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So far we have taken the conventional division of the pullet year into four periods for granted. We must now inquire more closely into the reality of this division to ascertain whether these cycles are really marked by distinct and definite division points in the curve of seasonal egg production.

1. Winter period. The data for the seasonal distribution of egg production are given in Table 6, and illustrated in Fig. 6. The general impression gained from a glance at Fig. 6 is one of regularity and smoothness. The increase in mean production from November to March is uninterrupted and steady. This part of the curve differs from that describing seasonal variation in the Barred Rocks. (Pearl and Surface (1909) part 2 page 90) Mean egg production in their birds increased through November, December, and January, but the rate of increase slackened perceptibly in February. This fall, Pearl and Surface concluded, marked the completion of the winter period. It was, they assumed the result of a pause or rest in physiological activity inserted between the superimposed winter period and the onset of the natural fecundity of the mating season. Goodale (1918) has considered the whole question of the winter cycle and has given rules for its detection. Applying his criteria to data from Rhode Island Reds he was unable to demonstrate a winter cycle in any but a few of the birds in his flock, and this only, by a careful study of individual records. Our present study is limited to groups rather than to individuals. It is necessary in considering breed characteristics to state the results in terms applicable to the whole group. Our conclusions concerning a winter cycle in Wyandottes must thence apply to that hypothetical bird, the average Wyandotte. From the form of the curve as plotted in Fig. 6, it is quite evident that there is no point of division in a period of as long as a month between the winter and spring production in this breed. The actual mean production increases each month up to March. The rate of increase, however, is perhaps more important. Additions to the mean in these months are mainly due to additions to the number of birds laying for the first time; and the efficiency of the flock in these months is to be gauged by the fall in the relative number of zero producers, and by the proportion between the actual number of eggs laid per

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Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug.

Sept. Oct. Fig. 7. Comparison or high, low, and medium producing pullets on the basis of monthly distribution

of egg production. Low

Medium-

High

bird per month and the total possible number as fixed by the number of days in the month. In November 523 birds failed to lay any eggs at all, or about 58 per cent of the flock. (See Table II). In December this proportion is 39 per cent, in January 20 per cent, in February 8 per cent, and in March 1 per cent. It then remains practically stationary during April and May. The rate of decrease in zero producers (which in this case is the same as the rate of increase in the numbers of birds beginning to lay) is fairly uniform. The decrease amounts to 19 per cent from November to December; 19 per cent from December to January; 12 per cent from January to February, and 7 per cent from February to March. The important fact, however, is that there is no evidence of a cessation of laying on the part of any considerable portion of the flock in either January, February, or March. If this occurred the number of zero producers should be found to increase, whereas it shows a marked decrease. Here, as in mean production, the winter "cycle” grades imperceptibly into the spring cycle.

per bird

+ 7.29

TABLE 8 MONTHLY VARIATION IN THE EFFICIENCY OF EGG PRODUCTION

BASED ON NINE YEARS RECORDS. Possible Actual Actual no. x100 Increase no. of eggs no. of eggs

Possible no. over preMonth per bird

(Efficiency %)(1) vious month Nov. 30

4.57
15.23

+15.23* Dec. 31

8.16
26.32

+11.09 Jan. 31 10.42

33.61 Feb. 28.33

12.62
44.72

+11.12 Mar. 31

17.79
57.39

+12.67 Apr. 30

18.01

60.01 May 31

18.00
58.06

1.95 June 30

16.24
54.17

3.89 July 31

14.64
47.23

6.94 Aug. 31

14.91

48.10 14.06 46.87

1.23 Oct. 31

10.07
32.48

-14.39 (1) This column gives the percent yield of the flock in each month. It is to be read: in November the flock (or average bird) produced 15.23% of the total number of eggs which could possibly be produced in November, etc. The average Wyandotte is therei ore 15.23% efficient in November.

*This increase is calculated on the assumption that egg production in the previ. ous month, October, was zero. This is certainly not true but in the absence of in. formation on October production all increase is credited to November. The indicat. ed November increase is therefore greater than the actual.

+ 2.62

+ .87

Sept.

30

The proportion between the mean number of eggs actually laid and the total possible number is given in Table 8. The significant column for our purpose is that giving the percentage increase of production during the winter months. This gives a truer picture of the actual circumstances than the means for the various months, because the variation in the number of days in the several months has been eliminated by reducing all to a percentage basis. This is especially noticeable in the case of February where the mean production is based on only 28 laying days in 6 years and 29 days in three years (average 28.33 days). The increase in rate of November production is probably not as high as given, since some eggs have doubtless been laid before the opening of the contest. The increase of December over November may likewise be too high, because of the delay in beginning egg production as an after effect of shipment of the birds. By January this effect has probably ceased to operate and the rate of interest in January has slackened. This represents only a decline in the rate of increase, not a decline in mean production. It may be an indication of a winter cycle which would then end a full month before the natural spring breeding season begins. I am inclined to think, however, that the lessened rate in January is due rather to an exaggeration of the delayed December increase. Certainly the increase of March over February is not significantly different from the increase of February over January; and if these Wyandottes resembled the Barred Rocks in this respect, it is between these two months, February and March, that we should find our clearest evidence of the existence of a winter cycle. The absence of such evidence indicates that in these contest Wyandottes the existence of a winter cycle cannot be affirmed.

The above data are treated en masse, and the conclusions are limited to the whole number of birds considered as a group. The dissection of this group into its component individuals might throw some light on the existence of a winter cycle in certain individuals. Such a minute analysis will not be attemped here. We have instead separated the birds into the 21 fecundity groups used in the seriation of the annual distributions. These differ by 15 egg each, and the distribution of egg laying in the various months is shown for each group in Table 9. This table is discussed in greater detail elsewhere.

TABLE 9

MONTHLY DISTRIBUTION OF TOTAL EGG PRODUCTION BY FECUNDITY CLASSES/CONTESTS OF 1911-1919.

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Class

0- 14
15- 29
30-44
45- 59
60- 74
75- 89
90-104
105-119
120-134
135-149
150-164
165-179
180-194
195-209
210-224
225-239
240-254
255-269
270-284)
285-299
300-314)

64
82
91
125
130
111
85
54
32
12
7

3

9 4
2 9 12 17
33 52 62

77
23 40 39 37
45 60 53 142
61 142

208 269
119 182 293 500
118 216 465 871
172 407 743 1157
444 925 1241 1554
646 1183 1516 1852
544 1159 1531 1649
805 1183 1268 1292
446 800

945 914
304 524 586 601
138

227 223 238
133 167 112

120

2
6
24
145
106
308
498
924
1471
1612
2200
2503
2157
1690
1157
707
273
153

11

3
36
122
111
341
560
981
1410
1648
2183
2436
2251
1743
1205
687
272
166

30
49
88
379
579
912
1323
1632
2246
2461
2205
1850
1174
747
283
179

2
8
28
17
70
343
480
848
1141
1411
2050
2244
1995
1639
1115
716
303
163

6
1
4
18
46
232
376
693
1015
1262
1857
2028
1913
1513
1038
667
259
173

1
24
17
42
186
417
750
998
1337
1937
2100
1916
1527
1055
646
294
161

2
1
24 1

7 5
11
162 66
352 221
665 363
859 548
1163 776
1832 1186
1994 1423
1840 1511
1544 1131
1018

840
673 582
244 179
161 141

28
38
211
604
613
2317
4163
7230
10465
13320
19655
22386
20671
17185
11707
7440
2933
1829

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