- Email: [email protected]
Shell Evaluation of White and Brown Egg Strains by Deformation, Breaking Strength, Shell Thickness and Specific Gravity
COMPOSITION OF ISOLATED ERYTHROCYTE NUCLEI
Neelin, J. M., and G. C. Butler, 1961. A comparison of histones from chicken tissues by zone electrophoresis in starch gel. Can. J. Biochem. Physiol. 39: 485-491. Nelson, R. D., and J. J. Yunis, 1969. Species and tissue specificity of very lysine-rich and serine-rich histones. Exp. Cell Res. 57: 311-318. Stedman, E., and E. Stedman, 1943. Probable function of histone as a regulator of mitosis. Nature, 152: 556-557. Stellwagen, R. H., and R. D. Cole, 1969. Chromosomal proteins. Ann. Rev. Biochem. 38: 951-990. Vadali, G., and J. M. Neelin, 1968. A comprehensive fractionation procedure for avian erythrocyte histones. Eur. J. Biochem. 5: 330-338.
Shell Evaluation of White and Brown Egg Strains by Deformation, Breaking Strength, Shell Thickness and Specific Gravity 2. STEPWISE REGRESSION ANALYSIS OF EGG CHARACTERISTICS ON METHODS OF ASSESSING SHELL STRENGTH PHILIP L. POTTS, K. W. WASHBURN AND K. K. HALE
Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication March 15, 1974)
ABSTRACT The egg characteristics of shell thickness, specific gravity, egg weight, width/length ratio and tint of the brown shell eggs were regressed on the shell strength measurements of non-destructive deformation and breaking strength. Six commercially available laying strains (3 white egg and 3 brown egg) were used to determine differences between strains and differences between white and brown strains. Specific gravity was the most important contributor to deformation of white and brown shell eggs when non-destructive variables were considered. However, when the destructive measure of shell thickness was added to the model it became the most important contributor to deformation for the brown shell eggs, whereas specific gravity remained the most important contributor for the white shell eggs. With breaking strength as the dependent variable, the most important source of variation in Hatch 1 was thickness for the brown shell eggs and specific gravity for the white eggs. However, in Hatch 2 thickness was the most important contributor for both white and brown shell eggs. Specific gravity remained significant in the white egg strains and became insignificant in the brown egg strains. Tint did not contribute significantly to either deformation or breaking strength in the brown egg strains. POULTRY SOEMCE 53: 2167-2174, 1974
INTRODUCTION ARIOUS methods have been used to assess egg shell strength including nondestructive deformation (Schoorl and Boersma, 1962) and direct measures of breaking strength. Only a few studies (Richards and Swanson, 1965; Hunton, 1969; Perek and
V
Snapir, 1970) determined which egg characteristics contributed the most variation to egg shell strength or quality measurements. Significant correlations between the shell strength measurements of deformation (nondestructive) and breaking strength (destructive) with the egg characteristics of shell
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
Isaacks, R. E., and B. G. Santos, 1973. Studies on nuclei of Paramecium aurelia. II. Amino acid composition and electrophoretic properties of the chromosomal basic proteins. J. Protozool. 20: 482489. Lucas, A. M., and C. Jamroz, 1961. Atlas of Avian Hematology. U.S. Department of Agriculture, Agriculture Monograph 25, Washington, D.C., p. 113. Neelin, J. M., 1968. Variability in cell-specific and common histones of avian erythrocytes. Can. J. Biochem. 46: 241-247. Neelin, J. M., and G. C. Butler, 1959. The fractionation of the histones of calf thymus and chicken erythrocytes by cation-exchange chromatography with sodium salts. Can. J. Biochem. Physiol. 37: 843-859.
2167
2168
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
MATERIALS AND METHODS Measurements of egg shell characteristics of shell thickness, specific gravity, egg weight, width/length ratio and tint of the brown shell eggs were regressed on the shell strength assessments of deformation and breaking strength to determine which egg characteristics contributed the greatest amount of variation to the shell strength measures. Two brown egg (Hubbard and Warren) and three white egg strains (Hyline, DeKalb and Babcock) were used in Hatch 1, while in Hatch 2, an additional brown egg strain (Tatum) was added and a Tatum white egg strain replaced the DeKalb strain. For each hatch, the chicks were obtained from commercial hatcheries in the same week, reared under the same conditions in floor pens and placed in single 25.4 x 40.6 cm. laying cages
at 18 weeks of age. Birds were fed a commercial laying diet which contained 2968 kcal./kilogram metabolizable energy and 16.7% protein with a total calcium and phosphorus content of 2.9% and .39%, respectively. No supplemental calcium was provided. In the first hatch, 1,444 eggs were collected from 20 birds of each strain during two one-week periods when they had been in production approximately three months (Trial 1) and seven months (Trial 2). Data on five to seven eggs per bird were averaged per characteristic measured to obtain the individual values for each bird in Trial 1 and 2 of Hatch 1. These values for Trial 1 and Trial 2 were pooled in the regression studies for Hatch 1 and for comparisons with Hatch 2. In Hatch 2, eggs were collected from 50 birds of each strain for two periods of two days each when the birds had been in production three months. The data for the two collection periods were averaged to obtain the values used in Hatch 2. In Hatch 1, the breaking strength, non-destructive deformation, shell thickness, specific gravity, egg weight, width/length ratio, egg production and tint of brown shell eggs were measured. In Hatch 2, only breaking strength, non-destructive deformation, shell thickness and specific gravity were measured since correlation analysis of Hatch 1 data indicated that only these variables were significant. However, egg weight and width/length ratio were found to contribute significandy to the dependent variable in certain prediction equations. A modification of the non-destructive deformation apparatus (Marius NU, Utrecht, Holland) developed by Schoorl and Boersma (1962) was used to assess shell deformation. The technique measures the inward movement of the shell when subjected to 500 gms. of weight via a rod 0.5 cm. in diameter. An Instron Quasi-static loader (Instron Corporation, 2500 Washington Street, Canton, Massachusetts) which measures the pressure re-
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
thickness and specific gravity were reported by Potts and Washburn (1974). This work reported high statistical correlations between the two strength measurements but did not indicate which shell characteristics accounted for the most variation in either of the shell strength measurements. Potts and Washburn (1974) also reported differences in brown and white egg strains in the measurements of shell thickness, specific gravity, deformation and breaking strength. The present study was conducted (1) to determine which egg characteristics contribute the greatest amount of variation in the shell strength measurements, (2) to determine whether the egg characteristics studied contribute equally in brown and white shell eggs, (3) to assess the importance of tint in the evaluation of shell strength in brown shell eggs and (4) where deformation or breaking strength instruments are not available, to determine which of the destructive and/or non-destructive measurements can be used in regression prediction equations to evaluate shell strength.
SHELL STRENGTH ASSESSMENT
tion as the dependent variable and then using breaking strength as the dependent variable. The analysis was conducted separately for brown and white egg strains but strains within trials were pooled. When deformation was the dependent variable in Hatch 1, the analysis was computed first using the non-destructive independent variables of specific gravity, width/length ratio, egg weight and tint (for brown shell eggs) and then using the non-destructive methods as well as the destructive measures of shell thickness as independent variables. Breaking strength was not used as an independent variable since it was determined only for one trial of Hatch 1. In Hatch 2, deformation as the dependent variable and independent variables of thickness, specific gravity and breaking strength were used. Breaking strength in Trial 2 of Hatch 1 and in both trials combined in Hatch 2 was used as the dependent variable. Thickness width/length ratio, weight, specific gravity and tint (brown eggs) were used as the independent variables in Hatch 1 with thickness and specific gravity used as the independent variables in Hatch 2. RESULTS AND DISCUSSION Mean values for shell thickness, specific gravity, nondestructive deformation and breaking strength in Hatch 1 and 2 for various
TABLE 1.—Shell thickness, specific gravity, deformation and breaking strength means for the various strains: Hatch 1 and 2 Brown egg strains White egg strains Measurement Hubbard Warren Tatum Tatum Babcock DeKalb Hyline Thickness 32.4a 32.7 ab 34.6° 33.0""= Hatch 1 33.3"° — — (mm. x .01) 32.2" 32.6 ab 33.0s* 34.0= 35.3 d Hatch 2 33.2"° — Specific 1.082" Hatch 1 1.080" 1.082" 1.085" 1.081" — — gravity Hatch 2 1.084a 1.085" 1.089"= 1.086" 1.089"= 1.086" — Deformation 2.60"b 2.40" 2.50"" 2.60"b Hatch 1 2.70 b — — (.001 mm.) 2.68" Hatch 2 2.70 b 2.64" 2.39" 2.61" 2.25" — Breaking Hatch 1 3.31 b 3.60" 3.45" 3.04" 3.27" — — strength (kg.) 3.17" 3.39" 3.36" Hatch 2 3.09" 3.32" 3.25" — abc Those means with the same superscript within each hatch were not significantly different (P £ .05).
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
quired to break the shell, was used to measure breaking strength. The specific gravity of the whole egg held in storage for approximately four hours after oviposition was measured by the flotation method using salt solutions ranging in specific gravity from 1.070 to 1.100 with gradients of .005. The average shell thickness (without membrane) of two points at the equatorial region was measured to the nearest .01 mm. using a vice caliper. Tint of the brown shell eggs was objectively determined by a scoring system of 1-10 based on increasing intensity of color. The relative magnitude of contribution by the various egg characteristics to variation in the dependent variable was determined by a stepwise multiple regression analysis (Dixon, 1973) using Biomedical Computer Program BMD02R which computes a sequence of multiple linear regression equations in a stepwise manner. A single variable, which contributes the greatest reduction in the error sums of squares, is added to the regression equation in a stepwise manner until all variables are used. A prediction equation can then be formed which includes those independent variables that significantly reduce the error of predicting the value of the dependent variable. In Hatch 1 and Hatch 2, the regression analysis was computed first using deforma-
2169
2170
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
TABLE 2.—Stepwise regression analysis of variation in egg characteristics of brown egg strains Dependent variable—deformation Independent variables, non-destructive Hatch 1 Independent variable r1 RSQ2 Specific gravity -.82 .68** W/L .16 .70 Egg weight .32 .70 Tint .00 .70 Independent variable Shell thickness Specific gravity Breaking strength
Hatch 2 r1 ^~7% -.70 -.65
RSQ2 .60** .65** .69**
Independent variables, destructive and non-destructive Hatch 1 Independent r' RSQ2 variable .85** Shell thickness -.85 .32 .88** Egg weight -.16 .90** W/L -.82 91** Specific gravity .00 .91 Tint 'Simple correlation coefficient with dependent variable. 2 Cumulative amount of variation accounted for in dependent variable (value of multiple correlation coefficient squared). "Indicates statistically significant contribution of independent variable to variation in dependent variable (**P < .01; *P £ .05).
the model, they add little since shell thickness has already added most of their contribution to variability. Similar results were obtained from Hatch 2 when the contribution of the variables of shell thickness, specific gravity and breaking strength to deformation were determined (Table 2). Shell thickness accounted for 60% of the variation in deformation with specific gravity (which would include variation in width/length ratio and egg weight in addition to thickness) accounting for an additional 5% and breaking strength an additional 4%. This points out the fact that variation in specific gravity is influenced by thickness with shape and weight of the egg contributing a minor
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
strains are presented in Table 1. Differences were calculated for the various strains only within hatches since different strains were used in Hatch 2. Shell thickness measurements were consistent over both hatches in that the brown shell eggs were generally thinner than the white shell eggs. Hubbard eggs exhibited the thinnest shells in both hatches and Hyline along with Babcock in Hatch 2 had the thickest shells. Since specific gravity is directly related to shell thickness, similar relationship between strains was expected and observed. The brown egg strains recorded the lowest specific gravity readings with the Hubbard strain again having the lowest readings with Hyline and Babcock in Hatch 2 having the highest specific gravities. Deformation readings (lower value, stronger shells) for the brown shell eggs were higher on the average in both hatches than the average of the white eggs with the exception of the Babcock strain in Hatch 1. No significant differences were found between strains in either hatch for breaking strength (higher value, stronger shells) with the exception of the Babcock strain in Hatch 1. However, significant variation was detected with the use of the deformation apparatus. When non-destructive deformation was held as the dependent variable (brown shell eggs) and a stepwise regression analysis of remaining non-destructive values computed, only variation in specific gravity contributed significantly to variation in deformation (Table 2) with 68% of the variability in deformation being explained by variation in specific gravity. When the destructive measure of shell thickness was added to the non-destructive measures as an independent variable, it became the primary contributor to variability in deformation, accounting for 85% of the variation in deformation (Table 2). The variability of deformation can be attributed primarily to shell thickness. When egg weight and width/length are included in
SHELL STRENGTH ASSESSMENT
2171
but significant part to the variation. Once variation in the specific components that make up specific gravity are removed, specific gravity may become a relatively unimportant contributor to deformation. Assuming that deformation is actually measuring resistance of the shell to breakage, these findings suggest that in brown egg strains a good criterion of selection against shell breakage might be specific gravity. However, identification of individuals with ability to lay eggs with superior specific gravity might best be made by considering thickness, size and shape. If selection was on the basis of specific gravity alone, the variables of thickness, shape and egg weight could vary in any combination. The stepwise regression analysis of egg
Table 4 illustrates the relative differences in sources of variation of breaking strength. In Hatch 1 the most significant source of variation was thickness for the brown shell eggs. However, specific gravity was the most important source of variation in the white shell eggs. Thickness was the most significant source of variation in breaking strength for both white and brown shell eggs of Hatch 2. Specific gravity was a significant contributor to breaking strength with white shell eggs but was not with brown shell eggs. The differences in Hatch 1 and 2 could be attributed to the different strains used, the time of year the data were collected, or due to genetic change in the strains themselves. Prediction equations for non-destructive deformation and breaking strength with the various traits as independent variables for
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
TABLE 3.—Stepwise regression analysis variation characteristics from the white shell strains in egg characteristics of white egg strains are presented in Table 3. When deformation was the dependent variable, the only nonDependent variable—deformation destructive variable that contributed signifiIndependent variables, non-destructive Hatch 1 cant variation was specific gravity. As was Independent the case for brown eggs, variation in specific variable r1 RSQ2 Specific gravity -.82 .68** gravity accounted for 68% of the variability Egg weight .00 .68 in deformation. In contrast to the brown egg W/L .17 .69 strains, when thickness was added as an Hatch 2 independent variable, specific gravity still Independent variable r1 RSQ2 accounted for the majority of the variation (67%) although thickness, weight and Thickness -.56 .39** Specific gravity -.63 .44** width/length ratio all contributed signifiBreaking strength - .54 ; 4 5 ** cantly to the variation in deformation. These Independent variables, destructive and non-defindings suggest the possibility that factors structive related to specific gravity other than Hatch 1 Independent thickness, shape and weight such as porosity variable r1 RSQ 2 or shell matrix structure may be more imporSpecific gravity -.82 .67** tant in determining shell strength in some .70** Thickness -.78 72** Weight .00 strains than in others. They could explain W/L .17 !73** the observation that brown eggs may have 'Simple correlation coefficient with dependent thinner shells than white eggs but may break variable. 2 Cumulative amount of variation accounted for less readily (Hunton, 1969). Potts and Washin dependent variable. * indicates statistically significant contribution burn (1974) reported that although brown eggs of independent variable to variation in dependent had a lower specific gravity, shell thickness variable (**P •& .01; *P •& .05). and deformation, their breaking strength was superior to comparable white eggs.
2172
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
TABLE 4.—Stepwise regression analysis for trial 2 of hatch 1 and hatch 2 with breaking strength as the dependent variable Dependent variable—breaking strength Hatch 1, Trial 2 Variable Thickness W/L Weight Specific gravity Tint
Brown eggs r1 .78 .36 .32 .78 .09
RSQ2 .61** .77** .82** .83 .84
Variable Specific gravity Weight W/L Thickness
White eggs r .79 .06 .27 .72
the white and brown egg strains in Hatch 1 and 2 are presented in Table 5. In Hatch 1 two equations with non-destructive deformation as the dependent variable, and one equation with breaking strength as the dependent variable, were calculated for both white and brown egg strains. All white egg strain values were pooled as were the brown egg strain values. The variables that contributed significantly were the same for both brown and white egg strains using destructive and non-destructive measures. The significantly contributing variables for the breaking strength were similar; however, specific gravity did not contribute significantly in the brown egg strains. In Hatch 2, equations with non-destructive deformation and breaking strength as the dependent variables were calculated for the pooled values of the white and brown egg strains. The coefficients of the variables were similar in both the white and brown egg strains for the non-destructive deformation equation. The variables and their coefficients were similar for the breaking strength equation with the exception of specific gravity, which did not contribute significantly to the variation.
RSQ .41** '.46** dependent
A limited amount of investigative work has been published that compares brown and white shell eggs. However, studies have been reported which have regressed several variables on crushing strength. Hunton (1969) reported a regression study in which energy was found to contribute the greatest amount to crushing strength with stiffness of the shell, egg weight, deformation at failure, mean backscatter, non-destructive deformation and mean shell thickness contributing to crushing strength to a lesser degree. Richards and Swanson (1965) reported that shell thickness was the best single predictor of crushing strength. The present experiment is in agreement only in the brown egg strains where specific gravity did not contribute significantly to the variation. However, specific gravity contributed the greatest amount of variation in the white egg strains in the non-destructive as well as the breaking strength equations in Hatch 1. As in the equations with deformation as the dependent variable, the most important factor contributing to breaking strength in Hatch 2 was thickness. The differences could be due to the different strains, the time of year the
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
Hatch 2 Brown eggs White eggs r Variable r Variable RSQ 40** .64 Thickness .64 Thickness .59 Specific gravity Specific gravity '.40 .47 1 Simple correlation coefficient with dependent variable. 2 Cumulative amount of variation accounted for by independent variable. * indicates statistically significant contribution of independent variable to variation in variable (**P s; .01; *P < .05).
RSQ .62** .64* .66* .67
7.074 -4.751
Hatch # 2 White egg strains Deformation as dep var Breaking strength as dep var
+
-
_
0.022X, 0.O22X, 0.070X,
0.022X, —
0.082X,
0.037X, 0.131X,
+ + +
0.066X,
+
X,
-
+
-
+
0.170X2 O.HOXj 0.438X2
0.924X2
_
+
-
+
—
O.I8OX2 0.026X2
_
—
—
O.O22X3 0.128X 0.128X,3
—
0.016X3 0.060X3
_
Variables X3
— 0.333X2
+
X^
-
+
+ +
Brown egg strains + 0.030X, -_ 0.190X2 Deformation as dep var y == 8.332 + O.19OX2 — -2.500 Breaking strength as dep var — + O.74OX2 — y = 'Non-destructive deformation as dependent variable. Variables: X, specific gravity, X2 thickness, X X* breaking strength.
y == y =
9.141 -10.591
9.285
Brown egg strains Non-destructive variables 1 y = Destructive & non-destructive variables 1 y = Breaking strength as dep var y ==
Hatch # 1 Constant White egg strains Non-destructive variables' y = 7.898 Destructive & non-destructive 8.434 y = Breaking strength as dep var y == -13.609
TABLE 5.—Prediction equations for the various traits measured with non-destructive deformation and
ded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
2174
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
commercial egg processing practices. Correlation of these data with more objective measurements such as deformation, breaking strength, thickness, specific gravity, etc. should permit formation of more accurate predictions on shell quality. REFERENCES Dixon, W. J., 1973. Biomedical Computer Programs, University of California Press, Berkeley, California. Hunton, P., 1969. The measurement of egg shell strength. A comparison of four methods. British Poultry Sci. 10: 281-289. Perek, M., and N. Snapir, 1970. Interrelationships between shell quality and egg production and egg and shell weights in white leghorn and white rock hens. British Poultry Sci. 11: 133-145. Potts, P. L., and K. W. Washburn, 1974. Shell evaluation of white and brown egg strains by deformation, breaking strength, shell thickness and specific gravity. 1. Relationships to egg characteristics. Poultry Sci. 53: 1123-1128. Richards, J. F., and M. H. Swanson, 1965. The relationship of egg shape to shell strength. Poultry Sci. 44: 1555-1558. Schoorl, P., and H. Y. Boersma, 1962. Research on the quality of the egg shell. 12th Wld's. Poultry Congress, Sidney, 432-435.
NEWS AND NOTES (Continued from page 2162)
Vice President—C. E. Black, and Members of the Executive Committee—K. C. Barrens, B. P. Cardon, and R. H. White-Stevens. F. H. Baker, President of the American Society of Animal Science, named O. D. Butler to replace Dr. Cardon, who is now a member of the Executive Committee and hence no longer a representative of A.S.A.S. News from C.A.S.T., Vol. 1, No. 1., contained the following: A treatise on "Environmental Impact Analysis Reports and Environmental Impact Statements," prepared at the request of the Food and Drug Administration, was submitted to F.D.A. in February. The
requirement for information of the kind contained in the document originated with the National Environmental Policy Act of 1969. The members of the C.A.S.T. task force included William J. Stadelman (Chairman), Purdue University; D. S. Frear, A.R.S., U.S.D.A., Fargo, North Dakota; Jerry L. Hamelink, Purdue University; Darrell W. Nelson, Purdue University; W. H. Pfander, University of Missouri; Gerald W. Probst, Eli Lilly and Company; Joseph Shapiro, University of Minnesota; Lee E. Sommers, Purdue University; J. B. Weber, North Carolina State University; and Robert Zwickey, Merck, Sharp & Dohme Research Laboratories. Areas
(Continued on page 2192)
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
data were collected, or due to the genetic change in the strains themselves. Perek and Snapir (1970) reported a study in which shell weight, egg weight and egg production were regressed on shell quality. They reported shell weight to be the variable contributing the greatest amount of variation to shell quality with egg weight and egg production contributing a lesser amount. These data suggest caution in assuming that all white egg strains' or all brown egg strains' shell strength can be estimated with the same prediction equation. Although differences between brown and white eggs have been emphasized, there are also differences between the strains of either the white egg or brown egg layers (Potts and Washburn, 1974). RSQ (cumulative amount of variation accounted for in the dependent variable by the independent variables) values for deformation and breaking strength indicate that a significant proportion of the sources of variation for these shell quality estimates has not been measured. The true measure of shell quality may best be estimated by obtaining emperical data on shell integrity through
Neelin, J. M., and G. C. Butler, 1961. A comparison of histones from chicken tissues by zone electrophoresis in starch gel. Can. J. Biochem. Physiol. 39: 485-491. Nelson, R. D., and J. J. Yunis, 1969. Species and tissue specificity of very lysine-rich and serine-rich histones. Exp. Cell Res. 57: 311-318. Stedman, E., and E. Stedman, 1943. Probable function of histone as a regulator of mitosis. Nature, 152: 556-557. Stellwagen, R. H., and R. D. Cole, 1969. Chromosomal proteins. Ann. Rev. Biochem. 38: 951-990. Vadali, G., and J. M. Neelin, 1968. A comprehensive fractionation procedure for avian erythrocyte histones. Eur. J. Biochem. 5: 330-338.
Shell Evaluation of White and Brown Egg Strains by Deformation, Breaking Strength, Shell Thickness and Specific Gravity 2. STEPWISE REGRESSION ANALYSIS OF EGG CHARACTERISTICS ON METHODS OF ASSESSING SHELL STRENGTH PHILIP L. POTTS, K. W. WASHBURN AND K. K. HALE
Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication March 15, 1974)
ABSTRACT The egg characteristics of shell thickness, specific gravity, egg weight, width/length ratio and tint of the brown shell eggs were regressed on the shell strength measurements of non-destructive deformation and breaking strength. Six commercially available laying strains (3 white egg and 3 brown egg) were used to determine differences between strains and differences between white and brown strains. Specific gravity was the most important contributor to deformation of white and brown shell eggs when non-destructive variables were considered. However, when the destructive measure of shell thickness was added to the model it became the most important contributor to deformation for the brown shell eggs, whereas specific gravity remained the most important contributor for the white shell eggs. With breaking strength as the dependent variable, the most important source of variation in Hatch 1 was thickness for the brown shell eggs and specific gravity for the white eggs. However, in Hatch 2 thickness was the most important contributor for both white and brown shell eggs. Specific gravity remained significant in the white egg strains and became insignificant in the brown egg strains. Tint did not contribute significantly to either deformation or breaking strength in the brown egg strains. POULTRY SOEMCE 53: 2167-2174, 1974
INTRODUCTION ARIOUS methods have been used to assess egg shell strength including nondestructive deformation (Schoorl and Boersma, 1962) and direct measures of breaking strength. Only a few studies (Richards and Swanson, 1965; Hunton, 1969; Perek and
V
Snapir, 1970) determined which egg characteristics contributed the most variation to egg shell strength or quality measurements. Significant correlations between the shell strength measurements of deformation (nondestructive) and breaking strength (destructive) with the egg characteristics of shell
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
Isaacks, R. E., and B. G. Santos, 1973. Studies on nuclei of Paramecium aurelia. II. Amino acid composition and electrophoretic properties of the chromosomal basic proteins. J. Protozool. 20: 482489. Lucas, A. M., and C. Jamroz, 1961. Atlas of Avian Hematology. U.S. Department of Agriculture, Agriculture Monograph 25, Washington, D.C., p. 113. Neelin, J. M., 1968. Variability in cell-specific and common histones of avian erythrocytes. Can. J. Biochem. 46: 241-247. Neelin, J. M., and G. C. Butler, 1959. The fractionation of the histones of calf thymus and chicken erythrocytes by cation-exchange chromatography with sodium salts. Can. J. Biochem. Physiol. 37: 843-859.
2167
2168
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
MATERIALS AND METHODS Measurements of egg shell characteristics of shell thickness, specific gravity, egg weight, width/length ratio and tint of the brown shell eggs were regressed on the shell strength assessments of deformation and breaking strength to determine which egg characteristics contributed the greatest amount of variation to the shell strength measures. Two brown egg (Hubbard and Warren) and three white egg strains (Hyline, DeKalb and Babcock) were used in Hatch 1, while in Hatch 2, an additional brown egg strain (Tatum) was added and a Tatum white egg strain replaced the DeKalb strain. For each hatch, the chicks were obtained from commercial hatcheries in the same week, reared under the same conditions in floor pens and placed in single 25.4 x 40.6 cm. laying cages
at 18 weeks of age. Birds were fed a commercial laying diet which contained 2968 kcal./kilogram metabolizable energy and 16.7% protein with a total calcium and phosphorus content of 2.9% and .39%, respectively. No supplemental calcium was provided. In the first hatch, 1,444 eggs were collected from 20 birds of each strain during two one-week periods when they had been in production approximately three months (Trial 1) and seven months (Trial 2). Data on five to seven eggs per bird were averaged per characteristic measured to obtain the individual values for each bird in Trial 1 and 2 of Hatch 1. These values for Trial 1 and Trial 2 were pooled in the regression studies for Hatch 1 and for comparisons with Hatch 2. In Hatch 2, eggs were collected from 50 birds of each strain for two periods of two days each when the birds had been in production three months. The data for the two collection periods were averaged to obtain the values used in Hatch 2. In Hatch 1, the breaking strength, non-destructive deformation, shell thickness, specific gravity, egg weight, width/length ratio, egg production and tint of brown shell eggs were measured. In Hatch 2, only breaking strength, non-destructive deformation, shell thickness and specific gravity were measured since correlation analysis of Hatch 1 data indicated that only these variables were significant. However, egg weight and width/length ratio were found to contribute significandy to the dependent variable in certain prediction equations. A modification of the non-destructive deformation apparatus (Marius NU, Utrecht, Holland) developed by Schoorl and Boersma (1962) was used to assess shell deformation. The technique measures the inward movement of the shell when subjected to 500 gms. of weight via a rod 0.5 cm. in diameter. An Instron Quasi-static loader (Instron Corporation, 2500 Washington Street, Canton, Massachusetts) which measures the pressure re-
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
thickness and specific gravity were reported by Potts and Washburn (1974). This work reported high statistical correlations between the two strength measurements but did not indicate which shell characteristics accounted for the most variation in either of the shell strength measurements. Potts and Washburn (1974) also reported differences in brown and white egg strains in the measurements of shell thickness, specific gravity, deformation and breaking strength. The present study was conducted (1) to determine which egg characteristics contribute the greatest amount of variation in the shell strength measurements, (2) to determine whether the egg characteristics studied contribute equally in brown and white shell eggs, (3) to assess the importance of tint in the evaluation of shell strength in brown shell eggs and (4) where deformation or breaking strength instruments are not available, to determine which of the destructive and/or non-destructive measurements can be used in regression prediction equations to evaluate shell strength.
SHELL STRENGTH ASSESSMENT
tion as the dependent variable and then using breaking strength as the dependent variable. The analysis was conducted separately for brown and white egg strains but strains within trials were pooled. When deformation was the dependent variable in Hatch 1, the analysis was computed first using the non-destructive independent variables of specific gravity, width/length ratio, egg weight and tint (for brown shell eggs) and then using the non-destructive methods as well as the destructive measures of shell thickness as independent variables. Breaking strength was not used as an independent variable since it was determined only for one trial of Hatch 1. In Hatch 2, deformation as the dependent variable and independent variables of thickness, specific gravity and breaking strength were used. Breaking strength in Trial 2 of Hatch 1 and in both trials combined in Hatch 2 was used as the dependent variable. Thickness width/length ratio, weight, specific gravity and tint (brown eggs) were used as the independent variables in Hatch 1 with thickness and specific gravity used as the independent variables in Hatch 2. RESULTS AND DISCUSSION Mean values for shell thickness, specific gravity, nondestructive deformation and breaking strength in Hatch 1 and 2 for various
TABLE 1.—Shell thickness, specific gravity, deformation and breaking strength means for the various strains: Hatch 1 and 2 Brown egg strains White egg strains Measurement Hubbard Warren Tatum Tatum Babcock DeKalb Hyline Thickness 32.4a 32.7 ab 34.6° 33.0""= Hatch 1 33.3"° — — (mm. x .01) 32.2" 32.6 ab 33.0s* 34.0= 35.3 d Hatch 2 33.2"° — Specific 1.082" Hatch 1 1.080" 1.082" 1.085" 1.081" — — gravity Hatch 2 1.084a 1.085" 1.089"= 1.086" 1.089"= 1.086" — Deformation 2.60"b 2.40" 2.50"" 2.60"b Hatch 1 2.70 b — — (.001 mm.) 2.68" Hatch 2 2.70 b 2.64" 2.39" 2.61" 2.25" — Breaking Hatch 1 3.31 b 3.60" 3.45" 3.04" 3.27" — — strength (kg.) 3.17" 3.39" 3.36" Hatch 2 3.09" 3.32" 3.25" — abc Those means with the same superscript within each hatch were not significantly different (P £ .05).
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
quired to break the shell, was used to measure breaking strength. The specific gravity of the whole egg held in storage for approximately four hours after oviposition was measured by the flotation method using salt solutions ranging in specific gravity from 1.070 to 1.100 with gradients of .005. The average shell thickness (without membrane) of two points at the equatorial region was measured to the nearest .01 mm. using a vice caliper. Tint of the brown shell eggs was objectively determined by a scoring system of 1-10 based on increasing intensity of color. The relative magnitude of contribution by the various egg characteristics to variation in the dependent variable was determined by a stepwise multiple regression analysis (Dixon, 1973) using Biomedical Computer Program BMD02R which computes a sequence of multiple linear regression equations in a stepwise manner. A single variable, which contributes the greatest reduction in the error sums of squares, is added to the regression equation in a stepwise manner until all variables are used. A prediction equation can then be formed which includes those independent variables that significantly reduce the error of predicting the value of the dependent variable. In Hatch 1 and Hatch 2, the regression analysis was computed first using deforma-
2169
2170
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
TABLE 2.—Stepwise regression analysis of variation in egg characteristics of brown egg strains Dependent variable—deformation Independent variables, non-destructive Hatch 1 Independent variable r1 RSQ2 Specific gravity -.82 .68** W/L .16 .70 Egg weight .32 .70 Tint .00 .70 Independent variable Shell thickness Specific gravity Breaking strength
Hatch 2 r1 ^~7% -.70 -.65
RSQ2 .60** .65** .69**
Independent variables, destructive and non-destructive Hatch 1 Independent r' RSQ2 variable .85** Shell thickness -.85 .32 .88** Egg weight -.16 .90** W/L -.82 91** Specific gravity .00 .91 Tint 'Simple correlation coefficient with dependent variable. 2 Cumulative amount of variation accounted for in dependent variable (value of multiple correlation coefficient squared). "Indicates statistically significant contribution of independent variable to variation in dependent variable (**P < .01; *P £ .05).
the model, they add little since shell thickness has already added most of their contribution to variability. Similar results were obtained from Hatch 2 when the contribution of the variables of shell thickness, specific gravity and breaking strength to deformation were determined (Table 2). Shell thickness accounted for 60% of the variation in deformation with specific gravity (which would include variation in width/length ratio and egg weight in addition to thickness) accounting for an additional 5% and breaking strength an additional 4%. This points out the fact that variation in specific gravity is influenced by thickness with shape and weight of the egg contributing a minor
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
strains are presented in Table 1. Differences were calculated for the various strains only within hatches since different strains were used in Hatch 2. Shell thickness measurements were consistent over both hatches in that the brown shell eggs were generally thinner than the white shell eggs. Hubbard eggs exhibited the thinnest shells in both hatches and Hyline along with Babcock in Hatch 2 had the thickest shells. Since specific gravity is directly related to shell thickness, similar relationship between strains was expected and observed. The brown egg strains recorded the lowest specific gravity readings with the Hubbard strain again having the lowest readings with Hyline and Babcock in Hatch 2 having the highest specific gravities. Deformation readings (lower value, stronger shells) for the brown shell eggs were higher on the average in both hatches than the average of the white eggs with the exception of the Babcock strain in Hatch 1. No significant differences were found between strains in either hatch for breaking strength (higher value, stronger shells) with the exception of the Babcock strain in Hatch 1. However, significant variation was detected with the use of the deformation apparatus. When non-destructive deformation was held as the dependent variable (brown shell eggs) and a stepwise regression analysis of remaining non-destructive values computed, only variation in specific gravity contributed significantly to variation in deformation (Table 2) with 68% of the variability in deformation being explained by variation in specific gravity. When the destructive measure of shell thickness was added to the non-destructive measures as an independent variable, it became the primary contributor to variability in deformation, accounting for 85% of the variation in deformation (Table 2). The variability of deformation can be attributed primarily to shell thickness. When egg weight and width/length are included in
SHELL STRENGTH ASSESSMENT
2171
but significant part to the variation. Once variation in the specific components that make up specific gravity are removed, specific gravity may become a relatively unimportant contributor to deformation. Assuming that deformation is actually measuring resistance of the shell to breakage, these findings suggest that in brown egg strains a good criterion of selection against shell breakage might be specific gravity. However, identification of individuals with ability to lay eggs with superior specific gravity might best be made by considering thickness, size and shape. If selection was on the basis of specific gravity alone, the variables of thickness, shape and egg weight could vary in any combination. The stepwise regression analysis of egg
Table 4 illustrates the relative differences in sources of variation of breaking strength. In Hatch 1 the most significant source of variation was thickness for the brown shell eggs. However, specific gravity was the most important source of variation in the white shell eggs. Thickness was the most significant source of variation in breaking strength for both white and brown shell eggs of Hatch 2. Specific gravity was a significant contributor to breaking strength with white shell eggs but was not with brown shell eggs. The differences in Hatch 1 and 2 could be attributed to the different strains used, the time of year the data were collected, or due to genetic change in the strains themselves. Prediction equations for non-destructive deformation and breaking strength with the various traits as independent variables for
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
TABLE 3.—Stepwise regression analysis variation characteristics from the white shell strains in egg characteristics of white egg strains are presented in Table 3. When deformation was the dependent variable, the only nonDependent variable—deformation destructive variable that contributed signifiIndependent variables, non-destructive Hatch 1 cant variation was specific gravity. As was Independent the case for brown eggs, variation in specific variable r1 RSQ2 Specific gravity -.82 .68** gravity accounted for 68% of the variability Egg weight .00 .68 in deformation. In contrast to the brown egg W/L .17 .69 strains, when thickness was added as an Hatch 2 independent variable, specific gravity still Independent variable r1 RSQ2 accounted for the majority of the variation (67%) although thickness, weight and Thickness -.56 .39** Specific gravity -.63 .44** width/length ratio all contributed signifiBreaking strength - .54 ; 4 5 ** cantly to the variation in deformation. These Independent variables, destructive and non-defindings suggest the possibility that factors structive related to specific gravity other than Hatch 1 Independent thickness, shape and weight such as porosity variable r1 RSQ 2 or shell matrix structure may be more imporSpecific gravity -.82 .67** tant in determining shell strength in some .70** Thickness -.78 72** Weight .00 strains than in others. They could explain W/L .17 !73** the observation that brown eggs may have 'Simple correlation coefficient with dependent thinner shells than white eggs but may break variable. 2 Cumulative amount of variation accounted for less readily (Hunton, 1969). Potts and Washin dependent variable. * indicates statistically significant contribution burn (1974) reported that although brown eggs of independent variable to variation in dependent had a lower specific gravity, shell thickness variable (**P •& .01; *P •& .05). and deformation, their breaking strength was superior to comparable white eggs.
2172
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
TABLE 4.—Stepwise regression analysis for trial 2 of hatch 1 and hatch 2 with breaking strength as the dependent variable Dependent variable—breaking strength Hatch 1, Trial 2 Variable Thickness W/L Weight Specific gravity Tint
Brown eggs r1 .78 .36 .32 .78 .09
RSQ2 .61** .77** .82** .83 .84
Variable Specific gravity Weight W/L Thickness
White eggs r .79 .06 .27 .72
the white and brown egg strains in Hatch 1 and 2 are presented in Table 5. In Hatch 1 two equations with non-destructive deformation as the dependent variable, and one equation with breaking strength as the dependent variable, were calculated for both white and brown egg strains. All white egg strain values were pooled as were the brown egg strain values. The variables that contributed significantly were the same for both brown and white egg strains using destructive and non-destructive measures. The significantly contributing variables for the breaking strength were similar; however, specific gravity did not contribute significantly in the brown egg strains. In Hatch 2, equations with non-destructive deformation and breaking strength as the dependent variables were calculated for the pooled values of the white and brown egg strains. The coefficients of the variables were similar in both the white and brown egg strains for the non-destructive deformation equation. The variables and their coefficients were similar for the breaking strength equation with the exception of specific gravity, which did not contribute significantly to the variation.
RSQ .41** '.46** dependent
A limited amount of investigative work has been published that compares brown and white shell eggs. However, studies have been reported which have regressed several variables on crushing strength. Hunton (1969) reported a regression study in which energy was found to contribute the greatest amount to crushing strength with stiffness of the shell, egg weight, deformation at failure, mean backscatter, non-destructive deformation and mean shell thickness contributing to crushing strength to a lesser degree. Richards and Swanson (1965) reported that shell thickness was the best single predictor of crushing strength. The present experiment is in agreement only in the brown egg strains where specific gravity did not contribute significantly to the variation. However, specific gravity contributed the greatest amount of variation in the white egg strains in the non-destructive as well as the breaking strength equations in Hatch 1. As in the equations with deformation as the dependent variable, the most important factor contributing to breaking strength in Hatch 2 was thickness. The differences could be due to the different strains, the time of year the
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
Hatch 2 Brown eggs White eggs r Variable r Variable RSQ 40** .64 Thickness .64 Thickness .59 Specific gravity Specific gravity '.40 .47 1 Simple correlation coefficient with dependent variable. 2 Cumulative amount of variation accounted for by independent variable. * indicates statistically significant contribution of independent variable to variation in variable (**P s; .01; *P < .05).
RSQ .62** .64* .66* .67
7.074 -4.751
Hatch # 2 White egg strains Deformation as dep var Breaking strength as dep var
+
-
_
0.022X, 0.O22X, 0.070X,
0.022X, —
0.082X,
0.037X, 0.131X,
+ + +
0.066X,
+
X,
-
+
-
+
0.170X2 O.HOXj 0.438X2
0.924X2
_
+
-
+
—
O.I8OX2 0.026X2
_
—
—
O.O22X3 0.128X 0.128X,3
—
0.016X3 0.060X3
_
Variables X3
— 0.333X2
+
X^
-
+
+ +
Brown egg strains + 0.030X, -_ 0.190X2 Deformation as dep var y == 8.332 + O.19OX2 — -2.500 Breaking strength as dep var — + O.74OX2 — y = 'Non-destructive deformation as dependent variable. Variables: X, specific gravity, X2 thickness, X X* breaking strength.
y == y =
9.141 -10.591
9.285
Brown egg strains Non-destructive variables 1 y = Destructive & non-destructive variables 1 y = Breaking strength as dep var y ==
Hatch # 1 Constant White egg strains Non-destructive variables' y = 7.898 Destructive & non-destructive 8.434 y = Breaking strength as dep var y == -13.609
TABLE 5.—Prediction equations for the various traits measured with non-destructive deformation and
ded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
2174
P. L. POTTS, K. W. WASHBURN AND K. K. HALE
commercial egg processing practices. Correlation of these data with more objective measurements such as deformation, breaking strength, thickness, specific gravity, etc. should permit formation of more accurate predictions on shell quality. REFERENCES Dixon, W. J., 1973. Biomedical Computer Programs, University of California Press, Berkeley, California. Hunton, P., 1969. The measurement of egg shell strength. A comparison of four methods. British Poultry Sci. 10: 281-289. Perek, M., and N. Snapir, 1970. Interrelationships between shell quality and egg production and egg and shell weights in white leghorn and white rock hens. British Poultry Sci. 11: 133-145. Potts, P. L., and K. W. Washburn, 1974. Shell evaluation of white and brown egg strains by deformation, breaking strength, shell thickness and specific gravity. 1. Relationships to egg characteristics. Poultry Sci. 53: 1123-1128. Richards, J. F., and M. H. Swanson, 1965. The relationship of egg shape to shell strength. Poultry Sci. 44: 1555-1558. Schoorl, P., and H. Y. Boersma, 1962. Research on the quality of the egg shell. 12th Wld's. Poultry Congress, Sidney, 432-435.
NEWS AND NOTES (Continued from page 2162)
Vice President—C. E. Black, and Members of the Executive Committee—K. C. Barrens, B. P. Cardon, and R. H. White-Stevens. F. H. Baker, President of the American Society of Animal Science, named O. D. Butler to replace Dr. Cardon, who is now a member of the Executive Committee and hence no longer a representative of A.S.A.S. News from C.A.S.T., Vol. 1, No. 1., contained the following: A treatise on "Environmental Impact Analysis Reports and Environmental Impact Statements," prepared at the request of the Food and Drug Administration, was submitted to F.D.A. in February. The
requirement for information of the kind contained in the document originated with the National Environmental Policy Act of 1969. The members of the C.A.S.T. task force included William J. Stadelman (Chairman), Purdue University; D. S. Frear, A.R.S., U.S.D.A., Fargo, North Dakota; Jerry L. Hamelink, Purdue University; Darrell W. Nelson, Purdue University; W. H. Pfander, University of Missouri; Gerald W. Probst, Eli Lilly and Company; Joseph Shapiro, University of Minnesota; Lee E. Sommers, Purdue University; J. B. Weber, North Carolina State University; and Robert Zwickey, Merck, Sharp & Dohme Research Laboratories. Areas
(Continued on page 2192)
Downloaded from http://ps.oxfordjournals.org/ at Univ of Iowa-Law Library on June 17, 2015
data were collected, or due to the genetic change in the strains themselves. Perek and Snapir (1970) reported a study in which shell weight, egg weight and egg production were regressed on shell quality. They reported shell weight to be the variable contributing the greatest amount of variation to shell quality with egg weight and egg production contributing a lesser amount. These data suggest caution in assuming that all white egg strains' or all brown egg strains' shell strength can be estimated with the same prediction equation. Although differences between brown and white eggs have been emphasized, there are also differences between the strains of either the white egg or brown egg layers (Potts and Washburn, 1974). RSQ (cumulative amount of variation accounted for in the dependent variable by the independent variables) values for deformation and breaking strength indicate that a significant proportion of the sources of variation for these shell quality estimates has not been measured. The true measure of shell quality may best be estimated by obtaining emperical data on shell integrity through