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Errors in Measuring and Calculating Eggshell Quality1
EDUCATION AND PRODUCTION Errors in Measuring and Calculating Eggshell Quality1 R. H. HARMS,2 A. G. ABDALLAH,3 and D. R. SLOAN Poultry Science Department, University of Florida, Gainesville, Florida 32611-0930
1994 Poultry Science 73:599-602
INTRODUCTION Specific gravity (SG) of eggs is often used for measuring eggshell quality. This measurement is an indirect measure of the amount of shell deposited on the egg. Specific gravity is the ratio of egg weight to egg volume. The most accurate method of measuring SG is to weigh the egg and then measure its volume by immersing it in water and measuring the volume of water that it displaces. This is time consuming and the method most commonly used is to pass the egg through a series of salt solutions that have different SG. The egg will float in the solution when the SG of the solution is greater than the
Received for publication October 21, 1993. Accepted for publication January 11, 1994. Florida Agricultural Experiment Journal Number Series R-03440. 2 To whom correspondence should be addressed. ^Present address: Animal Production Research Institute, Nadi Al-Sad St., Dokki, Egypt.
SG of the eggs. However, there are sources of error in this method and these errors were evaluated by Voisey and Hamilton (1977). Harms et al. (1990) proposed a formula for calculating the weight of an eggshell without breaking the egg. Egg weight and SG of the egg were the only two actual measurements required after the density of the shell and egg contents were established. A density of 1.031 was used for egg content as suggested by Stadelman and Cotterill (1973). The density of the eggshell with membrane (2.028) was determined (Harms et al, 1990). The calculated shell weight (SW) was highly correlated with measured SW (Harms et al, 1990). In further experiments the calculated SW again correlated very well with measured SW. However, the calculated SW was sometime greater and sometime less than actual SW. Therefore, the present study was conducted to determine the cause of these differences and evaluate potential errors in measuring and calculating eggshell quality.
599
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
ABSTRACT Three experiments were conducted to examine potential errors in measuring or calculating eggshell quality. In Experiment 1, specific gravity of eggs was measured in increments of .001 and .0025, and the increments of .0025 were combined for increments of .005. Average specific gravity of a group of eggs increased significantly as the increments of solution increased. These increased specific gravity values resulted in significant increases in calculated eggshell weight. In Experiment 2, egg content density was measured after eggs were stored at three temperatures. As the temperature during storage increased, egg content density decreased. This decreased egg content density resulted in a significant increase in calculated eggshell weight. In Experiment 3, eggshell weights were measured and calculated for two groups of hens. Specific gravity of eggs was measured in increments of .001, and egg content density of eggs from that flock was used for calculating shell weight. Shell weight and calculated weight agreed very well. (Key words: egg storage, eggshell quality, specific gravity, eggshell weight, layer)
600
HARMS ET AL.
MATERIALS AND METHODS
the contents was divided by the volume to determine the ECD.
Experiment 1
Experiment 2 Eggs were collected from 560 Hy-Line W36® hens 40 wk of age. Eggs were randomly sorted into three groups of 160 each. One group was stored in a layer house in which the temperature was not allowed to fall below 24 C. Another group was stored at 22 C. The third group was stored in an egg cooler that was maintained at 16 C. The eggs were gathered at 1600 h and remained in their respective storage room until 1000 h the next day at which time the egg content density (ECD) was determined. The ECD was determined by breaking approximately 40 eggs into a 2,000-cc volumetric flask with the neck calibrated in 1-cc increments. The weight of the egg contents were determined. The weight of
Registered trademark Hy-Line International, West Des Moines, IA 50265.
Experiment 3 Three hundred eggs were collected at 1600 h from Hy-Line W36® hens 42 wk of age. One hundred and fifty eggs were from hens that were selected as laying eggs with light weight shells and the other 150 were selected from hens laying eggs with heavy shells. The procedure of Abdallah et al. (1993) was used for the selection of the two groups of hens. Eggs were stored at 24 C in the room where the SG solutions were kept. Specific gravity was determined the next day at 1000 h. Specific gravity solutions were changed in increments of .001 ranging from 1.065 to 1.090. The ECD was determined immediately after measuring SG. The other procedures were the same as used in Experiment 1. All data were analyzed using a one-way analyses of variance with the individual egg as the experimental unit. Differences between treatment means were determined by Duncan's multiple range test (1955). RESULTS AND DISCUSSION Experiment 1 Specific gravity of eggs was significantly lower when the measurement was made with solutions in increments of .001 as compared to increments of .0025 (Table 1). An increase in SG was found when the increments of the solution were increased from .0025 to .005. It is evident that larger increments in saline solutions result in values greater than the actual SG of the eggsThe incremental change in the SG of solutions clearly affect the calculated SW when using the formula proposed by Harms et al. (1990) (Table 2). Calculated SW increased significantly as the increments of saline solutions increased. This indicates that it is essential to accurately measure SG when using the formula of Harms et al. (1990). Also, when comparing results between two laboratories it is essential that both laboratories use the same increments of saline solution. This is best done by using increments of .001.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
Four trials were conducted using eggs from Hy-Line W36®4 hens 28 wk of age at the initiation of the study. There were 591, 561,450, and 553 eggs in Experiments 1,2,3, and 4, respectively. Eggs were collected each week on Tuesday at 1600 h on 4 successive wk (Weeks 28 to 31) and stored for 18 h at 22 C in the same room with the SG solutions. Two series of saline solutions were used. Specific gravity of one series of solutions was changed in increments of .001 and ranged from 1.065 to 1.095. The SG of the second series of solutions was changed in increments of .0025 and also ranged from 1.065 to 1.095. Fifteen gallons of each solution was used to minimize dilution. Eggs were passed through the first series of solutions and then rinsed in water before being passed through the second series of solution. Specific gravity of eggs for the .005-increment solutions were obtained by combining the values obtained in the second series (i.e., those eggs with SG of 1.0775 and 1.080 were combined for the 1.080 values). The average SG for the eggs measured in the three different SG measurements were used to calculate SW using the formula of Harms et al. (1990).
ERRORS IN EGGSHELL QUALITY MEASUREMENTS
601
TABLE 1. Specific gravity of eggs when measured in solutions of three incremental changes
Trial 1 2 3 4
591 561 450 553
.001
.0025
.005
SEM
c
1111
Specific gravity increments 1
Number of eggs
834" 850* 823" 839"
2 2 2 2
811 829= 804c 818c
a_<:
Means within a row with no common superscript differ significantly (P < .05). !Coded 1.0XXX.
Experiment 3
Egg content density was significantly different (P < .05) when the eggs were stored overnight at three different temperatures (Table 3). When these three ECD measures were used, the calculated SW differed significantly. Eggs stored at a minimum of 24 C resulted in a calculated SW of 5.52 g as compared with 5.22 g for eggs stored at 22 C, and 5.08 g for eggs stored at 16 C. The accuracy of the value used for ECD clearly influences the calculated SW. Therefore, an accurate ECD must be used when comparing calculated SW for hens of different ages because ECD changes with age of the hen (Sloan, 1993). Also, ECD changes with breed or strain of hen, as the yolk: albumen differs with age and strain of hen (Hussein et al, 1993). This necessitates having the correct ECD with each group of hens.
The measured and calculated SW for eggs from hens laying eggs with heavy or light shells agreed very well (Table 4). The difference between the measured SW for the two groups was .52 g as compared to a difference of .58 g in calculated SW. The difference of .06 g in SW for the two groups was a result in a .02 g heavier calculated SW for Group 1 and a .04 g lower calculated SW for Group 2. These differences are within the expected variance of the measurements. These data indicate that the SW can be accurately calculated using the formula of Harms et al. (1990) provided that the correct ECD and SG are used. The data in the present study demonstrate some of the variables in measuring eggshell weight using SG as the measurement. Voisey and Hamilton (1977) had previously reported that measurement in SG was affected by temperature of saline
TABLE 2. Calculated eggshell weight using different increments of specific gravity
TABLE 3. Measured egg content density and calculated shell weight using egg content density of eggs stored at three temperatures
Specific gravity increments Trial
.001
(
1 2 3 4
4.96 5.19<: 4.96c 5.19<= a_c
.005
.0025 b
5.06 5.28b 5.05b 5.28b
SEM
_
5.18* 5.39> 5.15* 5.40*
.02 .02 .02 .02
M e a n s within a r o w w i t h n o c o m m o n superscripts differ significantly (P < .05).
Temperature
Egg content density
Calculated shell weight
(C) 24 22 16
1.0301 c 1.0330b 1.0343"
(g) 5.52* 5.22b 5.08<=
.0003
.03
SEM
a-^Means within a c o l u m n w i t h n o c o m m o n superscript differ significantly (P < .05).
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
Experiment 2
602
HARMS ET AL.
TABLE 4. Measured and calculated shell weight of two groups of hens Group1
Measured
1 2 SEM
5.43" 4.91b .04
Calculated (g) 5.45a 4.87b .04
solutions, calibrating and reading hydrometers, hairline cracks in the shell, and cooling of solutions by stored eggs. The present data indicate that SW can be calculated using egg weight and SG of eggs when measured in increments of .001. However, it is necessary to use an accurate ECD.
Abdallah, A. G., R. H. Harms, and O. El-Husseiny, 1993. Performance of hens laying eggs with heavy or light shell weight when fed diets with different calcium and phosphorus levels. Poultry Sci. 72: 1881-1891. Ehancan, D. B., 1955. Multiple range and multiple F test. Biometrics 11:1-42. Harms, R. H., A. F. Rossi, D. R. Sloan, R. D. Miles, and R. B. Christmas, 1990. A method for estimating shell weight and correcting specific gravity for egg weight in eggshell studies. Poultry Sci. 69: 48-52. Hussein, S. M., R. H. Harms, and D. M. Janky, 1993. Effect of age and breed on the yolk albumen ratio in hen eggs. Poultry Sci. 72:594-597. Sloan, D. R., R. H. Harms, A. G. Abdallah, K. K. Kuchinski, and S. M. Hussein, 1993. Influence of age of hen on density of egg content. Poultry Sci. 72(Suppl. l):193.(Abstr.) Stadelman, W. J., and O. J. Cotterill, 1973. Page 195 in: Egg Science and Technology. The AVI Publishing Co., Inc., Westport, CT. Voisey, P. W., and R.M.G. Hamilton, 1977. Sources of error in specific gravity measurements by the flotation method. Poultry Sci. 56:1457-1462.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
ab ' Means in a column with no common superscript differ significantly (P < .05). 1 Group 1 was selected as hens laying eggs with heavy shell and Group 2 selected for laying eggs with light shells. Egg content density was 1.0292.
REFERENCES
1994 Poultry Science 73:599-602
INTRODUCTION Specific gravity (SG) of eggs is often used for measuring eggshell quality. This measurement is an indirect measure of the amount of shell deposited on the egg. Specific gravity is the ratio of egg weight to egg volume. The most accurate method of measuring SG is to weigh the egg and then measure its volume by immersing it in water and measuring the volume of water that it displaces. This is time consuming and the method most commonly used is to pass the egg through a series of salt solutions that have different SG. The egg will float in the solution when the SG of the solution is greater than the
Received for publication October 21, 1993. Accepted for publication January 11, 1994. Florida Agricultural Experiment Journal Number Series R-03440. 2 To whom correspondence should be addressed. ^Present address: Animal Production Research Institute, Nadi Al-Sad St., Dokki, Egypt.
SG of the eggs. However, there are sources of error in this method and these errors were evaluated by Voisey and Hamilton (1977). Harms et al. (1990) proposed a formula for calculating the weight of an eggshell without breaking the egg. Egg weight and SG of the egg were the only two actual measurements required after the density of the shell and egg contents were established. A density of 1.031 was used for egg content as suggested by Stadelman and Cotterill (1973). The density of the eggshell with membrane (2.028) was determined (Harms et al, 1990). The calculated shell weight (SW) was highly correlated with measured SW (Harms et al, 1990). In further experiments the calculated SW again correlated very well with measured SW. However, the calculated SW was sometime greater and sometime less than actual SW. Therefore, the present study was conducted to determine the cause of these differences and evaluate potential errors in measuring and calculating eggshell quality.
599
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
ABSTRACT Three experiments were conducted to examine potential errors in measuring or calculating eggshell quality. In Experiment 1, specific gravity of eggs was measured in increments of .001 and .0025, and the increments of .0025 were combined for increments of .005. Average specific gravity of a group of eggs increased significantly as the increments of solution increased. These increased specific gravity values resulted in significant increases in calculated eggshell weight. In Experiment 2, egg content density was measured after eggs were stored at three temperatures. As the temperature during storage increased, egg content density decreased. This decreased egg content density resulted in a significant increase in calculated eggshell weight. In Experiment 3, eggshell weights were measured and calculated for two groups of hens. Specific gravity of eggs was measured in increments of .001, and egg content density of eggs from that flock was used for calculating shell weight. Shell weight and calculated weight agreed very well. (Key words: egg storage, eggshell quality, specific gravity, eggshell weight, layer)
600
HARMS ET AL.
MATERIALS AND METHODS
the contents was divided by the volume to determine the ECD.
Experiment 1
Experiment 2 Eggs were collected from 560 Hy-Line W36® hens 40 wk of age. Eggs were randomly sorted into three groups of 160 each. One group was stored in a layer house in which the temperature was not allowed to fall below 24 C. Another group was stored at 22 C. The third group was stored in an egg cooler that was maintained at 16 C. The eggs were gathered at 1600 h and remained in their respective storage room until 1000 h the next day at which time the egg content density (ECD) was determined. The ECD was determined by breaking approximately 40 eggs into a 2,000-cc volumetric flask with the neck calibrated in 1-cc increments. The weight of the egg contents were determined. The weight of
Registered trademark Hy-Line International, West Des Moines, IA 50265.
Experiment 3 Three hundred eggs were collected at 1600 h from Hy-Line W36® hens 42 wk of age. One hundred and fifty eggs were from hens that were selected as laying eggs with light weight shells and the other 150 were selected from hens laying eggs with heavy shells. The procedure of Abdallah et al. (1993) was used for the selection of the two groups of hens. Eggs were stored at 24 C in the room where the SG solutions were kept. Specific gravity was determined the next day at 1000 h. Specific gravity solutions were changed in increments of .001 ranging from 1.065 to 1.090. The ECD was determined immediately after measuring SG. The other procedures were the same as used in Experiment 1. All data were analyzed using a one-way analyses of variance with the individual egg as the experimental unit. Differences between treatment means were determined by Duncan's multiple range test (1955). RESULTS AND DISCUSSION Experiment 1 Specific gravity of eggs was significantly lower when the measurement was made with solutions in increments of .001 as compared to increments of .0025 (Table 1). An increase in SG was found when the increments of the solution were increased from .0025 to .005. It is evident that larger increments in saline solutions result in values greater than the actual SG of the eggsThe incremental change in the SG of solutions clearly affect the calculated SW when using the formula proposed by Harms et al. (1990) (Table 2). Calculated SW increased significantly as the increments of saline solutions increased. This indicates that it is essential to accurately measure SG when using the formula of Harms et al. (1990). Also, when comparing results between two laboratories it is essential that both laboratories use the same increments of saline solution. This is best done by using increments of .001.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
Four trials were conducted using eggs from Hy-Line W36®4 hens 28 wk of age at the initiation of the study. There were 591, 561,450, and 553 eggs in Experiments 1,2,3, and 4, respectively. Eggs were collected each week on Tuesday at 1600 h on 4 successive wk (Weeks 28 to 31) and stored for 18 h at 22 C in the same room with the SG solutions. Two series of saline solutions were used. Specific gravity of one series of solutions was changed in increments of .001 and ranged from 1.065 to 1.095. The SG of the second series of solutions was changed in increments of .0025 and also ranged from 1.065 to 1.095. Fifteen gallons of each solution was used to minimize dilution. Eggs were passed through the first series of solutions and then rinsed in water before being passed through the second series of solution. Specific gravity of eggs for the .005-increment solutions were obtained by combining the values obtained in the second series (i.e., those eggs with SG of 1.0775 and 1.080 were combined for the 1.080 values). The average SG for the eggs measured in the three different SG measurements were used to calculate SW using the formula of Harms et al. (1990).
ERRORS IN EGGSHELL QUALITY MEASUREMENTS
601
TABLE 1. Specific gravity of eggs when measured in solutions of three incremental changes
Trial 1 2 3 4
591 561 450 553
.001
.0025
.005
SEM
c
1111
Specific gravity increments 1
Number of eggs
834" 850* 823" 839"
2 2 2 2
811 829= 804c 818c
a_<:
Means within a row with no common superscript differ significantly (P < .05). !Coded 1.0XXX.
Experiment 3
Egg content density was significantly different (P < .05) when the eggs were stored overnight at three different temperatures (Table 3). When these three ECD measures were used, the calculated SW differed significantly. Eggs stored at a minimum of 24 C resulted in a calculated SW of 5.52 g as compared with 5.22 g for eggs stored at 22 C, and 5.08 g for eggs stored at 16 C. The accuracy of the value used for ECD clearly influences the calculated SW. Therefore, an accurate ECD must be used when comparing calculated SW for hens of different ages because ECD changes with age of the hen (Sloan, 1993). Also, ECD changes with breed or strain of hen, as the yolk: albumen differs with age and strain of hen (Hussein et al, 1993). This necessitates having the correct ECD with each group of hens.
The measured and calculated SW for eggs from hens laying eggs with heavy or light shells agreed very well (Table 4). The difference between the measured SW for the two groups was .52 g as compared to a difference of .58 g in calculated SW. The difference of .06 g in SW for the two groups was a result in a .02 g heavier calculated SW for Group 1 and a .04 g lower calculated SW for Group 2. These differences are within the expected variance of the measurements. These data indicate that the SW can be accurately calculated using the formula of Harms et al. (1990) provided that the correct ECD and SG are used. The data in the present study demonstrate some of the variables in measuring eggshell weight using SG as the measurement. Voisey and Hamilton (1977) had previously reported that measurement in SG was affected by temperature of saline
TABLE 2. Calculated eggshell weight using different increments of specific gravity
TABLE 3. Measured egg content density and calculated shell weight using egg content density of eggs stored at three temperatures
Specific gravity increments Trial
.001
(
1 2 3 4
4.96 5.19<: 4.96c 5.19<= a_c
.005
.0025 b
5.06 5.28b 5.05b 5.28b
SEM
_
5.18* 5.39> 5.15* 5.40*
.02 .02 .02 .02
M e a n s within a r o w w i t h n o c o m m o n superscripts differ significantly (P < .05).
Temperature
Egg content density
Calculated shell weight
(C) 24 22 16
1.0301 c 1.0330b 1.0343"
(g) 5.52* 5.22b 5.08<=
.0003
.03
SEM
a-^Means within a c o l u m n w i t h n o c o m m o n superscript differ significantly (P < .05).
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
Experiment 2
602
HARMS ET AL.
TABLE 4. Measured and calculated shell weight of two groups of hens Group1
Measured
1 2 SEM
5.43" 4.91b .04
Calculated (g) 5.45a 4.87b .04
solutions, calibrating and reading hydrometers, hairline cracks in the shell, and cooling of solutions by stored eggs. The present data indicate that SW can be calculated using egg weight and SG of eggs when measured in increments of .001. However, it is necessary to use an accurate ECD.
Abdallah, A. G., R. H. Harms, and O. El-Husseiny, 1993. Performance of hens laying eggs with heavy or light shell weight when fed diets with different calcium and phosphorus levels. Poultry Sci. 72: 1881-1891. Ehancan, D. B., 1955. Multiple range and multiple F test. Biometrics 11:1-42. Harms, R. H., A. F. Rossi, D. R. Sloan, R. D. Miles, and R. B. Christmas, 1990. A method for estimating shell weight and correcting specific gravity for egg weight in eggshell studies. Poultry Sci. 69: 48-52. Hussein, S. M., R. H. Harms, and D. M. Janky, 1993. Effect of age and breed on the yolk albumen ratio in hen eggs. Poultry Sci. 72:594-597. Sloan, D. R., R. H. Harms, A. G. Abdallah, K. K. Kuchinski, and S. M. Hussein, 1993. Influence of age of hen on density of egg content. Poultry Sci. 72(Suppl. l):193.(Abstr.) Stadelman, W. J., and O. J. Cotterill, 1973. Page 195 in: Egg Science and Technology. The AVI Publishing Co., Inc., Westport, CT. Voisey, P. W., and R.M.G. Hamilton, 1977. Sources of error in specific gravity measurements by the flotation method. Poultry Sci. 56:1457-1462.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on May 29, 2015
ab ' Means in a column with no common superscript differ significantly (P < .05). 1 Group 1 was selected as hens laying eggs with heavy shell and Group 2 selected for laying eggs with light shells. Egg content density was 1.0292.
REFERENCES