EGG PRODUCTION IN THE FOUR SEASONS

It has become customary to regard the conventional pullet year (November 1 to October 30) as consisting of four parts, each corresponding roughly with one season of the year, although actually based on biological interpretations of the changes occurring in the reproductive and allied systems of the fowl. These divisions were first used in this country at the Maine Agricultural Experiment Station and for detailed information the reader is referred to Maine Station Bulletins No. 166 and 205.(9) The four periods are (1) Winter, November 1 to the end of February; (2) Spring or mating season, March 1 to May 30; (3) Summer, June 1 to August 31; (4) Autumn, September 1 to October 31. These of course are only arbitrary points used to break up a continuous physiological process for convenience in record keeping and notation, but the closeness of their approach to actual changes in the physiological condition of the fowl has been inferred from the fact that even when egg records only are considered, each of these seasons is characterized by certain peculiarities which distinguish it from the oth

ers.

MEAN

The information on seasonal variation in mean production in these Wyandottes is given in Table 6. Mean production in the four winter months is about 35.8 eggs; this rises to 53.8 eggs for the three spring months and falls during the three summer months to 45.8 eggs and 24.1 eggs in the autumn which consists of only two months. The percentages of the total eggs laid in any one season are more easily compared than the mean, since these provide information on the intensity of production apart from the mean and by use of percentages breeds and years characterized by different mean production can be compared directly. In Table 8 we find that in the nine years about 22.4 per cent of the yearly production occurs in the winter period, about 33.7 per cent in the spring, 28.7 per cent in the summer and 15.1 per cent in the autumn. Spring is, therefore, the period of greatest fecundity, and winter, when correction for the number of months is made, is the period of lowest fecundity.

(9) See also Pearl, R. (1912)

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.

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1. Winter period. The data for the seasonal distribution of egg production are given in Table 6, and illustrated in Fig. 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 peIt 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 seaGoodale (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

High

Low

Medium

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.

It is to be

(1) This column gives the percent yield of the flock in each month. 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 therefore 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 information on October production all increase is credited to November. The indicated November increase is therefore greater than the actual.