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Relationship of Yolk Cholesterol and Onset of Egg Production1
Relationship of Yolk Cholesterol and Onset of Egg Production1 CRAIG W. BAIR, WILLIAM W. MARION, and DONALD K. HOTCHKISS
Departments of Food Technology, Animal Science, and Statistics, Iowa State University, Ames, Iowa 50011 (Received for publication February 28, 1979)
INTRODUCTION
(1971), "good" layers deposited a significantly (P<.01) greater amount of cholesterol per week in their eggs than did "inferior" layers. Nevertheless, the latter laid eggs contained significantly (P<.05) more cholesterol, both when expressed as per whole yolk and per gram of yolk. It is assumed that these investigations and others, for the most part, were performed on eggs from hens well into their egg production cycle. There is no evidence, however, of data available on cholesterol content of chicken eggs immediately after onset of egg production. Therefore, an experiment was conducted to study yolk cholesterol in chicken eggs immediately after commencement of egg laying.
Cholesterol content of chicken eggs continues to receive considerable attention (Becker et al., 1977; Cunningham, 1977; Naber, 1976; Washburn and Nix, 1974; Washburn et al., 1976). In a study on nutrient re-evaluation of shell eggs, Cotterill et al. (1977) reported that chicken eggs contained 270 mg cholesterol per yolk or 14.3 mg/g of yolk, Rangachar et al. (1970) found that yolk cholesterol from several breeds of chickens had a mean value of 12.9 mg/g, while Feeley et al. (1972) suggest an average cholesterol value of 14.8 mg/g of yolk. More recently, Bair and Marion (1978), in a study of yolk cholesterol in eggs from various avian species, found that cholesterol averaged 243 mg per egg or 14.0 mg/g of yolk among various lines of chickens, which included 7 inbred lines and 15 various breeds. Reports on chicken egg cholesterol values by Turk and Barnett (1970; 1971) showed that egg strains tended to have lower egg cholesterol values than did broiler strains, both when expressed as per egg and also as per gram of whole egg. This may indicate a negative relationship between egg production and yolk cholesterol level. However, Washburn and Nix (1974), in a study of genetic basis for yolk cholesterol, concluded that differences in egg production may not be related to differences in yolk cholesterol levels. According to Bartov et al.
MATERIALS AND METHODS
1 Journal Paper No. J-9437 of the Iowa Agriculture and Home Economics Experiment Station. Project 2028, a contributing project to North Central Regional Research Project 133.
Twenty-five chickens from a Leghorn inbred line were raised under the same environmental and dietary conditions at the Poultry Science Research Center, Iowa State University, Ames, Iowa. The first five eggs laid by the hens upon commencement of egg production were collected, prepared, and stored preceding yolk cholesterol analysis (Bair and Marion, 1978). The colorimetric assay for yolk cholesterol was undertaken utilizing a modified procedure of Pearson et al. (1953), also described by Bair and Marion (1978). Analysis of variance and means (Snedecor and Cochran, 1973) were calculated for whole egg weight, yolk weight, and cholesterol (mg/g of yolk) to determine if any differences existed between the cholesterol content of the first five eggs laid by the hens. A comparison also was made to determine if significant differences existed between cholesterol levels obtained in
666
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 21, 2015
ABSTRACT Cholesterol concentration in chicken egg yolk decreased significantly from an average of 18.9 to 15.8 mg/g of yolk from the first to fifth egg after the onset of production. On the basis of previous studies, there is reason to believe that the final average of 15.8 still is greater than that normally expected at a later time in the production cycle. Hens differed statistically in yolk cholesterol values. Other differences included an increase in egg weight and yolk weight during the test period. 1980 Poultry Science 59:666-668
RESEARCH NOTE
667
TABLE 1. Means and standard errors for egg weight, yolk weight, and cholesterol based on pooled data from 25 hens Egg no.
Whole egg weight
Yolk weight
Cholesterol
(g) 44.2 ± 5.42 45.2 ± 3.98 46.6 ± 5.26 47.8 ± 5.95 48.2 ± 6.05 46.4
(g) 11.2 ± 2.14 11.7 + 1.48 12.1 + 1.69 12.2 + 1.79 12.1 ± 1.71 11.9
(mg/g of yolk)
1 2 3 4 5 Average
RESULTS AND DISCUSSION Significant differences ( P < . 0 1 ) were f o u n d in y o l k cholesterol levels a m o n g t h e first five eggs laid b y t h e chickens. T h e average cholesterol value of t h e initial egg p r o d u c e d b y t h e 25 hens was 18.9 mg/g of y o l k ; t h e fifth egg was considerably less rich in y o l k cholesterol, 15.8 mg/g of yolk. T h e general t r e n d was a gradual r e d u c t i o n in yolk cholesterol from t h e first t o t h e fifth egg, whereas averages for whole egg a n d y o l k weight steadily increased with each subsequent egg (Table 1). Nichols et al. ( 1 9 6 3 ) , in a s t u d y of y o l k size and cholesterol concent r a t i o n , indicated an inverse relationship between the two. Yolk cholesterol m e a s u r e m e n t s of t h e first egg for t h e 25 hens ranged from 13.7 t o 23.2 mg/g of yolk, t h e lower value coming from a hen whose eggs contained consistently less cholesterol t h a n any others. However, t h e variance in t h e range of cholesterol values decreased s o m e w h a t in s u b s e q u e n t eggs. T h e results indicate t h a t significant differences in y o l k cholesterol d o exist, n o t only within hens (i.e., a m o n g t h e first five eggs analyzed), b u t also b e t w e e n hens in t h e average a m o u n t of y o l k cholesterol. T h e overall m e a n of 17.1 mg cholesterol per gram of y o l k f o u n d in this s t u d y is significantly higher t h a n m o s t values r e p o r t e d b y other researchers (Bair and Marion, 1 9 7 8 ; Cotterill et al, 1 9 7 7 ; Feeley et al, 1 9 7 2 ; Rangachar et al, 1970). However, w h e n expressed on a whole egg basis, t h e cholesterol c o n t e n t is only 2 0 3 mg/egg, whereas Bair and Marion ( 1 9 7 8 ) and Cotterill et al. ( 1 9 7 7 ) reported 243 and 2 7 0
m g / y o l k , respectively. This difference arises as a c o n s e q u e n c e of t h e smaller egg size characteristic for t h e first few eggs. T h e d a t a indicate t h a t yolk cholesterol in eggs i m m e d i a t e l y after c o m m e n c e m e n t of egg p r o d u c t i o n is significantly different from t h a t of eggs laid b y h e n s well i n t o their laying cycle.
REFERENCES Bair, C. W., and W. W. Marion, 1978. Yolk cholesterol in eggs from various avian species. Poultry Sci. 57:1260-1265. Bartov, I., S. Bornstein, and P. Budowski, 1971. Variability of cholesterol concentration in plasma and egg yolks on hens and evaluation of the effect of some dietary oils. Poultry Sci. 50:1357. Becker, W. A., J. V. Spencer, J. A. Verstrate, and L. W. Mirash, 1977. Genetic analysis of chicken egg yolk cholesterol. Poultry Sci. 5 6 : 8 9 5 - 9 0 1 . Cotterill, O. J., W. W. Marion, and E. C. Naber, 1977. A nutrient re-evaluation of shell eggs. Poultry Sci. 56:1927-1934. Cunningham, F. E., 1977. Composition of Araucana eggs. Poultry Sci. 56:463-467. Feeley, R., P. C. Criner, and B. K. Watt, 1972. Cholesterol content of foods. J. Amer. Diet. Ass. 61:134. Naber, E. C , 1976. The cholesterol problem, the egg and lipid metabolism in the laying hen. Poultry Sci. 55:14-30. Nichols, E. L., W. W. Marion, and S. L. Balloun, 1963. Effect of egg yolk size on yolk cholesterol concentration. Proc. Soc. Exp. Biol. Med. 112:378-380. Pearson, S., S. Stern, and T. H. McGauck, 1953. A rapid, accurate method for the determination of total cholesterol in serum. Anal. Chem. 25:813— 814. Rangachar, T.R.S., S.V.S. Setty, and R. Hedge, 1970. Cholesterol content in eggs of chicken and duck. Mysore J. Agr. Sci. 4:146. Snedecor, G. W., and W. G. Cochran, 1973. Statistical methods. 6th ed. Iowa State University Press, Ames, IA. Turk, D. E., and B. D. Barnett, 1970. Cholesterol content of market eggs. Poultry Sci. 49:1445.
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 21, 2015
this s t u d y and t h o s e values reported in t h e literature for eggs from chickens well into their egg p r o d u c t i o n cycle.
18.9 ± 2.38 17.6 ± 2.28 16.9 ± 2.26 16.1 ± 1.85 15.8+ 1.50 17.1
w 668
BAIR
Turk, D. E., and B. D. Barnett, 1971. Cholesterol content of market eggs. Poultry Sci. 50:1980— 1982. Washburn, K. W., H. L. Marks, and W. M. Britton, 1976. Carcass composition and changes in body
rAL. weight of lines selected for divergence in yolk cholesterol. Poultry Sci. 55:1980-1982. Washburn, K. W., and D. F. Nix, 1974. Genetic basis of yolk cholesterol content. Poultry Sci. 53.-109— 115.
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 21, 2015
k,
Departments of Food Technology, Animal Science, and Statistics, Iowa State University, Ames, Iowa 50011 (Received for publication February 28, 1979)
INTRODUCTION
(1971), "good" layers deposited a significantly (P<.01) greater amount of cholesterol per week in their eggs than did "inferior" layers. Nevertheless, the latter laid eggs contained significantly (P<.05) more cholesterol, both when expressed as per whole yolk and per gram of yolk. It is assumed that these investigations and others, for the most part, were performed on eggs from hens well into their egg production cycle. There is no evidence, however, of data available on cholesterol content of chicken eggs immediately after onset of egg production. Therefore, an experiment was conducted to study yolk cholesterol in chicken eggs immediately after commencement of egg laying.
Cholesterol content of chicken eggs continues to receive considerable attention (Becker et al., 1977; Cunningham, 1977; Naber, 1976; Washburn and Nix, 1974; Washburn et al., 1976). In a study on nutrient re-evaluation of shell eggs, Cotterill et al. (1977) reported that chicken eggs contained 270 mg cholesterol per yolk or 14.3 mg/g of yolk, Rangachar et al. (1970) found that yolk cholesterol from several breeds of chickens had a mean value of 12.9 mg/g, while Feeley et al. (1972) suggest an average cholesterol value of 14.8 mg/g of yolk. More recently, Bair and Marion (1978), in a study of yolk cholesterol in eggs from various avian species, found that cholesterol averaged 243 mg per egg or 14.0 mg/g of yolk among various lines of chickens, which included 7 inbred lines and 15 various breeds. Reports on chicken egg cholesterol values by Turk and Barnett (1970; 1971) showed that egg strains tended to have lower egg cholesterol values than did broiler strains, both when expressed as per egg and also as per gram of whole egg. This may indicate a negative relationship between egg production and yolk cholesterol level. However, Washburn and Nix (1974), in a study of genetic basis for yolk cholesterol, concluded that differences in egg production may not be related to differences in yolk cholesterol levels. According to Bartov et al.
MATERIALS AND METHODS
1 Journal Paper No. J-9437 of the Iowa Agriculture and Home Economics Experiment Station. Project 2028, a contributing project to North Central Regional Research Project 133.
Twenty-five chickens from a Leghorn inbred line were raised under the same environmental and dietary conditions at the Poultry Science Research Center, Iowa State University, Ames, Iowa. The first five eggs laid by the hens upon commencement of egg production were collected, prepared, and stored preceding yolk cholesterol analysis (Bair and Marion, 1978). The colorimetric assay for yolk cholesterol was undertaken utilizing a modified procedure of Pearson et al. (1953), also described by Bair and Marion (1978). Analysis of variance and means (Snedecor and Cochran, 1973) were calculated for whole egg weight, yolk weight, and cholesterol (mg/g of yolk) to determine if any differences existed between the cholesterol content of the first five eggs laid by the hens. A comparison also was made to determine if significant differences existed between cholesterol levels obtained in
666
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 21, 2015
ABSTRACT Cholesterol concentration in chicken egg yolk decreased significantly from an average of 18.9 to 15.8 mg/g of yolk from the first to fifth egg after the onset of production. On the basis of previous studies, there is reason to believe that the final average of 15.8 still is greater than that normally expected at a later time in the production cycle. Hens differed statistically in yolk cholesterol values. Other differences included an increase in egg weight and yolk weight during the test period. 1980 Poultry Science 59:666-668
RESEARCH NOTE
667
TABLE 1. Means and standard errors for egg weight, yolk weight, and cholesterol based on pooled data from 25 hens Egg no.
Whole egg weight
Yolk weight
Cholesterol
(g) 44.2 ± 5.42 45.2 ± 3.98 46.6 ± 5.26 47.8 ± 5.95 48.2 ± 6.05 46.4
(g) 11.2 ± 2.14 11.7 + 1.48 12.1 + 1.69 12.2 + 1.79 12.1 ± 1.71 11.9
(mg/g of yolk)
1 2 3 4 5 Average
RESULTS AND DISCUSSION Significant differences ( P < . 0 1 ) were f o u n d in y o l k cholesterol levels a m o n g t h e first five eggs laid b y t h e chickens. T h e average cholesterol value of t h e initial egg p r o d u c e d b y t h e 25 hens was 18.9 mg/g of y o l k ; t h e fifth egg was considerably less rich in y o l k cholesterol, 15.8 mg/g of yolk. T h e general t r e n d was a gradual r e d u c t i o n in yolk cholesterol from t h e first t o t h e fifth egg, whereas averages for whole egg a n d y o l k weight steadily increased with each subsequent egg (Table 1). Nichols et al. ( 1 9 6 3 ) , in a s t u d y of y o l k size and cholesterol concent r a t i o n , indicated an inverse relationship between the two. Yolk cholesterol m e a s u r e m e n t s of t h e first egg for t h e 25 hens ranged from 13.7 t o 23.2 mg/g of yolk, t h e lower value coming from a hen whose eggs contained consistently less cholesterol t h a n any others. However, t h e variance in t h e range of cholesterol values decreased s o m e w h a t in s u b s e q u e n t eggs. T h e results indicate t h a t significant differences in y o l k cholesterol d o exist, n o t only within hens (i.e., a m o n g t h e first five eggs analyzed), b u t also b e t w e e n hens in t h e average a m o u n t of y o l k cholesterol. T h e overall m e a n of 17.1 mg cholesterol per gram of y o l k f o u n d in this s t u d y is significantly higher t h a n m o s t values r e p o r t e d b y other researchers (Bair and Marion, 1 9 7 8 ; Cotterill et al, 1 9 7 7 ; Feeley et al, 1 9 7 2 ; Rangachar et al, 1970). However, w h e n expressed on a whole egg basis, t h e cholesterol c o n t e n t is only 2 0 3 mg/egg, whereas Bair and Marion ( 1 9 7 8 ) and Cotterill et al. ( 1 9 7 7 ) reported 243 and 2 7 0
m g / y o l k , respectively. This difference arises as a c o n s e q u e n c e of t h e smaller egg size characteristic for t h e first few eggs. T h e d a t a indicate t h a t yolk cholesterol in eggs i m m e d i a t e l y after c o m m e n c e m e n t of egg p r o d u c t i o n is significantly different from t h a t of eggs laid b y h e n s well i n t o their laying cycle.
REFERENCES Bair, C. W., and W. W. Marion, 1978. Yolk cholesterol in eggs from various avian species. Poultry Sci. 57:1260-1265. Bartov, I., S. Bornstein, and P. Budowski, 1971. Variability of cholesterol concentration in plasma and egg yolks on hens and evaluation of the effect of some dietary oils. Poultry Sci. 50:1357. Becker, W. A., J. V. Spencer, J. A. Verstrate, and L. W. Mirash, 1977. Genetic analysis of chicken egg yolk cholesterol. Poultry Sci. 5 6 : 8 9 5 - 9 0 1 . Cotterill, O. J., W. W. Marion, and E. C. Naber, 1977. A nutrient re-evaluation of shell eggs. Poultry Sci. 56:1927-1934. Cunningham, F. E., 1977. Composition of Araucana eggs. Poultry Sci. 56:463-467. Feeley, R., P. C. Criner, and B. K. Watt, 1972. Cholesterol content of foods. J. Amer. Diet. Ass. 61:134. Naber, E. C , 1976. The cholesterol problem, the egg and lipid metabolism in the laying hen. Poultry Sci. 55:14-30. Nichols, E. L., W. W. Marion, and S. L. Balloun, 1963. Effect of egg yolk size on yolk cholesterol concentration. Proc. Soc. Exp. Biol. Med. 112:378-380. Pearson, S., S. Stern, and T. H. McGauck, 1953. A rapid, accurate method for the determination of total cholesterol in serum. Anal. Chem. 25:813— 814. Rangachar, T.R.S., S.V.S. Setty, and R. Hedge, 1970. Cholesterol content in eggs of chicken and duck. Mysore J. Agr. Sci. 4:146. Snedecor, G. W., and W. G. Cochran, 1973. Statistical methods. 6th ed. Iowa State University Press, Ames, IA. Turk, D. E., and B. D. Barnett, 1970. Cholesterol content of market eggs. Poultry Sci. 49:1445.
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 21, 2015
this s t u d y and t h o s e values reported in t h e literature for eggs from chickens well into their egg p r o d u c t i o n cycle.
18.9 ± 2.38 17.6 ± 2.28 16.9 ± 2.26 16.1 ± 1.85 15.8+ 1.50 17.1
w 668
BAIR
Turk, D. E., and B. D. Barnett, 1971. Cholesterol content of market eggs. Poultry Sci. 50:1980— 1982. Washburn, K. W., H. L. Marks, and W. M. Britton, 1976. Carcass composition and changes in body
rAL. weight of lines selected for divergence in yolk cholesterol. Poultry Sci. 55:1980-1982. Washburn, K. W., and D. F. Nix, 1974. Genetic basis of yolk cholesterol content. Poultry Sci. 53.-109— 115.
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 21, 2015
k,