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The Correlation Between Age at the Laying of the First Egg and the Weight of Eggs During the First Laying Year in White Leghorns*
POULTRY SCIENCE VOL. I V
A P E I L - M A Y , 1925
No. 4
WILLIAM A. LIPPINCOTT, SYLVIA L. PARKER AND LUBLLA M. SCHAUMBURG I t was shown i n a n earlier p a p e r , (Lippincott, 1921)^ t h a t the correlation between age at the laying of the first egg a n d the mean weight of the first ten eggs laid by each of 123 Single Comb W h i t e Leghorn pullets was of a high order (r = 0.7139 ± .0293). Quite recently J u U (1924)^ has calculated the same correlation for 40 B a r r e d P l y m o u t h Rock pullets and found t h a t r = 0.845 ±: 0.030. D a t a are now available upon which to calculate the correla tion between age at the l a y i n g of the first egg a n d the m e a n weight of eggs laid d u r i n g each successive t h i r t y - d a y period of the 360 days following the onset of laying, for 60 Single Comb W h i t e Leghorns. MATERIAL
The birds serving as the source of these d a t a belonged to the pedigreed a n d somewhat inbred flock of K a n s a s State Agricul t u r a l College. They comprised a selected group, from an original flock of 124 pullets which was systematically culled on the basis of vigor and production d u r i n g the last four periods covered in * Contribution No. 28 from the Department of Poultry Husbandry, Kansas Agricultural Experiment Station, and No. 1 from the Division of Poultry Husbandry, University of California, Agricultural Experiment Station. 1 Lippincott, W. Α., 1921, Preliminary note on the correlation between age at first laying and size of first eggs in pullets. Jour. Amer. Assn's Instr. Invest. Poultry Husbandry, 7:73-74. 2 JuU, M. Α., 1924, Egg weight in relation to production. II. The na ture and causes of changes in egg weight in relation to annual produc tion in pullets. POULTRY SCIENCE, 3:153-172. 127
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THE CORRELATION B E T W E E N AGE AT T H E LAYING OF T H E FIRST EGG AND T H E W E I G H T OF EGGS DURING THE FIRST LAYING YEAR IN W H I T E LEGHORNS*
128
POULTRY SCIENCE
METHOD OP RECORDING AND TABUDATING DATA
Every egg laid by each individual was weighed and the weight recorded to the nearest 0.5 gram. The mean egg weight for each bird for each 30 day period and for the entire 360 days was then calculated. In making up the correlation tables, the class range used for weight was 5 grams, for age 25 days, and for production 50 eggs. Tables were also made using finer groupings, 2 grams for weight, 10 days for age, and 25 eggs for production, but since none of the coefficients differed appreciably from those calculated with coarser groupings, the more condensed tables are presented. The probable errors of all the constants, including the mean egg weights, are on the basis of the number of birds, rather than the number of eggs, as N, since it is the one measure of age at. first egg that determines in which group a bird is placed. As Harris (1914)^ has stated it, "the degree of trustΛvorthiness of a con stant is perhaps not greater than is indicated by the lowest num ber of actual measurements, irrespective of the number of as sociated measures taken. ' ' RESULTS
The correlation coefficients relating age at first egg and mean weight of eggs for the twelve periods are presented in Table I, together with the mean egg weights of all the eggs for each period, and the mean egg production. The twelve correlation Tables from which the coefficients were computed are included as Tables X to X X I at the end of the report. It will be noted from Table I that the correlation is quite high for the first two periods. It is progressively lower, but still probably significant, for the next three periods. During the sixth to the ninth periods, inclusive, the coefficient becomes prae3 Harris, J. Α., 1914, The relationship between the weight of the seed planted and the characteristics of the plant produced. II. Biometrika, 10:72-84.
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this report. The total production for the sixty pullets was 11,902 eggs, or a mean production per individual for' 360 days of 198.37 ± 3.96 eggs. The birds were all hatched between the third week in March and the middle of May, 1921, and showed no correlation between the date of hatching and age at the lay ing of the first egg, ( r = . 0 0 8 ^ .087). The average age at which they began to lay was 194.17 ± 1.89 days, and the average weight of all the eggs was 52.19 i .35 grams.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
129
TABLE I—CORRÉLATION BETWEEN A G E AT F I R S T EGG AND M E A N W E I G H T OF EGGS, MEAN W E I G H T OF EGGS, AND MEAN EGG PRODUCTION BY T H I R T Y DAY PERIODS, FOR SIXTY SINGLE COMB W H I T E LEGHORNS Mean AVeight of E g g s
Coefficient of Correlation
.666 ± .649 ± .428 ± .314 ± .304 ± .079 ± .196 ± .096 ± .233 ± .371 ± .483 ± .437 ±
1 2 3 4 5 6 7 S 9 10 11 12
46.49 ± 50.07 ± 52.31 ± 53.82 ± 53.85 ± 54.02 ± 52.81 ± 52.38 ± 51.62 ± 52.05 ± 52.58 ± 54.18 ±
.048 .052 .072 .081 .079 .087 .084 .086 .084 .076 .067 .070
.447 ± .071
360 Days
Mean E g g Production
.44 .40 .39 .38 .34 .37 .39 .40 .41 .43 .54 .55
16.90 ± 15.63 ± 16.98 ± 15.53 ± 18.78 ± 19.63 ± 19.55 ± 17.60 ± 15.35 ± 15.25 ± 14.75 ± 12.40 ±
52.19 ± .35
.55 .64 .56 .60 .49 .64 .43 .52 .55 .52 .53 .56
198.37 ± 3.96
tically zero, while in the last three periods it again rises to a significant positive correlation. The relation of the degree of correlation to the mean egg production in the respective periods is shown graphically in
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FIGURE 1—Showing the periodic v a r i a t i o n in t h e correlation between age a t first egg and t h e mean weight of eggs, a n d in the mean egg pro duction for 60 S. C. W h i t e Leghorn pullets.
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Thirty Day Period
POULTRY
130
SCIENCE
TABLE I I — M E A N JEGG "WEIGHTS FOB SIXTY SINGI^E COMB W H I T E LEGHORNS, CLASSIFIED BY AGE AT F I R S T EGG AND BY 30 DAY LAYING PERIODS AGE I N DAYS AT F I R S T EGG Period
151-
176-
201-
226-
251-
1 2 3 i 5 6 7 8 9 10 11 12
41.22±.57 45.41±.32 50.01±.35 51.57it.42 52.76±.45 52.92±.47 51.23±.54 51.69±:.60 50.00±.65 49.95±.57 48.19±.88 49.17±.90
44.77±.49 48.77±.51 51.20±.47 52.57d=.55 53.53±.49 53.36±.48 52.33±.51 51.73±.51 50.81±.54 50.97±.53 50.58±.65 52.91±.65
49.51± .68 52.69± .69 54.86-t- .80 56.00± .80 56.08-1- .81 55.96± .99 54.61±1.08 52.72-1-1.21 53.12-t-l.06 53.04-4-1.11 54.77±1.40 57.59 + 1.25
53.03±.32 54.82-^-.68 56.70-1-.53 56.90±.60 57.07-i-.47 56.07±.83 55.27±.77 55.45-i-.59 55.55-1-.37 57.10dz.16 60.37±.48 60.87±.42
52.70±2.18 54.60±1.96 54.55±1.07 53.95±1.21 52.85±1.31 49.55+1.79 49.00± .95 48.95± .79 50.45± .50 53.00± .29 54.55± .21 55.05± .93
360 Days
49.82±.44
51.39±.47
54.26± .74
56.44±.31
52.66±1.04
The data of Table I I are shown graphically in Figure 2. The drop in mean egg weight in the group over 251 days old at first egg, while significant in most of the periods, when tested by the probable errors, is based on two birds only. The curve of egg weights of these two birds is, therefore, not included in Figure 2, as it would merely confuse the other curves and is based on too small a number of birds to be trustworthy. Figure 2 shows that the birds which began laying at earlier ages never laid eggs which were as large on the average as the eggs of later maturing birds for the corresponding period.
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Figure 1. In a general way it appears that the correlation between the mean weight of eggs and the age of the pullet at first laying exhibits a periodic variation which is the inverse of the curve of variation in egg production. Table I I gives the mean egg weight for the sixty pullets classified both by age at first egg and by period, and Table I I I the regression lines fitted to these observed regression means. The main point brought out by both Tables is that during the first few and last few periods, for every addition of 25 days in age at first egg, there is an increase of about 3 grams in mean egg weight, or more than an ounce per dozen, which is a commercially important difference. Through the middle periods, however, the regression lines become nearly horizontal.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
131
Figure 3 shows the same curves as Figure 2, but each successive curve set ahead a twenty-five day interval so that mean egg weights for the four groups of birds are plotted against the
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FiGtTRE 2—Showing t h e periodic variations in mean egg weights of birds classified by age at first egg. TABLE I I I — P I T T E D REGKESSION L I N E S FOR GROUP OF SIXTY SINGLE COMB W H I T E LEGHORNS
Régression of Egg Weight on Age at First Egg
Period
W W W W W W W "W W W
1 2 3 4 5 6 7 8 9 10 11 12 360 Days W: A:
= = = = = = = = = ==
w = w = w =
.1433A .1524A .0794A .0549A .0500A .0140A .0373A .0187A .0455A .0766A .1269A .1172A
-f -1-f + -f -1-\+ -1+ + +
.0858A +
17.95 20.26 36.83 42.82 44.74 51.15 45.72 48.06 42.77 36.87 27.12 30.90 35.06
: predicted egg weiglit In grams. = actual age in days at la.ving of the first egg.
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POULTRY
132
SCIENCE
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FIGURE 3—Showing the age and seasonal variations in mean egg weights of birds classified by age at first egg.
Figure 3 indicates that in this group of sixty Single Comb White Leghorns, age at laying of the first egg was an important factor in the course of the age and seasonal distribution of egg weight. It would be very interesting to have more extensive data on the relationships and to have the curves carried on into the later years' production. Table IV summarizes the correlation coefficients for the entire 360 day period, computed from Tables VII to IX, and compares them with the corresponding coefficients for the forty Barred Plymouth Eocks analyzed by Jul! in the paper already noted. The correlation between age at first egg and mean weight of all eggs is positive and significant ( r = . 4 4 7 ± .071). This is
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average age of birds and against average date of laying of eggs. The latter two scales coincide because it was found that the average date of hatching was the same for each group of birds, so that seasonal effect and age effect in this experiment cannot be separated. These effects might be separated for a few individual birds within a group, but there were not enough such birds to make the comparisons significant.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
133
TABLE IV — COERELATION COEFFICIENTS FOR GROUP OF SIXTY SINGLE COMB W H I T E LEGHORNS, COMPARED W I T H GROUP OF F O R T Ï BARRED P L Ï M O U T H ROCKS
( D a t a of
Jul!)
Mean egg weight and age at first egg Total production and age at first egg Total production and mean egg weight Egg wt. and age, with production constant Production and age, with egg wt. constant Production and egg wt., with age constant
60 Single Comb White Leghorns
40 Barred Plymouth Eocks (Jull)
+.447±.071 + .359±.076 + .330±.078 + .373±.075 + .250+.082 + .206±.083
+ .548+.075 —.295±.097 —.019 ±.107 + .568±.072 —.340±.094 + .178±.103
not quite so high as the coefficient found by Jull, but is of the same general order. The correlation between age at first egg and total production is also positive and significant, (r^.359±.076). This result is directly contrary to that found by Jull, Rice (1915),* Hays et al (1923 and 1924),= and other workers, and to the belief generally held by practical breeders, in the efficacy of early maturity as a point of selection in breeding for high egg production. Since the four remaining correlation coefficients are combinations of the same three variables, the further differences in Table IV all follow from this primary one. Because of this difference it has seemed best to examine the data of the entire original group of 124 birds as far as they are available, to determine in so far as possible to what extent the various constants for the selected group are representative of the entire flock. Since the culled birds were not discarded until within the last four periods, it is possible to compare the correlation between age at first egg and total production for 240 days for the two groups of birds. The 60 selected pullets gave a correlation for the 240 days practically identical with that for 360 days, (r = .362 =t .076), while the coefficient for the culled birds, though not statistically significant, is comparable to that obtained by other workers, (r = —.188 i t .084). The difference * Rice, J. E., 1915, T h e distrihution of egg production, Cornell Countryman, 12:5-8 5 Hays, P . Α., and Bennett, J. S., 1923, Correlation of sexual m a t u r i t y to a n n u a l egg record. POULTRY SCIENCE, 2:205-206. Hays, F . Α., San born, R., and J a m e s , L·. L·., 1924, Correlation studies on winter fecun dity, Mass. Agr. Exp. Sta. Bui., 220:44-53.
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Correlation Coefficients Variables Correlated
POULTRY
134
SCIENCE
TABLE V — S A M E DATA AS I N TABLE I, BUT FOR E N T I R E GROUP OF BIRDS I N FLOCK AT E A C H PERIOD T h i r t y Day Period
No. of B i r d s Laying
Coefficient of Correlation
Mean W e i g h t of E g g s
Mean E g g Production
1 2 3 4 5 6 7 8 9 10 11 12
124 121 119 119 122 122 121 122 112 91 76 60
.640±.036 .489±.047 .295±.057 .172±.060 .148±.06O .066±.061 .104±.061 .035±.061 .168±.062 .381±.060 .564±:.053 .437±.070
47.53±.30 50.83±.26 52.61±.36 53.80±.25 54.19+.25 54.03±.25 52.81±.26 52.54±.27 51.78±.26 52.21±.32 52.77±.48 54:i8±.55
16.71±.39 16.32±.45 16.59±.40 15.50±.42 17.76±.35 19.13±.45 17.81+.30 16.18±.37 14.78±.39 13.36 + .44 12.21±.50 9.44±.56
The coefficients follow the same general trend as those for the selected group, starting with a fairly high positive correlation, decreasing to no correlation and increasing again toward the end of the first laying year. The coefficients for the first eight periods when practically the entire flock was laying are all someAvhat lower than the corresponding constants for the selected group. The differences are not significant, however, and are in part due to three birds which began laying at 295, 310, and 333 days, laid eggs of only average size, and died in the fifth and ninth periods. The evidence as far as available, then, supports the general trend of the correlation coefficients. The same fact is shown in a little different form by the data of Table VI, which present the regression means for the culled birds only. The general similarity of these means to those presented in Table I I is very apparent, with slight differences as was the case with the correlation coefficients. The most note-
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between the two coefficients is statistically significant, (diff. = .550 ± .113). There is also a significant difference between the average age at which the two groups of birds began to lay. The culled birds were a significantly later maturing group, beginning to lay at 214.22 ± 3.36 days, which is 20.05 i 3.86 days later than the average age of the selected group. Table V shows the coefficients of correlation between age at first egg and mean weights of eggs for as many of the original group of 124 birds as were laying, in each period.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
135
TABLE VI — MEAN EGG W E I G H T S FOE T H E BIRDS W H I C H D I D N O T COMPLETE THE 360 D A Y L A Ï I K G PEEIOD FOR T H E PERIODS FOE W H I C H DATA ARE AVAILABLE
1 2 3 4 5 6 7 8 9 10 11
151-
176-
201-
43.8* 45.8 47.2 48.1 51.0 50.6 52.2 53.2
45.51± .54 49.44± .60 51.41± .65 53.36± .67 54.05± .60 54.32± .61 53.18± .67 53.06± .68 51.69±: .57 50.73± .68 50.70±1.13
49.20±.46 51.80±.42 53.48i.45 54.26±.47 54.55±.57 54.14±.58 53.00±.54 52.80±.53 52.42±.47 52.41zt.63 56.70+.36
226-
51.03+ .51 52.66± .61 53.76± .62 54.07± .56 53.66± .48 52.93± .50 51.49± .45 51.27± .50 51.01± .85 56.57±1.37 57.87±1.00
25154.70±1.29 57.45±1.12 55.40±1.38 56.35±2.46 56.25±2.17 54.75±1.22 54.50±1.43 54.15±1.88
* No probable error could be calculated as only one bird in this classification.
worthy difference is in the group over 251 days old at first egg. This group in the selected flock comprised two birds only and exhibited a drop in mean egg weight which was not considered trustworthy because of the small number of birds. In the culled flock there were also only two birds in the group 251-275 days old at first egg and their mean egg weights were in every period the highest of the flock. SUMMARY
In a flock of 60 Single Comb White Leghorn pullets which completed a 360 day laying period the following results were found : The correlation between age at the laying of the first egg and the weight of eggs during the first twelve thirty-day laying periods exhibited a rather regular variation starting at -|- .666 ± .048, decreasing to practically zero during the middle periods and then increasing to -\- .437 ± .070 in the twelfth thirty-day period. Age at laying of the first egg was an important factor in the age and seasonal distribution of egg weights during the entire course of the first laying year. These results were corroborated by an analysis of the available data of the entire original flock of 124 pullets. The correlation between age at first egg and total production for the 60 selected birds was positive ( r = -|- .359 ± .076). This
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AGE IN DAYS A T F I R S T EGG Period
136
POULTRY
SCIENCE
TABLE V I I — SHOWING T H E COKRELATION BETWEEN A G E AT F I R S T EGG AND THE MEAN W E I G H T o r A L L EGGS OF E A C H BIRD FOB 360 D A Y PERIOD r =
. 4 4 7 ± .071
EGG W E I G H T IN GRAMS Age in Days at First Egg 151176201226251Total
TOTAL
40-
45-
50-
55-
i
9 8 2
2 15 2
1 6 5 4
3
19
21
60-
'Ï
12 32 10 4 2
1
60
2 16
TABLE V I I I — SHOWING T H E CORRELATION BETWEEN AGE AT F I R S T EGO AND THE TOTAL EGG PRODUCTION FOB 360 D A Y S Γ=
.359 ± . 0 7 6
TOTAL EGG PRODUCTION Age in Days at First Egg
TOTAL
50-
100-
150-
200-
250-
1
1 7
7 10 2 2
3 3 1
--
Ο
7
60
151176201226251-
—
—
—
3 12 5 1 2
Total
1
8
21
23
13 QO
10 4
TABLE I X — SHOWING T H E CORRELATION BETWEEN TOTAL EGG PRODUCTION FOR 360 D A Y S AND T H E M E A N W E I G H T o r THG EGGS OP E A C H BIRD r = .330 ± . 0 7 8 TOTAL EGG PRODUCTION Mean E g g Weight in Grams
TOTAL
50-
100-
150-
200-
250-
2 3 2
—
3 19 21 16 1
7
60
4045505560-
Î
2 5 1
3 10 5 3
—
—
—
4 8 10 1
Total
1
8
21
23
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result was not supported by the available data on the euUed birds and is contrary to the results of other investigators. No explanation of this divergence can be offered.
WEIGHT
OF EGGS
TABLE X — S H O W I N G
DURING
FIRST
LAYING
YEAR
137
T H E CORRELATION BETWEEN A G E TS D A Y S AT F I R S T
EGG AND T H E MEAN W E I G H T OF EGGS OF E A C H BIRD , F I R S T T H I R T Y D A Y PERIOD
Age in Days at First Egg 151176201226251Total
EGG W E I G H T IN GRAMS
35-
40-
45-
50-
55-
3 3
9 16 1
ÎÔ 3
2 6 4
Î
—
— 26
1 14
—
6
1 2
12
60-
— 0
TOTAL
12 32 10 4 2 60
TABLE X I — SHOWING T H E CORRELATION BETWEEN A G E I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T OF EGGS OF E A C H BIRD SECOND T H I R T Y DAY PERIOD
Γ — .649 ± .052 Age in Days at First Egg 151176201226251Total
EGG W E I G H T IN GRAMS
35-
40-
45-
4 3
7 16 2
—
—
—
0
7
25
50-
55-
60-
9 5 1 1 16
2 3 3 1 9
^_ — 0
TOTAL
11 30 10 4 2 57
TABUB X I I — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T or EGGS OF E A C H BIRD T H I R D T H I R T Y DAY PERIOD
r = .428±: .072 Age in Days at First Egg 151176201226251Total
EGG W E I G H T IN GRAMS TOTAL
35- 1
40-
45-
50-
2
4 10 1
7 15 5 1 28
—
—
—
0
2
15
55-
60-
3 2 4 1 10
Ϊ
2
— 3
11 31 10 4 2 58
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r = .666 ± .048
POULTRY
138
SCIENCE
TABLE X I I I — SHOWING T H E CORRELATION BETWEEN A G E I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OF E A C H BIRD F O U R T H T H I R T Y DAY PERIOD
EGG W E I G H T IN GRAMS
Age In D a y s
TOTAL
at First Egg -
35-
151176201226251Total
4e-
45-
50-
55-
1
2 7 1
9 12 3 1 1 26
1 8 4 3 1 17
—
—
—
0
1
10
60-
Î
2
— 3
12 29 10 4 2 57
TABLE XIV — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OF E A C H BIRD F I F T H T H I R T Y D A Y PERIOD
r = . 3 0 4 ± .079 EGG W E I G H T IN GRAMS
Age in Days
TOTAL
at First Egg
35-
151176201226251Total
40-
45-
50-
55-
1 6
9 13 4
2 11 4 4 1 22
__ —
—
—
Ϊ
0
0
7
27
60-
2 2
— 4
12 32 10 4 2 60
TABLE XV — SHOWING T H E CORRELATION BETWEEN A G E I N DAYS AT F I R S T EGG AND T H E ΜΕΑ,Ν W E I G H T OF EGGS OP E A C H BIRD S I X T H T H I R T Y D A Y PERIOD
r = .079 ± . 0 8 7 Age in D a y s at First Egg
151176201226251Total
EGG W E I G H T IN GRAMS TOTAL
35-
40-
45-
__
Î
5 2
— 0
1
·
1 8
50-
55-
60-
10 14 2 1 1 28
2 9 4 3
2 2
—
—
18
4
12 31 10 4 2 59
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Γ = .314 I t .081
WEIGHT
OF EGGS
DURING
FIRST
LAYING
139
YEAR
TABLE X V I — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E MBLA^N W E I G H T OF EGGS OF E A C H BIRD SEVENTH T H I R T Y D A Y PmiioD
EGG W E I G H T IN GRAMS
Age in Days at First Egg
TOTAL
•
35-
40-
45-
50-
55-
60-
Î
6 8 1
4 12 4 2 1 23
2 10 3 2
Î
—
—
17
3
151176201226251-
__
—
Total
0
1
__
1 16
2
12 32 10 4 2 60
TABLE X V I I — S H O W I N G T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T OF EGGS OP E A C H BIRD E I G H T H T H I R T Y DAY- PERIOD r =
Age in Days at First Egg
EGG W E I G H T IN GRAMS TOTAL
35-
.40-
-_
151176201226251Total
. 0 9 6 ± .086
3 1
__ --
—
0
4
45-
50-
55-
60-
4 9 3
7 13 3 2 1 26
1 6 2 2
Ï
1 17
1
—
--
11
2
12 32 10 4 2 60
TABLE X V I I I — S H O W I N G T H E CORRELATION B E T W E E N AGE I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T OF EGGS OF E A C H BIRD N I N T H T H I R T Y DAY PERIOD r = .233 ± . 0 8 4
Age in Days at First Egg
EGG W E I G H T IN GRAMS TOTAL
35-
40-
45-
50-
55-
60-
1
Ï
7 11 1
1 5 3 2
__
151176201226251-
--
--
1
4 12 4 2 1
Total
1
2
20
23
1
--
__ —
12 30 10 4 2
11
1
5S
1
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
r = . 1 9 6 ± .084
POULTRY
140
SCIENCE
TABUB X I X — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OP EGGS OP E A C H BIRD T E N T H T H I R T Y D A Y PERIOD
EGG W E I G H T IN GRAMS
Age in Days
TOTAL
at First Egg
35-
151176201226251Total
40-
45-
50-
3 1
8 11 1
2 10 3
- 1 8 4 4
2 17
—
—
17
1
—
—
—
0
4
20
55-
6011 32 10 4 2 59
Î
TABLE X X — SHOWING T H E COBRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OP E A C H BIRD E L E V E N T H T H I R T Y D A Y PERIOD
r = . 4 9 3 ± .067 Age In Days at First Egg
151176201226251Total
EGG W E I G H T IN GRAMS TOTAL
35-
40-
45-
50-
55-
Î
3 5 1
6 7 1
1 12 2
2 7 4 1 1 15
__
„_
—
—
—
1
9
14
1 16
6012 32 10 4 2 60
2 3
— 5
TABLE X X I '— SHOWING T H E CORRELATION BETWEEN A G E I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OP E A C H BIRD T W E L F T H THIRTY- D A Y PERIOD
r = .437 ± .070 EGG ΛVEIGHT IN GRAMS
Age in Days at First Egg
151176201226251Total
TOTAL
35-
40-
45-
50-
55-
—
2 3 1
6 6
2 12 2
0
6
12
2 7 3 1 1 14
•
1
17
60-
65-
"3 4 3
'Î
10
1
1
12 32 10 4 2 60
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
r = .371 I t .076
A P E I L - M A Y , 1925
No. 4
WILLIAM A. LIPPINCOTT, SYLVIA L. PARKER AND LUBLLA M. SCHAUMBURG I t was shown i n a n earlier p a p e r , (Lippincott, 1921)^ t h a t the correlation between age at the laying of the first egg a n d the mean weight of the first ten eggs laid by each of 123 Single Comb W h i t e Leghorn pullets was of a high order (r = 0.7139 ± .0293). Quite recently J u U (1924)^ has calculated the same correlation for 40 B a r r e d P l y m o u t h Rock pullets and found t h a t r = 0.845 ±: 0.030. D a t a are now available upon which to calculate the correla tion between age at the l a y i n g of the first egg a n d the m e a n weight of eggs laid d u r i n g each successive t h i r t y - d a y period of the 360 days following the onset of laying, for 60 Single Comb W h i t e Leghorns. MATERIAL
The birds serving as the source of these d a t a belonged to the pedigreed a n d somewhat inbred flock of K a n s a s State Agricul t u r a l College. They comprised a selected group, from an original flock of 124 pullets which was systematically culled on the basis of vigor and production d u r i n g the last four periods covered in * Contribution No. 28 from the Department of Poultry Husbandry, Kansas Agricultural Experiment Station, and No. 1 from the Division of Poultry Husbandry, University of California, Agricultural Experiment Station. 1 Lippincott, W. Α., 1921, Preliminary note on the correlation between age at first laying and size of first eggs in pullets. Jour. Amer. Assn's Instr. Invest. Poultry Husbandry, 7:73-74. 2 JuU, M. Α., 1924, Egg weight in relation to production. II. The na ture and causes of changes in egg weight in relation to annual produc tion in pullets. POULTRY SCIENCE, 3:153-172. 127
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THE CORRELATION B E T W E E N AGE AT T H E LAYING OF T H E FIRST EGG AND T H E W E I G H T OF EGGS DURING THE FIRST LAYING YEAR IN W H I T E LEGHORNS*
128
POULTRY SCIENCE
METHOD OP RECORDING AND TABUDATING DATA
Every egg laid by each individual was weighed and the weight recorded to the nearest 0.5 gram. The mean egg weight for each bird for each 30 day period and for the entire 360 days was then calculated. In making up the correlation tables, the class range used for weight was 5 grams, for age 25 days, and for production 50 eggs. Tables were also made using finer groupings, 2 grams for weight, 10 days for age, and 25 eggs for production, but since none of the coefficients differed appreciably from those calculated with coarser groupings, the more condensed tables are presented. The probable errors of all the constants, including the mean egg weights, are on the basis of the number of birds, rather than the number of eggs, as N, since it is the one measure of age at. first egg that determines in which group a bird is placed. As Harris (1914)^ has stated it, "the degree of trustΛvorthiness of a con stant is perhaps not greater than is indicated by the lowest num ber of actual measurements, irrespective of the number of as sociated measures taken. ' ' RESULTS
The correlation coefficients relating age at first egg and mean weight of eggs for the twelve periods are presented in Table I, together with the mean egg weights of all the eggs for each period, and the mean egg production. The twelve correlation Tables from which the coefficients were computed are included as Tables X to X X I at the end of the report. It will be noted from Table I that the correlation is quite high for the first two periods. It is progressively lower, but still probably significant, for the next three periods. During the sixth to the ninth periods, inclusive, the coefficient becomes prae3 Harris, J. Α., 1914, The relationship between the weight of the seed planted and the characteristics of the plant produced. II. Biometrika, 10:72-84.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
this report. The total production for the sixty pullets was 11,902 eggs, or a mean production per individual for' 360 days of 198.37 ± 3.96 eggs. The birds were all hatched between the third week in March and the middle of May, 1921, and showed no correlation between the date of hatching and age at the lay ing of the first egg, ( r = . 0 0 8 ^ .087). The average age at which they began to lay was 194.17 ± 1.89 days, and the average weight of all the eggs was 52.19 i .35 grams.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
129
TABLE I—CORRÉLATION BETWEEN A G E AT F I R S T EGG AND M E A N W E I G H T OF EGGS, MEAN W E I G H T OF EGGS, AND MEAN EGG PRODUCTION BY T H I R T Y DAY PERIODS, FOR SIXTY SINGLE COMB W H I T E LEGHORNS Mean AVeight of E g g s
Coefficient of Correlation
.666 ± .649 ± .428 ± .314 ± .304 ± .079 ± .196 ± .096 ± .233 ± .371 ± .483 ± .437 ±
1 2 3 4 5 6 7 S 9 10 11 12
46.49 ± 50.07 ± 52.31 ± 53.82 ± 53.85 ± 54.02 ± 52.81 ± 52.38 ± 51.62 ± 52.05 ± 52.58 ± 54.18 ±
.048 .052 .072 .081 .079 .087 .084 .086 .084 .076 .067 .070
.447 ± .071
360 Days
Mean E g g Production
.44 .40 .39 .38 .34 .37 .39 .40 .41 .43 .54 .55
16.90 ± 15.63 ± 16.98 ± 15.53 ± 18.78 ± 19.63 ± 19.55 ± 17.60 ± 15.35 ± 15.25 ± 14.75 ± 12.40 ±
52.19 ± .35
.55 .64 .56 .60 .49 .64 .43 .52 .55 .52 .53 .56
198.37 ± 3.96
tically zero, while in the last three periods it again rises to a significant positive correlation. The relation of the degree of correlation to the mean egg production in the respective periods is shown graphically in
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a
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IS
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i;
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7
a
A
10
i/
f
TH
i£6 £//n re/o/ioiT Me«
tetweeji
.
77 uieiji f of egg,
FIGURE 1—Showing the periodic v a r i a t i o n in t h e correlation between age a t first egg and t h e mean weight of eggs, a n d in the mean egg pro duction for 60 S. C. W h i t e Leghorn pullets.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
Thirty Day Period
POULTRY
130
SCIENCE
TABLE I I — M E A N JEGG "WEIGHTS FOB SIXTY SINGI^E COMB W H I T E LEGHORNS, CLASSIFIED BY AGE AT F I R S T EGG AND BY 30 DAY LAYING PERIODS AGE I N DAYS AT F I R S T EGG Period
151-
176-
201-
226-
251-
1 2 3 i 5 6 7 8 9 10 11 12
41.22±.57 45.41±.32 50.01±.35 51.57it.42 52.76±.45 52.92±.47 51.23±.54 51.69±:.60 50.00±.65 49.95±.57 48.19±.88 49.17±.90
44.77±.49 48.77±.51 51.20±.47 52.57d=.55 53.53±.49 53.36±.48 52.33±.51 51.73±.51 50.81±.54 50.97±.53 50.58±.65 52.91±.65
49.51± .68 52.69± .69 54.86-t- .80 56.00± .80 56.08-1- .81 55.96± .99 54.61±1.08 52.72-1-1.21 53.12-t-l.06 53.04-4-1.11 54.77±1.40 57.59 + 1.25
53.03±.32 54.82-^-.68 56.70-1-.53 56.90±.60 57.07-i-.47 56.07±.83 55.27±.77 55.45-i-.59 55.55-1-.37 57.10dz.16 60.37±.48 60.87±.42
52.70±2.18 54.60±1.96 54.55±1.07 53.95±1.21 52.85±1.31 49.55+1.79 49.00± .95 48.95± .79 50.45± .50 53.00± .29 54.55± .21 55.05± .93
360 Days
49.82±.44
51.39±.47
54.26± .74
56.44±.31
52.66±1.04
The data of Table I I are shown graphically in Figure 2. The drop in mean egg weight in the group over 251 days old at first egg, while significant in most of the periods, when tested by the probable errors, is based on two birds only. The curve of egg weights of these two birds is, therefore, not included in Figure 2, as it would merely confuse the other curves and is based on too small a number of birds to be trustworthy. Figure 2 shows that the birds which began laying at earlier ages never laid eggs which were as large on the average as the eggs of later maturing birds for the corresponding period.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
Figure 1. In a general way it appears that the correlation between the mean weight of eggs and the age of the pullet at first laying exhibits a periodic variation which is the inverse of the curve of variation in egg production. Table I I gives the mean egg weight for the sixty pullets classified both by age at first egg and by period, and Table I I I the regression lines fitted to these observed regression means. The main point brought out by both Tables is that during the first few and last few periods, for every addition of 25 days in age at first egg, there is an increase of about 3 grams in mean egg weight, or more than an ounce per dozen, which is a commercially important difference. Through the middle periods, however, the regression lines become nearly horizontal.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
131
Figure 3 shows the same curves as Figure 2, but each successive curve set ahead a twenty-five day interval so that mean egg weights for the four groups of birds are plotted against the
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FiGtTRE 2—Showing t h e periodic variations in mean egg weights of birds classified by age at first egg. TABLE I I I — P I T T E D REGKESSION L I N E S FOR GROUP OF SIXTY SINGLE COMB W H I T E LEGHORNS
Régression of Egg Weight on Age at First Egg
Period
W W W W W W W "W W W
1 2 3 4 5 6 7 8 9 10 11 12 360 Days W: A:
= = = = = = = = = ==
w = w = w =
.1433A .1524A .0794A .0549A .0500A .0140A .0373A .0187A .0455A .0766A .1269A .1172A
-f -1-f + -f -1-\+ -1+ + +
.0858A +
17.95 20.26 36.83 42.82 44.74 51.15 45.72 48.06 42.77 36.87 27.12 30.90 35.06
: predicted egg weiglit In grams. = actual age in days at la.ving of the first egg.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
^
POULTRY
132
SCIENCE
is
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FIGURE 3—Showing the age and seasonal variations in mean egg weights of birds classified by age at first egg.
Figure 3 indicates that in this group of sixty Single Comb White Leghorns, age at laying of the first egg was an important factor in the course of the age and seasonal distribution of egg weight. It would be very interesting to have more extensive data on the relationships and to have the curves carried on into the later years' production. Table IV summarizes the correlation coefficients for the entire 360 day period, computed from Tables VII to IX, and compares them with the corresponding coefficients for the forty Barred Plymouth Eocks analyzed by Jul! in the paper already noted. The correlation between age at first egg and mean weight of all eggs is positive and significant ( r = . 4 4 7 ± .071). This is
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
average age of birds and against average date of laying of eggs. The latter two scales coincide because it was found that the average date of hatching was the same for each group of birds, so that seasonal effect and age effect in this experiment cannot be separated. These effects might be separated for a few individual birds within a group, but there were not enough such birds to make the comparisons significant.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
133
TABLE IV — COERELATION COEFFICIENTS FOR GROUP OF SIXTY SINGLE COMB W H I T E LEGHORNS, COMPARED W I T H GROUP OF F O R T Ï BARRED P L Ï M O U T H ROCKS
( D a t a of
Jul!)
Mean egg weight and age at first egg Total production and age at first egg Total production and mean egg weight Egg wt. and age, with production constant Production and age, with egg wt. constant Production and egg wt., with age constant
60 Single Comb White Leghorns
40 Barred Plymouth Eocks (Jull)
+.447±.071 + .359±.076 + .330±.078 + .373±.075 + .250+.082 + .206±.083
+ .548+.075 —.295±.097 —.019 ±.107 + .568±.072 —.340±.094 + .178±.103
not quite so high as the coefficient found by Jull, but is of the same general order. The correlation between age at first egg and total production is also positive and significant, (r^.359±.076). This result is directly contrary to that found by Jull, Rice (1915),* Hays et al (1923 and 1924),= and other workers, and to the belief generally held by practical breeders, in the efficacy of early maturity as a point of selection in breeding for high egg production. Since the four remaining correlation coefficients are combinations of the same three variables, the further differences in Table IV all follow from this primary one. Because of this difference it has seemed best to examine the data of the entire original group of 124 birds as far as they are available, to determine in so far as possible to what extent the various constants for the selected group are representative of the entire flock. Since the culled birds were not discarded until within the last four periods, it is possible to compare the correlation between age at first egg and total production for 240 days for the two groups of birds. The 60 selected pullets gave a correlation for the 240 days practically identical with that for 360 days, (r = .362 =t .076), while the coefficient for the culled birds, though not statistically significant, is comparable to that obtained by other workers, (r = —.188 i t .084). The difference * Rice, J. E., 1915, T h e distrihution of egg production, Cornell Countryman, 12:5-8 5 Hays, P . Α., and Bennett, J. S., 1923, Correlation of sexual m a t u r i t y to a n n u a l egg record. POULTRY SCIENCE, 2:205-206. Hays, F . Α., San born, R., and J a m e s , L·. L·., 1924, Correlation studies on winter fecun dity, Mass. Agr. Exp. Sta. Bui., 220:44-53.
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Correlation Coefficients Variables Correlated
POULTRY
134
SCIENCE
TABLE V — S A M E DATA AS I N TABLE I, BUT FOR E N T I R E GROUP OF BIRDS I N FLOCK AT E A C H PERIOD T h i r t y Day Period
No. of B i r d s Laying
Coefficient of Correlation
Mean W e i g h t of E g g s
Mean E g g Production
1 2 3 4 5 6 7 8 9 10 11 12
124 121 119 119 122 122 121 122 112 91 76 60
.640±.036 .489±.047 .295±.057 .172±.060 .148±.06O .066±.061 .104±.061 .035±.061 .168±.062 .381±.060 .564±:.053 .437±.070
47.53±.30 50.83±.26 52.61±.36 53.80±.25 54.19+.25 54.03±.25 52.81±.26 52.54±.27 51.78±.26 52.21±.32 52.77±.48 54:i8±.55
16.71±.39 16.32±.45 16.59±.40 15.50±.42 17.76±.35 19.13±.45 17.81+.30 16.18±.37 14.78±.39 13.36 + .44 12.21±.50 9.44±.56
The coefficients follow the same general trend as those for the selected group, starting with a fairly high positive correlation, decreasing to no correlation and increasing again toward the end of the first laying year. The coefficients for the first eight periods when practically the entire flock was laying are all someAvhat lower than the corresponding constants for the selected group. The differences are not significant, however, and are in part due to three birds which began laying at 295, 310, and 333 days, laid eggs of only average size, and died in the fifth and ninth periods. The evidence as far as available, then, supports the general trend of the correlation coefficients. The same fact is shown in a little different form by the data of Table VI, which present the regression means for the culled birds only. The general similarity of these means to those presented in Table I I is very apparent, with slight differences as was the case with the correlation coefficients. The most note-
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
between the two coefficients is statistically significant, (diff. = .550 ± .113). There is also a significant difference between the average age at which the two groups of birds began to lay. The culled birds were a significantly later maturing group, beginning to lay at 214.22 ± 3.36 days, which is 20.05 i 3.86 days later than the average age of the selected group. Table V shows the coefficients of correlation between age at first egg and mean weights of eggs for as many of the original group of 124 birds as were laying, in each period.
WEIGHT
OF EGGS DURING
FIRST
LAYING
YEAR
135
TABLE VI — MEAN EGG W E I G H T S FOE T H E BIRDS W H I C H D I D N O T COMPLETE THE 360 D A Y L A Ï I K G PEEIOD FOR T H E PERIODS FOE W H I C H DATA ARE AVAILABLE
1 2 3 4 5 6 7 8 9 10 11
151-
176-
201-
43.8* 45.8 47.2 48.1 51.0 50.6 52.2 53.2
45.51± .54 49.44± .60 51.41± .65 53.36± .67 54.05± .60 54.32± .61 53.18± .67 53.06± .68 51.69±: .57 50.73± .68 50.70±1.13
49.20±.46 51.80±.42 53.48i.45 54.26±.47 54.55±.57 54.14±.58 53.00±.54 52.80±.53 52.42±.47 52.41zt.63 56.70+.36
226-
51.03+ .51 52.66± .61 53.76± .62 54.07± .56 53.66± .48 52.93± .50 51.49± .45 51.27± .50 51.01± .85 56.57±1.37 57.87±1.00
25154.70±1.29 57.45±1.12 55.40±1.38 56.35±2.46 56.25±2.17 54.75±1.22 54.50±1.43 54.15±1.88
* No probable error could be calculated as only one bird in this classification.
worthy difference is in the group over 251 days old at first egg. This group in the selected flock comprised two birds only and exhibited a drop in mean egg weight which was not considered trustworthy because of the small number of birds. In the culled flock there were also only two birds in the group 251-275 days old at first egg and their mean egg weights were in every period the highest of the flock. SUMMARY
In a flock of 60 Single Comb White Leghorn pullets which completed a 360 day laying period the following results were found : The correlation between age at the laying of the first egg and the weight of eggs during the first twelve thirty-day laying periods exhibited a rather regular variation starting at -|- .666 ± .048, decreasing to practically zero during the middle periods and then increasing to -\- .437 ± .070 in the twelfth thirty-day period. Age at laying of the first egg was an important factor in the age and seasonal distribution of egg weights during the entire course of the first laying year. These results were corroborated by an analysis of the available data of the entire original flock of 124 pullets. The correlation between age at first egg and total production for the 60 selected birds was positive ( r = -|- .359 ± .076). This
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AGE IN DAYS A T F I R S T EGG Period
136
POULTRY
SCIENCE
TABLE V I I — SHOWING T H E COKRELATION BETWEEN A G E AT F I R S T EGG AND THE MEAN W E I G H T o r A L L EGGS OF E A C H BIRD FOB 360 D A Y PERIOD r =
. 4 4 7 ± .071
EGG W E I G H T IN GRAMS Age in Days at First Egg 151176201226251Total
TOTAL
40-
45-
50-
55-
i
9 8 2
2 15 2
1 6 5 4
3
19
21
60-
'Ï
12 32 10 4 2
1
60
2 16
TABLE V I I I — SHOWING T H E CORRELATION BETWEEN AGE AT F I R S T EGO AND THE TOTAL EGG PRODUCTION FOB 360 D A Y S Γ=
.359 ± . 0 7 6
TOTAL EGG PRODUCTION Age in Days at First Egg
TOTAL
50-
100-
150-
200-
250-
1
1 7
7 10 2 2
3 3 1
--
Ο
7
60
151176201226251-
—
—
—
3 12 5 1 2
Total
1
8
21
23
13 QO
10 4
TABLE I X — SHOWING T H E CORRELATION BETWEEN TOTAL EGG PRODUCTION FOR 360 D A Y S AND T H E M E A N W E I G H T o r THG EGGS OP E A C H BIRD r = .330 ± . 0 7 8 TOTAL EGG PRODUCTION Mean E g g Weight in Grams
TOTAL
50-
100-
150-
200-
250-
2 3 2
—
3 19 21 16 1
7
60
4045505560-
Î
2 5 1
3 10 5 3
—
—
—
4 8 10 1
Total
1
8
21
23
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
result was not supported by the available data on the euUed birds and is contrary to the results of other investigators. No explanation of this divergence can be offered.
WEIGHT
OF EGGS
TABLE X — S H O W I N G
DURING
FIRST
LAYING
YEAR
137
T H E CORRELATION BETWEEN A G E TS D A Y S AT F I R S T
EGG AND T H E MEAN W E I G H T OF EGGS OF E A C H BIRD , F I R S T T H I R T Y D A Y PERIOD
Age in Days at First Egg 151176201226251Total
EGG W E I G H T IN GRAMS
35-
40-
45-
50-
55-
3 3
9 16 1
ÎÔ 3
2 6 4
Î
—
— 26
1 14
—
6
1 2
12
60-
— 0
TOTAL
12 32 10 4 2 60
TABLE X I — SHOWING T H E CORRELATION BETWEEN A G E I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T OF EGGS OF E A C H BIRD SECOND T H I R T Y DAY PERIOD
Γ — .649 ± .052 Age in Days at First Egg 151176201226251Total
EGG W E I G H T IN GRAMS
35-
40-
45-
4 3
7 16 2
—
—
—
0
7
25
50-
55-
60-
9 5 1 1 16
2 3 3 1 9
^_ — 0
TOTAL
11 30 10 4 2 57
TABUB X I I — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T or EGGS OF E A C H BIRD T H I R D T H I R T Y DAY PERIOD
r = .428±: .072 Age in Days at First Egg 151176201226251Total
EGG W E I G H T IN GRAMS TOTAL
35- 1
40-
45-
50-
2
4 10 1
7 15 5 1 28
—
—
—
0
2
15
55-
60-
3 2 4 1 10
Ϊ
2
— 3
11 31 10 4 2 58
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
r = .666 ± .048
POULTRY
138
SCIENCE
TABLE X I I I — SHOWING T H E CORRELATION BETWEEN A G E I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OF E A C H BIRD F O U R T H T H I R T Y DAY PERIOD
EGG W E I G H T IN GRAMS
Age In D a y s
TOTAL
at First Egg -
35-
151176201226251Total
4e-
45-
50-
55-
1
2 7 1
9 12 3 1 1 26
1 8 4 3 1 17
—
—
—
0
1
10
60-
Î
2
— 3
12 29 10 4 2 57
TABLE XIV — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OF E A C H BIRD F I F T H T H I R T Y D A Y PERIOD
r = . 3 0 4 ± .079 EGG W E I G H T IN GRAMS
Age in Days
TOTAL
at First Egg
35-
151176201226251Total
40-
45-
50-
55-
1 6
9 13 4
2 11 4 4 1 22
__ —
—
—
Ϊ
0
0
7
27
60-
2 2
— 4
12 32 10 4 2 60
TABLE XV — SHOWING T H E CORRELATION BETWEEN A G E I N DAYS AT F I R S T EGG AND T H E ΜΕΑ,Ν W E I G H T OF EGGS OP E A C H BIRD S I X T H T H I R T Y D A Y PERIOD
r = .079 ± . 0 8 7 Age in D a y s at First Egg
151176201226251Total
EGG W E I G H T IN GRAMS TOTAL
35-
40-
45-
__
Î
5 2
— 0
1
·
1 8
50-
55-
60-
10 14 2 1 1 28
2 9 4 3
2 2
—
—
18
4
12 31 10 4 2 59
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
Γ = .314 I t .081
WEIGHT
OF EGGS
DURING
FIRST
LAYING
139
YEAR
TABLE X V I — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E MBLA^N W E I G H T OF EGGS OF E A C H BIRD SEVENTH T H I R T Y D A Y PmiioD
EGG W E I G H T IN GRAMS
Age in Days at First Egg
TOTAL
•
35-
40-
45-
50-
55-
60-
Î
6 8 1
4 12 4 2 1 23
2 10 3 2
Î
—
—
17
3
151176201226251-
__
—
Total
0
1
__
1 16
2
12 32 10 4 2 60
TABLE X V I I — S H O W I N G T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T OF EGGS OP E A C H BIRD E I G H T H T H I R T Y DAY- PERIOD r =
Age in Days at First Egg
EGG W E I G H T IN GRAMS TOTAL
35-
.40-
-_
151176201226251Total
. 0 9 6 ± .086
3 1
__ --
—
0
4
45-
50-
55-
60-
4 9 3
7 13 3 2 1 26
1 6 2 2
Ï
1 17
1
—
--
11
2
12 32 10 4 2 60
TABLE X V I I I — S H O W I N G T H E CORRELATION B E T W E E N AGE I N D A Y S AT F I R S T EGG AND T H E MEAN W E I G H T OF EGGS OF E A C H BIRD N I N T H T H I R T Y DAY PERIOD r = .233 ± . 0 8 4
Age in Days at First Egg
EGG W E I G H T IN GRAMS TOTAL
35-
40-
45-
50-
55-
60-
1
Ï
7 11 1
1 5 3 2
__
151176201226251-
--
--
1
4 12 4 2 1
Total
1
2
20
23
1
--
__ —
12 30 10 4 2
11
1
5S
1
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
r = . 1 9 6 ± .084
POULTRY
140
SCIENCE
TABUB X I X — SHOWING T H E CORRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OP EGGS OP E A C H BIRD T E N T H T H I R T Y D A Y PERIOD
EGG W E I G H T IN GRAMS
Age in Days
TOTAL
at First Egg
35-
151176201226251Total
40-
45-
50-
3 1
8 11 1
2 10 3
- 1 8 4 4
2 17
—
—
17
1
—
—
—
0
4
20
55-
6011 32 10 4 2 59
Î
TABLE X X — SHOWING T H E COBRELATION BETWEEN AGE I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OP E A C H BIRD E L E V E N T H T H I R T Y D A Y PERIOD
r = . 4 9 3 ± .067 Age In Days at First Egg
151176201226251Total
EGG W E I G H T IN GRAMS TOTAL
35-
40-
45-
50-
55-
Î
3 5 1
6 7 1
1 12 2
2 7 4 1 1 15
__
„_
—
—
—
1
9
14
1 16
6012 32 10 4 2 60
2 3
— 5
TABLE X X I '— SHOWING T H E CORRELATION BETWEEN A G E I N D A Y S AT F I R S T EGG AND T H E M E A N W E I G H T OF EGGS OP E A C H BIRD T W E L F T H THIRTY- D A Y PERIOD
r = .437 ± .070 EGG ΛVEIGHT IN GRAMS
Age in Days at First Egg
151176201226251Total
TOTAL
35-
40-
45-
50-
55-
—
2 3 1
6 6
2 12 2
0
6
12
2 7 3 1 1 14
•
1
17
60-
65-
"3 4 3
'Î
10
1
1
12 32 10 4 2 60
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
r = .371 I t .076