OF THE DOMESTIC FOWL

TABLE 5

DISTRIBUTION OF TOTAL EGG PRODUCTION BY MONTHS AND YEARS.

f Nov. Dec. Jan. Feb.

Mar.

Apr.

May June July Aug. Sept.

Oct.

Totals

TABLE 6

| 655 2.08| 4.74| 6.03| 7.22| 11.43| 11.89| 12.28 10.57 9.61| 9.70 8.89 5.56| 100.00

VARIATION IN MONTHLY PRODUCTION.

The distribution of egg production of the 655 Barred Rock pullets in each month of the year is given in Appendix Table IIa, in which are shown the numbers of birds laying the numbers of eggs (0..........31) set down in the left hand column. The monthly averages and variation constants in Table 7 have been calculated directly from the frequency distributions in these tables. In Table IIb, the frequencies of Table IIa are stated as percentages of the total number of birds present. From this table the proportion of the flock laying a given number of eggs can be read off directly. Thus in November the proportion of the flock not laying is 61.22 per cent; the proportion laying one egg each in this month is 5.95 per cent, the proportion laying twenty-five eggs apiece is .15 per cent, etc.

These tables give a good idea of the changes in egg production which take place in this breed from November of the pullet year through the following October. One of the best indications of these changes is given by the proportion of birds which lay no eggs at all in each month. These proportions have been extracted from Table IIb and are given in Table 12. Over sixty per cent of these pullets were not laying in the first month of the contest. We may assume that most of these had not laid at all, while a few may have laid before the first of November and then stopped. The proportion of birds not laying decreases very rapidly to March and then falls slightly to reach a low point in April, when practically all members of the flock are laying. The proportion not laying remains very low through May, June, July and August, rises somewhat in September and rises abruptly in October to nearly twenty-six per cent of the flock. The fall in the number of birds not laying in the early months of the contest is occasioned by the attainment of maturity on the part of more and more birds; the slight rise in the proportion during the summer probably represents additions to those temporarily out of action because of broodiness, molting, etc., while the decided increase in the number of zero producers in the fall represents completion of the first yearly cycle by many of the birds and a cessation of egg production until the molt which takes place at this time is completed.

OF THE DOMESTIC FOWL

The great variability of the birds in each month is also to be noted. In each month they range in egg production from zero to twenty-five or thirty eggs. The range is greatest in the months after March, although it is not more than five eggs below the maximum in any single month. Out of the whole 655 birds, seven actually attained the maximum production in any single month.

Other resemblances between egg production in the different months may be seen in the similarities in the general form of their frequency distributions. The frequency curve for each month is roughly bimodal, and denotes two classes of birds; one characterized by laying few or no eggs; the other laying fifteen or more eggs.

Calculation of the constants for these distributions verifies and extends our conclusions from a rough inspection of the data. These constants are contained in Table 7, to which we may now turn.

MEAN PRODUCTION. The average number of eggs laid in several of the months by these Barred Rocks and by contest fowls in general is affected by circumstances which are peculiar to laying contest conditions. In the first place the year is limited arbitrarily at both ends and although the period over

which the records extend (November 1 to October 31) corresponds roughly to a natural pullet year, it does not include the whole first year egg production of all of the fowls, which may not conform exactly to a calendar year. Some of the fowls have laid before reaching the contest and others continue to lay after they leave. The curve of average egg production does not, therefore, begin at or near zero, but at an average of slightly over three eggs for the first month. Production in this first month is also affected by the recent ship

Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Fig. 5. Monthly variation in mean egg production of 655 Barred Rock pullets.

ment and change of conditions under which the birds live and the November and probably the December averages are for this reason lower than they would be for similar birds which had not been subjected to such changes*. The averages for November and December probably do not accurately represent the general features of the beginning egg production of Barred Rocks. After this time there is no reason to suppose that the monthly averages are not representative.

The records of the Maine Station Barred Rock pullets from 1899 to 1907 as reported by Pearl and Surface (1911 Part II p. 89) show that these pullets which entered the laying house directly from the rearing quarters laid 3.6 per cent of their eggs in November and 6.9 per cent in December whereas the contest pullets laid 2.1 per cent in November and 4.7 per cent in December. Under the Maine Station conditions, 28 per cent of the annual egg production occurred between November 1 and March 1 while under contest condition only 20 per cent of the annual production occurred in this period.

OF THE DOMESTIC FOWL

The changes in mean egg production throughout the twelve months are shown in the diagram in Fig. 5. The changes illustrated in this diagram need little comment for they are similar in the main features with those occurring in fowls in general, and are now quite familiar. The curve is regular and smooth. The changes in egg production are not random changes, but follow an orderly sequence which has its basis in the regular seasonal changes which take place in the reproductive system of the fowl. These changes result in a period of increasing egg production from November to February; a sudden rise to a high level maintained, and in the Barred Rocks slightly increased, through March, April and May; a fall to a somewhat lower level of production in July and August and a sudden drop in October. The departures of this curve from a unified single cycle are chiefly at the beginning, when egg production has already attained some magnitude; and at the end when it is still decreasing and cut off not by a natural stop, but by the artificial termination of the records. The ascent from November to December is probably steeper than it would be under natural conditions, since the increases in egg production at this time represent not only additions to the number of birds laying, but also the natural increase which would have taken place in November if changes had not taken place in the environment of the birds.*

STANDARD DEVIATION. In the second column of Table 7 are shown the changes in the relative variability of the fowls. These changes are likewise orderly with the exception of November when on account of the differences in maturity (due to variations in time of hatching, innate differences and persisting effects of the variable conditions under which the different pens of fowls have been kept) we should expect the standard deviation to be greater than at any other time. These tendencies to variation are, however, probably offset by a single cause acting on all of the fowls which tends to restrict variationi. e. the shipment and change of conditions of all of the birds

*Since this was written Harris and Lewis (1923) have contributed valuable data on the time of beginning and cessation of laying in contest birds. The relation of these factors to annual and monthly variation in egg production will be considered in the final bulletin of tihs series.