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The Relationship of Clutch Position and Time Interval Between Eggs to Eggshell Quality*
The Relationship of Clutch Position and Time Interval Between Eggs to Eggshell Quality* L A W R E N C E R.
BERG
Division of Poultry Husbandry, Washington Agricultural Experiment Stations, Western Washington Experiment Station, Puyallup, Washington (Received for publication, May 31, 1945)
length to egg production. Atwood (1929a, 1929b) observed that the longer the cycle the shorter was the interval between the laying of successive eggs. He has also shown that the interval between the laying of the last two eggs of a cycle is usually greater than any other interval in the cycle, and that the intervals at or about the middle of the cycle are shorter than the intervals at either extremity. The observations of Atwood were confirmed by Heywang (1938). Warren and Scott (1935a, 193SV) have shown that the reason for differences in interval length between different birds can largely be accounted for by variations in the time the eggs remain in the uterine portion of the oviduct. They observed that eggs laid within 25 hours of the previously laid egg remained in the uterus 18.0 hours whereas an egg produced in 30 hours remained in the uterus 21.6 hours. Shell formation has been shown to be a function of the uterus. Asmundson and Burmester (1938) showed that resecting parts of the uterus would cause marked decreases in weight of shell produced. The rate of egg shell formation has been studied by Burmester, Scott, and Card (1939). * Published as Scientific Paper No. 644, College of Agriculture and Agricultural Experiment Stations, State College of Washington, Pullman.
These investigators found that the rate of calcium carbonate deposition on the egg is relatively slow during the first three hours the egg is in the uterus, and that after the third hour the rate of deposition increases quickly and assumes a constant figure which is maintained until the time of layingDuring the course of measuring the thickness of shells of eggs laid by the same bird over a period of time, the author observed considerable variation in the thickness of shells produced from one day to the next. I t was further noted that the shells of the first and last egg of clutches of three or more eggs were usually thicker than the intervening eggs. In summarizing data presented, Wilhelm (1940) concluded that there is little decrease in shell thickness between the first and last eggs of the same clutch of 1, 2, 3, and 4- egg clutches. Although he does not draw any conclusions from the fact, Wilhelm's data indicate that the first and last eggs of three and four egg clutches are thicker than the shells of the intervening eggs. Taylor and Lerner (1939) showed that the second egg of a clutch has a thinner shell than the first egg and that it is possible to eliminate the difference in thickness of shell of the two eggs by selective breeding. The review of the literature indicates that shell thickness of eggs laid by the
SSS
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investigators have studied SEVERAL the relationship of the cycle or clutch
556
LAWRENCE R. BERG
METHOD OF PROCEDURE
Five groups of birds were used to secure the data presented. Three of the groups consisted of 36 White Leghorn pullets each. The remaining two groups consisted of 36 White Leghorn hens in their second year of production, and 72 New Hampshire pullets, respectively. Observations for thickness and smoothness were made on all of the shells of the eggs produced by each group over a period of 30 days. Data on the interval of time elapsing from one oviposition to the next was recorded to within one-half hour for all of the eggs produced during the experimental period by three of the groups. Eggs for observation from the various groups were secured at different seasons of the year. The birds were maintained in individual batteries in the same house. All of the birds in any group received the same ration. Likewise the rations fed the various groups were essentially the same. The rations used were recommended laying ra-
tions, considered to be adquate in the factors known to affect shell quality. Shell thickness was measured on air dried shells, with membranes intact, which had been washed free of all adhering albumen at the time of breaking. The average thickness of each shell was determined by making three measurements at the equatorial plane of each shell by means of a micrometer having a convex anvil. Shell smoothness was scored by the method of Miller and Bearse (1934). The method employed gives an egg free of any calcareous nodules a score of 0 with scores of 1, 2, and 3 indicating an increasing magnitude of roughness. RESULTS
Clutch Position and Shell Thickness The averages of the data on shell thickness and smoothness obtained from each group of birds are presented in Table 1. The data indicate that a relationship exists between shell thickness and the position of the egg in the clutch. In two-egg clutches the shell of the second egg tended to be thicker than that of the first egg. The magnitude of difference was not the same with each group of birds studied, but the tendency existed in each case. Of all the two-egg clutches studied, 65.5 percent had thicker shells on the second egg, 28.2 percent were thicker on the first egg, and the shells were of the same thickness in 6.3 percent of the clutches. A study of 300 three-egg clutches shows that the shell of the first egg tended to be slightly thicker than that of the second egg, and that the shell of the third egg averaged thicker than that of either the first or second egg. In 43.2 percent of the clutches the shells of the first and third eggs were thicker than that of the second egg. Increasing magnitude of thickness from the first to the second to the third shell was observed in 21.2 percent of the
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same hen vary from day to day, the variation being partially due at least to the position of the egg in the clutch. Since the last egg in the clutch tends to have a thicker shell than the eggs intervening between the first and last egg, and since a longer time interval has been shown to elapse in forming the last egg, the extra time involved in laying eggs between two hens with different intervals of time being shown to be spent in the uterus, and since it has been shown that shell material is secreted during the entire time the egg is in the uterus, it may be hypothesized that the thickness of shells within a clutch is correlated with the time interval involved in the formation of each egg. Data are herein presented in support of this hypothesis. The effect of the position of the egg in the cycle on shell smoothness is also indicated.
Average (jf
6
W.L. W.L. W.L. W.L. N.H.
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W.L. W.L. W.L. W.L. N.H.
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pullets pullets hens pullets pullets
pullets pullets hens pullets pullets
pullets pullets hens pullets pullets
pullets pullets hens pullets pullets
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W.L. W.L. W.L. W.L. N.H.
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No. of eggs in clutch
Nov. Dec. Feb. March Nov.
Nov. Dec. Feb. March Nov.
Nov. Dec. Feb. March Nov.
Nov. Dec. Feb. March Nov.
Nov. Dec. Feb. March Nov.
23
8 6 1 3 5
55 .68 1.00 1.00 .70 .60 .76
36.4 36.4 39.0 36.1 34.0 36.0
.60 .67
37.0 37.7
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35.4
117
35.5
34.5 35.4 35.1 34.3 33.0
.61 .54 1.06 1.02 .59
35.9 37.0 35.4 35.7 33.7
21 24 17 20 35
1.23 .93
34.3
.73
34.6
300
35.6 32.3
35.1 34.7 35.9 34.7 33.0
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35.8 34.9 36.2 35.0 33.2
40 33 38 89 100
12 9 0 22 12
35.6
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34.7
447
34.4
33.7 35.1 36.3 35.7 33.3
34.4
34.8 31.3
35.5 35.8
34.3
35.3 36.0 36.8 35.3 34.8
.49 .49 .93 .92 .76
35.2 35.3 36.0 34.4 33.5
50 95 94 60 148
.93 .56 1.18 1.35 .91
34.0 35.3 35.0 34.5 32.8
.83
33.7
32.8 34.2 35.0 34.6 33.1 33.6
.96
33.4 34.8 35.3 35.1 31.9
.68 .60 1.00 1.20 1.10
34.3
34.1 31.3
35.6 36.8
35.8
35.9 37.2 36.1 35.8 34.8
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1.24
33.9
1.07
.78 .72 1.66 1.33
35.5 36.0
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.96
35.4
34.1
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35.8 36.1 36.5 35.7 34.3
34.3 30.2
1.48 1.00
.73 .61
.79
.67 .46 1.00 1.15 .79
.81
.61 .50 .91 1.06 .74
.91
.58 .68 1.10 1.10 .96
35.3 32.1 35.4 33.0 34.9 34.7 35.4 32.4 33.8
1.21 .93 1.00 1.50 1.30 1.10 1.06
36.8 37.9 1.57 1.13
.93 .83
.84
.74 .54 1.26 1.15 .74
.90
.68 .80 1.00 1.50 1.00
1.13
1.68 .83
.70 .78
35.5
34.8 37.1 37.0 36.5 33.7
1.02
.79 1.10 1.00 1.50 1.00
Month No. 1 2 3 4 ' 5 6 7 eggs of observed clutches Shell* Smooth Shell Smooth Shell Smooth Shell Smooth Shell Smooth Shell Smooth Shell Smooth thick score thick score thick score thick score thick score thick score thick score
Position of egg in clutch
TABLE 1.—Mean shell thickness and smoothness of successive eggs in clutches of different lengths
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clutches and in 11.3 percent of the clutches the shell of the second egg was thicker than the shell of either the first or third egg. The remaining clutches were distributed over the other six possible patterns. That the shells of the first and last egg of four-egg clutches averaged thicker than shells of the intervening eggs is indicated from a study of 117 four-egg clutches. The shell of the last egg tended to be slightly thicker than that of the first egg, and that of the second egg slightly thicker than that of the third egg. The shells of the first and last eggs were thicker than the shells of the second and third eggs in 57 percent of the clutches studied. The shells of the eggs in the other four-egg clutches followed no particular pattern, being well distributed among the 23 possible patterns. In five, six, and seven-egg clutches the shells of the first and last eggs averaged thicker than the shells of the intervening eggs. The shells of the second and fourth eggs of five-egg clutches were of practically the same thickness, and both were thicker than the shell of the third egg. In the six and seven-egg clutches shell thickness decreased until the next to the last egg. The shell of the second egg of these longer clutches, however, was thicker than the shell of the egg next to the last egg.
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EGGSHELL QUALITY ACCORDING TO CLUTCH POSITION AND TIME INTERVAL
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FIG. 1. Average shell thickness and time interval between eggs, of eggs laid in different positions within clutches of different lengths. * Figures on lines indicate average time interval between eggs.
EGGSHELL QUALITY ACCORDING TO CLUTCH POSITION AND T I M E INTERVAL
561
Time Interval and Shell Thickness Table 2 and Figure 1 present the average data on shell thickness obtained on the shells of the eggs for which the time interval was secured. The data indicate that increases or decreases in the time interval between eggs within a clutch is accompanied by corresponding increases or decreases in shell thickness. In order to determine if a correlation did exist between the changes in time interval and changes in shell thickness, the correlation between
Time Interval in Egg Formation
and the deviation in thickness of shells from the thickness of the shell of thefirstegg in the clutch
TABLE 3.—The correlation between time interval
The amount of time elapsing from one oviposition to the next when eggs were laid in different length clutches is presented in Table 2. Since the eggs were gathered every half-hour the time indicated should be on an average within IS minutes of the actual time elapsed. An average of 28.9 hours elapsed between the laying of the eggs in the two-egg clutches. The mean elapsed time for the second and third eggs of three-egg clutches was 26.7 and 28.1 hours, respectively. With each increasing length of clutch the time interval between eggs decreased. In the four-egg clutches there was an increasing time interval for each succeeding egg. The average amount of time elapsing between successive eggs in the 5, 6, and 7-egg clutches decreased until the next to the last egg, the time interval of the next to the last egg being slightly greater than that of the preceding egg and that of the last egg greater than for any of the other eggs. In the clutches of 3, 4, 5, 6, and 7 eggs more time elapsed in the formation of the last egg of the clutch than did in the formation of any of the other eggs succeeding the first egg.
Eggs in clutch
Degrees of freedom
Sample value ofr
3 4 S 6 7
428 218 158 57 40
.337 .330 .261 .316 .435
Value of r Value of r at 5 % atl% level level of sigof significance nificance .098 .138 .159 .258 .304
.128 .181 .208 .333 .393
time interval and the change in thickness of each shell from the thickness of the shell of the first egg of the clutch was determined for the eggs in the 3, 4, 5, 6, and 7egg clutches by the method of Snedecor (1937). Table 3 presents the sample value of r for each of the different length clutches. With the 3, 4, 5, and 7-egg clutches the sample value of r was highly significant and with the 6-egg clutches it was significant, indicating that differences in the thickness of egg shells of a bird may be due to differences in the time elapsed in formation of the eggs. DISCUSSION
The data presented indicate that the thickness of the shells of eggs will tend to vary according to the position of the egg
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Shell smoothness of the eggs in six-egg clutches followed a pattern similar to that of the five-egg clutches. No pattern for shell smoothness in seven egg-clutches is apparent from the few clutches available for study. In the four, five, and six-egg clutches it may be noted that the shells within the crutch became progressively rougher in the same manner that they became thinner. As shell thickness increased at or near the end of the clutch, the shells became smoother.
562
LAWRENCE R. BERG
One might speculate as to the reason why the shell of the first egg of a clutch of three or more eggs is thicker than the shells of the eggs intervening between the first and last egg. No information is available which would indicate that the time interval in formation of the first egg is any greater than for the succeeding eggs of the clutch. It is possible however that the first egg of the clutch does remain in the uterus for a longer period of time and as a result a thicker shell is formed. Another explanation may be similar to the one given by Conrad and Scott (1942) as to the reason for the increased size of the first egg of a clutch. These workers observed
that egg white'accumulates at a fairly constant rate between the times of passage of eggs through the magnum, and does so even when this period includes the pause between clutches. If the magnum functions in this manner it is possible that the uterus does also and that the increased shell thickness of the first egg of the longer clutches is due to the availability of increased amounts of shell forming material in the uterus as the egg is formed. If the uterus does form and store within its glands shell forming material during the period when no egg is present in the uterus it must be at a slower rate than when an egg is present. This is suggested by the fact that during the additional approximately two hours which the last egg of the clutch apparently spends in the uterus as much shell is deposited as might have accumulated in the 24-hour period of pause preceding the first egg of the clutch, as is indicated by the similar thickness of shells of the first and last eggs of the longer clutches. Wilhelm (1940) using the Chi square for independence test on his data concluded that shell thickness is not independent of egg weight, whereas Taylor and Lerner (1939) concluded that shell thickness is to a great degree independent of egg weight. Assuming that egg weight decreases with each succeeding egg in a clutch, the data herein reported, showing that the shells of the last egg of the clutch were thicker than that of the preceding egg, would tend to indicate that shell thickness is independent of egg weight. The data presented on the time interval between eggs within different length clutches confirm the data presented by Atwood (1929) and Heywang (1938) as to the relative amount of time elapsing between the laying of successive eggs in a clutch. The data also presents further evidence that the time interval between eggs
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within the clutch. From these results one may assume that in order to determine the mean shell thickness for a bird it is necessary to measure at least all of the shells produced in one clutch. The results of the experiment would tend to substantiate the contentions of Warren and Scott (1935a, 1935b) that the difference in interval length between eggs of different birds is due to variations in time the egg spends in the uterus, and of Burmester and co-workers (1939) that shell material is. deposited during the entire time the egg is present in the uterus. If the findings of these workers are correct it would be expected that the last egg of clutches of three or more eggs would be thicker than the other eggs succeeding the first egg because of the increased time which has been shown to elapse in the formation of the last egg. That the added time involved in the formation of the last egg of the clutch is spent in shell and not albumen formation is further suggested by the fact that egg size has been shown by Bennion and Warren (1933) and Wilhelm (1940) to decrease with each succeeding egg in a clutch and not to increase with the last egg as shell thickness tends to do.
EGGSHELL QUALITY ACCORDING TO CLUTCH POSITION AND TIME INTERVAL
decreases as the length of the clutch increases. Heywang also observed a highly significant difference between the Leghorn and Rhode Island Red birds which he studied in the mean of all time intervals between the laying of successive eggs, the Leghorns having the greater time interval. No such difference was noted between the New Hampshire and White Leghorn birds used in the present study. SUMMARY
clutches the shells tended to become rougher with the first three or four eggs and then slightly smoother with the last one or two eggs of the clutch. LITERATURE CITED
Asmundson, V. S., and B. R. Burmester, 1938. The effect of resecting a part of the uterus on the formation of the hen's egg. Poultry Sci. 17:126-130. Atwood, Horace, 1929a. Observations concerning the time factor in egg production. Poultry Sci. 8: 137-140. , 1929b. A study of the time factor in egg production. West Virginia Agr. Exp. Sta. Bui. 223: 3-11. Bennion, Noel L., and D. C. Warren, 1933. Some factors affecting egg size in the domestic fowl. Poultry Sci. 12:362-367. Burmester, B. R.,H. M. Scott, andL. E. Card, 1939. Rate of egg shell formation in the hen. Proceedings of the seventh world's poultry congress and exposition, pp. 99-101. Conrad, R. M., a n d H . M. Scott, 1942. The accumulation of protein in the oviduct of the fowl. Poultry Sci. 21:81-85. Heywang, Burt W., 1938. The time factor in egg production. Poultry Sci. 17:240-247. Miller, M. W., and G. E. Bearse, 1934. Phosphorus requirements of laying hens. Wash. Agr. Exp. Sta. Bull. 306:5-20. Snedecor, G. W., 1937. Statistical Methods. Collegiate Press Inc., Ames, Iowa. Taylor, Lewis W., and I. Michael Lerner, 1939. Inheritance of eggshell thickness in White Leghorn pullets. Jour. Agr. Res. 58:383-396. Warren, D. C , and H . M. Scott, 1935a. The time factor in egg formation. Poultry Sci. 14:195-207. , 1935b. Physiological factors influencing the rate of egg formation in the domestic hen. Jour. Agr. Res. 51:565-572. Wilhelm, L. A., 1940. Some factors affecting variations in egg shell quality. Poultry Sci. 19:246253.
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A study has been made of the relationship of the position of the egg within a clutch and of the time elapsing from one oviposition to the next to shell thickness and smoothness. The data presented indicate that shell thickness varies according to the position of the egg within the clutch. The shell of the second egg of the two egg clutches studied was thicker than that of the first egg. In clutches of three or more eggs the shells of the first and last eggs were thicker than those of the intervening eggs. Data and discussion are presented to indicate that the last egg of the longer clutches has a thicker shell than that of the eggs intervening between the first and last eggs because of an increased period of time which the last egg spends in the uterus. The shells of the first egg of the clutch were smoother than other eggs in the clutch. In two and three-egg clutches the shells became rougher as the position in the clutch advanced. In 4, 5, and 6-egg
563
BERG
Division of Poultry Husbandry, Washington Agricultural Experiment Stations, Western Washington Experiment Station, Puyallup, Washington (Received for publication, May 31, 1945)
length to egg production. Atwood (1929a, 1929b) observed that the longer the cycle the shorter was the interval between the laying of successive eggs. He has also shown that the interval between the laying of the last two eggs of a cycle is usually greater than any other interval in the cycle, and that the intervals at or about the middle of the cycle are shorter than the intervals at either extremity. The observations of Atwood were confirmed by Heywang (1938). Warren and Scott (1935a, 193SV) have shown that the reason for differences in interval length between different birds can largely be accounted for by variations in the time the eggs remain in the uterine portion of the oviduct. They observed that eggs laid within 25 hours of the previously laid egg remained in the uterus 18.0 hours whereas an egg produced in 30 hours remained in the uterus 21.6 hours. Shell formation has been shown to be a function of the uterus. Asmundson and Burmester (1938) showed that resecting parts of the uterus would cause marked decreases in weight of shell produced. The rate of egg shell formation has been studied by Burmester, Scott, and Card (1939). * Published as Scientific Paper No. 644, College of Agriculture and Agricultural Experiment Stations, State College of Washington, Pullman.
These investigators found that the rate of calcium carbonate deposition on the egg is relatively slow during the first three hours the egg is in the uterus, and that after the third hour the rate of deposition increases quickly and assumes a constant figure which is maintained until the time of layingDuring the course of measuring the thickness of shells of eggs laid by the same bird over a period of time, the author observed considerable variation in the thickness of shells produced from one day to the next. I t was further noted that the shells of the first and last egg of clutches of three or more eggs were usually thicker than the intervening eggs. In summarizing data presented, Wilhelm (1940) concluded that there is little decrease in shell thickness between the first and last eggs of the same clutch of 1, 2, 3, and 4- egg clutches. Although he does not draw any conclusions from the fact, Wilhelm's data indicate that the first and last eggs of three and four egg clutches are thicker than the shells of the intervening eggs. Taylor and Lerner (1939) showed that the second egg of a clutch has a thinner shell than the first egg and that it is possible to eliminate the difference in thickness of shell of the two eggs by selective breeding. The review of the literature indicates that shell thickness of eggs laid by the
SSS
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investigators have studied SEVERAL the relationship of the cycle or clutch
556
LAWRENCE R. BERG
METHOD OF PROCEDURE
Five groups of birds were used to secure the data presented. Three of the groups consisted of 36 White Leghorn pullets each. The remaining two groups consisted of 36 White Leghorn hens in their second year of production, and 72 New Hampshire pullets, respectively. Observations for thickness and smoothness were made on all of the shells of the eggs produced by each group over a period of 30 days. Data on the interval of time elapsing from one oviposition to the next was recorded to within one-half hour for all of the eggs produced during the experimental period by three of the groups. Eggs for observation from the various groups were secured at different seasons of the year. The birds were maintained in individual batteries in the same house. All of the birds in any group received the same ration. Likewise the rations fed the various groups were essentially the same. The rations used were recommended laying ra-
tions, considered to be adquate in the factors known to affect shell quality. Shell thickness was measured on air dried shells, with membranes intact, which had been washed free of all adhering albumen at the time of breaking. The average thickness of each shell was determined by making three measurements at the equatorial plane of each shell by means of a micrometer having a convex anvil. Shell smoothness was scored by the method of Miller and Bearse (1934). The method employed gives an egg free of any calcareous nodules a score of 0 with scores of 1, 2, and 3 indicating an increasing magnitude of roughness. RESULTS
Clutch Position and Shell Thickness The averages of the data on shell thickness and smoothness obtained from each group of birds are presented in Table 1. The data indicate that a relationship exists between shell thickness and the position of the egg in the clutch. In two-egg clutches the shell of the second egg tended to be thicker than that of the first egg. The magnitude of difference was not the same with each group of birds studied, but the tendency existed in each case. Of all the two-egg clutches studied, 65.5 percent had thicker shells on the second egg, 28.2 percent were thicker on the first egg, and the shells were of the same thickness in 6.3 percent of the clutches. A study of 300 three-egg clutches shows that the shell of the first egg tended to be slightly thicker than that of the second egg, and that the shell of the third egg averaged thicker than that of either the first or second egg. In 43.2 percent of the clutches the shells of the first and third eggs were thicker than that of the second egg. Increasing magnitude of thickness from the first to the second to the third shell was observed in 21.2 percent of the
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same hen vary from day to day, the variation being partially due at least to the position of the egg in the clutch. Since the last egg in the clutch tends to have a thicker shell than the eggs intervening between the first and last egg, and since a longer time interval has been shown to elapse in forming the last egg, the extra time involved in laying eggs between two hens with different intervals of time being shown to be spent in the uterus, and since it has been shown that shell material is secreted during the entire time the egg is in the uterus, it may be hypothesized that the thickness of shells within a clutch is correlated with the time interval involved in the formation of each egg. Data are herein presented in support of this hypothesis. The effect of the position of the egg in the cycle on shell smoothness is also indicated.
Average (jf
6
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pullets pullets hens pullets pullets
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Nov. Dec. Feb. March Nov.
Nov. Dec. Feb. March Nov.
Nov. Dec. Feb. March Nov.
Nov. Dec. Feb. March Nov.
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23
8 6 1 3 5
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36.4 36.4 39.0 36.1 34.0 36.0
.60 .67
37.0 37.7
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35.4
117
35.5
34.5 35.4 35.1 34.3 33.0
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35.9 37.0 35.4 35.7 33.7
21 24 17 20 35
1.23 .93
34.3
.73
34.6
300
35.6 32.3
35.1 34.7 35.9 34.7 33.0
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35.8 34.9 36.2 35.0 33.2
40 33 38 89 100
12 9 0 22 12
35.6
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34.7
447
34.4
33.7 35.1 36.3 35.7 33.3
34.4
34.8 31.3
35.5 35.8
34.3
35.3 36.0 36.8 35.3 34.8
.49 .49 .93 .92 .76
35.2 35.3 36.0 34.4 33.5
50 95 94 60 148
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34.0 35.3 35.0 34.5 32.8
.83
33.7
32.8 34.2 35.0 34.6 33.1 33.6
.96
33.4 34.8 35.3 35.1 31.9
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34.3
34.1 31.3
35.6 36.8
35.8
35.9 37.2 36.1 35.8 34.8
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1.24
33.9
1.07
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35.5 36.0
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.96
35.4
34.1
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35.8 36.1 36.5 35.7 34.3
34.3 30.2
1.48 1.00
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.79
.67 .46 1.00 1.15 .79
.81
.61 .50 .91 1.06 .74
.91
.58 .68 1.10 1.10 .96
35.3 32.1 35.4 33.0 34.9 34.7 35.4 32.4 33.8
1.21 .93 1.00 1.50 1.30 1.10 1.06
36.8 37.9 1.57 1.13
.93 .83
.84
.74 .54 1.26 1.15 .74
.90
.68 .80 1.00 1.50 1.00
1.13
1.68 .83
.70 .78
35.5
34.8 37.1 37.0 36.5 33.7
1.02
.79 1.10 1.00 1.50 1.00
Month No. 1 2 3 4 ' 5 6 7 eggs of observed clutches Shell* Smooth Shell Smooth Shell Smooth Shell Smooth Shell Smooth Shell Smooth Shell Smooth thick score thick score thick score thick score thick score thick score thick score
Position of egg in clutch
TABLE 1.—Mean shell thickness and smoothness of successive eggs in clutches of different lengths
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558 oo th core
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clutches and in 11.3 percent of the clutches the shell of the second egg was thicker than the shell of either the first or third egg. The remaining clutches were distributed over the other six possible patterns. That the shells of the first and last egg of four-egg clutches averaged thicker than shells of the intervening eggs is indicated from a study of 117 four-egg clutches. The shell of the last egg tended to be slightly thicker than that of the first egg, and that of the second egg slightly thicker than that of the third egg. The shells of the first and last eggs were thicker than the shells of the second and third eggs in 57 percent of the clutches studied. The shells of the eggs in the other four-egg clutches followed no particular pattern, being well distributed among the 23 possible patterns. In five, six, and seven-egg clutches the shells of the first and last eggs averaged thicker than the shells of the intervening eggs. The shells of the second and fourth eggs of five-egg clutches were of practically the same thickness, and both were thicker than the shell of the third egg. In the six and seven-egg clutches shell thickness decreased until the next to the last egg. The shell of the second egg of these longer clutches, however, was thicker than the shell of the egg next to the last egg.
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In the two and three-egg clutches observed the shells had a tendency to become rougher as the position in the clutch advanced. The same relationship held true for the first three eggs of the four-egg clutches. The fourth egg was, however, on an average smoother than the third egg. The first three eggs in five-egg clutches tended to become rougher with each succeeding egg. The fourth and fifth eggs averaged smoother than the third egg but were rougher than the first and second eggs.
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EGGSHELL QUALITY ACCORDING TO CLUTCH POSITION AND TIME INTERVAL
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FIG. 1. Average shell thickness and time interval between eggs, of eggs laid in different positions within clutches of different lengths. * Figures on lines indicate average time interval between eggs.
EGGSHELL QUALITY ACCORDING TO CLUTCH POSITION AND T I M E INTERVAL
561
Time Interval and Shell Thickness Table 2 and Figure 1 present the average data on shell thickness obtained on the shells of the eggs for which the time interval was secured. The data indicate that increases or decreases in the time interval between eggs within a clutch is accompanied by corresponding increases or decreases in shell thickness. In order to determine if a correlation did exist between the changes in time interval and changes in shell thickness, the correlation between
Time Interval in Egg Formation
and the deviation in thickness of shells from the thickness of the shell of thefirstegg in the clutch
TABLE 3.—The correlation between time interval
The amount of time elapsing from one oviposition to the next when eggs were laid in different length clutches is presented in Table 2. Since the eggs were gathered every half-hour the time indicated should be on an average within IS minutes of the actual time elapsed. An average of 28.9 hours elapsed between the laying of the eggs in the two-egg clutches. The mean elapsed time for the second and third eggs of three-egg clutches was 26.7 and 28.1 hours, respectively. With each increasing length of clutch the time interval between eggs decreased. In the four-egg clutches there was an increasing time interval for each succeeding egg. The average amount of time elapsing between successive eggs in the 5, 6, and 7-egg clutches decreased until the next to the last egg, the time interval of the next to the last egg being slightly greater than that of the preceding egg and that of the last egg greater than for any of the other eggs. In the clutches of 3, 4, 5, 6, and 7 eggs more time elapsed in the formation of the last egg of the clutch than did in the formation of any of the other eggs succeeding the first egg.
Eggs in clutch
Degrees of freedom
Sample value ofr
3 4 S 6 7
428 218 158 57 40
.337 .330 .261 .316 .435
Value of r Value of r at 5 % atl% level level of sigof significance nificance .098 .138 .159 .258 .304
.128 .181 .208 .333 .393
time interval and the change in thickness of each shell from the thickness of the shell of the first egg of the clutch was determined for the eggs in the 3, 4, 5, 6, and 7egg clutches by the method of Snedecor (1937). Table 3 presents the sample value of r for each of the different length clutches. With the 3, 4, 5, and 7-egg clutches the sample value of r was highly significant and with the 6-egg clutches it was significant, indicating that differences in the thickness of egg shells of a bird may be due to differences in the time elapsed in formation of the eggs. DISCUSSION
The data presented indicate that the thickness of the shells of eggs will tend to vary according to the position of the egg
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Shell smoothness of the eggs in six-egg clutches followed a pattern similar to that of the five-egg clutches. No pattern for shell smoothness in seven egg-clutches is apparent from the few clutches available for study. In the four, five, and six-egg clutches it may be noted that the shells within the crutch became progressively rougher in the same manner that they became thinner. As shell thickness increased at or near the end of the clutch, the shells became smoother.
562
LAWRENCE R. BERG
One might speculate as to the reason why the shell of the first egg of a clutch of three or more eggs is thicker than the shells of the eggs intervening between the first and last egg. No information is available which would indicate that the time interval in formation of the first egg is any greater than for the succeeding eggs of the clutch. It is possible however that the first egg of the clutch does remain in the uterus for a longer period of time and as a result a thicker shell is formed. Another explanation may be similar to the one given by Conrad and Scott (1942) as to the reason for the increased size of the first egg of a clutch. These workers observed
that egg white'accumulates at a fairly constant rate between the times of passage of eggs through the magnum, and does so even when this period includes the pause between clutches. If the magnum functions in this manner it is possible that the uterus does also and that the increased shell thickness of the first egg of the longer clutches is due to the availability of increased amounts of shell forming material in the uterus as the egg is formed. If the uterus does form and store within its glands shell forming material during the period when no egg is present in the uterus it must be at a slower rate than when an egg is present. This is suggested by the fact that during the additional approximately two hours which the last egg of the clutch apparently spends in the uterus as much shell is deposited as might have accumulated in the 24-hour period of pause preceding the first egg of the clutch, as is indicated by the similar thickness of shells of the first and last eggs of the longer clutches. Wilhelm (1940) using the Chi square for independence test on his data concluded that shell thickness is not independent of egg weight, whereas Taylor and Lerner (1939) concluded that shell thickness is to a great degree independent of egg weight. Assuming that egg weight decreases with each succeeding egg in a clutch, the data herein reported, showing that the shells of the last egg of the clutch were thicker than that of the preceding egg, would tend to indicate that shell thickness is independent of egg weight. The data presented on the time interval between eggs within different length clutches confirm the data presented by Atwood (1929) and Heywang (1938) as to the relative amount of time elapsing between the laying of successive eggs in a clutch. The data also presents further evidence that the time interval between eggs
Downloaded from http://ps.oxfordjournals.org/ by guest on June 6, 2015
within the clutch. From these results one may assume that in order to determine the mean shell thickness for a bird it is necessary to measure at least all of the shells produced in one clutch. The results of the experiment would tend to substantiate the contentions of Warren and Scott (1935a, 1935b) that the difference in interval length between eggs of different birds is due to variations in time the egg spends in the uterus, and of Burmester and co-workers (1939) that shell material is. deposited during the entire time the egg is present in the uterus. If the findings of these workers are correct it would be expected that the last egg of clutches of three or more eggs would be thicker than the other eggs succeeding the first egg because of the increased time which has been shown to elapse in the formation of the last egg. That the added time involved in the formation of the last egg of the clutch is spent in shell and not albumen formation is further suggested by the fact that egg size has been shown by Bennion and Warren (1933) and Wilhelm (1940) to decrease with each succeeding egg in a clutch and not to increase with the last egg as shell thickness tends to do.
EGGSHELL QUALITY ACCORDING TO CLUTCH POSITION AND TIME INTERVAL
decreases as the length of the clutch increases. Heywang also observed a highly significant difference between the Leghorn and Rhode Island Red birds which he studied in the mean of all time intervals between the laying of successive eggs, the Leghorns having the greater time interval. No such difference was noted between the New Hampshire and White Leghorn birds used in the present study. SUMMARY
clutches the shells tended to become rougher with the first three or four eggs and then slightly smoother with the last one or two eggs of the clutch. LITERATURE CITED
Asmundson, V. S., and B. R. Burmester, 1938. The effect of resecting a part of the uterus on the formation of the hen's egg. Poultry Sci. 17:126-130. Atwood, Horace, 1929a. Observations concerning the time factor in egg production. Poultry Sci. 8: 137-140. , 1929b. A study of the time factor in egg production. West Virginia Agr. Exp. Sta. Bui. 223: 3-11. Bennion, Noel L., and D. C. Warren, 1933. Some factors affecting egg size in the domestic fowl. Poultry Sci. 12:362-367. Burmester, B. R.,H. M. Scott, andL. E. Card, 1939. Rate of egg shell formation in the hen. Proceedings of the seventh world's poultry congress and exposition, pp. 99-101. Conrad, R. M., a n d H . M. Scott, 1942. The accumulation of protein in the oviduct of the fowl. Poultry Sci. 21:81-85. Heywang, Burt W., 1938. The time factor in egg production. Poultry Sci. 17:240-247. Miller, M. W., and G. E. Bearse, 1934. Phosphorus requirements of laying hens. Wash. Agr. Exp. Sta. Bull. 306:5-20. Snedecor, G. W., 1937. Statistical Methods. Collegiate Press Inc., Ames, Iowa. Taylor, Lewis W., and I. Michael Lerner, 1939. Inheritance of eggshell thickness in White Leghorn pullets. Jour. Agr. Res. 58:383-396. Warren, D. C , and H . M. Scott, 1935a. The time factor in egg formation. Poultry Sci. 14:195-207. , 1935b. Physiological factors influencing the rate of egg formation in the domestic hen. Jour. Agr. Res. 51:565-572. Wilhelm, L. A., 1940. Some factors affecting variations in egg shell quality. Poultry Sci. 19:246253.
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A study has been made of the relationship of the position of the egg within a clutch and of the time elapsing from one oviposition to the next to shell thickness and smoothness. The data presented indicate that shell thickness varies according to the position of the egg within the clutch. The shell of the second egg of the two egg clutches studied was thicker than that of the first egg. In clutches of three or more eggs the shells of the first and last eggs were thicker than those of the intervening eggs. Data and discussion are presented to indicate that the last egg of the longer clutches has a thicker shell than that of the eggs intervening between the first and last eggs because of an increased period of time which the last egg spends in the uterus. The shells of the first egg of the clutch were smoother than other eggs in the clutch. In two and three-egg clutches the shells became rougher as the position in the clutch advanced. In 4, 5, and 6-egg
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