralis major (p. major) and pectoralis minor (p. minor) muscles; 2) to compare muscle fiber type and diameters of different age
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 27, 2015
ABSTRACT Six trials were conducted to determine the influence of muscle (pectoralis major w& pectoralis minor) and location within the muscle on fiber type and diameter in four different age groups of chicken. Broilers obtained from a commercial processing plant, Athens Canadian Randombred chickens, roasters, and broiler breeder hens were killed via cervical dislocation. Muscle samples were removed from the anterior, middle, and posterior areas of the pectoralis major (p. major), and from the anterior and posterior areas of the pectoralis minor (p. minor). Frozen transverse muscle sections, 10 mm thick, were prepared at -20 C, stained for adenosine phosphatase activity, and photomicrographed for fiber typing and fiber diameter measurement. No differences were found in fiber types by age group, sex, or location within the muscle. The p. minor muscle had more intermediate fibers than the p. major muscle. Fiber diameters were significantly larger in the posterior portion of the p. major muscle than in the anterior or middle portions in two of the broiler trials, the female roasters, and the breeder hens. No significant differences in fiber diameter were noted for the p. minor muscle. (Key words: muscle fiber type, muscle fiber diameter, breast muscle, pectoralis major, pectoralis minor)
CHICKEN BREAST FIBER TYPE AND DIAMETER
chickens of four types: broilers, Athens Canadian Randombred (ACRB) chickens, roasters, and broiler breeder hens. MATERIALS AND METHODS
(Fisher Scientific, Fair Lawn, NJ). The preparations were then used for subsequent fiber type analysis and fiber diameter measurements. Each preparation was examined visually at 200 X magnification. Three separate fields (free of freezing and sectioning artifacts or blood vessels) from each sample preparation were photographed using Kodak Technical Pan #2315 film (Eastman Kodak, Rochester, NY) on a Leitz Ortholux II microscope (E. Leitz, Inc., Rockleigh, NJ). On each roll of film, one exposure was devoted to a photograph of a stage micrometer at the same magnification to act as a gauge for subsequent fiber diameter measurements. Fiber types were identified, counted, and expressed as a percentage of the number of fibers per field in two out of the three best negatives from each sample. Type I (red), intermediate, and Type II (white) fibers were identified according to the procedure descriptions of Sarnat (1983) and confirmed by comparison to gastrocnemius preparations. Five fiber diameters from each of the two photomicrographs per area were measured directly using the micrometer negative for each roll as a standard. Fiber diameter was defined as the shortest cross-section of each fiber. This resulted in ten fiber diameters from two separate preparations or fields per location, five locations/bird, or 400 total fiber diameter measurements/trial. Statistical analysis was performed using the Statistical Analysis System general linear models procedures and Duncan multiple range tests (SAS, 1982). Main effects were muscle, location within muscle, sex, and trial (or age group). Due to significant interactions among main effects, intramuscular location effects were determined by sex within trial (or age group) for each muscle. RESULTS AND DISCUSSION
Fiber Types. Examinations of the gastrocnemius muscle preparations (Trial 1) provided evidence of clearly differentiated red, intermediate, and white fiber types (data not shown), as described by Sarnat (1983). However, no Type I or red fibers were found in any of the fields from the p. major or p. minor preparations in any of the six trials. Muscle fibers in the broiler p. major muscle were observed to be almost exclusively Type II or white fibers. Only one intermediate fiber was found in the p. major in the three broiler trials, which calculated to
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 27, 2015
Eight birds for each of six trials were obtained and prepared as follows. Trials 1 to 3 used Peterson-Arbor Acre broilers obtained from a commercial processing plant at 55, 53, and 51 days of age, respectively. Birds were held at least 12 h, with free access to feed and water. Trial 4 was conducted using Peterson-Arbor Acre roaster chickens obtained from the same processing plant at broiler age, and held with free access to feed and water until 80 days of age. Trial 5 used ACRB chickens (Hess, 1962) at 81 days of age and treated the same as the broilers. Trial 6 was conducted using Arbor Acre broiler breeder hens obtained from a commercial breeding farm at 460 days of age and held for 36 h, with free access to feed and water. Birds were killed via cervical dislocation; skin and feathers were removed from the breast area, and tissue samples approximately 8 mm x 8mm x 3 mm were taken from three locations of the p.major (M. pectoralis, Baumel et al., 1979) and from two locations of the p. minor (M. supracoracoideus, Baumel et al., 1979) within 2 min of death. These areas corresponded to the anterior (cranial), middle and posterior (caudal) sections of p. major and p. minor muscles described by Papa and Fletcher (1988). The excised muscle sections were placed on cork pads, frozen at -160 C in 2-methylbutane cooled in liquid nitrogen (Sarnat, 1983; Dubowitze and Brooke, 1973), and stored at -50 C. The 40 samples (8 birds x 5 locations)/trial were brought to -20 C, trimmed square to facilitate transverse sectioning, and sectioned with a cryostat microtome (American Optical, Buffalo, NY). Three to six nonserial sections, 10 |xm thick and at least 100 |xm apart (in depth), were taken from each sample. Cut sections were placed on individual cover slips at room temperature and stained as a group using acid-preincubated myosin adenosine phosphatase (ATPase) stain at a pH of 4.3 (Sarnat, 1983). One broiler trial (Trial 3) used alkaline preincubated ATPase (pH 9.8) (Sarnat, 1983) to compare with the acid preincubation method. Sections prepared from the gastrocnemius (Trial 1) were used as a dark meat control to aid in identifying red fibers. The stained samples (on coverslips) were then mounted on microscope slides using Per-
909
910
SMITH AND FLETCHER
group) x location interactions, and also sex x location interactions, all data are presented by sex within each trial (or age group). Results for p. major and p. minor muscle fiber diameters for the broiler Trials 1 to 3 are presented in Table 1. In Trial 1, fiber diameters in the anterior sections for both males and females were significantly smaller (P<.05) than in the posterior sections. This pattern was also evident for both males and females in Trial 3, although no significant differences by location were observed in Trial 2. The significant location x trial interaction can be seen in the differences between the location patterns in Trial 2, in which the fiber diameters from the anterior, middle, and posterior locations were not significantly different, and Trials 1 and 3, where the anterior location's fiber diameters were significantly greater than those of either the middle or posterior location. The trial x sex interaction is apparent in Trial 1, where there was a significant difference between fiber diameters in the three locations in the males, but none between those in the anterior and middle locations of the females. No significant differences by location were found within the p. minor muscle. Mean diameters of p. major muscle fibers as determined in Trials 4 to 6 are presented in Table 2. Fiber diameters of ACRB (Trial 4) showed no significant differences with respect to location within the muscle. The same was true for the roaster males, although results for roaster females in Trial 4 were similar to those in Trials 1 and 3: fiber diameters in the anterior and middle locations were significantly less than those in the posterior location (P< .05). The diameters of p. major fibers in breeder hens were also significantly smaller in the anterior and middle locations than those in the posterior locations. The difference in fiber diameters by location between the male and female roasters explains the significant sex X location interaction. No significant differences in fiber diameter by location within the p. minor muscle were observed. Mean body weights by sex and averaged across sex for each of the age groups are presented in Table 3. As expected, males had significantly greater body weights than females in each of the classes, except for breeder hens, in which no male birds were included. Breeder hens had the highest body weights, followed by roasters, broilers, and ACRB chickens. The results from these experiments indicate that, although no difference in muscle fiber types could be detected, differences in muscle fiber
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less than a .01% occurrence. Approximately 1.8% of the fibers observed in the broiler p. minor were classified as intermediate. Broiler Trial 2, which used alkaline preincubated ATPase, produced results consistent with the acidpreincubated staining. Of the p. major samples examined for the ACRB chickens, only one intermediate fiber was observed, which calculated to a relative percentage of .03%. The p. minor had a higher percentage, with 5.6% of the fibers classified as intermediate. The roaster chickens exhibited no intermediate fibers in either of the pectoral muscles. The breeder hens also had no intermediate fibers in the p. major, but the p. minor was observed to have approximately 2.1% intermediate fibers. In the six trials, where there was a low occurrence of nonwhite fibers, no differences in fiber type were noted for locations or sexes. The relative ratios of intermediate to white fibers were similar to those in previous reports. Kiessling (1977) reported a ratio of 96% white and 4% red fibers in broiler p. major muscle, whereas Wiskus et al. (1976) reported a range of 90 to 100% white and 0 to 10% intermediate fibers in turkey breast muscle. In the present study, transverse muscle sections were excised from the central portions of the muscle locations, and further trimming before sectioning would have given a sample from the center of the muscle. Samples taken from the smaller birds (ACRB) resulted in proportionately less trim and a sample which contained more peripheral tissue. Suzuki (1978) used an alkaline preincubation ATPase stain to characterize muscle fiber types within superficial and deep regions (near the sternum) of the p. major in chicken. The superficial area was composed of over 99% white fibers, with the rest being intermediate. The deeper region, closer to the sternum, contained 54% intermediate fibers, almost 17% white fibers, and 29% red fibers. Suzuki's results were based on deep samples taken from broilers and young layer-type birds (6 wk old) and superficial samples from older layers (adults); however, the superficial samples were taken from the middle portion of the muscle, whereas the deep samples were taken from the anterior (cranial) region of the muscle.This could partially explain why no red and very few intermediate fibers were found in the present study. Fiber Diameters. Muscle fiber diameter data were analyzed by muscle and location within muscle. As there were a number of trial (or age
59 : 11*
9a 9a 49 : 1 2 a
46 ± 10 D 44 ± ll b 64 ± 13 a
46 ± 1 0 D 43 ± 10 c 54 ± 12 a
50 ± 46 ±
Female
Male
48 ± 14a 51 ± 1 4 a
49 ± 11" 43 ± 1 2 a 49 + 1 4 a
Male
51 ± l l a 51 ± 9 a 57 ± 1 7 a 63 ± 13 a 56 ± 1 0 a
53 ± 10a 56 ± 1 3 a 54 + 1 3 a
55 : 17 a 55 : 15 a
46 ± 10 a 50 ± ll a
Male (Mm)
Roasters
53 : 13 a 49 : 12 a 46 : 10 a
Female
ACRB (Trial 4) Male
a.b'Means within each column and muscle with differing superscripts are significantly different (P-C05).
Pectoralis minor
Anterior Middle Posterior Anterior Posterior
Intramuscular location
4 5
5 4 5
F
Athens
(Mm)
TABLE 2, Mean diameter (± SD) ofpectoralis major and minor muscle fibers by location and sex from roaster, and broiler breeder hens
Pectoralis major
Muscle
Anterior Middle Posterior Anterior Posterior
Intramuscular location
Means within each column and muscle with differing superscripts are significantly different (P-C05).
Pectoralis minor
Pectoralis major
Muscle
TABLE 1. Pectoralis major and minor muscle fiber diameter means (± SD) by location and sex f
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912
SMITH AND FLETCHER TABLE 3. Mean body weights (± SD) by age group and sex
Sex
Broilers1
ACRB 2
Male Female
2,216 ± 148 a 1,744 ± 7 1 b
X
2,039 ± 276^
Roasters
Breeder hens
2,002 ± 191 a 1,630 ± 9 5 b
2,770 ± 278 a 2,472 ± 357 b
3,714 + 293
1,863 ± 246 z
2,584 ± 345 x
3,714 ± 293 v
(g)
a ' b Means in each column with differing superscripts are significantly different (P<.05). Means in each row with differing superscripts are significantly different (P<.05). 1
Average of Trials 1 to 3.
2
Athens Canadian Randombred chickens.
ACKNOWLEDGMENT
This study was supported in part by state and Hatch funds allocated to the Georgia Agricultural Experiment Stations of the University of Georgia. REFERENCES Ashmore, C. R., andL. Doerr, 1971. Postnatal development of fiber types in normal and dystrophic skeletal muscle of the chick. Exp. Neurol. 30:431^136. 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, UK. Dubowitze, V., and M. H. Brooke, 1973. Muscle Biopsy: A Modern Approach. W. B. Saunders Co., London, England UK. Forrest, J. C , E. D. Aberle, H. B. Hedrick, M. D. Judge, and R. A. Merkel, 1975. Principles of Meat Science. W. H. Freeman and Co., San Francisco, CA.
Gauthier, G. F., 1970. The ultrastmcture of three fiber types in mammalian skeletal muscle. Pages 103-130 in: Physiology and Biochemistry of Muscle as Food. 2nd ed. E. J. Brisky, R. G. Cassens, and B. B. Marsh, ed., Univ. Wise. Press, Madison, WI. Goodwin, T. L., L. E. Andrews, and J. E. Webb, 1969. The influence of age, sex, and energy level on the tenderness of broilers. Poultry Sci. 48:548-552. Guhne, W., 1970. Tenderness of broiler meat dependent on weight, sex, and age of the birds. World's Poult. Sci. J. 26:739. (Abstr.) Herring, H. K., R. G. Cassens, and E. J. Briskey, 1965. Further studies on bovine muscle tenderness as influenced by carcass position, sarcomere length, and fiber diameter. J. Food Sci. 30:1049-1054. Hess, C. W., 1962. Randombred populations of the Southern Regional Poultry Breeding Project. World's Poult. Sci. J. 18:147-152. Hiner, R. L., O. G. Hankins, H. S. Sloane, C. R. Fellers, and E. E. Anderson, 1953. Fiber diameter in relation to tenderness of beef muscle. Food Res. 18:364-376. Joubert, D. M., 1956. An analysis of factors influencing postnatal growth and development of the muscle fibre. J. Agric. Sci. 47:59-102. Kiessling, K. H., 1977. Muscle structure and function in the goose, quail, pheasant, guinea hen, and chicken. Comp. Biochem. Physiol. 57:287-292. Lowe, B., 1948. Factors affecting the palatability of poultry with emphasis on histological post-mortem changes. Adv. Food Res. 1:203-256. May, K. N., R. L. Saffle, D. L. Downing, and J. J. Powers, 1962. Interrelations of post-mortem changes with tenderness of chicken and pork. Food Technol. 16:72-78. Papa, C. M., and D. L. Fletcher, 1988. Pectoralis muscle shortening and rigor development at different locations within the broiler breast. Poultry Sci. (in press). Romanul, F.C.A., 1964. Enzymes in muscle. I. Histochemical studies of enzymes in individual muscle fibers. Arch. Neurol. 2:355-368. Sarnat, H. B., 1983. Muscle Pathology and Histochemistry. Am. Soc. Clin. Pathol. Press, Chicago, IL. SAS Institute, Inc., 1982. SAS User's Guide: Statistics. SAS Inst., Inc., Cary, NC. Shrimpton, D. H., and W. S. Miller, 1960. Some causes of toughness in broilers. II. Effects of breed, management, and sex. Br. Poult. Sci. 1:111-120. Stadelman, W. J., G. C. Mostert, and R. B. Harrington,
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 27, 2015
diameters existed with respect to locations within the broiler p. major muscle. These differences in muscle fiber diameter may be related to differences in rate of rigor onset and degree of sarcomere shortening previously reported by Papa and Fletcher (1988). It is well documented in red meat species that muscle fiber diameter increases with age up to maturity. Because male chickens were significantly heavier than females, but no consistent pattern in muscle fiber diameter with respect to sex was noted-although in red meat species males generally have larger muscle fiber diameters (Forrest et al., 1975)—it appears that muscle fiber diameter is influenced more by age than body size. It would also appear that, as posterior muscle portions consistently had larger-diameter fibers across all classes, differences by location within muscle are a histological constant, and not the result of relative fiber maturity within the muscle.
CHICKEN BREAST FIBER TYPE AND DIAMETER 1966. Effect of aging time, sex, strain, and age on resistance to shear of turkey meat. Food Technol. 20:110-114. Suzuki, A., 1978. Histochemistry of the chicken skeletal muscles. II. Distribution and diameter of three fiber types. Tohoku J. Agric. Res. 29:38-41. Tuma, H. J., J. H. Venable, P. R. Wuthier, and R. L. Hendrickson, 1962. Relationship of fiber diameter to
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tenderness and meatiness as influenced by bovine age. J. Anim. Sci. 21:33-36. Varadarajulu, P., and F. E. Cunningham, 1971. A histological study of turkey meat as related to sensory characteristics. Poultry Sci. 50:1144-1149. Wiskus, K. J., P. B. Addis, and R. T-I. Ma, 1976. Distribution of 4R, 2R, and 2W fibers in turkey muscles. Poultry Sci. 55:562-572.
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1988 Poultry Science 67:908-913 INTRODUCTION
A number of factors such as age, sex, and strain have been shown to affect meat tenderness. These factors have also been shown to affect muscle fiber type and diameter. However, few studies have established a direct cause and effect relationship between muscle fiber type and diameter to subsequent meat tenderness. Older birds have been shown to yield tougher meat than younger birds (Lowe, 1948; Shrimpton and Miller, 1960; May et al., 1962; Stadelman et al., 1966). Guhne (1970) stated age was a more important influence on breast meat tenderness than sex or body weight. Goodwin et al. (1969) reported that female broiler breast meat was tougher than male broiler breast meat. May et al. (1962) found that meat from 72-wk-old laying hens was significantly tougher than meat from 10-wk-old broilers. A positive relationship between muscle fiber diameter and meat toughness has been reported in red meat species (Hiner etal., 1953; Herring et al., 1965; Tuma et al., 1962). Fiber diameter has been shown to be affected by body weight, age and sex (Joubert, 1956; Varadarajulu and Cunning-
'To whom correspondence should be addressed.
908
ham, 1971). Thus, it is well established that as an animal ages, the muscle fiber diameter increases and the meat becomes tougher. Tuma et al. (1962) reported that the relationship between fiber diameter and shear force became variable when adjusted for age, indicating that age was more important than fiber diameter in meat tenderness. Age is also important for fiber type, as intermediate fibers change to white fibers (Ashmore and Doerr, 1971). Differences in muscle fiber diameter within specific muscles have been reported in bovine longissimus dorsi (Tuma et al., 1962), several muscles of the rat (Romanul, 1964; Gauthier, 1970) and chick sartorius and adductor muscles (Ashmore and Doerr, 1971). Papa and Fletcher (1988) reported that the post-mortem rate and degree of shortening were affected by location within the broiler pectoralis major muscle. Rate and degree of shortening have also been shown to influence subsequent meat texture. The purpose of this study was to determine if the locational differences reported by Papa and Fletcher (1988) could in part be explained by differences in muscle fiber type or diameter. Specific objectives included: 1) to determine muscle fiber type and diameter by location within the pectoralis major (p. major) and pectoralis minor (p. minor) muscles; 2) to compare muscle fiber type and diameters of different age
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 27, 2015
ABSTRACT Six trials were conducted to determine the influence of muscle (pectoralis major w& pectoralis minor) and location within the muscle on fiber type and diameter in four different age groups of chicken. Broilers obtained from a commercial processing plant, Athens Canadian Randombred chickens, roasters, and broiler breeder hens were killed via cervical dislocation. Muscle samples were removed from the anterior, middle, and posterior areas of the pectoralis major (p. major), and from the anterior and posterior areas of the pectoralis minor (p. minor). Frozen transverse muscle sections, 10 mm thick, were prepared at -20 C, stained for adenosine phosphatase activity, and photomicrographed for fiber typing and fiber diameter measurement. No differences were found in fiber types by age group, sex, or location within the muscle. The p. minor muscle had more intermediate fibers than the p. major muscle. Fiber diameters were significantly larger in the posterior portion of the p. major muscle than in the anterior or middle portions in two of the broiler trials, the female roasters, and the breeder hens. No significant differences in fiber diameter were noted for the p. minor muscle. (Key words: muscle fiber type, muscle fiber diameter, breast muscle, pectoralis major, pectoralis minor)
CHICKEN BREAST FIBER TYPE AND DIAMETER
chickens of four types: broilers, Athens Canadian Randombred (ACRB) chickens, roasters, and broiler breeder hens. MATERIALS AND METHODS
(Fisher Scientific, Fair Lawn, NJ). The preparations were then used for subsequent fiber type analysis and fiber diameter measurements. Each preparation was examined visually at 200 X magnification. Three separate fields (free of freezing and sectioning artifacts or blood vessels) from each sample preparation were photographed using Kodak Technical Pan #2315 film (Eastman Kodak, Rochester, NY) on a Leitz Ortholux II microscope (E. Leitz, Inc., Rockleigh, NJ). On each roll of film, one exposure was devoted to a photograph of a stage micrometer at the same magnification to act as a gauge for subsequent fiber diameter measurements. Fiber types were identified, counted, and expressed as a percentage of the number of fibers per field in two out of the three best negatives from each sample. Type I (red), intermediate, and Type II (white) fibers were identified according to the procedure descriptions of Sarnat (1983) and confirmed by comparison to gastrocnemius preparations. Five fiber diameters from each of the two photomicrographs per area were measured directly using the micrometer negative for each roll as a standard. Fiber diameter was defined as the shortest cross-section of each fiber. This resulted in ten fiber diameters from two separate preparations or fields per location, five locations/bird, or 400 total fiber diameter measurements/trial. Statistical analysis was performed using the Statistical Analysis System general linear models procedures and Duncan multiple range tests (SAS, 1982). Main effects were muscle, location within muscle, sex, and trial (or age group). Due to significant interactions among main effects, intramuscular location effects were determined by sex within trial (or age group) for each muscle. RESULTS AND DISCUSSION
Fiber Types. Examinations of the gastrocnemius muscle preparations (Trial 1) provided evidence of clearly differentiated red, intermediate, and white fiber types (data not shown), as described by Sarnat (1983). However, no Type I or red fibers were found in any of the fields from the p. major or p. minor preparations in any of the six trials. Muscle fibers in the broiler p. major muscle were observed to be almost exclusively Type II or white fibers. Only one intermediate fiber was found in the p. major in the three broiler trials, which calculated to
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 27, 2015
Eight birds for each of six trials were obtained and prepared as follows. Trials 1 to 3 used Peterson-Arbor Acre broilers obtained from a commercial processing plant at 55, 53, and 51 days of age, respectively. Birds were held at least 12 h, with free access to feed and water. Trial 4 was conducted using Peterson-Arbor Acre roaster chickens obtained from the same processing plant at broiler age, and held with free access to feed and water until 80 days of age. Trial 5 used ACRB chickens (Hess, 1962) at 81 days of age and treated the same as the broilers. Trial 6 was conducted using Arbor Acre broiler breeder hens obtained from a commercial breeding farm at 460 days of age and held for 36 h, with free access to feed and water. Birds were killed via cervical dislocation; skin and feathers were removed from the breast area, and tissue samples approximately 8 mm x 8mm x 3 mm were taken from three locations of the p.major (M. pectoralis, Baumel et al., 1979) and from two locations of the p. minor (M. supracoracoideus, Baumel et al., 1979) within 2 min of death. These areas corresponded to the anterior (cranial), middle and posterior (caudal) sections of p. major and p. minor muscles described by Papa and Fletcher (1988). The excised muscle sections were placed on cork pads, frozen at -160 C in 2-methylbutane cooled in liquid nitrogen (Sarnat, 1983; Dubowitze and Brooke, 1973), and stored at -50 C. The 40 samples (8 birds x 5 locations)/trial were brought to -20 C, trimmed square to facilitate transverse sectioning, and sectioned with a cryostat microtome (American Optical, Buffalo, NY). Three to six nonserial sections, 10 |xm thick and at least 100 |xm apart (in depth), were taken from each sample. Cut sections were placed on individual cover slips at room temperature and stained as a group using acid-preincubated myosin adenosine phosphatase (ATPase) stain at a pH of 4.3 (Sarnat, 1983). One broiler trial (Trial 3) used alkaline preincubated ATPase (pH 9.8) (Sarnat, 1983) to compare with the acid preincubation method. Sections prepared from the gastrocnemius (Trial 1) were used as a dark meat control to aid in identifying red fibers. The stained samples (on coverslips) were then mounted on microscope slides using Per-
909
910
SMITH AND FLETCHER
group) x location interactions, and also sex x location interactions, all data are presented by sex within each trial (or age group). Results for p. major and p. minor muscle fiber diameters for the broiler Trials 1 to 3 are presented in Table 1. In Trial 1, fiber diameters in the anterior sections for both males and females were significantly smaller (P<.05) than in the posterior sections. This pattern was also evident for both males and females in Trial 3, although no significant differences by location were observed in Trial 2. The significant location x trial interaction can be seen in the differences between the location patterns in Trial 2, in which the fiber diameters from the anterior, middle, and posterior locations were not significantly different, and Trials 1 and 3, where the anterior location's fiber diameters were significantly greater than those of either the middle or posterior location. The trial x sex interaction is apparent in Trial 1, where there was a significant difference between fiber diameters in the three locations in the males, but none between those in the anterior and middle locations of the females. No significant differences by location were found within the p. minor muscle. Mean diameters of p. major muscle fibers as determined in Trials 4 to 6 are presented in Table 2. Fiber diameters of ACRB (Trial 4) showed no significant differences with respect to location within the muscle. The same was true for the roaster males, although results for roaster females in Trial 4 were similar to those in Trials 1 and 3: fiber diameters in the anterior and middle locations were significantly less than those in the posterior location (P< .05). The diameters of p. major fibers in breeder hens were also significantly smaller in the anterior and middle locations than those in the posterior locations. The difference in fiber diameters by location between the male and female roasters explains the significant sex X location interaction. No significant differences in fiber diameter by location within the p. minor muscle were observed. Mean body weights by sex and averaged across sex for each of the age groups are presented in Table 3. As expected, males had significantly greater body weights than females in each of the classes, except for breeder hens, in which no male birds were included. Breeder hens had the highest body weights, followed by roasters, broilers, and ACRB chickens. The results from these experiments indicate that, although no difference in muscle fiber types could be detected, differences in muscle fiber
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 27, 2015
less than a .01% occurrence. Approximately 1.8% of the fibers observed in the broiler p. minor were classified as intermediate. Broiler Trial 2, which used alkaline preincubated ATPase, produced results consistent with the acidpreincubated staining. Of the p. major samples examined for the ACRB chickens, only one intermediate fiber was observed, which calculated to a relative percentage of .03%. The p. minor had a higher percentage, with 5.6% of the fibers classified as intermediate. The roaster chickens exhibited no intermediate fibers in either of the pectoral muscles. The breeder hens also had no intermediate fibers in the p. major, but the p. minor was observed to have approximately 2.1% intermediate fibers. In the six trials, where there was a low occurrence of nonwhite fibers, no differences in fiber type were noted for locations or sexes. The relative ratios of intermediate to white fibers were similar to those in previous reports. Kiessling (1977) reported a ratio of 96% white and 4% red fibers in broiler p. major muscle, whereas Wiskus et al. (1976) reported a range of 90 to 100% white and 0 to 10% intermediate fibers in turkey breast muscle. In the present study, transverse muscle sections were excised from the central portions of the muscle locations, and further trimming before sectioning would have given a sample from the center of the muscle. Samples taken from the smaller birds (ACRB) resulted in proportionately less trim and a sample which contained more peripheral tissue. Suzuki (1978) used an alkaline preincubation ATPase stain to characterize muscle fiber types within superficial and deep regions (near the sternum) of the p. major in chicken. The superficial area was composed of over 99% white fibers, with the rest being intermediate. The deeper region, closer to the sternum, contained 54% intermediate fibers, almost 17% white fibers, and 29% red fibers. Suzuki's results were based on deep samples taken from broilers and young layer-type birds (6 wk old) and superficial samples from older layers (adults); however, the superficial samples were taken from the middle portion of the muscle, whereas the deep samples were taken from the anterior (cranial) region of the muscle.This could partially explain why no red and very few intermediate fibers were found in the present study. Fiber Diameters. Muscle fiber diameter data were analyzed by muscle and location within muscle. As there were a number of trial (or age
59 : 11*
9a 9a 49 : 1 2 a
46 ± 10 D 44 ± ll b 64 ± 13 a
46 ± 1 0 D 43 ± 10 c 54 ± 12 a
50 ± 46 ±
Female
Male
48 ± 14a 51 ± 1 4 a
49 ± 11" 43 ± 1 2 a 49 + 1 4 a
Male
51 ± l l a 51 ± 9 a 57 ± 1 7 a 63 ± 13 a 56 ± 1 0 a
53 ± 10a 56 ± 1 3 a 54 + 1 3 a
55 : 17 a 55 : 15 a
46 ± 10 a 50 ± ll a
Male (Mm)
Roasters
53 : 13 a 49 : 12 a 46 : 10 a
Female
ACRB (Trial 4) Male
a.b'Means within each column and muscle with differing superscripts are significantly different (P-C05).
Pectoralis minor
Anterior Middle Posterior Anterior Posterior
Intramuscular location
4 5
5 4 5
F
Athens
(Mm)
TABLE 2, Mean diameter (± SD) ofpectoralis major and minor muscle fibers by location and sex from roaster, and broiler breeder hens
Pectoralis major
Muscle
Anterior Middle Posterior Anterior Posterior
Intramuscular location
Means within each column and muscle with differing superscripts are significantly different (P-C05).
Pectoralis minor
Pectoralis major
Muscle
TABLE 1. Pectoralis major and minor muscle fiber diameter means (± SD) by location and sex f
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SMITH AND FLETCHER TABLE 3. Mean body weights (± SD) by age group and sex
Sex
Broilers1
ACRB 2
Male Female
2,216 ± 148 a 1,744 ± 7 1 b
X
2,039 ± 276^
Roasters
Breeder hens
2,002 ± 191 a 1,630 ± 9 5 b
2,770 ± 278 a 2,472 ± 357 b
3,714 + 293
1,863 ± 246 z
2,584 ± 345 x
3,714 ± 293 v
(g)
a ' b Means in each column with differing superscripts are significantly different (P<.05). Means in each row with differing superscripts are significantly different (P<.05). 1
Average of Trials 1 to 3.
2
Athens Canadian Randombred chickens.
ACKNOWLEDGMENT
This study was supported in part by state and Hatch funds allocated to the Georgia Agricultural Experiment Stations of the University of Georgia. REFERENCES Ashmore, C. R., andL. Doerr, 1971. Postnatal development of fiber types in normal and dystrophic skeletal muscle of the chick. Exp. Neurol. 30:431^136. 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, UK. Dubowitze, V., and M. H. Brooke, 1973. Muscle Biopsy: A Modern Approach. W. B. Saunders Co., London, England UK. Forrest, J. C , E. D. Aberle, H. B. Hedrick, M. D. Judge, and R. A. Merkel, 1975. Principles of Meat Science. W. H. Freeman and Co., San Francisco, CA.
Gauthier, G. F., 1970. The ultrastmcture of three fiber types in mammalian skeletal muscle. Pages 103-130 in: Physiology and Biochemistry of Muscle as Food. 2nd ed. E. J. Brisky, R. G. Cassens, and B. B. Marsh, ed., Univ. Wise. Press, Madison, WI. Goodwin, T. L., L. E. Andrews, and J. E. Webb, 1969. The influence of age, sex, and energy level on the tenderness of broilers. Poultry Sci. 48:548-552. Guhne, W., 1970. Tenderness of broiler meat dependent on weight, sex, and age of the birds. World's Poult. Sci. J. 26:739. (Abstr.) Herring, H. K., R. G. Cassens, and E. J. Briskey, 1965. Further studies on bovine muscle tenderness as influenced by carcass position, sarcomere length, and fiber diameter. J. Food Sci. 30:1049-1054. Hess, C. W., 1962. Randombred populations of the Southern Regional Poultry Breeding Project. World's Poult. Sci. J. 18:147-152. Hiner, R. L., O. G. Hankins, H. S. Sloane, C. R. Fellers, and E. E. Anderson, 1953. Fiber diameter in relation to tenderness of beef muscle. Food Res. 18:364-376. Joubert, D. M., 1956. An analysis of factors influencing postnatal growth and development of the muscle fibre. J. Agric. Sci. 47:59-102. Kiessling, K. H., 1977. Muscle structure and function in the goose, quail, pheasant, guinea hen, and chicken. Comp. Biochem. Physiol. 57:287-292. Lowe, B., 1948. Factors affecting the palatability of poultry with emphasis on histological post-mortem changes. Adv. Food Res. 1:203-256. May, K. N., R. L. Saffle, D. L. Downing, and J. J. Powers, 1962. Interrelations of post-mortem changes with tenderness of chicken and pork. Food Technol. 16:72-78. Papa, C. M., and D. L. Fletcher, 1988. Pectoralis muscle shortening and rigor development at different locations within the broiler breast. Poultry Sci. (in press). Romanul, F.C.A., 1964. Enzymes in muscle. I. Histochemical studies of enzymes in individual muscle fibers. Arch. Neurol. 2:355-368. Sarnat, H. B., 1983. Muscle Pathology and Histochemistry. Am. Soc. Clin. Pathol. Press, Chicago, IL. SAS Institute, Inc., 1982. SAS User's Guide: Statistics. SAS Inst., Inc., Cary, NC. Shrimpton, D. H., and W. S. Miller, 1960. Some causes of toughness in broilers. II. Effects of breed, management, and sex. Br. Poult. Sci. 1:111-120. Stadelman, W. J., G. C. Mostert, and R. B. Harrington,
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diameters existed with respect to locations within the broiler p. major muscle. These differences in muscle fiber diameter may be related to differences in rate of rigor onset and degree of sarcomere shortening previously reported by Papa and Fletcher (1988). It is well documented in red meat species that muscle fiber diameter increases with age up to maturity. Because male chickens were significantly heavier than females, but no consistent pattern in muscle fiber diameter with respect to sex was noted-although in red meat species males generally have larger muscle fiber diameters (Forrest et al., 1975)—it appears that muscle fiber diameter is influenced more by age than body size. It would also appear that, as posterior muscle portions consistently had larger-diameter fibers across all classes, differences by location within muscle are a histological constant, and not the result of relative fiber maturity within the muscle.
CHICKEN BREAST FIBER TYPE AND DIAMETER 1966. Effect of aging time, sex, strain, and age on resistance to shear of turkey meat. Food Technol. 20:110-114. Suzuki, A., 1978. Histochemistry of the chicken skeletal muscles. II. Distribution and diameter of three fiber types. Tohoku J. Agric. Res. 29:38-41. Tuma, H. J., J. H. Venable, P. R. Wuthier, and R. L. Hendrickson, 1962. Relationship of fiber diameter to
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tenderness and meatiness as influenced by bovine age. J. Anim. Sci. 21:33-36. Varadarajulu, P., and F. E. Cunningham, 1971. A histological study of turkey meat as related to sensory characteristics. Poultry Sci. 50:1144-1149. Wiskus, K. J., P. B. Addis, and R. T-I. Ma, 1976. Distribution of 4R, 2R, and 2W fibers in turkey muscles. Poultry Sci. 55:562-572.
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