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The Relationship of Egg Shape to Time of Oviposition and Egg Shell Quality
The Relationship of Egg Shape to Time of Oviposition and Egg Shell Quality DAVID A. ROLAND, SR. Poultry Science Department, Alabama Agricultural Experiment Station, Auburn University, Auburn, Alabama 36830 and Florida Agricultural Experiment Station, University of Florida, Gainesville, Florida 32611 (Received for publication January 19,1978)
INTRODUCTION The later in the day the egg is laid the better the egg shell (Roland et al., 1973); however, the reason for this is not known. It has been hypothesized that the increase in light hours for hens laying eggs during the afternoon would explain the improvement in shell quality. However, more recently, Roland et al. (1977) found that increasing or decreasing the calcium level of the diet had no influence on the variation in shell quality due to oviposition time. They suggested that the variation in shell quality was not caused by inadequate dietary calcium in the small intestine at night. In earlier studies, Roland and Harms (1974) demonstrated that eggs laid during the afternoon were smaller than eggs laid during the morning. Even though it would take less calcium to put shell with equal thickness on a smaller egg than on a larger one, they did not believe that egg weight was responsible for the variation of shell quality, for two reasons. First, egg weight does not continue to decline during the afternoon; and second, when morning and afternoon eggs of the same weights were compared, the afternoon eggs had the highest specific gravity. The influence of egg shape on the birds 1978 Poultry Sci 57:1723-1727
ability to produce eggs with maximum egg shell quality has not been reported even though it has been shown that egg curvature (egg shape) affects shell strength (Voisey and Hunt, 1967; Anderson et al, 1970; Richards and Swanson, 1965). Egg shape (shape index) has also been shown to vary according to strain of bird, size of egg, and position of egg in the clutch (Marble, 1942; Pearl, 1909; Benjamin, 1920; Pearl and Curtis, 1916; Romanoff and Romanoff, 1949). If the shape index values of eggs laid during the afternoon were larger (more spherical) than eggs laid during the morning, the afternoon eggs would have less surface area and should require less shell to form eggs with equal shell thickness. This could explain why afternoon eggs have better shells. The following experiments were conducted to determine: 1) the relationship of egg shape and time of oviposition on shell quality and 2) to determine if the variation in shape index (surface area of eggs) within a flock is great enough to influence thickness with a given amount of shell.
1723
PROCEDURE Experiment
1. A total of 1510 Babcock hens
Downloaded from http://ps.oxfordjournals.org/ at Dalhousie University on April 13, 2015
ABSTRACT Experiments were conducted to determine the relationship of egg shape to time of oviposition and egg shell quality. Eggs were collected at 2-hr intervals throughout the day and depending upon the experiment various measurements (egg weight, shape index, shell weight, shell thickness, or specific gravity) were determined. The results indicated that eggs laid during the afternoon had a higher shape index (rounder eggs) than eggs laid during the morning. The afternoon eggs also had a higher specific gravity, shell weight, shell thickness, and were smaller than eggs laid during the morning. A large variation in shape index occurred among eggs. It was concluded that the difference in shape between times of oviposition would not explain the variation in shell quality due to time of oviposition, but that the large variation in egg shape among birds is a significant factor in determining the bird's ability to produce eggs with maximum shell thickness with a given amount of shell.
ROLAND, SR.
1724
Shape index was expressed as the width of the egg divided by the length (SI = (W/L) X 100). The smaller the shape index, the more oblong the egg; the larger the shape index, the more spherical the egg, meaning the least surface area per unit egg. Since it is extremely difficult and time consuming to estimate (with a high degree of accuracy) the surface area of any irregular or asymmetrically shaped object (Dunn and Schneider, 1923; Mueller and Scott, 1940; Bonnet and Mongin, 1965; Carter, 1968; Besch et ah, 1968; Carter and Jones, 1970), the formula for measuring the surface area of an ellipsoid was used, 27Tb2
3av
2bV^b5
sin
"
y/^T2
where v = egg volume or weight, a = one-half the length of the long axis, and b = one-half the length of the short axis. Eggs may be spherical, elliptical, biconical, or conical in shape; however, the above formula was used because most eggs are ellipsoidal in shape. The data from each experiment were subjected to an analysis of variance, and the multiple range test of Duncan (1955) as modified by Kramer (1956) was utilized to determine significant differences. To analyze the difference in shell weight (Experiments 4 to 6) and shell thickness (Experiment 7), a comparison of sample means with paired observations as described by Steel and Torrie (1960) was used. RESULTS AND DISCUSSION Experiments I to 3. The results of these experiments confirm the previous reports of
TABLE 1.—Specific gravity, egg weight, and shape index in relation to time of oviposition (Experiment 1) Values expressed as means + SEM Specific gravity
Time 1800 0600 0800 1000 1200 1400 1600
-
0600 0800 1000 1200 1400 1600 1800
hr hr hr hr hr hr hr
1.081 c 1.081 c 1.081 c 1.084 b 1.084 b 1.087 a 1.086 ab
Shape index
Egg
weight (g) .0010 .0001 .0004 .0005 .0005 .0006 .0009
63.7ab 64.5 a 63.3ab 62.3ab 61.2 C 61.9bc 62.2ab
.6 .3 .3 .3 .3 .5 .8
a,b,c,Values followed by different letters in the same column are significantly different (P<.05).
72.99 a 73.20 a 73.32 a 73.23 a 73.45 a 73.68 a 73.46 a
.49 19 .32 .22 .23 .30 .39
Downloaded from http://ps.oxfordjournals.org/ at Dalhousie University on April 13, 2015
were used. Eggs were collected at 0600 and at 2-hr intervals the following day from 0600 to 2000 hr. All hens were fed a commercial-type corn-soy diet. Egg weight, shape index, egg specific gravity, shell weight, and shell thickness were determined. The hens were on an 18-hr light day from 0200 to 2000 hr. Experiments 2 and 3. These experiments were conducted similar to Experiment 1 except that in Experiment 2, eggs were collected from 460 Babcock hens and in Experiment 3, eggs were collected from 1000 Babcock hens. Egg specific gravity, egg weight, and shape index were determined only on eggs collected from 0600 to 1800 hr. The hens were on a 15-hr light day from 0500 to 2000 hr. Experiments 4 through 6. Egg weight and specific gravity were determined on a large number of eggs from three different populations. From each population approximately 50 pairs of eggs were selected. Each of the eggs within a pair had the same specific gravity and same egg weight to within .2 g but had shape index differences greater than 3.00 units. Shell weight of each egg was determined. Experiment 7. Egg weight, shell thickness, shell weight, and shape index were determined on 968 eggs. Pairs of eggs were selected which had shape index difference greater than 3.00 units, egg weight difference less than or equal to .1 g, and shell weight difference less than or equal to .06 g. There were 54 pairs of eggs which met these three criteria. Egg specific gravity was determined using graded sodium chloride solutions. Shell thickness was determined at three locations around the middle of the egg. The shells were air-dried for 48 hr and shell plus membrane weight determined.
EGG SHAPE AND EGG SHELL QUALITY
1725
TABLE 2.—Specific gravity, egg weight, and shape index in relation to time of oviposition (Experiment 2) Values expressed as means ± SEM Specific gravity
Time 0600 0800 1000 1200 1400 1600 a
0800 1000 1200 1400 1600 1800
hr hr hr hr hr hr
1.085 c 1.085 c 1.085 c 1.086 b c 1.088a*> 1.089 a
.0007 .0004 .0005 .0007 .0006 .0006
66.1b 64.8b 63.0* 61.5 a 62.3 a 60.8 a
.7 .5 .6 .5 .6 .9
72.64 a 72.77 a 72.61 a 72.02 a 73.25 a 73.94 a
.43 .24 .37 .36 .38 .47
,C
Values followed by different letters in the same column are significantly different (P<.05).
Roland and Harms (1974) that specific gravity is greater and weight is less for eggs laid during the afternoon than for eggs laid during the morning (Tables 1, 2, and 3). Shell weight, percent shell, and shell thickness were also greater for eggs laid during the afternoon than for eggs laid during the morning (Table 4). The results indicate that shape index was greater for the afternoon eggs (Tables 1, 2, and 3). Although shape index values were not significantly different between the 2-hr time periods, when shape index of all eggs (within experiment) laid during the morning was compared to that of the afternoon eggs, the difference was significant (P<.05) in Experiments 1 and 2 but not in Experiment 3. When the shape index of all eggs laid during the morning (72.78 ± .13) (Experiment 1 to 3) was compared to that of all eggs laid during the afternoon (73.32 ± .16), the difference was also significant (P<.05). Using the same egg weight (63.36 g) for eggs
laid during the morning and afternoon and the formula for an ellipsoid, it was calculated that the average surface area of the morning eggs was 78.17 cm 2 vs. 78.11 cm 2 for the afternoon eggs. To calcify this extra .06 cm 2 of surface area on the morning egg, it would take .08% more shell or 4.8 mg more for a 6 g shell. However, it is believed that this difference would explain only a small amount (approximately 3.1%) of the improvement in shell quality of afternoon eggs. Experiments 4 to 7. There was no significant treatment time experiment interaction in Experiments 4 to 6; therefore, the data were combined. The results indicate that it takes significantly more shell for an oblong egg (5.786 g) than it does for a spherical egg (5.723 g) to have the same specific gravity (Table 5). This is equal to approximately 5.5 mg more shell per .50 unit decrease in shape index, which is very close to the 4.8 mg per .54 unit difference in shape index or .06 cm 2 of surface
TABLE 3.—Specific gravity, egg weight, and shape index in relation to time of oviposition (Experiment 3) Values expressed as means + SEM Specific gravity
Time 1800 0600 0800 1000 1200 1400 1600
-
0600 0800 1000 1200 1400 1600 1800
hr hr hr hr hr hr hr
1.077C 1.078= 1.077C 1.078 c 1.08lt> 1.084 a 1.083 a b
Shape index
Egg weight (g) .0007 .0005 .0007 .0007 .0007 .0011 .0020
66.3 a 67.5 a 63.5 b c 63.3 b c 63.2 C 63.1 b c 65.9ab
.5 .5 .4 .5 .4 .9 1.3
• Values followed by different letters in the same column are significantly different (P-C05).
72.30 a 72.39 a 72.38 a 72.47 a 72.47 a 72.94 a 73.38 a
.26 .34 .46 .37 .38 .58 .72
Downloaded from http://ps.oxfordjournals.org/ at Dalhousie University on April 13, 2015
'
-
Shape index
Egg weight (g)
ROLAND, SR.
1726
TABLE 4.—Shell weight, percent shell, and shell thickness in relation to time of oviposition (Experiment 1) Values are expressed as means ± SEM Shell weight (g)
Time 1800 0600 0800 1000 1200 1400 1600
-
hr hr hr hr hr hr hr
5.69b 5.78b 5.76b 5.90ab 5.90»b 5.95* 5.93 a b
8.93 b 8.97b 9.09 b 9.47 a 9.46 a 9.61 a 9.54a
.10 .04 .04 .05 .05 .06 .09
.382C .383 c .393b .389 b c .400 a .406 a .398 a b
.18 .05 .05 .06 .07 .08 .13
.006 .002 .002 .002 .002 .003 .003
Values followed by different letters in the same column are significantly different (P<.05).
for an ellipsoid, it was calculated that an egg with a shape index of 90.37 would have a surface area of 76.99 cm 2 vs. 89.90 cm 2 for an egg with a shape index of 61.23. With equivalent thickness and density of shell, the oblong egg would require 3.78% (227 mg for a 6 g shell) more shell than the round egg. Since the average difference in shell weight of eggs laid between 1800 to 1200 hr and 1200 to 1800 hr was only 150 mg (Table 4), it is believed that the variation in shape index within a population is a significant factor in determining the birds ability to obtain maximum shell quality.
area as calculated using the formula for an ellipsoid. The results of Experiment 7 indicated that an oblong egg having the same egg weight and shell weight (to within .1 g) as a spherical egg had a significantly thinner shell than the spherical egg (Table 6). This surface area of the oblong egg and spherical egg was calculated to be 77.36 cm 2 and 76.70 cm 2 , respectively. It would take .86% more shell (50 mg) to calcify the oblong egg to the same shell thickness. This is equal to 4.8 mg more shell per .50 unit decrease in shape index which is very close to the 5.5 mg and 4.8 mg per .50 or .54 unit difference in shape index as measured directly or using the formula for an ellipsoid. Although there is little difference in shape index due to time of oviposition, there is a large variation in shape index among eggs. The results of Experiments 1, 2, and 3 indicated that there was considerable variation in index which ranged from a low of 60 to a high of 90 (Fig. 1). Using a 63.36 g egg and the formula
These studies demonstrate that shape index of eggs can have a definite influence on the bird's ability to produce eggs with maximum shell quality. Egg shape is a heritable characteristic (Romanoff and Romanoff, 1949). Thus, selection for a more spherical shape should allow the hen to produce thicker shells with a given amount of shell. Since no within-hen comparsons were made in these studies, the effects of heritability and the extent of the
TABLE 5.—Various criteria of oblong and spherical e ggs (Experiments 4, 5, and 6)
TABLE 6.— Various criteria of oblong and spherical eggs (Experiment 7)
Type egg
Type egg
Criteria
Oblong
Spherical
Criteria
Oblong
Spherical
Egg weight (g) Specific gravity Shape index Shell weight (g)
65.18 1.082 69.71 5.786 a
65.19 1.082 75.43 5.723b
Egg weight (g) Shell weight (g) Shape index Shell thickness (mm)
62.33 5.83 70.38 .389 a
62.33 5.84 75.64 .398 b
' Values followed by different letters in the same row are significantly different (P<.05).
' Values followed by different letters in the same row are significantly different (P<.05).
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a
0600 0800 1000 1200 1400 1600 1800
Thickness (mm)
Shell (%)
EGG SHAPE AND EGG SHELL QUALITY
18
16
A
14
12
10
!
8
6
2
0
[
-
61
JV
/-~^. /rr' yf
64
. Vr"~N >s
'
67
70
73
76
79
82
'•••
:
85
•
88
•-
91
SHAPE INDEX
FIG. 1. Variation in shape index from three different populations of hens (Experiments 1, 2, and 3).
effect of clutch position on egg shape can not be differentiated. ACKNOWLEDGMENT
Special thanks to L. P. Burton, Chairman of Mathematics Department, Auburn University, for his aid and advice in the mathematical calculations. REFERENCES Anderson, G. B., T. C. Carter, and M. R. Jones, 1970. Some factors affecting dynamic fracture of egg shells in battery cages. Page 53—60 in Factors affecting egg grading. B. M. Freeman and R. J. Gordon, ed. British Poultry Sci., Ltd., Edinburg. Benjamin, Earl W., 1920. A study of selections for the size, shape and color of hen's eggs. Cornell University, Memoir 31:191-312. Besch, E. L., S. J. Sluka, and A. H. Smith, 1968. Determination of surface area using profile record-
ings. Poultry Sci. 4 7 : 8 2 - 8 5 . Bonet, Y., and P. Mongin, 1965. Mesure de la surface de l'oeuf. Annu. Zootech. 14:311-317. Carter, T. C , 1968. The hen's egg; A mathematical model with three parameters. Brit. Poultry Sci. 9:165-171. Carter, T. C , and R. M. Jones, 1970. The hen's egg: Shell shape and size parameters and their interrelations. Brit. Poultry Sci. 11:179-188. Duncan, D. B„ 1955. Multiple range and multiple F tests. Biometrics 11:231-240. Dunn, L. C , and M. Schneider, 1923. An approximate method of calculating the surface area of eggs. Poultry Sci. 2 : 9 0 - 9 2 . Kramer, C. Y., 1956. Extension of multiple range test to group means with unequal numbers of replications. Biometrics 12:307—310. Marble, D. R., 1943. Genetics of egg shape. Poultry Sci. 2 2 : 6 1 - 7 1 . Mueller, C. D., and H. M. Scott, 1940. The porosity of the egg shell in relation to hatchability. Poultry Sci. 19:163-166. Pearl, R., 1909. Studies on the physiology of reproduction in the domestic fowl. I. Regulation in morphogenetic activity of the oviduct. J. Exp. Zool. 6: 339-350. Pearl, R., and M. R. Curtis, 1916. Studies on the physiology of reproduction in the domestic fowl. XV. Dwarf eggs. J. Agr. Res. 6:997-1042. Richards, J. F., and M. H. Swanson, 1965. The relationship of egg shape to shell strength. Poultry Sci. 44:1555-1558. Roland, D. A., Sr., B. L. Damron, and R. H. Harms, 1977. Specific gravity of eggs as influenced by dietary calcium and time of oviposition. Poultry Sci. 56:717-719. Roland, D. A., Sr., and R. H. Harms, 1974. Specific gravity of eggs in relation to egg weight and time of oviposition. Poultry Sci. 53:1494—1498. Roland, D. A., Sr., D. R. Sloan, and R. H. Harms, 1973. Calcium metabolism in the laying hen. 6. Shell quality in relation to time of oviposition. Poultry Sci. 52:506-509. Romanoff, A. L., and A. J. Romanoff, 1949. The avian egg. John Wiley and Sons, Inc., New York. Steel, E. D. R., and J. H. Torrie, 1960. Principles and procedures of statistics. McGraw-Hill Book Company, inc., New York. Voisey, P. W., and J. R. Hunt, 1967. Physical properties of egg shells. 4. Stress distribution in the shell. Brit. Poultry Sci. 8 : 2 6 3 - 2 7 1 .
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INTRODUCTION The later in the day the egg is laid the better the egg shell (Roland et al., 1973); however, the reason for this is not known. It has been hypothesized that the increase in light hours for hens laying eggs during the afternoon would explain the improvement in shell quality. However, more recently, Roland et al. (1977) found that increasing or decreasing the calcium level of the diet had no influence on the variation in shell quality due to oviposition time. They suggested that the variation in shell quality was not caused by inadequate dietary calcium in the small intestine at night. In earlier studies, Roland and Harms (1974) demonstrated that eggs laid during the afternoon were smaller than eggs laid during the morning. Even though it would take less calcium to put shell with equal thickness on a smaller egg than on a larger one, they did not believe that egg weight was responsible for the variation of shell quality, for two reasons. First, egg weight does not continue to decline during the afternoon; and second, when morning and afternoon eggs of the same weights were compared, the afternoon eggs had the highest specific gravity. The influence of egg shape on the birds 1978 Poultry Sci 57:1723-1727
ability to produce eggs with maximum egg shell quality has not been reported even though it has been shown that egg curvature (egg shape) affects shell strength (Voisey and Hunt, 1967; Anderson et al, 1970; Richards and Swanson, 1965). Egg shape (shape index) has also been shown to vary according to strain of bird, size of egg, and position of egg in the clutch (Marble, 1942; Pearl, 1909; Benjamin, 1920; Pearl and Curtis, 1916; Romanoff and Romanoff, 1949). If the shape index values of eggs laid during the afternoon were larger (more spherical) than eggs laid during the morning, the afternoon eggs would have less surface area and should require less shell to form eggs with equal shell thickness. This could explain why afternoon eggs have better shells. The following experiments were conducted to determine: 1) the relationship of egg shape and time of oviposition on shell quality and 2) to determine if the variation in shape index (surface area of eggs) within a flock is great enough to influence thickness with a given amount of shell.
1723
PROCEDURE Experiment
1. A total of 1510 Babcock hens
Downloaded from http://ps.oxfordjournals.org/ at Dalhousie University on April 13, 2015
ABSTRACT Experiments were conducted to determine the relationship of egg shape to time of oviposition and egg shell quality. Eggs were collected at 2-hr intervals throughout the day and depending upon the experiment various measurements (egg weight, shape index, shell weight, shell thickness, or specific gravity) were determined. The results indicated that eggs laid during the afternoon had a higher shape index (rounder eggs) than eggs laid during the morning. The afternoon eggs also had a higher specific gravity, shell weight, shell thickness, and were smaller than eggs laid during the morning. A large variation in shape index occurred among eggs. It was concluded that the difference in shape between times of oviposition would not explain the variation in shell quality due to time of oviposition, but that the large variation in egg shape among birds is a significant factor in determining the bird's ability to produce eggs with maximum shell thickness with a given amount of shell.
ROLAND, SR.
1724
Shape index was expressed as the width of the egg divided by the length (SI = (W/L) X 100). The smaller the shape index, the more oblong the egg; the larger the shape index, the more spherical the egg, meaning the least surface area per unit egg. Since it is extremely difficult and time consuming to estimate (with a high degree of accuracy) the surface area of any irregular or asymmetrically shaped object (Dunn and Schneider, 1923; Mueller and Scott, 1940; Bonnet and Mongin, 1965; Carter, 1968; Besch et ah, 1968; Carter and Jones, 1970), the formula for measuring the surface area of an ellipsoid was used, 27Tb2
3av
2bV^b5
sin
"
y/^T2
where v = egg volume or weight, a = one-half the length of the long axis, and b = one-half the length of the short axis. Eggs may be spherical, elliptical, biconical, or conical in shape; however, the above formula was used because most eggs are ellipsoidal in shape. The data from each experiment were subjected to an analysis of variance, and the multiple range test of Duncan (1955) as modified by Kramer (1956) was utilized to determine significant differences. To analyze the difference in shell weight (Experiments 4 to 6) and shell thickness (Experiment 7), a comparison of sample means with paired observations as described by Steel and Torrie (1960) was used. RESULTS AND DISCUSSION Experiments I to 3. The results of these experiments confirm the previous reports of
TABLE 1.—Specific gravity, egg weight, and shape index in relation to time of oviposition (Experiment 1) Values expressed as means + SEM Specific gravity
Time 1800 0600 0800 1000 1200 1400 1600
-
0600 0800 1000 1200 1400 1600 1800
hr hr hr hr hr hr hr
1.081 c 1.081 c 1.081 c 1.084 b 1.084 b 1.087 a 1.086 ab
Shape index
Egg
weight (g) .0010 .0001 .0004 .0005 .0005 .0006 .0009
63.7ab 64.5 a 63.3ab 62.3ab 61.2 C 61.9bc 62.2ab
.6 .3 .3 .3 .3 .5 .8
a,b,c,Values followed by different letters in the same column are significantly different (P<.05).
72.99 a 73.20 a 73.32 a 73.23 a 73.45 a 73.68 a 73.46 a
.49 19 .32 .22 .23 .30 .39
Downloaded from http://ps.oxfordjournals.org/ at Dalhousie University on April 13, 2015
were used. Eggs were collected at 0600 and at 2-hr intervals the following day from 0600 to 2000 hr. All hens were fed a commercial-type corn-soy diet. Egg weight, shape index, egg specific gravity, shell weight, and shell thickness were determined. The hens were on an 18-hr light day from 0200 to 2000 hr. Experiments 2 and 3. These experiments were conducted similar to Experiment 1 except that in Experiment 2, eggs were collected from 460 Babcock hens and in Experiment 3, eggs were collected from 1000 Babcock hens. Egg specific gravity, egg weight, and shape index were determined only on eggs collected from 0600 to 1800 hr. The hens were on a 15-hr light day from 0500 to 2000 hr. Experiments 4 through 6. Egg weight and specific gravity were determined on a large number of eggs from three different populations. From each population approximately 50 pairs of eggs were selected. Each of the eggs within a pair had the same specific gravity and same egg weight to within .2 g but had shape index differences greater than 3.00 units. Shell weight of each egg was determined. Experiment 7. Egg weight, shell thickness, shell weight, and shape index were determined on 968 eggs. Pairs of eggs were selected which had shape index difference greater than 3.00 units, egg weight difference less than or equal to .1 g, and shell weight difference less than or equal to .06 g. There were 54 pairs of eggs which met these three criteria. Egg specific gravity was determined using graded sodium chloride solutions. Shell thickness was determined at three locations around the middle of the egg. The shells were air-dried for 48 hr and shell plus membrane weight determined.
EGG SHAPE AND EGG SHELL QUALITY
1725
TABLE 2.—Specific gravity, egg weight, and shape index in relation to time of oviposition (Experiment 2) Values expressed as means ± SEM Specific gravity
Time 0600 0800 1000 1200 1400 1600 a
0800 1000 1200 1400 1600 1800
hr hr hr hr hr hr
1.085 c 1.085 c 1.085 c 1.086 b c 1.088a*> 1.089 a
.0007 .0004 .0005 .0007 .0006 .0006
66.1b 64.8b 63.0* 61.5 a 62.3 a 60.8 a
.7 .5 .6 .5 .6 .9
72.64 a 72.77 a 72.61 a 72.02 a 73.25 a 73.94 a
.43 .24 .37 .36 .38 .47
,C
Values followed by different letters in the same column are significantly different (P<.05).
Roland and Harms (1974) that specific gravity is greater and weight is less for eggs laid during the afternoon than for eggs laid during the morning (Tables 1, 2, and 3). Shell weight, percent shell, and shell thickness were also greater for eggs laid during the afternoon than for eggs laid during the morning (Table 4). The results indicate that shape index was greater for the afternoon eggs (Tables 1, 2, and 3). Although shape index values were not significantly different between the 2-hr time periods, when shape index of all eggs (within experiment) laid during the morning was compared to that of the afternoon eggs, the difference was significant (P<.05) in Experiments 1 and 2 but not in Experiment 3. When the shape index of all eggs laid during the morning (72.78 ± .13) (Experiment 1 to 3) was compared to that of all eggs laid during the afternoon (73.32 ± .16), the difference was also significant (P<.05). Using the same egg weight (63.36 g) for eggs
laid during the morning and afternoon and the formula for an ellipsoid, it was calculated that the average surface area of the morning eggs was 78.17 cm 2 vs. 78.11 cm 2 for the afternoon eggs. To calcify this extra .06 cm 2 of surface area on the morning egg, it would take .08% more shell or 4.8 mg more for a 6 g shell. However, it is believed that this difference would explain only a small amount (approximately 3.1%) of the improvement in shell quality of afternoon eggs. Experiments 4 to 7. There was no significant treatment time experiment interaction in Experiments 4 to 6; therefore, the data were combined. The results indicate that it takes significantly more shell for an oblong egg (5.786 g) than it does for a spherical egg (5.723 g) to have the same specific gravity (Table 5). This is equal to approximately 5.5 mg more shell per .50 unit decrease in shape index, which is very close to the 4.8 mg per .54 unit difference in shape index or .06 cm 2 of surface
TABLE 3.—Specific gravity, egg weight, and shape index in relation to time of oviposition (Experiment 3) Values expressed as means + SEM Specific gravity
Time 1800 0600 0800 1000 1200 1400 1600
-
0600 0800 1000 1200 1400 1600 1800
hr hr hr hr hr hr hr
1.077C 1.078= 1.077C 1.078 c 1.08lt> 1.084 a 1.083 a b
Shape index
Egg weight (g) .0007 .0005 .0007 .0007 .0007 .0011 .0020
66.3 a 67.5 a 63.5 b c 63.3 b c 63.2 C 63.1 b c 65.9ab
.5 .5 .4 .5 .4 .9 1.3
• Values followed by different letters in the same column are significantly different (P-C05).
72.30 a 72.39 a 72.38 a 72.47 a 72.47 a 72.94 a 73.38 a
.26 .34 .46 .37 .38 .58 .72
Downloaded from http://ps.oxfordjournals.org/ at Dalhousie University on April 13, 2015
'
-
Shape index
Egg weight (g)
ROLAND, SR.
1726
TABLE 4.—Shell weight, percent shell, and shell thickness in relation to time of oviposition (Experiment 1) Values are expressed as means ± SEM Shell weight (g)
Time 1800 0600 0800 1000 1200 1400 1600
-
hr hr hr hr hr hr hr
5.69b 5.78b 5.76b 5.90ab 5.90»b 5.95* 5.93 a b
8.93 b 8.97b 9.09 b 9.47 a 9.46 a 9.61 a 9.54a
.10 .04 .04 .05 .05 .06 .09
.382C .383 c .393b .389 b c .400 a .406 a .398 a b
.18 .05 .05 .06 .07 .08 .13
.006 .002 .002 .002 .002 .003 .003
Values followed by different letters in the same column are significantly different (P<.05).
for an ellipsoid, it was calculated that an egg with a shape index of 90.37 would have a surface area of 76.99 cm 2 vs. 89.90 cm 2 for an egg with a shape index of 61.23. With equivalent thickness and density of shell, the oblong egg would require 3.78% (227 mg for a 6 g shell) more shell than the round egg. Since the average difference in shell weight of eggs laid between 1800 to 1200 hr and 1200 to 1800 hr was only 150 mg (Table 4), it is believed that the variation in shape index within a population is a significant factor in determining the birds ability to obtain maximum shell quality.
area as calculated using the formula for an ellipsoid. The results of Experiment 7 indicated that an oblong egg having the same egg weight and shell weight (to within .1 g) as a spherical egg had a significantly thinner shell than the spherical egg (Table 6). This surface area of the oblong egg and spherical egg was calculated to be 77.36 cm 2 and 76.70 cm 2 , respectively. It would take .86% more shell (50 mg) to calcify the oblong egg to the same shell thickness. This is equal to 4.8 mg more shell per .50 unit decrease in shape index which is very close to the 5.5 mg and 4.8 mg per .50 or .54 unit difference in shape index as measured directly or using the formula for an ellipsoid. Although there is little difference in shape index due to time of oviposition, there is a large variation in shape index among eggs. The results of Experiments 1, 2, and 3 indicated that there was considerable variation in index which ranged from a low of 60 to a high of 90 (Fig. 1). Using a 63.36 g egg and the formula
These studies demonstrate that shape index of eggs can have a definite influence on the bird's ability to produce eggs with maximum shell quality. Egg shape is a heritable characteristic (Romanoff and Romanoff, 1949). Thus, selection for a more spherical shape should allow the hen to produce thicker shells with a given amount of shell. Since no within-hen comparsons were made in these studies, the effects of heritability and the extent of the
TABLE 5.—Various criteria of oblong and spherical e ggs (Experiments 4, 5, and 6)
TABLE 6.— Various criteria of oblong and spherical eggs (Experiment 7)
Type egg
Type egg
Criteria
Oblong
Spherical
Criteria
Oblong
Spherical
Egg weight (g) Specific gravity Shape index Shell weight (g)
65.18 1.082 69.71 5.786 a
65.19 1.082 75.43 5.723b
Egg weight (g) Shell weight (g) Shape index Shell thickness (mm)
62.33 5.83 70.38 .389 a
62.33 5.84 75.64 .398 b
' Values followed by different letters in the same row are significantly different (P<.05).
' Values followed by different letters in the same row are significantly different (P<.05).
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a
0600 0800 1000 1200 1400 1600 1800
Thickness (mm)
Shell (%)
EGG SHAPE AND EGG SHELL QUALITY
18
16
A
14
12
10
!
8
6
2
0
[
-
61
JV
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64
. Vr"~N >s
'
67
70
73
76
79
82
'•••
:
85
•
88
•-
91
SHAPE INDEX
FIG. 1. Variation in shape index from three different populations of hens (Experiments 1, 2, and 3).
effect of clutch position on egg shape can not be differentiated. ACKNOWLEDGMENT
Special thanks to L. P. Burton, Chairman of Mathematics Department, Auburn University, for his aid and advice in the mathematical calculations. REFERENCES Anderson, G. B., T. C. Carter, and M. R. Jones, 1970. Some factors affecting dynamic fracture of egg shells in battery cages. Page 53—60 in Factors affecting egg grading. B. M. Freeman and R. J. Gordon, ed. British Poultry Sci., Ltd., Edinburg. Benjamin, Earl W., 1920. A study of selections for the size, shape and color of hen's eggs. Cornell University, Memoir 31:191-312. Besch, E. L., S. J. Sluka, and A. H. Smith, 1968. Determination of surface area using profile record-
ings. Poultry Sci. 4 7 : 8 2 - 8 5 . Bonet, Y., and P. Mongin, 1965. Mesure de la surface de l'oeuf. Annu. Zootech. 14:311-317. Carter, T. C , 1968. The hen's egg; A mathematical model with three parameters. Brit. Poultry Sci. 9:165-171. Carter, T. C , and R. M. Jones, 1970. The hen's egg: Shell shape and size parameters and their interrelations. Brit. Poultry Sci. 11:179-188. Duncan, D. B„ 1955. Multiple range and multiple F tests. Biometrics 11:231-240. Dunn, L. C , and M. Schneider, 1923. An approximate method of calculating the surface area of eggs. Poultry Sci. 2 : 9 0 - 9 2 . Kramer, C. Y., 1956. Extension of multiple range test to group means with unequal numbers of replications. Biometrics 12:307—310. Marble, D. R., 1943. Genetics of egg shape. Poultry Sci. 2 2 : 6 1 - 7 1 . Mueller, C. D., and H. M. Scott, 1940. The porosity of the egg shell in relation to hatchability. Poultry Sci. 19:163-166. Pearl, R., 1909. Studies on the physiology of reproduction in the domestic fowl. I. Regulation in morphogenetic activity of the oviduct. J. Exp. Zool. 6: 339-350. Pearl, R., and M. R. Curtis, 1916. Studies on the physiology of reproduction in the domestic fowl. XV. Dwarf eggs. J. Agr. Res. 6:997-1042. Richards, J. F., and M. H. Swanson, 1965. The relationship of egg shape to shell strength. Poultry Sci. 44:1555-1558. Roland, D. A., Sr., B. L. Damron, and R. H. Harms, 1977. Specific gravity of eggs as influenced by dietary calcium and time of oviposition. Poultry Sci. 56:717-719. Roland, D. A., Sr., and R. H. Harms, 1974. Specific gravity of eggs in relation to egg weight and time of oviposition. Poultry Sci. 53:1494—1498. Roland, D. A., Sr., D. R. Sloan, and R. H. Harms, 1973. Calcium metabolism in the laying hen. 6. Shell quality in relation to time of oviposition. Poultry Sci. 52:506-509. Romanoff, A. L., and A. J. Romanoff, 1949. The avian egg. John Wiley and Sons, Inc., New York. Steel, E. D. R., and J. H. Torrie, 1960. Principles and procedures of statistics. McGraw-Hill Book Company, inc., New York. Voisey, P. W., and J. R. Hunt, 1967. Physical properties of egg shells. 4. Stress distribution in the shell. Brit. Poultry Sci. 8 : 2 6 3 - 2 7 1 .
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