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Factors Influencing Shell Quality of Aging Hens
Factors Influencing Shell Quality of Aging Hens DAVID A. ROLAND, SR. Poultry Science Department, Agricultural Experiment Station, Auburn University, Auburn, Alabama 36830 (Received for publication July 5, 1978)
1979 Poultry Science 58:774-777
INTRODUCTION Perhaps the three most common explanations (Petersen, 1965) given during the past to explain the decline in shell quality (thickness of the egg shell) as the hen ages have been that 1) her ability to absorb calcium decreases with age, 2) her ability to mobilize skeletal calcium decreases with age, and 3) her genetic potential for production through years of genetic selection increases at a faster rate than her ability to maintain adequate shell deposition. However, results of experiments conducted by Roland et al. (1978) indicated that the first two explanations may not be correct and that the increase in egg weight with no proportionate increase in shell deposition results in the decline in shell quality (Roland, et al, 1975). The following studies were conducted to determine the influence of hen age on shell deposition when environmental effects are minimized; determine the influence of egg size and shell quality during the early stages of production on subsequent shell quality; and determine the influence of rate of production on shell quality.
EXPERIMENTAL PROCEDURE
In Experiment 1, 150 eggs were collected at random from hens 8, 11, 14, or 17 months of age. Only eggs laid between 0900 hr and 1200 hr were collected. During this particular time, changes in egg specific gravity due to oviposi-
tion time are minimized (Roland et al, 1973). All hens were of the same strain, housed four per cage in an open-type house, and fed a commercial corn-soy diet. Egg weight, shell weight, specific gravity, and shell thickness were determined for all eggs. In Experiment 2, 82 hens fed a commercial corn-soy diet were used. Eggs laid during the first 10 months of lay were recorded. Eggs were selected for comparisons according to the following procedure. Those laid from 0800 hr to 1300 hr during the last 4 days of each month were collected and egg weight, specific gravity, shell weight, and shell thickness determined. The average weight of eggs laid by each hen during the 10-month period was determined. Hens laying the heavier eggs and those laying the lighter eggs were selected. The average weight of eggs laid the first 2 months and those laid the last 2 months was determined. Eggs from hens having the greater increase in egg weight and those having the smaller increase in egg weight during the test period were selected. Hens laying the higher number of eggs and those laying the lower number of eggs were determined. The average specific gravity for eggs laid the first 2 months and for those laid the last 2 months was determined. Hens producing eggs having the higher egg specific gravity during the first 2 months in lay were compared to hens having the lower egg specific gravity. In these comparisons the upper and lower 25% of the hens were selected and shell 774
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
ABSTRACT Two experiments were conducted in which eggs were collected from hens of different ages or from individually caged hens during their first 10 months of lay. Shell weight, egg weight, specific gravity, egg production, and shell thickness were the criteria evaluated. Results indicated that the total amount of shell deposited on the egg at 3-months of lay did not decrease but remained fairly constant or increased slightly throughout the remainder of the laying period. However, the increase in egg weight with no proportionate increase in shell deposition resulted in a decline in shell quality (shell thickness and specific gravity). Eggs which had the greater increase in size throughout lay had the greater decline in shell quality. Neither the number of eggs laid by the hen nor absolute egg size had any influence on shell quality. However, shell quality at the end of lay was directly related to shell quality at the beginning of lay.
SHELL QUALITY AND AGING HENS
775
TABLE 1. Influence of bird age on shell quality
Bird age (months)
Egg weight (g)
Shell weight
8(3)' 11 (6) 14(9) 17(12)
55.91d ± .282 57.20c ± .33 59.1 3 b ± .37 64.03a ± .39
5.23b 5.27*b 5.34*b 5.38a
Shell thickness (mm)
Specific gravity ± .04 ± .05 ± .05 ± .06
1.089* 1.084b 1.082c 1.077d
± ± ± ±
.367* ± .366* ± .356 b ± .353 b ±
.0004 .0005 .0005 .0005
.002 .003 .002 .003
1 2
Values in parenthesis represent months in lay. SEM ' ' Values followed by different letters in the same column are significantly different (P<.05).
RESULTS AND DISCUSSION T h e results of E x p e r i m e n t 1 (Table 1) indicated t h a t t h e a m o u n t of shell deposited on t h e egg at 3 m o n t h s of lay (5.23 g) did n o t decrease b u t remained fairly c o n s t a n t or increased slightly during t h e year of lay. However, from t h e third t o t h e twelfth m o n t h of lay, egg weight increased 8.12 g. Because egg weight increased 14.5% during this 9 m o n t h period and shell weight increased only 2.9%, specific gravity decreased 12 units. During t h e same 9 m o n t h period, shell thickness also decreased .014 m m . These studies confirm t h e previous r e p o r t s of Roland et al. ( 1 9 7 8 ) t h a t t h e decline in shell quality is n o t due t o t h e inability of t h e hens t o maintain shell deposition b u t d u e t o an increase in egg
size while shell deposition r e m a i n s fairly constant. This forces a decline in shell quality. In E x p e r i m e n t 2, t h e average egg weight of t h e birds laying t h e heavier egg was 58.47 g while t h e egg weight of those laying t h e smaller egg was 5 0 . 7 6 g (Table 2). T h e r e were n o significant differences in specific gravity or shell thickness, b u t as expected, shell weight was significantly greater for t h e heavier egg t h a n for t h e smaller egg. Hens laying smaller eggs, therefore, deposit less shell on t h e egg. This suggests t h a t t h e size of t h e egg laid b y t h e hen has little or n o influence on shell quality (specific gravity or shell thickness). T h e results s h o w n in Table 3, however, indicated t h a t t h e hens having t h e greater gain in egg weight t h r o u g h o u t t h e year had t h e greater decline in shell quality. A l t h o u g h t h e difference in specific gravity b e t w e e n eggs at t h e beginning of lay was n o t significant, egg specific gravity was significantly greater a n d shell thickness numerically greater ( a p p r o a c h i n g significance) for t h e eggs from hens t h a t had t h e least gain in egg weight t h r o u g h o u t t h e year c o m p a r e d t o t h e specific gravity of t h o s e t h a t
TABLE 2. Influence of egg weight on shell quality from eggs laid during the first 10 months of lay Egg weight Criteria
Greater than 57 j
Less than 57 g
Egg weight (g) Specific gravity Shell thickness (mm) Shell weight (g)
58.47 *± .33' 1.087* ± .001 .369* ± .004 5.31* ± .06
50.76 b 1.088* .369* 4.83 b
a,b Values followed by different letters in the same row are significantly different (P<.05). SEM
± ± ± ±
.37 .0007 .004 .07
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
weight, egg weight, shell thickness, and specific gravity c o m p a r e d . T h e data from each e x p e r i m e n t were subjected t o an analysis of variance and t h e multiple range test of D u n c a n ( 1 9 5 5 ) as modified b y K r a m e r ( 1 9 5 6 ) was utilized t o locate significant differences.
ROLAND, SR.
776
TABLE 3. Influence of egg weight gain on shell quality Gain greater than 10.5 g
Criteria
Average first 2 months
Egg weight (g) Specific gravity Shell thickness (mm) Shell weight (g)
47.58* 1.094* .397 a 4.77*
± ± ± ±
Gain less than 7.0 g Average last 2 months
.65' .001 .005 .09
61.68* + 1.082* ± .349 a ± 5.29 a ±
.72 .001 .008 .13
Average first 2 months
Average last 2 months
49.66 a ± .64 1.093a + .001 .395* + .004 4.99a ± .09
54.25b .+ 1.087 b ± .363 a ± 5.06 a ±
.71 .002 .006 .12
TABLE 4. Influence of number of eggs the hen lays on shell quality Eggs laid Criteria
Greater than 202 eggs
Less than 179 eggs
Number eggs Specific gravity Shell thickness (mm) Shell weight (g)
214* + 1' 1.087* ± .0007 .369* ± .003 5.03* ± .06
144 b 1.087* .369* 5.07*
± ± ± ±
7 .0010 .005 .11
a ' b Values followed by different letters in the same row are significantly different (P<.05). 'SEM
had the most gain. The differences in shell thickness were not significant. The results shown in Table 4 indicate that the number of eggs a hen lays has no influence on shell quality. It is believed that many breeders and researchers think that the egg production rate is greater than the hen's ability
to deposit shell. However, the results of this study indicate that this is not true. There were no significant differences in egg specific gravity, shell thickness, or weight between hens laying the greater number of eggs and those laying the smaller number of eggs throughout the 10month period.
TABLE 5. Relation of specific gravity of eggs at beginning of lay (average of first 2 months) to that at end of lay (average of last 2 months) Specific gravity greater than 1.097 g
Criteria Specific gravity Shell thickness (mm) Shell weight (g) Egg weight (g)
Average first 2 months 1.098* ± .0003' .411*+ .003 5.12* ± .08 49.10a + .50
Average last 2 months 1.088* ± .0012 .376*+ .006 5.53* ± .08 58.64* ± .68
Specific gravity less than 1.091 g Average last 2 months
Average first 2 months 1.088b + .381 b ± 4.78 b ± 50.81* +
.0011 .003 .08 .88
' Values followed by different letters in the same row are significantly different (P<.05). 'SEM
1.082 b .350 b 4.96 b 56.85*
± .0015 ± .005 ± .10 ± 1.0
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
a ' b Values followed by different letters in the same row are significantly different (P<.05). 'SEM
SHELL QUALITY AND AGING HENS
early stages of production was directly related to shell quality at the end of lay. REFERENCES Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1-42. Kramer, C. Y., 1956. Extension of multiple range tests to group means with unequal numbers of replications. Biometrics 12:307-310. Petersen, C. F., 1965. Factors influencing egg shell quality. World's Poultry Sci. J. 21:110-138. Roland, D. A., Sr., C. E. Putman, and R. L. Hilburn, 1978. Influence of age on the ability of hens to maintain egg shell calcification when stressed with inadequate dietary calcium. Poultry Sci. 57:1616— 1621. 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. 52:506-510. Roland, D. A., Sr., D. R. Sloan, and R. H. Harms, 1975. The ability of hens to maintain calcium deposition in the egg shell and egg yolk as the hen ages. Poultry Sci. 54:1720-1723.
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
The results shown in Table 5 indicate that birds having the best shell quality at the beginning of lay had the best shell quality at the end of lay. Birds that had the poorer shell quality at the beginning of lay had the poorer shell quality at the end of lay. In fact, the birds having the better shell quality at the beginning of lay had as good a shell quality at the end of 10 months of lay as the hens producing the poorer shells had at the beginning of lay. This suggests that hens may be selected for their ability to produce good or poor shells during their first 1 or 2 months in lay. The results of these experiments demonstrate that egg size has little relationship to shell quality; however, the increase in egg size from individual birds during the lay cycle appears to be the primary cause for the decline in shell quality as the hen ages. The number of eggs laid by the hen had little influence on shell quality; however, shell quality of eggs laid during the
777
1979 Poultry Science 58:774-777
INTRODUCTION Perhaps the three most common explanations (Petersen, 1965) given during the past to explain the decline in shell quality (thickness of the egg shell) as the hen ages have been that 1) her ability to absorb calcium decreases with age, 2) her ability to mobilize skeletal calcium decreases with age, and 3) her genetic potential for production through years of genetic selection increases at a faster rate than her ability to maintain adequate shell deposition. However, results of experiments conducted by Roland et al. (1978) indicated that the first two explanations may not be correct and that the increase in egg weight with no proportionate increase in shell deposition results in the decline in shell quality (Roland, et al, 1975). The following studies were conducted to determine the influence of hen age on shell deposition when environmental effects are minimized; determine the influence of egg size and shell quality during the early stages of production on subsequent shell quality; and determine the influence of rate of production on shell quality.
EXPERIMENTAL PROCEDURE
In Experiment 1, 150 eggs were collected at random from hens 8, 11, 14, or 17 months of age. Only eggs laid between 0900 hr and 1200 hr were collected. During this particular time, changes in egg specific gravity due to oviposi-
tion time are minimized (Roland et al, 1973). All hens were of the same strain, housed four per cage in an open-type house, and fed a commercial corn-soy diet. Egg weight, shell weight, specific gravity, and shell thickness were determined for all eggs. In Experiment 2, 82 hens fed a commercial corn-soy diet were used. Eggs laid during the first 10 months of lay were recorded. Eggs were selected for comparisons according to the following procedure. Those laid from 0800 hr to 1300 hr during the last 4 days of each month were collected and egg weight, specific gravity, shell weight, and shell thickness determined. The average weight of eggs laid by each hen during the 10-month period was determined. Hens laying the heavier eggs and those laying the lighter eggs were selected. The average weight of eggs laid the first 2 months and those laid the last 2 months was determined. Eggs from hens having the greater increase in egg weight and those having the smaller increase in egg weight during the test period were selected. Hens laying the higher number of eggs and those laying the lower number of eggs were determined. The average specific gravity for eggs laid the first 2 months and for those laid the last 2 months was determined. Hens producing eggs having the higher egg specific gravity during the first 2 months in lay were compared to hens having the lower egg specific gravity. In these comparisons the upper and lower 25% of the hens were selected and shell 774
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
ABSTRACT Two experiments were conducted in which eggs were collected from hens of different ages or from individually caged hens during their first 10 months of lay. Shell weight, egg weight, specific gravity, egg production, and shell thickness were the criteria evaluated. Results indicated that the total amount of shell deposited on the egg at 3-months of lay did not decrease but remained fairly constant or increased slightly throughout the remainder of the laying period. However, the increase in egg weight with no proportionate increase in shell deposition resulted in a decline in shell quality (shell thickness and specific gravity). Eggs which had the greater increase in size throughout lay had the greater decline in shell quality. Neither the number of eggs laid by the hen nor absolute egg size had any influence on shell quality. However, shell quality at the end of lay was directly related to shell quality at the beginning of lay.
SHELL QUALITY AND AGING HENS
775
TABLE 1. Influence of bird age on shell quality
Bird age (months)
Egg weight (g)
Shell weight
8(3)' 11 (6) 14(9) 17(12)
55.91d ± .282 57.20c ± .33 59.1 3 b ± .37 64.03a ± .39
5.23b 5.27*b 5.34*b 5.38a
Shell thickness (mm)
Specific gravity ± .04 ± .05 ± .05 ± .06
1.089* 1.084b 1.082c 1.077d
± ± ± ±
.367* ± .366* ± .356 b ± .353 b ±
.0004 .0005 .0005 .0005
.002 .003 .002 .003
1 2
Values in parenthesis represent months in lay. SEM ' ' Values followed by different letters in the same column are significantly different (P<.05).
RESULTS AND DISCUSSION T h e results of E x p e r i m e n t 1 (Table 1) indicated t h a t t h e a m o u n t of shell deposited on t h e egg at 3 m o n t h s of lay (5.23 g) did n o t decrease b u t remained fairly c o n s t a n t or increased slightly during t h e year of lay. However, from t h e third t o t h e twelfth m o n t h of lay, egg weight increased 8.12 g. Because egg weight increased 14.5% during this 9 m o n t h period and shell weight increased only 2.9%, specific gravity decreased 12 units. During t h e same 9 m o n t h period, shell thickness also decreased .014 m m . These studies confirm t h e previous r e p o r t s of Roland et al. ( 1 9 7 8 ) t h a t t h e decline in shell quality is n o t due t o t h e inability of t h e hens t o maintain shell deposition b u t d u e t o an increase in egg
size while shell deposition r e m a i n s fairly constant. This forces a decline in shell quality. In E x p e r i m e n t 2, t h e average egg weight of t h e birds laying t h e heavier egg was 58.47 g while t h e egg weight of those laying t h e smaller egg was 5 0 . 7 6 g (Table 2). T h e r e were n o significant differences in specific gravity or shell thickness, b u t as expected, shell weight was significantly greater for t h e heavier egg t h a n for t h e smaller egg. Hens laying smaller eggs, therefore, deposit less shell on t h e egg. This suggests t h a t t h e size of t h e egg laid b y t h e hen has little or n o influence on shell quality (specific gravity or shell thickness). T h e results s h o w n in Table 3, however, indicated t h a t t h e hens having t h e greater gain in egg weight t h r o u g h o u t t h e year had t h e greater decline in shell quality. A l t h o u g h t h e difference in specific gravity b e t w e e n eggs at t h e beginning of lay was n o t significant, egg specific gravity was significantly greater a n d shell thickness numerically greater ( a p p r o a c h i n g significance) for t h e eggs from hens t h a t had t h e least gain in egg weight t h r o u g h o u t t h e year c o m p a r e d t o t h e specific gravity of t h o s e t h a t
TABLE 2. Influence of egg weight on shell quality from eggs laid during the first 10 months of lay Egg weight Criteria
Greater than 57 j
Less than 57 g
Egg weight (g) Specific gravity Shell thickness (mm) Shell weight (g)
58.47 *± .33' 1.087* ± .001 .369* ± .004 5.31* ± .06
50.76 b 1.088* .369* 4.83 b
a,b Values followed by different letters in the same row are significantly different (P<.05). SEM
± ± ± ±
.37 .0007 .004 .07
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
weight, egg weight, shell thickness, and specific gravity c o m p a r e d . T h e data from each e x p e r i m e n t were subjected t o an analysis of variance and t h e multiple range test of D u n c a n ( 1 9 5 5 ) as modified b y K r a m e r ( 1 9 5 6 ) was utilized t o locate significant differences.
ROLAND, SR.
776
TABLE 3. Influence of egg weight gain on shell quality Gain greater than 10.5 g
Criteria
Average first 2 months
Egg weight (g) Specific gravity Shell thickness (mm) Shell weight (g)
47.58* 1.094* .397 a 4.77*
± ± ± ±
Gain less than 7.0 g Average last 2 months
.65' .001 .005 .09
61.68* + 1.082* ± .349 a ± 5.29 a ±
.72 .001 .008 .13
Average first 2 months
Average last 2 months
49.66 a ± .64 1.093a + .001 .395* + .004 4.99a ± .09
54.25b .+ 1.087 b ± .363 a ± 5.06 a ±
.71 .002 .006 .12
TABLE 4. Influence of number of eggs the hen lays on shell quality Eggs laid Criteria
Greater than 202 eggs
Less than 179 eggs
Number eggs Specific gravity Shell thickness (mm) Shell weight (g)
214* + 1' 1.087* ± .0007 .369* ± .003 5.03* ± .06
144 b 1.087* .369* 5.07*
± ± ± ±
7 .0010 .005 .11
a ' b Values followed by different letters in the same row are significantly different (P<.05). 'SEM
had the most gain. The differences in shell thickness were not significant. The results shown in Table 4 indicate that the number of eggs a hen lays has no influence on shell quality. It is believed that many breeders and researchers think that the egg production rate is greater than the hen's ability
to deposit shell. However, the results of this study indicate that this is not true. There were no significant differences in egg specific gravity, shell thickness, or weight between hens laying the greater number of eggs and those laying the smaller number of eggs throughout the 10month period.
TABLE 5. Relation of specific gravity of eggs at beginning of lay (average of first 2 months) to that at end of lay (average of last 2 months) Specific gravity greater than 1.097 g
Criteria Specific gravity Shell thickness (mm) Shell weight (g) Egg weight (g)
Average first 2 months 1.098* ± .0003' .411*+ .003 5.12* ± .08 49.10a + .50
Average last 2 months 1.088* ± .0012 .376*+ .006 5.53* ± .08 58.64* ± .68
Specific gravity less than 1.091 g Average last 2 months
Average first 2 months 1.088b + .381 b ± 4.78 b ± 50.81* +
.0011 .003 .08 .88
' Values followed by different letters in the same row are significantly different (P<.05). 'SEM
1.082 b .350 b 4.96 b 56.85*
± .0015 ± .005 ± .10 ± 1.0
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
a ' b Values followed by different letters in the same row are significantly different (P<.05). 'SEM
SHELL QUALITY AND AGING HENS
early stages of production was directly related to shell quality at the end of lay. REFERENCES Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1-42. Kramer, C. Y., 1956. Extension of multiple range tests to group means with unequal numbers of replications. Biometrics 12:307-310. Petersen, C. F., 1965. Factors influencing egg shell quality. World's Poultry Sci. J. 21:110-138. Roland, D. A., Sr., C. E. Putman, and R. L. Hilburn, 1978. Influence of age on the ability of hens to maintain egg shell calcification when stressed with inadequate dietary calcium. Poultry Sci. 57:1616— 1621. 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. 52:506-510. Roland, D. A., Sr., D. R. Sloan, and R. H. Harms, 1975. The ability of hens to maintain calcium deposition in the egg shell and egg yolk as the hen ages. Poultry Sci. 54:1720-1723.
Downloaded from http://ps.oxfordjournals.org/ at New York University on October 4, 2014
The results shown in Table 5 indicate that birds having the best shell quality at the beginning of lay had the best shell quality at the end of lay. Birds that had the poorer shell quality at the beginning of lay had the poorer shell quality at the end of lay. In fact, the birds having the better shell quality at the beginning of lay had as good a shell quality at the end of 10 months of lay as the hens producing the poorer shells had at the beginning of lay. This suggests that hens may be selected for their ability to produce good or poor shells during their first 1 or 2 months in lay. The results of these experiments demonstrate that egg size has little relationship to shell quality; however, the increase in egg size from individual birds during the lay cycle appears to be the primary cause for the decline in shell quality as the hen ages. The number of eggs laid by the hen had little influence on shell quality; however, shell quality of eggs laid during the
777