Poult. Sci.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Poult Sci 2007. 86:2134-2138
© 2007 Poultry Science Association
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Velleman, S. G.
Right arrow Articles by Nestor, K. E.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Velleman, S. G.
Right arrow Articles by Nestor, K. E.

GENETICS

The Effect of Genetic Increases in Egg Production and Age and Sex on Breast Muscle Development of Turkeys1

S. G. Velleman2, C. S. Coy, J. W. Anderson and K. E. Nestor

Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691

2 Corresponding author: velleman.1{at}osu.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Pectoralis major muscle morphology was studied in both sexes of a turkey line (E) selected long-term for increased egg production and its randombred control (RBC1) from 25 d of incubation through 20 wk posthatch. Pectoralis major muscle samples from 10 individuals from each line-sex-age subgroup were obtained in a manner to prevent contraction. The muscle samples were dehydrated, cleared, embedded in paraffin, sectioned, incubated, and rehydrated before staining with hematoxylin and eosin. Representative sections were given a score by 4 individuals based on breast muscle morphology. The scores ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Scores from 2 to 4 were intermediate to these extremes. The pectoralis major muscle morphology scores were highest at 25 d of incubation and declined greatly at 1 wk of age. The scores increased from 1 to 4 wk of age and remained constant through 20 wk of age. Males had higher scores than females. In the current study, there was no significant difference between the E and RBC1 lines. Based on the results of 3 experiments (2 published and the present one) using the E and RBC1 lines, it appears that genetic increases in egg production may be associated with a slight reduction in pectoralis major muscle morphology scores at 16 wk of age.

Key Words: turkey • egg production • age • sex • breast muscle morphology


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Commercial turkeys are the result of a cross of a sire line (or sire line cross) and a dam line (or dam line cross). In general, sire lines are selected for improved growth-related traits, whereas dam lines are selected for both increased growth and improved reproduction traits. Because breast muscles are very important commercially, major emphasis has been placed on improving conformation of the turkey. Although growth rate and muscling have improved in commercial turkeys over the years (Nestor et al., 1969; Havenstein et al., 2004, 2007), problems have developed. The turkey processing industry has experienced a meat quality problem that is similar to the pale, soft, and exudative (PSE) condition in swine (Sosnicki and Wilson, 1991). Turkey PSE meat when cooked has a soft texture, poor meat binding, poor juiciness due to reduced water-holding capacity, and increased yield losses.

The PSE condition in turkeys may be associated with changes in the turkey musculoskeletal system resulting from selection for increased growth rate. Wilson et al. (1990) studied muscle structure and enzyme activity to 16 wk of age in turkey lines selected for rapid growth. Muscle damage was observed in all lines studied. However, more muscle degeneration and higher levels of plasma creatine kinase were observed in the faster-growing lines.

Velleman et al. (2003b) compared breast muscle development in an experimental turkey line (F) selected long-term for increased 16-wk BW, its randombred control line (RBC2), and a commercial sire line (B). Beginning at 8 wk posthatch, differences in breast muscle fiber morphology were observed among the different lines. The RBC2 line maintained well-organized muscle fibers and muscle fiber bundles with large capillary networks throughout the duration of the study from 25 d of incubation through 20 wk posthatch. In contrast, the F line began to show muscle fiber degeneration at 8 wk post-hatch, and limited capillary beds were observed as development proceeded. The B line had intermediate muscle morphology between the F and RBC2 lines, but by 20 wk posthatch, significant muscle fiber degeneration was present with limited capillary supply.

During the study of Velleman et al. (2003b), it was apparent that visual observation of muscle sections was sometimes more informative than actual tissue measurements in evaluating breast muscle morphology. In later studies (Velleman et al., 2003a; Velleman and Nestor, 2004, 2005, 2006), a subjective rating system was developed in which muscle sections were analyzed by 4 people familiar with muscle morphology. Scores were assigned from 1 to 5, with 1 indicating little or no extracellular matrix and indistinct muscle fibers and 5 indicating large extracellular spacing and distinct muscle fibers. Ratings of 2 to 4 were intermediate to these extremes.

Using the breast muscle morphology scores, Velleman et al. (2003a) found that maternal inheritance was an important source of variation at 16 wk of age in reciprocal crosses of the F and B lines. The breast muscle morphology scores of the F1 individuals were similar to those of the female parent. Similar results were obtained in reciprocal crosses of the F and RBC2 lines by Velleman and Nestor (2004) and in reciprocal crosses of a line (E) selected long-term for increased egg production and its randombred control (RBC1) by Velleman and Nestor (2006).

Because the commercial turkey is produced by crossing sire and dam lines, and maternal inheritance was observed in breast muscle morphology, the effect of genetic increases in egg production on breast muscle morphology scores was studied by Velleman and Nestor (2005, 2006) by comparing the E and RBC1 lines. When the scores were based on birds at 8 and 16 wk of age, there was no significant difference in the scores between lines, but the lines interacted with age. At 16 wk of age in a later generation of the E line, Velleman and Nestor (2006) observed that the breast morphology scores were significantly higher in the RBC1 line than in the E line for males and sexes combined but not for females. To clarify the effect of genetic changes in egg production on breast muscle morphology and to study the effect of age on morphology, the E and RBC1 lines were compared from 25 d of incubation through 20 wk of age in the present study.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Genetic Stocks and Management of Birds

The RBC1 line is a randombred control line (McCartney, 1964) that was closed in 1960. The RBC1 line has been maintained without conscious selection using a paired mating system (Nestor, 1977b). With the system of maintenance and number of parental pairs used (48 in generations 1 and 2 and 36 thereafter), little genetic change was expected or observed (Nestor, 1977a; Noble et al., 1995).

The E line was a subline of the RBC1 line developed by selecting only for increased egg production for various periods (84 d in generations 1 to 3, 180 d in generations 4 through 26, and 250 d thereafter) and was maintained with the paired mating system (48 pairs in the first 2 generations, 36 pairs in generations 3 to 5, and 72 pairs thereafter). Details of the maintenance of the E line and response to selection have been given previously (McCartney et al., 1968; Nestor, 1971; Anthony et al., 1991; Nestor et al., 1996). The E line was in the 46th generation of selection at the time of the present study.

Eggs from the E and RBC1 lines were collected in a single 2-wk hatch and incubated together in the same incubator. The resulting offspring were grown, sexes separate, in confinement in different houses. All birds were provided a declining protein ration system based on the schedule for males (Naber and Touchburn, 1970) with periodic upgrades of the rations so that they met or exceeded the current standards by the NRC. Continuous lighting was provided from hatching to 8 wk of age, at which time daylight was reduced to 12 h and remained at that level until the end of the experiment.

Immunohistochemistry

A sample size of 10 was used for each line-sex subgroup at 25 d of incubation and at 1, 4, 8, 16, and 20 wk posthatch. Details of the processing of embryonic pectoralis major muscle tissue were given by Velleman et al. (2002) and that for posthatch pectoralis major muscle tissue was given by Velleman et al. (2003c). In brief, the muscle samples were collected following the orientation of the fibers in such a manner to prevent contraction, dehydrated, cleared, embedded in paraffin, sectioned at 5µm, and mounted on slides. Before staining with hemotoxylin and eosin, the tissue sections were rehydrated using a graded series of ethanol from 100 to 50% with a final incubation in H2O. The stained sections were viewed for muscle morphological characteristics with an Olympus XI 70 microscope (Olympus America Inc., Melville, NY) and digitally recorded with an Olympus Magna Fire digital camera. Four sections from each embryo or bird were placed on a slide, and 5 fields of each section were viewed. Representative sections were scored (see introduction) from 1 to 5 by 4 individuals.

Statistical Analysis

The average breast muscle morphology scores were analyzed by an ANOVA with line, sex, and age as main effects using the GLM procedure of the SAS Institute (2001). All possible 2-way and 3-way interactions were included in the model. Means between ages were separated by repeated t-tests.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The breast morphology scores did not differ between lines, but the effects of age (P ≤ 0.001) and sex (P ≤ 0.05) were significant (Table 1Go). There were no significant interactions among the main effects. The largest breast morphology score was observed at 25 d of incubation. The average scores declined greatly from 25 d of incubation to 1 wk posthatch, increased from 1 to 4 wk, and remained steady from 4 through 20 wk. A representative muscle section from each age is shown in Figure 1Go. The muscle sections at 25 d of incubation had distinct muscle fibers and a large amount of extracellular spacing. The extracellular spacing and fiber bundle organization were almost nonexistent at 1 wk of age. Extracellular spacing and fiber bundle organization increased from 1 to 8 wk of age and remained relatively constant through 20 wk of age. Some damage to the muscle fiber bundles was apparent at 16 through 20 wk of age. The breast muscle morphology scores were higher in males than in females.


View this table:
[in this window]
[in a new window]

  		Table 1. Effect of long-term selection for increased egg production and sex on breast muscle morphology at 25 d of incubation and at 1, 4, 8, 16, and 20 wk of age
 

Figure 1
View larger version (153K):
[in this window]
[in a new window]

  		Figure 1. Representative photographic images of the extracellular matrix and muscle fiber organization at A) embryonic d 25, B) 1 wk posthatch, C) 4 wk posthatch, D) 8 wk posthatch, E) 16 wk posthatch, and F) 20 wk posthatch. The scale bar represents 50 µm.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
The current study provides a detailed description from 25 d of incubation, which is just before hatch through 20 wk of age of breast muscle morphology in both sexes and 2 lines of turkeys. The most striking age effect was the change in morphology between 25 d of incubation and 1 wk of age and between 1 and 4 wk of age. Muscle growth occurs by 2 processes, hyperplasia and hypertrophy. Hyperplasia represents an increase in myoblast number by proliferation. This proliferation of myoblasts results in embryonic muscle fiber bundles containing primary and secondary myotubes (Miller and Stockdale, 1986). After hatch, further muscle growth is not through the proliferation of myoblasts but by the activation of myogenic satellite cells. Satellite cells are undifferentiated mononuclear myogenic cells that reside between the basal lamina and the plasmalemma of muscle fibers (Mauro, 1961). In adult tissue, satellite cells can be activated to proliferate and fuse to form new muscle fibers or fuse with existing muscle fibers to increase their size by hypertrophy. It is likely the decrease in score and reduced muscle fiber bundle organization at 1 wk post-hatch represents new muscle fiber synthesis by the fusion of satellite cells and the hypertrophy of existing fibers. By 4 wk posthatch, the muscle fiber bundles have reorganized.

Sixteen weeks of age seems to be a very important age in breast muscle development. This is the age at which maternal inheritance is apparent (Velleman et al., 2003a; Velleman and Nestor, 2004, 2006). Muscle damage due to growth selection for BW, although starting at 8 wk of age, is very apparent at 16 wk of age (Velleman et al., 2003b). Therefore, in several studies, line comparisons of breast muscle morphology were made at 16 wk of age with 8-wk data being included in some studies. Three experiments have been completed in which the E and RBC1 lines have been compared. In the first study, when measurements were made at 8 and 16 wk of age, the E and RBC1 lines did not differ in breast muscle morphology scores, but there was an interaction between age and line (Velleman and Nestor, 2005). At 16 wk of age, the scores (sexes combined) were 3.37 and 3.98, respectively, for the E and RBC1 lines. In a second study (Velleman and Nestor, 2006), the breast morphology scores were 3.16 and 3.84, respectively, for the combined sexes of the E and RBC1 lines, and the line difference was significant. In the current study, the breast muscle morphology scores were lower, and lines did not differ significantly for sexes combined (2.67 and 3.10, respectively, for the E and RBC1 lines). The consistency of the difference between the E and RBC1 lines in the 3 studies suggests that genetic increases in egg production may be associated with a slight reduction in breast muscle morphology scores. However, the reduction, if real, is less than that observed when selecting for increased growth rate (Velleman et al., 2003b; Velleman and Nestor, 2004).

Males had larger breast muscle morphology scores than females in the current study, similar to that observed by Velleman and Nestor (2005, 2006) when the E and RBC1 lines were used. Sex differences in the morphology scores were not present in studies (Velleman et al., 2003a; Velleman and Nestor, 2004) involving large-bodied lines.

In summary, the breast muscle morphology scores changed greatly from 25 d of incubation to 1 wk of age and from 1 to 4 wk of age, primarily due to the amount of extracellular spacing. Little change was observed from 4 to 20 wk of age. At 16 wk of age, the results of the current study and published research (Velleman and Nestor, 2005, 2006) suggest that genetic increases in egg production are associated with minor reductions in breast morphology scores, and males have better scores than females, unlike that observed with large-bodied lines.


   FOOTNOTES
 
1 Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Back

Received for publication April 20, 2007. Accepted for publication June 4, 2007.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Anthony, N. B., D. A. Emmerson, and K. E. Nestor. 1991. Genetics of growth and reproduction in the turkey. 12. Results of long-term selection for increased 180-day egg production. Poult. Sci. 70:1314–1322.[Web of Science][Medline]

Havenstein, G. B., P. R. Ferket, J. L. Grimes, M. A. Qureshi, and K. E. Nestor. 2004. Performance of 1966 vs. 2003 turkeys when fed representative 1966 and 2003 diets. Proc. World’s Poult. Congr., Istabul, Turkey.

Havenstein, G. B., P. R. Ferket, J. L. Grimes, M. A. Qureshi, and K. E. Nestor. 2007. Comparison of the performance of 1966- versus 2003-type turkeys when fed representative 1966 and 2003 turkey diets: Growth rate, livability, and feed conversion. Poult. Sci. 86:232–240.[Abstract/Free Full Text]

Mauro, A. 1961. Satellite cell of skeletal muscle fibers. J. Bio-phys. Biochem. Cytol. 9:493–495.[Medline]

McCartney, M. G. 1964. A randombred control population of turkeys. Poult. Sci. 43:730–744.

McCartney, M. G., K. E. Nestor, and W. R. Harvey. 1968. Genetics of growth and reproduction in the turkey. 2. Selection for increased body weight and egg production. Poult. Sci. 47:981–990.[Web of Science][Medline]

Miller, J. B., and F. E. Stockdale. 1986. Developmental regulation of the multiple myogenic cell lineages of the avian embryo. J. Cell Biol. 103:2197–2208.[Abstract/Free Full Text]

Naber, E. C., and S. P. Touchburn. 1970. Ohio poultry rations. Ohio Coop. Ext. Serv. Bull. 343. The Ohio State Univ., Columbus.

Nestor, K. E. 1971. Genetics of growth and reproduction in the turkey. 3. Further selection for increased egg production. Poult. Sci. 50:1672–1682.[Web of Science]

Nestor, K. E. 1977a. The stability of two randombred control populations of turkeys. Poult. Sci. 56:54–57.[Web of Science]

Nestor, K. E. 1977b. The use of a paired mating system for the maintenance of experimental populations of turkeys. Poult. Sci. 56:60–65.[Web of Science]

Nestor, K. E., M. G. McCartney, and N. Bachev. 1969. Relative contribution of genetics and environment to turkey improvement. Poult. Sci. 48:1944–1949.[Web of Science][Medline]

Nestor, K. E., D. O. Noble, J. Zhu, and Y. Moritsu. 1996. Direct and correlated responses to long-term selection for increased body weight and egg production in turkeys. Poult. Sci. 75:1180–1191.[Web of Science][Medline]

Noble, D. O., D. A. Emmerson, and K. E. Nestor. 1995. The stability of three randombred control lines of turkeys. Poult. Sci. 74:1074–1078.[Web of Science][Medline]

SAS Institute. 2001. SAS/STAT User’s Guide. Version 8 ed. SAS Inst. Inc., Cary, NC.

Sosnicki, A. A., and B. W. Wilson. 1991. Pathology of turkey skeletal muscle: Implications for the poultry industry. Food Struct. 10:317–326.

Velleman, S. G., J. Anderson, and K. E. Nestor. 2003a. Possible maternal inheritance of breast muscle morphology in turkeys at sixteen weeks of age. Poult. Sci. 82:1479–1484.[Abstract/Free Full Text]

Velleman, S. G., C. S. Coy, J. W. Anderson, R. A. Patterson, and K. E. Nestor. 2002. Effect of selection for growth rate on embryonic breast muscle development. Poult. Sci. 81:1113–1121.[Abstract/Free Full Text]

Velleman, S. G., C. S. Coy, J. W. Anderson, R. A. Patterson, and K. E. Nestor. 2003b. Effect of selection for growth rate on muscle damage during turkey breast muscle development. Poult. Sci. 82:1069–1074.[Abstract/Free Full Text]

Velleman, S. G., C. S. Coy, J. W. Anderson, R. A. Patterson, and K. E. Nestor. 2003c. Effect of selection for growth rate and inheritance on posthatch muscle development in turkeys. Poult. Sci. 82:1365–1372.[Abstract/Free Full Text]

Velleman, S. G., and K. E. Nestor. 2004. Inheritance of breast muscle morphology in turkeys at sixteen weeks of age. Poult. Sci. 83:1060–1066.[Abstract/Free Full Text]

Velleman, S. G., and K. E. Nestor. 2005. Effect of genetic increases in egg production, age, and sex on muscle development in turkeys. Poult. Sci. 84:1347–1349.[Abstract/Free Full Text]

Velleman, S. G., and K. E. Nestor. 2006. Inheritance of breast muscle morphology in a line of turkeys selected for increased egg production, its randombred control line, and reciprocal crosses between them. Poult. Sci. 85:2130–2134.[Abstract/Free Full Text]

Wilson, B. W., P. S. Nieberg, and R. J. Buhr. 1990. Turkey muscle growth and focal myopathy. Poult. Sci. 69:1553–1562.[Web of Science][Medline]





This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Velleman, S. G.
Right arrow Articles by Nestor, K. E.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Velleman, S. G.
Right arrow Articles by Nestor, K. E.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS