BACKGROUND
meat-type chickens have been intensively selected for a long time mainly on growth rate, which has reduced the age at market weight .
selection efforts have improved body composition .
however, these improvements have also led to indirect and sometimes deleterious effects on meat quality traits   <cit> .
the importance of these traits has increased following the development of further processing of chicken meat.
post-mortem ph appears to be a key factor in meat quality, since low ph increases the risk of producing pale meat with reduced water holding capacity, which affects the quality of further processed products  <cit> .
on the other hand, results from a study of breast meat samples taken from a commercial processing plant suggests that dark meat with high ph has a shorter shelf-life  <cit> .
stress and behavioral activity on the pre-slaughter shackle line and muscle glycogen content at slaughter time have been shown to be involved in the variations of ph <dig> and phu  <cit> .
high heritability  values were observed for several meat quality traits in chickens  slaughtered under controlled experimental conditions  <cit>  and in turkeys  slaughtered under commercial conditions  <cit> .
therefore, these traits could be efficiently improved by phenotypic selection.
however, only selection on collaterals could be applied, decreasing the efficiency and increasing the cost of such selection programs.
so, identifying markers and genes associated with meat characteristics would be of great interest.
although qtl have already been reported in chicken for many traits, there are very few qtl reported for meat characteristics  <cit> t. to our knowledge, the suggestive qtls for meat color on gga <dig>  gga <dig> and gga <dig> are the only ones reported for the chicken  <cit> .
in the present study, we have compared meat quality traits from two experimental chicken lines divergently selected for growth rate   <cit> .
we have also presently characterized their behavioral response on the schackle line, using measurements as described by debut et al.
<cit> .
after checking that meat quality traits differed between the two lines, an f <dig> population was produced and used for qtl detection, with  <dig> microsatellite markers.
the data were analyzed using qtlmap  <cit>  and qtlexpress  <cit>  softwares.
qtlmap makes no assumption either about fixation of the alleles in the founder lines or the number of the alleles segregating at qtl.
as in our experiment, the founder lines may not be fixed for the qtls alleles underlying meat quality traits, testing a corresponding free-assumption model is of special interest.
however, in the case where we are dealing with a biallelic qtl fixed in the founder lines, using a simpler model such as the one underlying qtlexpress software may be relevant.
the results obtained by this web-based software are also more comparable with those of other studies  <cit> .
several strong qtl controlling meat quality traits in chicken were revealed using both softwares.
RESULTS
characterization of meat quality traits in hg and lg founder lines as well as in their f <dig> cross
the phenotypic trait means and corresponding standard deviations for each founder line and their f <dig> cross are presented in table  <dig>  at  <dig> weeks of age, body weight  was  <dig> -fold higher  in the hg than in the lg line.
a large correlated response was also observed for abdominal fat which was about 12-fold higher  in hg birds compared with the lg birds.
a significant difference of lower magnitude was also observed for breast yield, which was higher  in hg birds.
interestingly, potentially correlated responses to divergent selection were observed for breast meat traits as well as for growth rate.
the color of breast meat was lighter  in hg chickens, which also exhibited lower redness  and yellowness  in meat color.
post-mortem ph values also differed between the two lines, with hg birds exhibiting lower ph <dig> and ultimate ph values.
furthermore, hg chickens exhibited a higher breast muscle glycogen-equivalent content at death than lg chickens .
behavioral measurements on the pre-slaughter shackle line clearly indicated that lg birds were less active than hg birds.
indeed, the percentage of straightening up events  was estimated at 18% in lg and 43% in hg .
in addition, median values for the duration of wing flapping  on the pre-slaughter shackle line were equal to  <dig> and  <dig> sec in lg and hg birds, respectively .
indeed, quite significant negative phenotypic correlations were found between ph <dig> and su or wf duration .
it was also of interest to compare phenotypic traits between the founder lines and the f <dig> progeny , although data were not obtained at the same time.
the average f <dig> traits were in the mid-range between the trait means of the founder lines, except for meat drip loss  and to a lower extent ph <dig> and breast yield .
the phenotypic correlations between meat traits estimated from the f <dig> population were small to moderate.
the most significant ones  were found between ph <dig> and dl , bco-y and bco-r  and between bco-y and phu .
qtl analysis of meat quality traits using qtlmap software
1bco-y = yellowness; dl = drip loss, ph <dig> = ph  <dig> minutes post-mortem; phu = ultimate ph; bco-r = redness; 2location and confidence interval in cm; 3likelihood ratio 4variance explained by the qtl  5chromosome-wide p-value; 6* = suggestive; 7** = genome-wide 1%
1bco-y = yellowness; dl = drip loss; ph <dig> = ph  <dig> minutes post-mortem; phu = ultimate ph; bco-r = redness.
qtl analysis of meat quality traits using qtlexpress software
qtlexpress analyses  confirmed two out of the five significant genome-wide qtls found by qtlmap, those for bco-y and bco-r on gga <dig>  in addition, the qtl for phu on gga <dig> was highly significant at the genome level with qtlexpress software, whereas it was only suggestive by qtlmap.
genetic map positions of the three qtls identified as genome-wide by qtlexpress, for bco-r and bco-y on gga <dig> and phu on gga <dig>  were about the same as those estimated by qtlmap.
high alleles for these qtls originated from the lg line for bco-r and bco-y and from the hg line for phu, which was consistent with the results by qtlmap.
qtlexpress also revealed two suggestive qtls for dl and ph <dig> on gga <dig>  confidence interval for the qtl affecting ph <dig> included the likeliest position estimated by qtlmap, and the origin of the high allele was confirmed to be from the hg line.
however, the confidence intervals estimated for dl by qtlexpress and qtlmap did not overlap ; furthermore, the origin of the high allele was found to be different, .
collectively, these results suggest two distinct qtl for dl on gga <dig> at positions  <dig> and  <dig> cm.
discussion
hg and lg chicken lines, which were obtained by divergent selection within a population originally derived from meat-type lines, represent a unique resource for analyzing the genetic control of growth related traits and the underlying mechanisms.
an f <dig> resource population was created by crossing the hg × lg lines  <cit>  to obtain this goal.
several meat quality traits were measured and the f <dig> progeny were genotyped.
we found several strong qtls for meat quality traits, which are first discussed in the hg and lg founder lines.
phenotypic traits in the hg and lg founder lines
hg birds had paler breast meat, i.e.
lower redness  and yellowness  and higher lightness values.
paler meat has also been observed in chicken selected for both high body weight and breast muscle yield than in their unselected controls, which appears to be related to a reduction in muscle heme pigment  content in the heavy bw chicken lines  <cit> .
heme pigment content was not measured in the hg and lg chickens.
higher lightness values in hg line could also result from a lower phu.
this is consistent with the negative phenotypic relationship  found between breast meat ultimate ph and lightness in the f <dig> population and in other studies reporting strong negative genetic correlations of - <dig>  in the chicken  <cit>  and of - <dig>  in the turkey  <cit> .
in chicken breast meat, the ultimate ph depends on muscle glycogen-equivalent content at death  <cit> .
indeed, the lower ultimate ph of hg breast meat coincides with higher glycogen content at death.
we also observed a significant difference between lines for ph <dig> values, with hg birds exhibiting lower ph <dig> values.
muscle activity before slaughter could hasten post-mortem glycolysis and decrease muscle ph <dig>  <cit> .
behavioral observations of birds on the pre-slaughter shackle line clearly showed that hg birds exhibited higher struggle activity at slaughter.
the comparison of hg and lg production and meat quality traits suggest that genetic selection for growth rate could change several bird characteristics, including behavior, muscle biochemistry and ultimately meat characteristics.
further research is needed to identify the mechanisms and genes underlying variations in the meat quality traits, which were identified by the present study.
comparison of qtlmap and qtlexpress for analysis of meat trait qtl
both qtlmap  <cit>  and qtlexpress  <cit>  software were used for analysis of qtl for meat quality traits.
no assumption about allele distribution was made with the qtlmap method.
association analyses were performed for each f <dig> parent, and residual variances were estimated for each sire family using a heteroskedastic model, which could increase the power of the analysis when several qtls govern a given trait  <cit> .
in contrast, the qtlexpress method assumed that alternative qtl alleles were fixed in the founder lines, and only one substitution effect was estimated over all families.
a good agreement was observed between the two methods, although the level of significance obtained by qtlmap was generally higher.
indeed, both methods revealed strong genome-wide qtl for meat redness and yellowness on gga <dig>  this was consistent with the fact that qtl alleles were segregating in all but one of the five f <dig> sire families, and appeared to be almost fixed in the founder lines.
the origin of the high alleles could be traced back to the lg line, which was consistent with the deeper coloring of meat observed in this line.
the qtl effects for meat redness and yellowness were consistent with the high positive correlation between these two traits and the similar positions of the two qtls.
hence, these two qtl are likely a single one affecting both traits.
further studies are required to determine if the protein coded by gene at this position exert a unique graduated response or a pleiotropic effect on meat color.
to our knowledge, only three suggestive qtls for meat color, located on gga <dig>  gga <dig> and gga <dig>  have been published for the chicken  <cit>  none of these meat-color qtl presented on the chicken qtl database  <cit> , was found in the present study, which could be due to the different genetic background of the birds or to differences in the method used to measure meat color.
three other genome-wide qtls were identified by qtlmap analysis for dl on gga <dig> and for ph <dig> on gga <dig> and gga <dig>  a qtl for dl on gga <dig> was only suggestive using qtlexpress, with the high allele coming from the hg line.
however, the origin of the high allele traced back to the lg line by qtlmap.
as discussed earlier, the two qtl identified by the different softwares at different positions  could represent two distinct qtls for which the alleles are mainly in a repulsive phase.
in such cases, the effect of the qtl is usually underestimated  <cit> .
this could explain why the effect of this qtl was the lowest one  estimated by qtlmap.
the qtl for ph <dig> on gga <dig> and gga <dig>  identified as genome-wide by qtlmap, were respectively found as suggestive and non-significant by qtlexpress.
such a discrepancy between the two methods could be due to the small number of heterozygous sires  and/or to changes in origin of the high allele according to sire families .
a similar feature was observed for two other suggestive qtls identified by qtlmap but not by qtlexpress .
one qtl was found for phu, which was identified as genome-wide by qtlexpress but only suggestive by qtlmap.
this was not expected because of the specificity of the two methods discussed above.
finally, it was surprising that no qtl was found for meat color lightness by either method of analysis, although the two founder lines were different in the bco-l trait.
however, the present genome scan only partially covered the complete chicken genome ; therefore, several qtl regions governing meat quality traits could have been missed.
the widely used "one lod drop-off method" was applied to obtain  <dig> percent confidence intervals of the qtl  <cit> .
this technique tends to under-estimate confidence interval sizes, and others  <cit>  have suggested using a 2-lod support interval to ensure reaching a  <dig> percent confidence interval.
some studies also showed that lod-score-based confidence intervals were biased  <cit> .
it should be noted that this method only provides a rough approximation of the confidence interval for locating a qtl.
thus, additional markers must be developed to refine the position of these meat quality qtl and to scan the regions of the genome not covered by the present study.
furthermore, new experimental designs such as recombinant progeny testing  <cit>  or advanced intercross lines  <cit>  could be used to refine the most interesting qtl regions.
CONCLUSIONS
several important qtls for meat traits have been described in a novel f <dig> resource population created from an intercross of hg and lg lines.
some relationships between some behavioral traits and meat ph were observed.
this is the first study to reveal significant qtl for meat quality traits in the chicken.
application of a statistical model that does not assume the number of alleles segregating for qtl and their origin in the founder lines appears to be a useful approach, as evidenced by obtaining a higher level of significance for the qtls.
pleiotropic effects were also suggested for some chromosomal regions.
this study indicates that divergent selection for growth rate has driven segregation of several meat quality traits.
once genes within chromosomal regions of interest have been precisely identified and the strength of qtl for meat quality determined, this could permit direct genetic selection through use of molecular markers, provided the same mechanisms are shared by commercial populations.

 meat-type chickens have been intensively selected for a long time mainly on growth rate, which has reduced the age at market weight. selection efforts have improved body composition. however, these improvements have also led to indirect and sometimes deleterious effects on meat quality traits. the importance of these traits has increased following the development of further processing of chicken meat. post-mortem ph appears to be a key factor in meat quality, since low ph increases the risk of producing pale meat with reduced water holding capacity, which affects the quality of further processed products. on the other hand, results from a study of breast meat samples taken from a commercial processing plant suggests that dark meat with high ph has a shorter shelf-life. stress and behavioral activity on the pre-slaughter shackle line and muscle glycogen content at slaughter time have been shown to be involved in the variations of ph and phu. high heritability values were observed for several meat quality traits in chickens slaughtered under controlled experimental conditions and in turkeys slaughtered under commercial conditions. therefore, these traits could be efficiently improved by phenotypic selection. however, only selection on collaterals could be applied, decreasing the efficiency and increasing the cost of such selection programs. so, identifying markers and genes associated with meat characteristics would be of great interest. although qtl have already been reported in chicken for many traits, there are very few qtl reported for meat characteristics t. to our knowledge, the suggestive qtls for meat color on gga gga and gga are the only ones reported for the chicken. in the present study, we have compared meat quality traits from two experimental chicken lines divergently selected for growth rate. we have also presently characterized their behavioral response on the schackle line, using measurements as described by debut et al.. after checking that meat quality traits differed between the two lines, an f population was produced and used for qtl detection, with microsatellite markers. the data were analyzed using qtlmap and qtlexpress softwares. qtlmap makes no assumption either about fixation of the alleles in the founder lines or the number of the alleles segregating at qtl. as in our experiment, the founder lines may not be fixed for the qtls alleles underlying meat quality traits, testing a corresponding free-assumption model is of special interest. however, in the case where we are dealing with a biallelic qtl fixed in the founder lines, using a simpler model such as the one underlying qtlexpress software may be relevant. the results obtained by this web-based software are also more comparable with those of other studies. several strong qtl controlling meat quality traits in chicken were revealed using both softwares.  characterization of meat quality traits in hg and lg founder lines as well as in their f cross the phenotypic trait means and corresponding standard deviations for each founder line and their f cross are presented in table at weeks of age, body weight was -fold higher in the hg than in the lg line. a large correlated response was also observed for abdominal fat which was about 12-fold higher in hg birds compared with the lg birds. a significant difference of lower magnitude was also observed for breast yield, which was higher in hg birds. interestingly, potentially correlated responses to divergent selection were observed for breast meat traits as well as for growth rate. the color of breast meat was lighter in hg chickens, which also exhibited lower redness and yellowness in meat color. post-mortem ph values also differed between the two lines, with hg birds exhibiting lower ph and ultimate ph values. furthermore, hg chickens exhibited a higher breast muscle glycogen-equivalent content at death than lg chickens. behavioral measurements on the pre-slaughter shackle line clearly indicated that lg birds were less active than hg birds. indeed, the percentage of straightening up events was estimated at 18% in lg and 43% in hg. in addition, median values for the duration of wing flapping on the pre-slaughter shackle line were equal to and sec in lg and hg birds, respectively. indeed, quite significant negative phenotypic correlations were found between ph and su or wf duration. it was also of interest to compare phenotypic traits between the founder lines and the f progeny, although data were not obtained at the same time. the average f traits were in the mid-range between the trait means of the founder lines, except for meat drip loss and to a lower extent ph and breast yield. the phenotypic correlations between meat traits estimated from the f population were small to moderate. the most significant ones were found between ph and dl, bco-y and bco-r and between bco-y and phu. qtl analysis of meat quality traits using qtlmap software 1bco-y = yellowness; dl = drip loss, ph = ph minutes post-mortem; phu = ultimate ph; bco-r = redness; 2location and confidence interval in cm; 3likelihood ratio 4variance explained by the qtl 5chromosome-wide p-value; 6* = suggestive; 7** = genome-wide 1% 1bco-y = yellowness; dl = drip loss; ph = ph minutes post-mortem; phu = ultimate ph; bco-r = redness. qtl analysis of meat quality traits using qtlexpress software qtlexpress analyses confirmed two out of the five significant genome-wide qtls found by qtlmap, those for bco-y and bco-r on gga in addition, the qtl for phu on gga was highly significant at the genome level with qtlexpress software, whereas it was only suggestive by qtlmap. genetic map positions of the three qtls identified as genome-wide by qtlexpress, for bco-r and bco-y on gga and phu on gga were about the same as those estimated by qtlmap. high alleles for these qtls originated from the lg line for bco-r and bco-y and from the hg line for phu, which was consistent with the results by qtlmap. qtlexpress also revealed two suggestive qtls for dl and ph on gga confidence interval for the qtl affecting ph included the likeliest position estimated by qtlmap, and the origin of the high allele was confirmed to be from the hg line. however, the confidence intervals estimated for dl by qtlexpress and qtlmap did not overlap; furthermore, the origin of the high allele was found to be different,. collectively, these results suggest two distinct qtl for dl on gga at positions and cm. discussion hg and lg chicken lines, which were obtained by divergent selection within a population originally derived from meat-type lines, represent a unique resource for analyzing the genetic control of growth related traits and the underlying mechanisms. an f resource population was created by crossing the hg × lg lines to obtain this goal. several meat quality traits were measured and the f progeny were genotyped. we found several strong qtls for meat quality traits, which are first discussed in the hg and lg founder lines. phenotypic traits in the hg and lg founder lines hg birds had paler breast meat, i.e. lower redness and yellowness and higher lightness values. paler meat has also been observed in chicken selected for both high body weight and breast muscle yield than in their unselected controls, which appears to be related to a reduction in muscle heme pigment content in the heavy bw chicken lines. heme pigment content was not measured in the hg and lg chickens. higher lightness values in hg line could also result from a lower phu. this is consistent with the negative phenotypic relationship found between breast meat ultimate ph and lightness in the f population and in other studies reporting strong negative genetic correlations of - in the chicken and of - in the turkey. in chicken breast meat, the ultimate ph depends on muscle glycogen-equivalent content at death. indeed, the lower ultimate ph of hg breast meat coincides with higher glycogen content at death. we also observed a significant difference between lines for ph values, with hg birds exhibiting lower ph values. muscle activity before slaughter could hasten post-mortem glycolysis and decrease muscle ph. behavioral observations of birds on the pre-slaughter shackle line clearly showed that hg birds exhibited higher struggle activity at slaughter. the comparison of hg and lg production and meat quality traits suggest that genetic selection for growth rate could change several bird characteristics, including behavior, muscle biochemistry and ultimately meat characteristics. further research is needed to identify the mechanisms and genes underlying variations in the meat quality traits, which were identified by the present study. comparison of qtlmap and qtlexpress for analysis of meat trait qtl both qtlmap and qtlexpress software were used for analysis of qtl for meat quality traits. no assumption about allele distribution was made with the qtlmap method. association analyses were performed for each f parent, and residual variances were estimated for each sire family using a heteroskedastic model, which could increase the power of the analysis when several qtls govern a given trait. in contrast, the qtlexpress method assumed that alternative qtl alleles were fixed in the founder lines, and only one substitution effect was estimated over all families. a good agreement was observed between the two methods, although the level of significance obtained by qtlmap was generally higher. indeed, both methods revealed strong genome-wide qtl for meat redness and yellowness on gga this was consistent with the fact that qtl alleles were segregating in all but one of the five f sire families, and appeared to be almost fixed in the founder lines. the origin of the high alleles could be traced back to the lg line, which was consistent with the deeper coloring of meat observed in this line. the qtl effects for meat redness and yellowness were consistent with the high positive correlation between these two traits and the similar positions of the two qtls. hence, these two qtl are likely a single one affecting both traits. further studies are required to determine if the protein coded by gene at this position exert a unique graduated response or a pleiotropic effect on meat color. to our knowledge, only three suggestive qtls for meat color, located on gga gga and gga have been published for the chicken none of these meat-color qtl presented on the chicken qtl database, was found in the present study, which could be due to the different genetic background of the birds or to differences in the method used to measure meat color. three other genome-wide qtls were identified by qtlmap analysis for dl on gga and for ph on gga and gga a qtl for dl on gga was only suggestive using qtlexpress, with the high allele coming from the hg line. however, the origin of the high allele traced back to the lg line by qtlmap. as discussed earlier, the two qtl identified by the different softwares at different positions could represent two distinct qtls for which the alleles are mainly in a repulsive phase. in such cases, the effect of the qtl is usually underestimated. this could explain why the effect of this qtl was the lowest one estimated by qtlmap. the qtl for ph on gga and gga identified as genome-wide by qtlmap, were respectively found as suggestive and non-significant by qtlexpress. such a discrepancy between the two methods could be due to the small number of heterozygous sires and/or to changes in origin of the high allele according to sire families. a similar feature was observed for two other suggestive qtls identified by qtlmap but not by qtlexpress. one qtl was found for phu, which was identified as genome-wide by qtlexpress but only suggestive by qtlmap. this was not expected because of the specificity of the two methods discussed above. finally, it was surprising that no qtl was found for meat color lightness by either method of analysis, although the two founder lines were different in the bco-l trait. however, the present genome scan only partially covered the complete chicken genome; therefore, several qtl regions governing meat quality traits could have been missed. the widely used "one lod drop-off method" was applied to obtain percent confidence intervals of the qtl. this technique tends to under-estimate confidence interval sizes, and others have suggested using a 2-lod support interval to ensure reaching a percent confidence interval. some studies also showed that lod-score-based confidence intervals were biased. it should be noted that this method only provides a rough approximation of the confidence interval for locating a qtl. thus, additional markers must be developed to refine the position of these meat quality qtl and to scan the regions of the genome not covered by the present study. furthermore, new experimental designs such as recombinant progeny testing or advanced intercross lines could be used to refine the most interesting qtl regions.  several important qtls for meat traits have been described in a novel f resource population created from an intercross of hg and lg lines. some relationships between some behavioral traits and meat ph were observed. this is the first study to reveal significant qtl for meat quality traits in the chicken. application of a statistical model that does not assume the number of alleles segregating for qtl and their origin in the founder lines appears to be a useful approach, as evidenced by obtaining a higher level of significance for the qtls. pleiotropic effects were also suggested for some chromosomal regions. this study indicates that divergent selection for growth rate has driven segregation of several meat quality traits. once genes within chromosomal regions of interest have been precisely identified and the strength of qtl for meat quality determined, this could permit direct genetic selection through use of molecular markers, provided the same mechanisms are shared by commercial populations. 
this study highlights the effects of divergent selection for growth rate on some behavioral traits, muscle biochemistry and ultimately meat quality traits. some qtls may in fact co-localize, suggesting pleiotropic effects for some chromosomal regions. association analyses were performed using maximum-likelihood interval mapping in qtlmap. the hg and lg birds exhibit large differences in body weight and abdominal fat content. several meat quality traits were lower in hg chickens. in contrast, meat color-lightness was higher in hg chickens, whereas meat drip loss was similar in both lines. several qtl regions were identified that are worthy of further characterization. the present study identified genome-wide significant qtls for all meat technological traits presently assessed in these chickens, except for meat lightness. hg birds were more active on the shackle line. further analyses with qtlexpress confirmed the two genome-wide qtls for meat color on gga failed to identify the genome-wide qtl for ph on gga and revealed only suggestive qtls for ph and dl on gga however, qtlexpress qualified the qtl for phu on gga as genome-wide. meat technological traits are important considerations for improving further processing of chicken meat. five genome-wide significant qtls were revealed: two for ph on gga and gga one for dl on gga one for bco-r and one for bco-y both on gga in addition, four suggestive qtls were identified by qtlmap for bco-y, phu, ph and dl on gga gga gga and gga respectively.
 meat technological traits are important considerations for improving further processing of chicken meat. these quality traits were originally characterized in experimental lines selected for high and low growth. presently, quantitative trait loci for these traits were analyzed in an f population issued from the hg × lg cross. a total of animals in full-sib families were genotyped for microsatellite markers covering linkage groups.  the hg and lg birds exhibit large differences in body weight and abdominal fat content. several meat quality traits were lower in hg chickens. in contrast, meat color-lightness was higher in hg chickens, whereas meat drip loss was similar in both lines. hg birds were more active on the shackle line. association analyses were performed using maximum-likelihood interval mapping in qtlmap. five genome-wide significant qtls were revealed: two for ph on gga and gga one for dl on gga one for bco-r and one for bco-y both on gga in addition, four suggestive qtls were identified by qtlmap for bco-y, phu, ph and dl on gga gga gga and gga respectively. the qtl effects, averaged on heterozygous families, ranged from to 31% of the phenotypic variance. further analyses with qtlexpress confirmed the two genome-wide qtls for meat color on gga failed to identify the genome-wide qtl for ph on gga and revealed only suggestive qtls for ph and dl on gga however, qtlexpress qualified the qtl for phu on gga as genome-wide.  the present study identified genome-wide significant qtls for all meat technological traits presently assessed in these chickens, except for meat lightness. this study highlights the effects of divergent selection for growth rate on some behavioral traits, muscle biochemistry and ultimately meat quality traits. several qtl regions were identified that are worthy of further characterization. some qtls may in fact co-localize, suggesting pleiotropic effects for some chromosomal regions. 