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The Relationship of Age on Ability of Hens to Maintain Egg Shell Calcification When Stressed with Inadequate Dietary Calcium
The Relationship of Age on Ability of Hens to Maintain Egg Shell Calcification When Stressed with Inadequate Dietary Calcium D. A. ROLAND, SR., C. E. POTMAN and R. L. HILBURN Poultry Science Department, Agricultural Experiment Station, Auburn University, Auburn University, Auburn, Alabama 36830 (Received for publication December 14,1977) ABSTRACT Two experiments were conducted comparing the ability of young and old hens to maintain eggshell calcification when stressed with inadequate dietary calcium. In Experiment 1, 90 young hens and 90 old hens were divided into three equal groups and fed a diet containing 3.00%, 1.75%, or 1.00% calcium. Egg weight, specific gravity, and shell weight were determined on all eggs laid during the 4-day experiment. Feed consumption and serum calcium were determined by treatment. Experiment 2 was conducted similar to Experiment 1, except eggs were collected for 5 days. Samples of feces and bone were obtained on the fifth day and analyzed for minerals. The results of both experiments demonstrated that the old hens were able to maintain egg specific gravity, egg shell weight, egg weight, egg production, and serum calcium as well or better than young hens when both were stressed for short periods with diets that contained inadequate dietary calcium. Feed consumption was not significantly reduced by dietary calcium deficiency during this brief experimental period. Percent calcium, sodium, magnesium, and manganese in the feces were significantly reduced in hens (young and old) when fed diets containing 1.75 or 1.00% calcium. Tibia weight and ash were significantly reduced in young and old hens by decreasing the dietary calcium. It was concluded that the decline in shell quality with hen age is not due to a decline in the hen's ability to absorb calcium or utilize skeletal calcium. INTRODUCTION
The reason for the decline in shell quality as the hen ages has been a mystery since the beginning of the egg industry. There are many factors including nutrition, physiology, genetics, management, environment, and disease which can influence shell quality. However, when all factors are optimized to current knowledge, shell quality continues to decline with hen age. Perhaps the two most common explanations (Peterson, 1965) given during the past 50 years for the decline in shell quality as the hen ages are-. 1) the amount of calcium the hen absorbs and retains to use in the shell calcification process decreases with age; and 2) the amount of skeletal calcium which is readily available for shell calcification decreases as the hen ages. However, recently it was shown that the amount of shell deposited on the egg does not decrease as the hen ages but remains relatively constant or slightly increases (Roland et al., 1975; Roland, 1977). The increase in egg size with a concurrent increase in surface area caused this constant amount of calcium to be spread thinner, producing the decline in shell quality. These results indicate that the above explanations for the decline in shell quality as the hen ages may not be correct. 1978 Poultry Sci 57:1616-1621
The following studies were conducted to determine the relationship of age on the ability of hens to maintain egg shell calcification when stressed with inadequate dietary calcium for short periods of time. PROCEDURE
Experiment 1. Ninety young hens approximately 8 months of age and 90 old hens approximately 19 months of age were used. Each age group was randomly divided into three equal groups. They were fed diets containing 3.00%, 1.75%, or 1.00% calcium for 4 days. It was believed that 4 days would be about the maximum length of time the birds could consume the diet containing the lowest level of calcium without having an extreme adverse effect on egg production and shell quality (Roland et al, 1973, 1974). All diets (Table 1) contained 2,816 kcal metabolizable energy per kilogram, 15.7% protein, and .75% phosphorus. Eggs laid during the immediate 5-day pre-experimental period and during the 4-day experimental period were collected and egg weight, shell plus membrane weight, and specific gravity determined. Feed consumption was determined daily. Blood was extracted by anterior heart puncture at the end of the
1616
RELATIONSHIP ON ABILITY OF HENS WHEN STRESSED WITH CALCIUM
1617
TABLE 1 .—Experimental diets Calcium, % Ingredients
3.00
1.75
Corn Soybean meal Alfalfa Limestone Dicalcium phosphate Salt Microingredients DL-methionine Sand
67.36 21.00 2.50 6.04 2.30 .30 .50 a .05 .00
67.36 21.00 2.50 2.83 2.30 .30 .50 a .05 3.21
1.00
(%) 67.36 21.00 2.50 .89 2.30 .30 .50 a .05 5.15
Supplied the following quantities per kilogram of diet: vitamin A, 6600 IU; vitamin D 3 , 2200 1CU; menadione dimethylpyrimidinol bisulfite, 22 mg; riboflavin, 4.4 mg; pantothenic acid, 13.2 mg; niacin, 39.6 mg; choline chloride, 499.4 mg; vitamin B 1 2 , 22 meg; ethoxyquin, .0125%; manganese, 60 mg; iron, 50 mg; copper, 6 mg; cobalt, .0198 mg; iodine, 1.1 mg; zinc, 35 mg.
experiment for serum calcium determinations. Experiment 2. The procedure for Experiment 2 was similar to Experiment 1 except hens were 3 weeks older and experimental diets were fed for 5 days. Feces were collected from 25 hens from each group for 24 hours during the last day and analyzed for various minerals. Both tibias were removed from 25 hens from each group and bone ash, bone weight, and mineral content determined. Mineral determinations using the procedures as described by Stonerock et al. (1975) were made on the serum, feces, and tibia using an atomic absorption spectrophotometer. The data obtained were subjected to statistical analysis, and treatment significance was determined by the multiple range test of Duncan (1955) as modified by Kramer (1956). RESULTS AND DISCUSSION The level of calcium in the diet did not significantly affect feed consumption in old or young hens in Experiments 1 or 2 (Table 2). The hens consumed an average of 96 g/day in Experiment 1, and 100 g per day in Experiment 2. Reducing the level of dietary calcium from 3.00% to 1.75% or to 1.00% significantly reduced egg production in the young hens in both experiments (Table 2). Reducing the level of dietary calcium from 3.00% to 1.75% or to 1.00% had no significant effect on egg production from old hens. There were no significant
differences in egg production at each calcium level between the young and old hens in Experiment 1. However, in Experiment 2 the young hens fed the 3.00% calcium diet laid significantly more eggs than the old hens fed the same diet. In Experiment 1, reducing dietary calcium in the young hens reduced serum calcium 8.6 mg per 100 ml (Table 2). In the old hens, serum calcium was decreased 8.0 mg per 100 ml. The results of Experiment 2 were similar to Experiment 1, with serum calcium decreasing 8.9 mg per 100 ml in the young hens and 6.4 mg per 100 ml in the old hens. Reducing dietary calcium from 3.00% to 1.00% reduced serum calcium 25.9% more in the young hens than in the old hens. Egg weight was not significantly influenced by dietary treatment, but egg weight of old hens was significantly greater than that of young hens in all but one instance (Table 2). Egg specific gravity (Table 3) was either numerically or significantly decreased in young and old hens (Experiment 1 and 2) within 2 days after the calcium level of the diet had been reduced to 1.75% or to 1.00%. In Experiment 1, the egg specific gravity on day four was significantly reduced in the young birds 7 units or 13 units by reducing dietary calcium from 3.00% to 1.75% or to 1.00%, respectively. However, in the old hens, reducing the calcium level from 3.00% to 1.00% resulted in a decrease in egg specific gravity of only 7 units. In Experiment 2, the results were similar to
57.3 b 58.4 b =
1 2
Egg weight (g)
1.00%Ca 96.7* 100.0* 60.8b 66.7b 20.0 d 19.7= 57.2 b 57.9=
1.75% Ca 96.4* 104.2* 62.5b 70.7 b 22.8b= 25.9 b 56.9 b 59.1 b =
Voung hens (dietary treatment)
2
0 1 2 3 4 5
1.089* 1.090* 1.088* 1.086* 1.088* 1.089*
1.083* 1.084* 1.087* 1.086* 1.085*
3.00% Ca 1.085* 1.080 b 1.075=d 1.074b 1.072= 1.087* 1.080= 1.076= 1.073= 1.073= 1.067=
1.00% Ca
1.75% Ca
1.077b 1.079= 1.077= 1.074= 1.079b 1.080b
1.077b 1.074= 1.076= 1.076° 1.075 b
3.00%
Egg specific gravity
Values followed by different letters in the same row are significantly different (P<.05).
1
Experiment
Young hens (dietary treatment)
TABLE 3 .—The ability of young and old hens to maintain egg specific gravity when stressed wi for short periods of time
' ' c ' Values followed by different letters in the same row are significantly different (P<.05).
0 1 2 3 4
Day
a
28.6* 28.6*
1 2
Serum calcium (mg/100 ml)
78.5* 80.0*
1 2
Egg production (% hen/day)
94.8* 105.6*
3.00% Ca
1 2
Experiment
Feed consumption (g/hen/day)
Criteria
TABLE 2.—The relationship of hen age on response to induced calcium stress for sho
tint mm
2
0 1 2 3 4 5
1.75% Ca 5.14 a 4.97ab 4.84ab 5.00 a b 4.63bc 5.44 a b 5.15 b c 5.38 b 5.04 b 4.9 5 b 4.92 b
3.00% Ca
5.21 a 5.26 a 5.23 a 5.29 a 5.16 a
5.57 a 5.54 a 5.93 a S.61 a 5.48 a 5.83 a 5.39 a b 4.86 c 4.96 c 4.33° 4.40 c 4.38C
5.26 a 4 94ab 4.34 d 4.52bc 4.13d
1.00% Ca
1.07 b .38 b .41a 1.74 a .03 b
8.65 a .63 a .44 a 1.72 a .04 a
Calcium Sodium Magnesium Potassium Manganese
.48 b .25 c .35 b 1.62 a .02 c
1.00% Ca
Expressed as percentage of dry weight.
a.b.c Values followed by the different letters in the same row are significantly different (P<.05).
1.75% Ca
3.00% Ca
Element (%) d
Young birds
9.53 a .64 a .44 a 1.90 a .04 a
3.00% Ca
TABLES.--Fecal mineral content as influenced by hen age and calcium level (Experiment 2)
5.25 a 5.27 a 5.60 a 5.10 b 5.27 a 5.60 a
5.36 a 5.00 a 5.20 a 5.06 a 4.82 a
3.00%
Egg shell weight (g)
' ' ' Values followed by different letters in the same row are significaittly different (P<.05).
1
Experiment
0 1 2 3 4
Day
Young hens (dietary treatment)
TABLE 4.—The ability of young and old hens to maintain shell weight when stressed with for short periods of time
1620
ROLAND, SR. ET AL.
TABLE 6.—Relationship of bird age and induced calcium stress on tibia and bird weight (Experiment 2) Hen age
Calcium
Tibia weight
Tibia ash
(%)
(g)
(%)
Young
3.00 1.75 1.00
5.75a 4.86<=d 4.78cd
57.94b 56.49 c 55.03 d
Old
3.00 1.75 1.00
5.33b S.Olbc 4.64c
60.62 a 59.00 b 56.23 c d
' ' ' Values followed by different letters in the same column are significantly different (P<.05).
Experiment 1. Within 5 days, specific gravity decreased 22 units in the young hens and only 15 units in the old hens. The decrease in specific gravity was much greater in Experiment 2 than Experiment 1 because Experiment 2 was extended 1 day longer. The specific gravity of eggs laid by young hens decreased 59% more than that of eggs from old hens. Egg shell weight (Table 4) was either numerically or significantly decreased in young and old hens (Experiment 1 and 2) within 2 days after the calcium level of the diet had been reduced to 1.75% or to 1.00%. In Experiment 1, reducing dietary calcium for 4 days in the young hens reduced the egg shell weight 1.03 g. In the old hens, egg shell weight decreased .54
g. The results of Experiment 2 were similar to Experiment 1, with egg shell weight being significantly reduced 1.45 g in the young hens and 1.28 g in the old hens. Shell weight was reduced 36% more in young hens than in old hens. There were no significant differences in the percent calcium, magnesium, potassium or manganese content of the feces between the young and old hens (Table 5). The calcium content of the feces was reduced from 8.65% to 1.07% to .48% in the young hens by reducing the dietary calcium level. This was a decrease of 8.17 units. In the old hens, reducing dietary calcium resulted in a decrease of 9.02 units from 9.53% to .51%. In general, the percent of sodium, magnesium, and manganese in the feces decreased in young and old hens as the dietary calcium level decreased. No significant differences were observed in the potassium content of the feces in either young or old hens as a result of dietary treatment. Tibia weight and ash were significantly decreased in both young and old hens by reducing the calcium level of the diet from 3.00% to 1.00% (Table 6). Reducing dietary calcium had no significant effect on percent tibia calcium in either young or old hens within the same treatment (Table 7). Reducing dietary calcium from 3.00% to 1.00% significantly increased percent tibia sodium and potassium in young and old hens but had no significant influence on magnesium and manganese. Percent tibia magnesium was significantly lower in the old hens than in the young hens. When
TABLE 7 .—Relationship of hen age and induced calcium stress on tibia mineral content (Experiment 2) Mineral (%) e Hen age
Calcium
Calcium
Sodium
Potassium
Magnesium
Manganesef
Young
3.00 1.75 1.00
40.20ab 41.45a 40.75 a b
1.03b .96 c 1.14a
.54b .50cd .65 a
.67a .70a .69 a
2.00ab 2.00ab 1.89 b
Old
3.00 1.75 1.00
40.14 a b 40.09 a b 39.62 b
.90 c .93 c 1.02 b
.38d .47 c .63a
.56b .57b .61b
1.93 a b 2.00 a b 2.1ia
' ' ' Values followed by different letters in the same column are significantly different (P<.05). Expressed as percentage of ash. Value X 10" 3 .
RELATIONSHIP ON ABILITY OF HENS WHEN STRESSED WITH CALCIUM the dietary calcium was reduced from 3.00% to 1.75%, the percent sodium (young hens)and potassium (young and old hens) was significantly reduced. Results of these studies demonstrated that age had no adverse effect on the hens' ability to maintain egg shell quality when subjected to short periods of calcium stress. However, young hens appeared to be more sensitive than old hens. The response of old hens to calcium stress in terms of mineral content of feces and bone suggested that the decline in shell quality with hen age was not due to a decline in the hens' ability to absorb calcium or utilize skeletal calcium. REFERENCES Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1—42. Kramer, C. Y., 1956. Extension of multiple range tests
1621
to group means with unequal numbers of replications. Biometrics 12:307—310. Peterson, C. F., 1965. Factors influencing egg shell quality. World's Poultry Sci. J. 21:110-138. Roland, D. A., Sr., 1977. A re-evaluation and new approach to solving the shell quality problem. Poultry Digest 36(419): 1 7 - 1 8 . Roland, 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. Roland, D. A., Sr., D. R. Sloan, H. R. Wilson, and R. H. Harms, 1973. Influence of dietary calcium deficiency on yolk and serum calcium, yolk and organ weights and other selected production criteria of the pullet. Poultry Sci. 52:2220—2225. Roland, D. A., Sr., D. R. Sloan, H. R. Wilson, and R. H. Harms, 1974. Relationship of calcium to reproductive abnormalities in the laying hen (Gallus domesticus). J. Nutr. 104:1079-1085. Stonerock, R. H., D. A. Roland, Sr., and R. A. Voitle, 1975. Status of the digestive system and tibiae of cropectomized hens at night. Poultry Sci. 54:466-472.
The reason for the decline in shell quality as the hen ages has been a mystery since the beginning of the egg industry. There are many factors including nutrition, physiology, genetics, management, environment, and disease which can influence shell quality. However, when all factors are optimized to current knowledge, shell quality continues to decline with hen age. Perhaps the two most common explanations (Peterson, 1965) given during the past 50 years for the decline in shell quality as the hen ages are-. 1) the amount of calcium the hen absorbs and retains to use in the shell calcification process decreases with age; and 2) the amount of skeletal calcium which is readily available for shell calcification decreases as the hen ages. However, recently it was shown that the amount of shell deposited on the egg does not decrease as the hen ages but remains relatively constant or slightly increases (Roland et al., 1975; Roland, 1977). The increase in egg size with a concurrent increase in surface area caused this constant amount of calcium to be spread thinner, producing the decline in shell quality. These results indicate that the above explanations for the decline in shell quality as the hen ages may not be correct. 1978 Poultry Sci 57:1616-1621
The following studies were conducted to determine the relationship of age on the ability of hens to maintain egg shell calcification when stressed with inadequate dietary calcium for short periods of time. PROCEDURE
Experiment 1. Ninety young hens approximately 8 months of age and 90 old hens approximately 19 months of age were used. Each age group was randomly divided into three equal groups. They were fed diets containing 3.00%, 1.75%, or 1.00% calcium for 4 days. It was believed that 4 days would be about the maximum length of time the birds could consume the diet containing the lowest level of calcium without having an extreme adverse effect on egg production and shell quality (Roland et al, 1973, 1974). All diets (Table 1) contained 2,816 kcal metabolizable energy per kilogram, 15.7% protein, and .75% phosphorus. Eggs laid during the immediate 5-day pre-experimental period and during the 4-day experimental period were collected and egg weight, shell plus membrane weight, and specific gravity determined. Feed consumption was determined daily. Blood was extracted by anterior heart puncture at the end of the
1616
RELATIONSHIP ON ABILITY OF HENS WHEN STRESSED WITH CALCIUM
1617
TABLE 1 .—Experimental diets Calcium, % Ingredients
3.00
1.75
Corn Soybean meal Alfalfa Limestone Dicalcium phosphate Salt Microingredients DL-methionine Sand
67.36 21.00 2.50 6.04 2.30 .30 .50 a .05 .00
67.36 21.00 2.50 2.83 2.30 .30 .50 a .05 3.21
1.00
(%) 67.36 21.00 2.50 .89 2.30 .30 .50 a .05 5.15
Supplied the following quantities per kilogram of diet: vitamin A, 6600 IU; vitamin D 3 , 2200 1CU; menadione dimethylpyrimidinol bisulfite, 22 mg; riboflavin, 4.4 mg; pantothenic acid, 13.2 mg; niacin, 39.6 mg; choline chloride, 499.4 mg; vitamin B 1 2 , 22 meg; ethoxyquin, .0125%; manganese, 60 mg; iron, 50 mg; copper, 6 mg; cobalt, .0198 mg; iodine, 1.1 mg; zinc, 35 mg.
experiment for serum calcium determinations. Experiment 2. The procedure for Experiment 2 was similar to Experiment 1 except hens were 3 weeks older and experimental diets were fed for 5 days. Feces were collected from 25 hens from each group for 24 hours during the last day and analyzed for various minerals. Both tibias were removed from 25 hens from each group and bone ash, bone weight, and mineral content determined. Mineral determinations using the procedures as described by Stonerock et al. (1975) were made on the serum, feces, and tibia using an atomic absorption spectrophotometer. The data obtained were subjected to statistical analysis, and treatment significance was determined by the multiple range test of Duncan (1955) as modified by Kramer (1956). RESULTS AND DISCUSSION The level of calcium in the diet did not significantly affect feed consumption in old or young hens in Experiments 1 or 2 (Table 2). The hens consumed an average of 96 g/day in Experiment 1, and 100 g per day in Experiment 2. Reducing the level of dietary calcium from 3.00% to 1.75% or to 1.00% significantly reduced egg production in the young hens in both experiments (Table 2). Reducing the level of dietary calcium from 3.00% to 1.75% or to 1.00% had no significant effect on egg production from old hens. There were no significant
differences in egg production at each calcium level between the young and old hens in Experiment 1. However, in Experiment 2 the young hens fed the 3.00% calcium diet laid significantly more eggs than the old hens fed the same diet. In Experiment 1, reducing dietary calcium in the young hens reduced serum calcium 8.6 mg per 100 ml (Table 2). In the old hens, serum calcium was decreased 8.0 mg per 100 ml. The results of Experiment 2 were similar to Experiment 1, with serum calcium decreasing 8.9 mg per 100 ml in the young hens and 6.4 mg per 100 ml in the old hens. Reducing dietary calcium from 3.00% to 1.00% reduced serum calcium 25.9% more in the young hens than in the old hens. Egg weight was not significantly influenced by dietary treatment, but egg weight of old hens was significantly greater than that of young hens in all but one instance (Table 2). Egg specific gravity (Table 3) was either numerically or significantly decreased in young and old hens (Experiment 1 and 2) within 2 days after the calcium level of the diet had been reduced to 1.75% or to 1.00%. In Experiment 1, the egg specific gravity on day four was significantly reduced in the young birds 7 units or 13 units by reducing dietary calcium from 3.00% to 1.75% or to 1.00%, respectively. However, in the old hens, reducing the calcium level from 3.00% to 1.00% resulted in a decrease in egg specific gravity of only 7 units. In Experiment 2, the results were similar to
57.3 b 58.4 b =
1 2
Egg weight (g)
1.00%Ca 96.7* 100.0* 60.8b 66.7b 20.0 d 19.7= 57.2 b 57.9=
1.75% Ca 96.4* 104.2* 62.5b 70.7 b 22.8b= 25.9 b 56.9 b 59.1 b =
Voung hens (dietary treatment)
2
0 1 2 3 4 5
1.089* 1.090* 1.088* 1.086* 1.088* 1.089*
1.083* 1.084* 1.087* 1.086* 1.085*
3.00% Ca 1.085* 1.080 b 1.075=d 1.074b 1.072= 1.087* 1.080= 1.076= 1.073= 1.073= 1.067=
1.00% Ca
1.75% Ca
1.077b 1.079= 1.077= 1.074= 1.079b 1.080b
1.077b 1.074= 1.076= 1.076° 1.075 b
3.00%
Egg specific gravity
Values followed by different letters in the same row are significantly different (P<.05).
1
Experiment
Young hens (dietary treatment)
TABLE 3 .—The ability of young and old hens to maintain egg specific gravity when stressed wi for short periods of time
' ' c ' Values followed by different letters in the same row are significantly different (P<.05).
0 1 2 3 4
Day
a
28.6* 28.6*
1 2
Serum calcium (mg/100 ml)
78.5* 80.0*
1 2
Egg production (% hen/day)
94.8* 105.6*
3.00% Ca
1 2
Experiment
Feed consumption (g/hen/day)
Criteria
TABLE 2.—The relationship of hen age on response to induced calcium stress for sho
tint mm
2
0 1 2 3 4 5
1.75% Ca 5.14 a 4.97ab 4.84ab 5.00 a b 4.63bc 5.44 a b 5.15 b c 5.38 b 5.04 b 4.9 5 b 4.92 b
3.00% Ca
5.21 a 5.26 a 5.23 a 5.29 a 5.16 a
5.57 a 5.54 a 5.93 a S.61 a 5.48 a 5.83 a 5.39 a b 4.86 c 4.96 c 4.33° 4.40 c 4.38C
5.26 a 4 94ab 4.34 d 4.52bc 4.13d
1.00% Ca
1.07 b .38 b .41a 1.74 a .03 b
8.65 a .63 a .44 a 1.72 a .04 a
Calcium Sodium Magnesium Potassium Manganese
.48 b .25 c .35 b 1.62 a .02 c
1.00% Ca
Expressed as percentage of dry weight.
a.b.c Values followed by the different letters in the same row are significantly different (P<.05).
1.75% Ca
3.00% Ca
Element (%) d
Young birds
9.53 a .64 a .44 a 1.90 a .04 a
3.00% Ca
TABLES.--Fecal mineral content as influenced by hen age and calcium level (Experiment 2)
5.25 a 5.27 a 5.60 a 5.10 b 5.27 a 5.60 a
5.36 a 5.00 a 5.20 a 5.06 a 4.82 a
3.00%
Egg shell weight (g)
' ' ' Values followed by different letters in the same row are significaittly different (P<.05).
1
Experiment
0 1 2 3 4
Day
Young hens (dietary treatment)
TABLE 4.—The ability of young and old hens to maintain shell weight when stressed with for short periods of time
1620
ROLAND, SR. ET AL.
TABLE 6.—Relationship of bird age and induced calcium stress on tibia and bird weight (Experiment 2) Hen age
Calcium
Tibia weight
Tibia ash
(%)
(g)
(%)
Young
3.00 1.75 1.00
5.75a 4.86<=d 4.78cd
57.94b 56.49 c 55.03 d
Old
3.00 1.75 1.00
5.33b S.Olbc 4.64c
60.62 a 59.00 b 56.23 c d
' ' ' Values followed by different letters in the same column are significantly different (P<.05).
Experiment 1. Within 5 days, specific gravity decreased 22 units in the young hens and only 15 units in the old hens. The decrease in specific gravity was much greater in Experiment 2 than Experiment 1 because Experiment 2 was extended 1 day longer. The specific gravity of eggs laid by young hens decreased 59% more than that of eggs from old hens. Egg shell weight (Table 4) was either numerically or significantly decreased in young and old hens (Experiment 1 and 2) within 2 days after the calcium level of the diet had been reduced to 1.75% or to 1.00%. In Experiment 1, reducing dietary calcium for 4 days in the young hens reduced the egg shell weight 1.03 g. In the old hens, egg shell weight decreased .54
g. The results of Experiment 2 were similar to Experiment 1, with egg shell weight being significantly reduced 1.45 g in the young hens and 1.28 g in the old hens. Shell weight was reduced 36% more in young hens than in old hens. There were no significant differences in the percent calcium, magnesium, potassium or manganese content of the feces between the young and old hens (Table 5). The calcium content of the feces was reduced from 8.65% to 1.07% to .48% in the young hens by reducing the dietary calcium level. This was a decrease of 8.17 units. In the old hens, reducing dietary calcium resulted in a decrease of 9.02 units from 9.53% to .51%. In general, the percent of sodium, magnesium, and manganese in the feces decreased in young and old hens as the dietary calcium level decreased. No significant differences were observed in the potassium content of the feces in either young or old hens as a result of dietary treatment. Tibia weight and ash were significantly decreased in both young and old hens by reducing the calcium level of the diet from 3.00% to 1.00% (Table 6). Reducing dietary calcium had no significant effect on percent tibia calcium in either young or old hens within the same treatment (Table 7). Reducing dietary calcium from 3.00% to 1.00% significantly increased percent tibia sodium and potassium in young and old hens but had no significant influence on magnesium and manganese. Percent tibia magnesium was significantly lower in the old hens than in the young hens. When
TABLE 7 .—Relationship of hen age and induced calcium stress on tibia mineral content (Experiment 2) Mineral (%) e Hen age
Calcium
Calcium
Sodium
Potassium
Magnesium
Manganesef
Young
3.00 1.75 1.00
40.20ab 41.45a 40.75 a b
1.03b .96 c 1.14a
.54b .50cd .65 a
.67a .70a .69 a
2.00ab 2.00ab 1.89 b
Old
3.00 1.75 1.00
40.14 a b 40.09 a b 39.62 b
.90 c .93 c 1.02 b
.38d .47 c .63a
.56b .57b .61b
1.93 a b 2.00 a b 2.1ia
' ' ' Values followed by different letters in the same column are significantly different (P<.05). Expressed as percentage of ash. Value X 10" 3 .
RELATIONSHIP ON ABILITY OF HENS WHEN STRESSED WITH CALCIUM the dietary calcium was reduced from 3.00% to 1.75%, the percent sodium (young hens)and potassium (young and old hens) was significantly reduced. Results of these studies demonstrated that age had no adverse effect on the hens' ability to maintain egg shell quality when subjected to short periods of calcium stress. However, young hens appeared to be more sensitive than old hens. The response of old hens to calcium stress in terms of mineral content of feces and bone suggested that the decline in shell quality with hen age was not due to a decline in the hens' ability to absorb calcium or utilize skeletal calcium. REFERENCES Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1—42. Kramer, C. Y., 1956. Extension of multiple range tests
1621
to group means with unequal numbers of replications. Biometrics 12:307—310. Peterson, C. F., 1965. Factors influencing egg shell quality. World's Poultry Sci. J. 21:110-138. Roland, D. A., Sr., 1977. A re-evaluation and new approach to solving the shell quality problem. Poultry Digest 36(419): 1 7 - 1 8 . Roland, 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. Roland, D. A., Sr., D. R. Sloan, H. R. Wilson, and R. H. Harms, 1973. Influence of dietary calcium deficiency on yolk and serum calcium, yolk and organ weights and other selected production criteria of the pullet. Poultry Sci. 52:2220—2225. Roland, D. A., Sr., D. R. Sloan, H. R. Wilson, and R. H. Harms, 1974. Relationship of calcium to reproductive abnormalities in the laying hen (Gallus domesticus). J. Nutr. 104:1079-1085. Stonerock, R. H., D. A. Roland, Sr., and R. A. Voitle, 1975. Status of the digestive system and tibiae of cropectomized hens at night. Poultry Sci. 54:466-472.