Effect of selection for growth rate and inheritance on posthatch muscle development in turkeys

The hypoxia-inducible factor 1 pathway plays a critical role in the development of breast muscle myopathies in broiler chickens: a comprehensive review

In light of the increased worldwide demand for poultry meat, genetic selection efforts have intensified to produce broiler strains that grow at a higher rate, have greater breast meat yield (BMY), and convert feed to meat more efficiently. The increased selection pressure for these traits, BMY in particular, has produced multiple breast meat quality defects collectively known as breast muscle myopathies (BMM). Hypoxia has been proposed as one of the major mechanisms triggering the onset and occurrence of these myopathies. In this review, the relevant literature on the causes and consequences of hypoxia in broiler breast muscles is reviewed and discussed, with a special focus on the hypoxia-inducible factor 1 (HIF-1) pathway. Muscle fiber hypertrophy induced by selective breeding for greater BMY reduces the space available in the perimysium and endomysium for blood vessels and capillaries. The hypoxic state that results from the lack of circulation in muscle tissue activates the HIF-1 pathway. This pathway alters energy metabolism by promoting anaerobic glycolysis, suppressing the tricarboxylic acid cycle and damaging mitochondrial function. These changes lead to oxidative stress that further exacerbate the progression of BMM. In addition, activating the HIF-1 pathway promotes fatty acid synthesis, lipogenesis, and lipid accumulation in myopathic muscle tissue, and interacts with profibrotic growth factors leading to increased deposition of matrix proteins in muscle tissue. By promoting lipidosis and fibrosis, the HIF-1 pathway contributes to the development of the distinctive phenotypes of BMM, including white striations in white striping-affected muscles and the increased hardness of wooden breast-affected muscles.

Effects of Spirogyra jaoensis as a dietary supplement on growth, pectoralis muscle performance, and small intestine morphology of broiler chickens

AIM

This study aimed to examine the effect of dietary Spirogyra jaoensis in starter feed on growth performance, pectoralis muscle (PM) growth, and small intestine morphology of broiler chickens.

MATERIALS AND METHODS

One hundred twenty one-day-old Cobb-500 broilers (body weight 46±2.6 g) were divided into four equal groups with 3 replicates in each group and given basal feed supplemented with dried S. jaoensis at doses of 0%, 0.5%, 1%, or 2%. The treatment was carried out until the chickens were 18 days old to examine growth of broiler chicks at starter period (8-21 days old).

RESULTS

Supplementation with S. jaoensis at doses of 0.5% and 1% resulted in increased weight and improved feed conversion ratio compared to the control group. At the end of treatment, chickens fed with 0.5% and 1% S. jaoensis weighed 428.3±47.8 g and 426.9±31.8 g, respectively, and were significantly heavier than the control group (373.1±44.1 g). Furthermore, parameters related to PM growth and small intestine morphology of chickens supplemented with 0.5% S. jaoensis in basal feed were improved compared to the control group.

CONCLUSION

The results of this research indicate that S. jaoensis at a dose of 0.5% improves growth performance, PM growth, and small intestine morphology in broiler chickens.

Fibrillar Collagen Organization Associated with Broiler Wooden Breast Fibrotic Myopathy

Wooden breast (WB) is a fibrotic myopathy affecting the pectoralis major (p. major) muscle in fast-growing commercial broiler lines. Birds with WB are phenotypically detected by the palpation of a hard p. major muscle. A primary feature of WB is the fibrosis of muscle with the replacement of muscle fibers with extracellular matrix proteins, such as collagen. The ability of a tissue to be pliable and stretch is associated with the organization of collagen fibrils in the connective tissue areas surrounding muscle fiber bundles (perimysium) and around individual muscle fibers (endomysium). The objective of this study was to compare the structure and organization of fibrillar collagen by using transmission electron microscopy in two fast-growing broiler lines (Lines A and B) with incidence of WB to a slower growing broiler Line C with no phenotypically detectable WB. In Line A, the collagen fibrils were tightly packed in a parallel organization, whereas in Line B, the collagen fibrils were randomly aligned. Tightly packed collagen fibrils arranged in parallel are associated with nonpliable collagen that is highly cross-linked. This will lead to a phenotypically hard p. major muscle. In Line C, the fibrillar collagen was sparse in its distribution. Furthermore, the average collagen fibril diameter and banding D-period length were altered in Line A p. major muscles affected with WB. Taken together, these data are suggestive of different fibrotic myopathies beyond just what is classified as WB in fast-growing broiler lines.

Thermal challenge alters the transcriptional profile of the breast muscle in turkey poults

Extremes in temperature represent environmental stressors that impact the well-being and economic value of poultry. As homeotherms, young poultry with immature thermoregulatory systems are especially susceptible to thermal extremes. Genetic variation and differences in gene expression resulting from selection for production traits, likely contribute to thermal stress response. This study was designed to investigate in vivo transcriptional changes in the breast muscle of young turkey poults from an unselected randombred line and one selected for 16 wk body weight under hot and cold thermal challenge. Newly hatched turkey poults were brooded for 3 d at one of 3 temperatures: control (35°C), cold (31°C), or hot (39°C). Samples of the pectoralis major were harvested and subjected to deep RNA sequencing. Significant differential gene expression was observed in both growth-selected and randombred birds at both temperature extremes when compared to control-brooded poults. Growth-selected birds responded to thermal stress through changes in genes predicted to have downstream transcriptional effects and that would result in reduced muscle growth. Slower growing randombred birds responded to thermal stress through modulation of lipid-related genes, suggesting reduction in lipid storage, transport, and synthesis, consistent with changes in energy metabolism required to maintain body temperature.

The effect of syndecan-4 and glypican-1 knockdown on the proliferation and differentiation of turkey satellite cells differing in age and growth rates

Posthatch skeletal muscle growth requires myogenic satellite cells and the dynamic expression of cell membrane-associated proteins. The membrane associated heparan sulfate proteoglycans, syndecan-4 and glypican-1, link the satellite cell niche to the intracellular environment. Sydnecan-4 and glypican-1 are differentially expressed with age in turkey satellite cells and their over-expression impacts both satellite cell proliferation and differentiation, but their effect on satellite cells from lines with different growth potentials is not known. The objective of the current study was to determine if syndecan-4 and glypican-1 regulation of satellite cell proliferation and differentiation is affected by age and growth selection. Pectoralis major satellite cells isolated at 1 d, 7 and 16-wk of age from a Randombred Control 2 (RBC2) line and a 16-wk body weight (F) line selected from the RBC2 line turkeys were studied. Syndecan-4 and glypican-1 expression was knocked down in both lines. The F-line cells proliferated faster than RBC2 line cells regardless of age, while differentiation tended to be greater in RBC2 line cells than F-line cells at each age. Syndecan-4 knockdown decreased proliferation at 7- and 16-wk but not 1 d cells, and increased differentiation at 1 d and 7 wk but not 16 wk cells. Glypican-1 knockdown differentially affected proliferation depending on cell age, whereas differentiation was decreased for 7- and 16-wk but not 1 d cells. These data suggest syndecan-4 and glypican-1 differentially affected satellite cell function in an age-dependent manner, but had little impact on differences in proliferation and differentiation due to growth selection.

Comparison of Muscle Fiber and Meat Quality Characteristics in Different Japanese Quail Lines

The aim of this study was to compare the growth performance, fiber characteristics of the pectoralis major muscle, and meat quality characteristics in the heavy weight (HW) and random bred control (RBC) quail lines and genders. The HW male exhibited more than two times greater body (245.7 vs 96.1 g, p<0.05) and pectoralis major muscle (PMW; 37.1 vs 11.1 g, p<0.05) weights compared to the RBC female. This growth performance in the HW line was associated with a greater muscle fiber area (1,502 vs 663.0 μm², p<0.001) compared to the RBC line. Greater muscle mass of the HW male was accompanied by a higher percentage of type IIB fiber compared to the HW female (64.0% vs 51.0%, p<0.05). However, muscle fiber hyperplasia (increase in fiber number) has had a somewhat limited effect on PMW between the two lines. On the other hand, the HW line harboring a higher proportion of type IIB fiber showed rapid pH decline at the early postmortem period (6.23 vs 6.41, p<0.05) and lighter meat surface (53.5 vs 47.3, p<0.05) compared to the RBC line harboring a lower proportion of type IIB fiber. There were no significant differences observed in the measurement of water-holding capacity including drip loss (2.74% vs 3.07%, p>0.05) and cooking loss (21.9% vs 20.4%, p>0.05) between the HW and RBC lines. Therefore, the HW quail line developed by selection from the RBC quail, was slightly different in the meat quality characteristics compared to the RBC line, and a marked difference was found in growth performance between the two quail lines.

Temporal myosin heavy chain isoform expression transitions faster in broiler chickens compared with Single Comb White Leghorns

Myosin heavy chain (MyHC), one of the major components in the contractile machinery of skeletal muscle fibers, is found in several isoforms during myogenesis. During chicken development, embryonic, neonatal, and adult MyHC isoforms are expressed. Broiler chickens have been selected for fast and large muscle growth, whereas Single Comb White Leghorn (SCWL) chickens have been selected for egg laying capabilities. This has led to an obvious difference in muscle growth and development with broilers being much larger than SCWL. The objective of this study was to determine if differences in muscle growth and development of SCWL and broilers are associated with differences in temporal expression of MyHC isoforms in skeletal muscle between the 2 breeds. Pectoralis major muscle (PM) was collected from SCWL and broilers at embryonic d 15, 17, and 19 and 1, 5, 11, 20, 27, and 33 d posthatch with n = 3 samples per time point and breed. Western blotting using 3 monoclonal antibodies (EB165, 2E9, and AB8) was performed to compare the expression patterns of embryonic/adult, neonatal, and adult isoforms of MyHC, respectively, for all time points in both SCWL and broiler chickens. Both broiler and SCWL chickens began expressing the neonatal MyHC isoform on d 5; however, SCWL chickens expressed the neonatal isoform much longer than broilers. The SCWL chickens had sustained expression of the neonatal MyHC isoform through d 27, whereas in broiler chickens the neonatal isoform was not expressed at d 20. Pectoralis major tissue from broiler chickens expressed the adult MyHC isoform as early as d 20, whereas the SCWL chickens began expressing the adult isoform later. The rate of transition to neonatal and adult MyHC isoforms in broilers and Leghorns is consistent with the faster maturation and growth of broilers relative to Leghorns. This relationship between faster growth of the PM and the rate of transition of MyHC isoforms within the fast skeletal muscle of the PM may indicate a selection marker for improvement of broiler PM growth.

Versican, matrix Gla protein, and death-associated protein expression affect muscle satellite cell proliferation and differentiation

Our previous transcriptional profiling study using a turkey skeletal muscle-specific oligonucleotide microarray revealed over 3,000 genes that were differentially expressed at 3 critical stages of muscle development: 18 d embryonic, 1 d posthatch, and 16 wk of age. The genes versican, matrix Gla protein (MGP), and death-associated protein (DAP) were selected to study for their potential effects on muscle satellite cell proliferation and differentiation, as their functions in other tissues are suggestive of possible key roles in the regulation of myogenesis and they are differentially expressed throughout muscle development in the turkey. Using small interfering RNA to knockdown the expression of these genes during proliferation and differentiation, each of the genes was found to differentially affect proliferation and differentiation. Versican and MGP predominantly affected proliferation with line effects, but later stages of differentiation were affected by the knockdown of versican and MGP. The underexpression of DAP inhibited myotube formation, which is a necessary stage in the development of muscle fibers. Without myotube development, muscle fiber formation will be inhibited or abolished. This is the first report that these genes with no previously documented functions with regard to muscle development play a critical role in muscle cell proliferation and differentiation.

Influence of parent flock age on embryonic metabolism in modern turkey strains

The metabolic response of some galliform embryos to embryonic heat production (EHP) and how incubation conditions have been adjusted to prevent overheating of embryos is well established in broiler breeders. However, the daily metabolic status of turkey embryos has not been studied or established in turkey embryos. The objectives of the current research were therefore to determine the respiratory (eggshell conductance, G) and metabolic status (EHP) of 2 modern turkey genetic strains [Hybrid (H) and Nicholas (N)] and 4 parent flock ages [young (Y, 30 wk), peak (P, 34 wk), mature (M, 55 wk), and old (O, 60 wk)] during incubation. To measure G, moisture loss from 15 eggs/genetic strain per flock age and saturated vapor pressure measured between the eggshell and its immediate environment were used. Daily embryonic O(2) consumption and CO(2) production rates were assessed 6 times each day from embryos of eggs (n = 11 eggs/genetic strain per flock age) incubated in individual metabolic chambers and were used to determined daily EHP. Data were analyzed using the mixed model procedure of SAS at P ≤ 0.05. The results showed that the G values (g/d per mmHg) were significantly different for the interaction between genetic strain and parent flock age (H × Y = 17.71, H × P = 17.53, H × M = 19.73, H × O = 26.46, N × Y = 16.70, N × P = 20.96; N × M = 25.47, N × O = 26.05; P = 0.0227). Daily EHP (mW) was higher in embryos from the O flock than in embryos from the Y flock during all days presented except at 8, 25, and 28 d of incubation (4 d: Y = 1.00, P = 0.93, M = 1.60, O = 1.75; 12 d: Y = 19.0, P = 20.0, M = 21.6, O = 23.4; 16 d: Y = 51.7, P = 60.5, M = 65.9, O = 70.8; 20 d: Y = 129, P = 146, M = 144, O = 155; 24 d: Y = 154, P = 188, M = 167, O = 180; 26 d: Y = 169, P = 199, M = 197, O = 230; and 27 d: Y = 231, P = 265, M = 288, O = 307; P < 0.05). The data showed that metabolic differences existed between embryos from flocks of different ages and that embryos from older flocks were metabolizing at a higher rate and could be subject to overheating, which requires further investigation. On the basis of the data, turkey eggs from flocks of different ages should be incubated separately for optimal physiological performance.

Effect of myofiber characteristics and thickness of perimysium and endomysium on meat tenderness of chickens

The objective of the present study was to evaluate the role of myofiber characteristics and the thickness of 2 major muscle membranes, perimysium and endomysium, in determining the breast meat tenderness of chickens. Birds from 2 breeds (White Leghorn and a line of broiler) were chosen. Chicks were sexed and wing-banded at hatch and were grown in separate cages in a single house. Sixty broilers and 60 White Leghorns were harvested at 6 wk of age, respectively, whereas another 60 White Leghorns were slaughtered at 18 wk of age. An equal number of males and females was maintained for each group. Body weight, breast muscle weight, pH, drip loss, cooking loss, Warner-Bratzler shear force value (SFV), total energy of shear force, fiber diameter, sarcomere length, myofiber density, and the thickness of endomysium and perimysium of the breast were determined for each bird. At 6 wk of age, histological examination indicated that the size of myofiber and thickness of endomysium and perimysium of broilers were larger than that those of White Leghorns (P < 0.01), whereas the SFV, drip loss, and cooking loss of broilers were smaller (P < 0.01). A comparison between the White Leghorns at 18 wk and the broilers at 6 wk, which were at similar BW but different ages, showed that the breast muscle weight of broilers was larger (P < 0.01) than that of White Leghorns. For breast muscle, the endomysium of broilers at 6 wk was thicker than that of White Leghorns at 18 wk (P < 0.01), whereas the perimysium was thinner (P < 0.01). The SFV, drip loss, and the cooking loss of broilers were smaller than those of White Leghorns at similar BW (P < 0.01). Meat tenderness was negatively correlated with myofiber density (-0.27) and the thickness of endomysium (-0.29) and positively correlated with the thickness of perimysium (0.20). It is suggested that muscle membrane should be considered in evaluating meat tenderness of the chicken.

The influence of age on maternal inheritance of breast muscle morphology in turkeys

It was apparent in previous studies at our institution using turkeys that measurements of muscle fibers and extracellular spacing were not adequate to explain what was observed in entire pectoralis major muscle sections. A rating system was developed in which muscle sections were rated from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Maternal inheritance was observed at 16 wk of age but not at 8 or 20 wk of age. The purpose of the current study was to determine the effect of age on maternal inheritance. A line (F) selected long-term for increased 16-wk BW, its randombred control (RBC2), and reciprocal crosses between them were compared from 8 through 18 wk of age. Samples of pectoralis major muscle were obtained in a manner to avoid muscle contraction. After being fixed and cross-sectioned, the muscle samples were stained with hematoxylin and eosin and rated by 4 individuals. No significant difference among genetic groups was observed in scores at 8 wk of age. At 10 wk of age, the F line had lower scores than the other genetic groups. Maternal inheritance was suggested at 12 wk of age. The scores for RBC2 were higher than those for F, whereas the F x RBC2 cross did not differ from the pure RBC2 line score at this age. Although the RBC2 x F scores were higher than the pure F-line scores at 12 wk, they were lower than those of the F x RBC2 crosses. From 14 through 18 wk of age, the scores for the RBC2 line were higher than those for the F line and the maternal inheritance was absolute because the value for the individual crosses did not differ from that of the maternal parent. Based on the results, the type of mating used to produce commercial turkeys would have a major effect on breast muscle morphology from 12 through 18 wk of age.

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

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.

Dam line and sire line effects on turkey embryo survival and thyroid hormone concentrations at the plateau stage in oxygen consumption

Inheritance of embryo thyroid function was measured in lines of turkeys. Two lines that had been selected for either increased egg production (E) or increased 16-wk BW (F) and their respective randombred controls (i.e., RBC1 and RBC2) were examined. Reciprocal crosses of dams and sires from each selected line and its randombred control were made to estimate sire line and dam line effects. Orthogonal contrasts were used to determine if the differences found were due to the presence of additive, nonadditive, or maternal, sex-linked, or both, gene effects. With the data involved, sex-linkage and maternal effects could not be separated. Embryo survival was measured for all lines and their reciprocal crosses. Crossing the RBC1 sire and E dam also resulted in better embryo survival and lower death losses at pipping than for the other cross- or purelines. Reciprocal crosses of the F and RBC2 lines showed better total embryo survival, and they survived pipping better than the F or RBC2 purelines. Thyroxine (T(4)) and triiodothyronine (T(3)) concentrations differed between the reciprocal crosses at external pipping, but the effects were inconsistent for the 2 data sets. Reciprocal tests indicated that maternal, sex-linked, or both, effects were present for T(3) concentrations at internal pipping in the E and RBC1 lines and at external pipping for the F and RBC2 lines. Reciprocal effects were significant for T(4) at internal pipping for both data sets. The RBC1 sire embryos had significantly higher T(3):T(4) ratios than the E line sire embryos at internal and external pipping, and the pureline RBC1 embryos had consistently higher ratios than the pureline E embryos. The differences for the T(3):T(4) ratios between these 2 lines at internal pipping, external pipping, and hatch appeared to be consistently additive in nature, although significant nonadditive or heterotic effects were present for the ratio at external pipping. Similar effects on the T(3):T(4) ratio were observed for the F and RBC2 lines at external pipping.

Inheritance of breast muscle morphology in a line of turkeys selected for increased egg production, its randombred control line, and reciprocal crosses between them

Breast muscle morphology was studied at 16 wk of age in a line (E) selected over 45 generations for increased egg production, its randombred control line (RBC1), and reciprocal crosses between the E and RBC1 lines. A sample of 10 birds per genetic group-sex subgroup was killed with restraint to prevent flapping of the wings. The skin was removed from the breast region and a sample of breast muscle was 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. Four sections from the same muscle from each bird were placed on a slide and the slides were viewed for muscle morphology characteristics with a microscope and digitally recorded. Five fields of each section were viewed. Representative sections of each bird 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 data were analyzed for sexes separate and combined. The E line had lower breast muscle morphology scores than the RBC1 line for males and sexes combined, indicating additive genetic variation in the scores. Nonadditive genetic variation was not an important source of variation for breast muscle morphology scores based on the contrast of the average of the parental lines with the average of the reciprocal crosses for males, females, or sexes combined. In 5 of 6 possible comparisons, the breast muscle morphology scores of the reciprocal cross were not significantly different from the line of the dam in the reciprocal cross. The only exception was for the E sire x RBC1 dam cross based on the data for females, wherein the breast muscle morphology scores were higher in the cross than in the pure RBC1 line. The results of the current study confirm the maternal inheritance of breast muscle morphology scores at 16 wk of age that has been previously reported.

Effect of genetic increases in egg production, age, and sex on muscle development in turkeys

Breast muscle morphology was studied at 8 and 16 wk of age in a line (E) selected over 44 generations for increased egg production and its randombred control line (RBC1). A sample of 20 birds per sex-line-age subgroup was killed with restraint to prevent flapping of the wings. The skin was removed from the breast region, and a sample of breast muscle was obtained in a manner to prevent contraction. The muscle samples were dehydrated, cleared, embedded in paraffin, sectioned, and incubated and rehydrated prior to staining with hematoxylin and eosin. Four sections from the same muscle from each bird were placed on a slide, and the slides were viewed for muscle morphological characteristics with a microscope and digitally recorded. Five fields of each section were viewed. Representative sections for each bird 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. Breast muscle morphology scores did not differ between lines or ages but there was a significant interaction between lines and ages. The scores increased in the RBC1 line from 8 to 16 wk of age, but the reverse was true for the E line. Scores were higher in males than females. The results of the present study suggest that selection for increased egg production in dam lines should not greatly influence breast muscle morphology in commercial turkeys.

Inheritance of breast muscle morphology in turkeys at sixteen weeks of age

The inheritance of morphology of the pectoralis major muscle in turkeys at 16 wk of age was studied in a randombred control line (RBC2), a subline (F) of RBC2 selected long term for increased 16 wk BW only, and F1 and F2 crosses of the F and RBC2 lines. Samples of pectoralis major muscle were obtained from 10 males and 10 females of each genetic group in a manner to avoid muscle contraction. After being fixed and cross sectioned, the muscle samples were stained with hematoxylin and eosin to view muscle morphology. The stained sections were analyzed for muscle fiber width, number of fibers in a 136-microm2 area, and extracellular matrix perimysial (PW) and endomysial (EW) width in areas of sections in which accurate measurements could be made. Because muscle damage was evident in some sections and, therefore, morphological measurements might not have provided a complete overview of muscle morphology, sections of the F2 crosses were subjectively rated by 4 people. The ratings ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Ratings of 2 to 4 were intermediate to these extremes. Creatine kinase concentrations of blood samples taken immediately prior to collecting muscle tissue were obtained and correlated with muscle section ratings within genetic group and sex. The F and RBC2 lines differed in PW and EW but not in individual fiber measurements. In the F1 generation, heterosis was -10.4% (P < or = 0.01), 19.7% (P < or = 0.05), -25.2% (P < or = 0.01), and -34.3% (P < or = 0.01), respectively, for fiber width, number of muscle fibers, PW, and EW. The F2 crosses differed only in EW based on measurements of sections in which accurate measurements could be made. However, based on subjective ratings of the muscle sections, possible maternal inheritance was suggested, as the orthogonal contrast was significant (P < or = 0.01) for crosses with F dams as F1 parents vs. those with RBC2 dams as F1 parents, confirming a previous study. The correlation coefficient between creatine kinase concentration and muscle section ratings was -0.282 (P < or = 0.01) after adjustment for line and sex effects.

Possible maternal inheritance of breast muscle morphology in turkeys at sixteen weeks of age

During the study of inheritance of breast muscle morphology of turkeys during embryonic development and posthatch in two experiments, interesting results were obtained at 16 wk of age. In experiment 1, an experimental line (F) selected long term for increased 16-wk BW was crossed reciprocally with a commercial sire line (B). Samples of pectoralis major muscle were obtained from three males and three females of each genetic group. The F line was reciprocally crossed with a randombred control line (RBC2) in experiment 2, and p. major muscle samples were taken from 10 males and 10 females of each genetic group. The RBC2 line was the base population for the F line. The muscle samples were obtained in a manner to avoid contraction. After fixing, the muscle samples were stained with hematoxylin and eosin to view muscle morphology. Distinct morphological types were observed in the muscle samples for the B, F, and RBC2 lines. The pectoralis major muscle from the B line was, in general, characterized by large fibers with a well-defined extracellular matrix (perimysial and endomysial spaces). Similar to the B line, representative samples of the RBC2 line had a well-defined extracellular matrix but muscle fiber size was not as large as that of the B line. Representative samples of the F line were characterized by a greatly reduced extracellular matrix with the muscle fibers not well defined. For the reciprocal crosses in both experiments, representative samples indicated the offspring had breast muscle morphology similar to that of the female parent, suggesting maternal inheritance. There was no sex effect on breast muscle morphology in either experiment. In order to study the consistency of the results, muscle morphology of representative sections of muscle were subjectively rated by four individuals. The ratings ranged from 1 (little extracellar matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Ratings of 2 to 4 were intermediate to these extremes. In experiment 1, ratings of the pure B line and the F sire x B dam cross were similar and higher than that of the pure F line and B sire x F dam cross, which did not differ in average rating. The results for experiment 2 were similar to those for experiment 1 in that the average ratings of the reciprocal crosses were similar to that of the female parental line. The results from the ratings support maternal inheritance of breast muscle morphology.