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Effects of the Blue Egg Shell Allele (O) on Egg Quality and Other Economic Traits in the Chicken1
BREEDING AND GENETICS Effects of the Blue Egg Shell Allele (0) on Egg Quality and Other Economic Traits in the Chicken1 M. SADJADI, 2 J. A. RENDEN, 3 F. H. BENOFF, 4 and J. A. HARPER Department of Poultry Science, Oregon State University, Corvallis, Oregon 97331-3402 (Received for publication September 20, 1982)
1983 Poultry Science 62:1717-1720 INTRODUCTION
The blue egg shell gene (O) is indigenous to the native South American breed of chicken known as Araucana and is inherited as an autosomal dominant gene (Punnett, 1933). The blue pigment permeates the entire shell (Punnett, 1933). Relatively few studies have been conducted to evaluate the difference in performance and egg quality of blue egg layers and white egg layers. Studies that have been conducted were not designed specifically to determine the effect of the O allele and alleles linked closely to this locus. Cunningham (1977) reported that shells of Araucana (blue) eggs were thicker than shells from either Leghorn (white) or Plymouth Rock (brown) eggs. Simmons and Somes (1978) indicated that Araucana eggs had larger yolks and less albumen for a given egg size than eggs from Leghorns; cholesterol content of these eggs was not measured. Anglin and Briles (1980) found that the amount of cholesterol per gram of yolk was similar among eggs from Araucana (AU), White Leghorn (WL), and Rhode Island Red (RIR) hens, although eggs
'Technical Paper No. 6356, Oregon Agricultural Experiment Station. Research done in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Oregon State University, Corvallis, OR 97331. 2 Peterson Industries, Decatur, AR 72722. 'Department of Poultry Science, Auburn University, Auburn, AL 36849. "Extension Poultry Science Department, University of Georgia, Athens, GA 30602.
from hens obtained by crosses of AU X RIR showed a significant reduction in the level of cholesterol. Reports in the popular literature have suggested low cholesterol levels in Araucana eggs (Hickman, 1974). The objective of this study was to determine the effects of the O allele and closely linked genes on internal and external egg quality and on reproductive performance in hens with similar genetic backgrounds. MATERIALS AND METHODS Araucana females homozygous dominant for the O allele were mated to Shaver Starcross " 2 8 8 " males homozygous recessive for the blue egg shell allele (oo) to produce heterozygous (Oo) Fl hybrids. Thirty-nine F x females were backcrossed to Shaver males using artificial insemination with individually collected semen from eight males to produce sisters in a 1:1 ratio of blue shell egg layers (Oo) and white shell egg layers (oo). The chicks were wingbanded and sexed upon hatching and were beak-trimmed at 12 days of age. All females within a hatch were brooded together. At 18 weeks of age, the hens were placed randomly in individual cages and received a standard laying ration containing 15% protein and 2,900 kcal/kg metabolizable energy throughout the experiment. Caged pullets received 14 hr of illumination daily and were provided with water for eight 15-min periods at 2-hr intervals during the light period. Data from 366 hens obtained from four hatches that survived to 40 weeks of age were analyzed in this experiment.
1717
Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015
ABSTRACT Araucana females homozygous dominant for the blue egg shell allele (O) were mated to homozygous recessive (oo) Shaver Starcross "288" males to produce F ( hybrids heterozygous at the blue egg-shell locus. The F t females were backcrossed to Shaver males producing full-sib sisters; half were blue egg layers and half white egg layers. The white egg layers had a significantly higher percent egg production than the blue egg layers (82 versus 79%). No significant differences between white and blue egg layers were found for shell quality, shell thickness, albumen weight, yolk weight, or yolk cholesterol. (Key words.- chickens, Araucana, shell color, egg qualities, cholesterol)
SADJADI ET AL.
1718
Yijk =
Hj + Gj + F k + E i j k
Where: Hj
is the ith hatch effect and considered a random effect, Gj is the genotypic effect of the jth genotype and considered a fixed effect, Fk is the effect of the k £ h full-sib family and considered a random effect, and Eijk is the residual error containing interaction and experimental error MS. Hatch was eliminated from the model in the determination of statistical difference in yolk cholesterol measures while hatch was dropped and day included in the statistical model in the testing of shell thickness differences. The significance of difference between white and blue egg layers for livability was determined
TABLE 1. Least squares means for body weight, sexual maturity, and percent egg production for white and blue egg layers Egg shell color phenotype Trait
White (N=179)
Blue (N=187)
Body weight, g 20 weeks 40 weeks
1444 a 1837 a
143 l a 1799 a
155 a
157 a
82 a
79b
97.8
98.9
Age at sexual maturity, days Hen-day egg production, %' Laying house livability, %
' Means within a row with the same superscript are not significantly (P<.05) different. 1
From sexual maturity to 280 days of age.
using chi 1973).
square
(Snedecor
and
Cochran,
RESULTS AND DISCUSSION
No significant differences were found in body weight at 20 or 40 weeks of age and at sexual maturity between white and blue egg layers (Table 1). Blue egg layers had significantly lower percent hen-day egg production compared with white egg layers. Somes et al. (1977) reported considerably lower egg production for Araucanas and speculated that this lowered egg production could be due to the presence of the O allele. Results of this study support Some's speculation, although the influence of genes closely linked to the O allele cannot be ruled out. The O/o locus is part of a tight linkage group #3 located on chromosome I (Somes, 1978). Laying house livability to 40 weeks of age was not statistically different for blue (98.9%) and white egg layers (97.8%). There were no significant differences between white and blue egg layers for any of the egg characteristics measured (Table 2). Similar results were reported by Anglin and Briles (1980). Somes et al. (1977) found equal yolk sizes for white and blue eggs, although Araucana eggs had a significantly greater yolkalbumen ratio. Simmons and Somes (1978) reported that blue eggs had a 28% larger yolk, 8% less albumen, and 6% less shell weight than white eggs. Differences that have been observed
Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015
Growth was determined by measuring body weights at 20 and 40 weeks of age. Sexual maturity and percent hen-day egg production to 40 weeks of age were determined for each hen. Shell quality was measured for hens of first hatch only from eggs collected during 2 days at 32 weeks of age using Instron measurement and Marius deformation methods described by Voisey and Hunt (1973). Individual egg weight, yolk weight, yolk color, albumen weight, shell weight, shell quality (specific gravity), and internal egg quality (Haugh unit) were determined for eggs collected during 3 days when hens were 40 weeks of age, regardless of hatch. The average egg weight, specific gravity, and Haugh unit for each hen were used in the statistical analyses. One yolk from each hen of Hatch 1 was frozen and saved for cholesterol determination. Frozen yolks were freeze dried for 57 hr, weighed, and stored at —10 C. Cholesterol was extracted by the method of Washburn and Nix (1974). Cholesterol content was determined according to Zlatkis et al. (1953). Two optical density readings were averaged for unknown cholesterol samples from each egg yolk. To determine the significance of differences between white and blue egg layers for the measured variables, the following statistical model was applied:
EFFECTS OF BLUE SHELL ALLELE
TABLE 2. Least squares means* for various egg characteristics for white and blue egg layers at 40 weeks of age Egg shell color phenotype Egg characteristics
Egg weight, g Albumen weight, g Yolk weight, g Shell weight, g Yolk color Haugh unit Specific gravity
White
Blue
( N = 179)
(N = 187)
57.6 33.4 16.3 7.9 9.9 75.0 1.0821
57.8 33.4 16.3 8.1 10.0 75.1 1.0820
(N = 62) Wet yolk weight, g Dry yolk weight, g Yolk moisture weight, g Cholesterol wet yolk, mg/g Cholesterol dry yolk, mg/g Cholesterol in total yolk, mg 1
(N= 187)
16.4 8.3 8.1
16.5 8.4 8.1
12.2
12.1
24.7
24.6
205.5
205.6
No significant differences (P«.05) phenotypes were observed.
between
TABLE 3. Least squares means1 for external egg quality for eggs of white and blue egg layers Egg shell color phenotype Trait
White (N = 62)
Instron (32 weeks) First day measurement 7.0 Second day measurement 6.9 Marius deformation (32 weeks) First day measurement 25.5 Second day 25.1 measurement
Blue (N = 75)
6.8 6.7 25.1 25.8
l No significant differences (P<.05) across phenotypes were observed.
nent weights, and interior and exterior shell quality measures indicating the presence of genetic difference for these traits in the population of layers studied. Interestingly, none of the yolk cholesterol measures varied among full-sib families suggesting that a homeostatic level for yolk cholesterol had been reached in this population of birds. In conclusion, the O allele or closely linked alleles exerted little influence on growth and quantitative egg measures but did depress egg number. It follows that most differences reported for Araucana eggs versus other eggs of other breeds probably are due to differences in genetic background. ACKNOWLEDGMENTS We wish to thank Suk Oh, Director of the Nutrition Research Institute, Mary P. Goeger, and Mohammad Alyan for their assistance. Araucana chickens were generously donated by Paul B. Siegel from Virginia Polytechnic Institute and State University, Blacksburg, VA. REFERENCES Anglin, H. A., and C. O. Briles, 1980. The genetic association of shell color with yolk cholesterol content in three breeds. Poultry Sci. 59:1578. (Abstr.) Cunningham, F. E., 1977. Composition of Araucana eggs. Poultry Sci. 56:463-467. Hickman, M., 1974. The amazing Aruacanas. Org. Gard. Farming. Dec:58-61. Punnett, R. C, 1933. Genetic studies in poultry, IX. The blue egg. J. Genet. 27:465-470. Simmons, R. W. Ill, and R. G. Somes, Jr., 1978. Inheritance studies of the yolk/albumen ratio of
Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015
between Araucana eggs and eggs from other breeds of domestic fowl in other studies cannot be attributed to the O allele alone because the gene was confounded with wide differences in genetic background. There was no significant difference between white and blue egg layers for cholesterol content of the yolk (Table 2). Similar results were reported by Anglin and Briles (1980) and by Cunningham (1977). However, Somes et al. (1977) found significantly greater yolk cholesterol concentrations in blue eggs than in white eggs. There were no significant differences between white and blue eggs for shell strength as indicated by Instron measures and Marius deformation (Table 3). Specific gravities for the two egg shell colors were not significantly different from each other (Table 2). These findings are similar to those reported by Cunningham (1977). Significant differences across full-sib families were observed for body weight, age at sexual maturity, hen-day egg production, egg compo-
1719
1720
SADJADI ET AL.
Araucana chicken eggs. Poultry Sci. 57:1163. (Abstr.) Snedecor, G. W., and W. G. Cochran, 1973. Statistical Methods. 6th ed. Iowa State Univ. Press, Ames, IA. Somes, R. G., 1978. Registry of poultry genetic stocks. Bull. #446, Storrs Agric. Exp. Sta., Univ. Connecticut, Storrs, CT. Somes, R. G., Jr., P. V. Francis, and J. J. Tlustohowicz, 1977. Protein and cholesterol content of Araucana chicken eggs. Poultry Sci. 56:1636—
1640. Voisey, P. W., and J. R. Hunt, 1973. Apparatus and techniques for measuring egg shell strength and other quality factors. Eng. Spec. 6176. Eng. Res. Serv., Agric. Can., Ottawa. Washburn, K. W., and D. F. Nix, 1974. A rapid technique for extraction of yolk cholesterol. Poultry Sci. 53:1118-1122. Zlatkis, A., B. Zak, and A. J. Boyle, 1953. A new method for the direct determination of serum cholesterol. J. Lab. Clin Med. 41:486-487. Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015
1983 Poultry Science 62:1717-1720 INTRODUCTION
The blue egg shell gene (O) is indigenous to the native South American breed of chicken known as Araucana and is inherited as an autosomal dominant gene (Punnett, 1933). The blue pigment permeates the entire shell (Punnett, 1933). Relatively few studies have been conducted to evaluate the difference in performance and egg quality of blue egg layers and white egg layers. Studies that have been conducted were not designed specifically to determine the effect of the O allele and alleles linked closely to this locus. Cunningham (1977) reported that shells of Araucana (blue) eggs were thicker than shells from either Leghorn (white) or Plymouth Rock (brown) eggs. Simmons and Somes (1978) indicated that Araucana eggs had larger yolks and less albumen for a given egg size than eggs from Leghorns; cholesterol content of these eggs was not measured. Anglin and Briles (1980) found that the amount of cholesterol per gram of yolk was similar among eggs from Araucana (AU), White Leghorn (WL), and Rhode Island Red (RIR) hens, although eggs
'Technical Paper No. 6356, Oregon Agricultural Experiment Station. Research done in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Oregon State University, Corvallis, OR 97331. 2 Peterson Industries, Decatur, AR 72722. 'Department of Poultry Science, Auburn University, Auburn, AL 36849. "Extension Poultry Science Department, University of Georgia, Athens, GA 30602.
from hens obtained by crosses of AU X RIR showed a significant reduction in the level of cholesterol. Reports in the popular literature have suggested low cholesterol levels in Araucana eggs (Hickman, 1974). The objective of this study was to determine the effects of the O allele and closely linked genes on internal and external egg quality and on reproductive performance in hens with similar genetic backgrounds. MATERIALS AND METHODS Araucana females homozygous dominant for the O allele were mated to Shaver Starcross " 2 8 8 " males homozygous recessive for the blue egg shell allele (oo) to produce heterozygous (Oo) Fl hybrids. Thirty-nine F x females were backcrossed to Shaver males using artificial insemination with individually collected semen from eight males to produce sisters in a 1:1 ratio of blue shell egg layers (Oo) and white shell egg layers (oo). The chicks were wingbanded and sexed upon hatching and were beak-trimmed at 12 days of age. All females within a hatch were brooded together. At 18 weeks of age, the hens were placed randomly in individual cages and received a standard laying ration containing 15% protein and 2,900 kcal/kg metabolizable energy throughout the experiment. Caged pullets received 14 hr of illumination daily and were provided with water for eight 15-min periods at 2-hr intervals during the light period. Data from 366 hens obtained from four hatches that survived to 40 weeks of age were analyzed in this experiment.
1717
Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015
ABSTRACT Araucana females homozygous dominant for the blue egg shell allele (O) were mated to homozygous recessive (oo) Shaver Starcross "288" males to produce F ( hybrids heterozygous at the blue egg-shell locus. The F t females were backcrossed to Shaver males producing full-sib sisters; half were blue egg layers and half white egg layers. The white egg layers had a significantly higher percent egg production than the blue egg layers (82 versus 79%). No significant differences between white and blue egg layers were found for shell quality, shell thickness, albumen weight, yolk weight, or yolk cholesterol. (Key words.- chickens, Araucana, shell color, egg qualities, cholesterol)
SADJADI ET AL.
1718
Yijk =
Hj + Gj + F k + E i j k
Where: Hj
is the ith hatch effect and considered a random effect, Gj is the genotypic effect of the jth genotype and considered a fixed effect, Fk is the effect of the k £ h full-sib family and considered a random effect, and Eijk is the residual error containing interaction and experimental error MS. Hatch was eliminated from the model in the determination of statistical difference in yolk cholesterol measures while hatch was dropped and day included in the statistical model in the testing of shell thickness differences. The significance of difference between white and blue egg layers for livability was determined
TABLE 1. Least squares means for body weight, sexual maturity, and percent egg production for white and blue egg layers Egg shell color phenotype Trait
White (N=179)
Blue (N=187)
Body weight, g 20 weeks 40 weeks
1444 a 1837 a
143 l a 1799 a
155 a
157 a
82 a
79b
97.8
98.9
Age at sexual maturity, days Hen-day egg production, %' Laying house livability, %
' Means within a row with the same superscript are not significantly (P<.05) different. 1
From sexual maturity to 280 days of age.
using chi 1973).
square
(Snedecor
and
Cochran,
RESULTS AND DISCUSSION
No significant differences were found in body weight at 20 or 40 weeks of age and at sexual maturity between white and blue egg layers (Table 1). Blue egg layers had significantly lower percent hen-day egg production compared with white egg layers. Somes et al. (1977) reported considerably lower egg production for Araucanas and speculated that this lowered egg production could be due to the presence of the O allele. Results of this study support Some's speculation, although the influence of genes closely linked to the O allele cannot be ruled out. The O/o locus is part of a tight linkage group #3 located on chromosome I (Somes, 1978). Laying house livability to 40 weeks of age was not statistically different for blue (98.9%) and white egg layers (97.8%). There were no significant differences between white and blue egg layers for any of the egg characteristics measured (Table 2). Similar results were reported by Anglin and Briles (1980). Somes et al. (1977) found equal yolk sizes for white and blue eggs, although Araucana eggs had a significantly greater yolkalbumen ratio. Simmons and Somes (1978) reported that blue eggs had a 28% larger yolk, 8% less albumen, and 6% less shell weight than white eggs. Differences that have been observed
Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015
Growth was determined by measuring body weights at 20 and 40 weeks of age. Sexual maturity and percent hen-day egg production to 40 weeks of age were determined for each hen. Shell quality was measured for hens of first hatch only from eggs collected during 2 days at 32 weeks of age using Instron measurement and Marius deformation methods described by Voisey and Hunt (1973). Individual egg weight, yolk weight, yolk color, albumen weight, shell weight, shell quality (specific gravity), and internal egg quality (Haugh unit) were determined for eggs collected during 3 days when hens were 40 weeks of age, regardless of hatch. The average egg weight, specific gravity, and Haugh unit for each hen were used in the statistical analyses. One yolk from each hen of Hatch 1 was frozen and saved for cholesterol determination. Frozen yolks were freeze dried for 57 hr, weighed, and stored at —10 C. Cholesterol was extracted by the method of Washburn and Nix (1974). Cholesterol content was determined according to Zlatkis et al. (1953). Two optical density readings were averaged for unknown cholesterol samples from each egg yolk. To determine the significance of differences between white and blue egg layers for the measured variables, the following statistical model was applied:
EFFECTS OF BLUE SHELL ALLELE
TABLE 2. Least squares means* for various egg characteristics for white and blue egg layers at 40 weeks of age Egg shell color phenotype Egg characteristics
Egg weight, g Albumen weight, g Yolk weight, g Shell weight, g Yolk color Haugh unit Specific gravity
White
Blue
( N = 179)
(N = 187)
57.6 33.4 16.3 7.9 9.9 75.0 1.0821
57.8 33.4 16.3 8.1 10.0 75.1 1.0820
(N = 62) Wet yolk weight, g Dry yolk weight, g Yolk moisture weight, g Cholesterol wet yolk, mg/g Cholesterol dry yolk, mg/g Cholesterol in total yolk, mg 1
(N= 187)
16.4 8.3 8.1
16.5 8.4 8.1
12.2
12.1
24.7
24.6
205.5
205.6
No significant differences (P«.05) phenotypes were observed.
between
TABLE 3. Least squares means1 for external egg quality for eggs of white and blue egg layers Egg shell color phenotype Trait
White (N = 62)
Instron (32 weeks) First day measurement 7.0 Second day measurement 6.9 Marius deformation (32 weeks) First day measurement 25.5 Second day 25.1 measurement
Blue (N = 75)
6.8 6.7 25.1 25.8
l No significant differences (P<.05) across phenotypes were observed.
nent weights, and interior and exterior shell quality measures indicating the presence of genetic difference for these traits in the population of layers studied. Interestingly, none of the yolk cholesterol measures varied among full-sib families suggesting that a homeostatic level for yolk cholesterol had been reached in this population of birds. In conclusion, the O allele or closely linked alleles exerted little influence on growth and quantitative egg measures but did depress egg number. It follows that most differences reported for Araucana eggs versus other eggs of other breeds probably are due to differences in genetic background. ACKNOWLEDGMENTS We wish to thank Suk Oh, Director of the Nutrition Research Institute, Mary P. Goeger, and Mohammad Alyan for their assistance. Araucana chickens were generously donated by Paul B. Siegel from Virginia Polytechnic Institute and State University, Blacksburg, VA. REFERENCES Anglin, H. A., and C. O. Briles, 1980. The genetic association of shell color with yolk cholesterol content in three breeds. Poultry Sci. 59:1578. (Abstr.) Cunningham, F. E., 1977. Composition of Araucana eggs. Poultry Sci. 56:463-467. Hickman, M., 1974. The amazing Aruacanas. Org. Gard. Farming. Dec:58-61. Punnett, R. C, 1933. Genetic studies in poultry, IX. The blue egg. J. Genet. 27:465-470. Simmons, R. W. Ill, and R. G. Somes, Jr., 1978. Inheritance studies of the yolk/albumen ratio of
Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015
between Araucana eggs and eggs from other breeds of domestic fowl in other studies cannot be attributed to the O allele alone because the gene was confounded with wide differences in genetic background. There was no significant difference between white and blue egg layers for cholesterol content of the yolk (Table 2). Similar results were reported by Anglin and Briles (1980) and by Cunningham (1977). However, Somes et al. (1977) found significantly greater yolk cholesterol concentrations in blue eggs than in white eggs. There were no significant differences between white and blue eggs for shell strength as indicated by Instron measures and Marius deformation (Table 3). Specific gravities for the two egg shell colors were not significantly different from each other (Table 2). These findings are similar to those reported by Cunningham (1977). Significant differences across full-sib families were observed for body weight, age at sexual maturity, hen-day egg production, egg compo-
1719
1720
SADJADI ET AL.
Araucana chicken eggs. Poultry Sci. 57:1163. (Abstr.) Snedecor, G. W., and W. G. Cochran, 1973. Statistical Methods. 6th ed. Iowa State Univ. Press, Ames, IA. Somes, R. G., 1978. Registry of poultry genetic stocks. Bull. #446, Storrs Agric. Exp. Sta., Univ. Connecticut, Storrs, CT. Somes, R. G., Jr., P. V. Francis, and J. J. Tlustohowicz, 1977. Protein and cholesterol content of Araucana chicken eggs. Poultry Sci. 56:1636—
1640. Voisey, P. W., and J. R. Hunt, 1973. Apparatus and techniques for measuring egg shell strength and other quality factors. Eng. Spec. 6176. Eng. Res. Serv., Agric. Can., Ottawa. Washburn, K. W., and D. F. Nix, 1974. A rapid technique for extraction of yolk cholesterol. Poultry Sci. 53:1118-1122. Zlatkis, A., B. Zak, and A. J. Boyle, 1953. A new method for the direct determination of serum cholesterol. J. Lab. Clin Med. 41:486-487. Downloaded from http://ps.oxfordjournals.org/ at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on May 21, 2015