« PreviousContinue »
this breed the average number of eggs laid in the separate months and seasons of the year; to determine the absolute and relative variability in egg production at different periods; to examine the differences existing between high and low producing fowls in the seasonal distribution of their laying; to find out if possible whether distinct seasonal cycles of egg production are characteristic of this breed and finally to trace the general trend of changes which have taken place in the seasonal distribution of egg production in this sample of Wyandottes during nine years.
To study these questions the original records must be retabulated to show the frequency distribution for each separate month. This has been done and the raw data for the combined nine years are presented in Appendix Table IIa and IIb, which show for each month in the year the number and percentage of birds laying no eggs, the number laying 1, 2, 3,—30 eggs. The constants describing the general character of monthly production have been calculated directly from the data arranged in unit classes. Information on mean production in the separate months of each of the nine years is given by the actual number of eggs laid and the percentage of yearly production occurring in each month of each year in Tables 5 and 6.
The principal constants deduced from the monthly frequencies are given in Table 7.
(a) Mean Production
The average number of eggs laid per bird is found to rise steadily and rapidly from between four and five eggs in November to a maximum of about eighteen in the months of March, April and May. The differences in egg production between these latter months are not significant. After May the mean falls slowly through June and July, increases very slightly in August and finally drops suddenly in October. The mean, however, is never as low again as it was in November and December. These changes are shown graphically in Fig. 6. The general form of this graph is similar to others deduced from data on egg production in Barred Plymouth Rocks (Pearl and Surface 1910) and Leghorns (Card 1917) (Ball and Alder 1917). In certain particulars it differs from these :
TABLE 5 DISTRIBUTION OF Toral Egg Production by Months AND YEARS.
1911 641 1271 265 475 820 12781 1242 1000 912 955 1015 975 718 9782
Total 903 41247374 9395 11393 16043 16265 16257 14675 132071347212652 9073 143930
*This table contains the data of table 5 stated in the form of percentages for direct comparison between months and years. is to be read (line 1): In 1911 64 Wyandotte pullets laid in November 1.30 per cent of their year's total of eggs, in December they laid 2.71 per cent of the year's total, etc.
Deviation of Variation Nov. 4.57+.16 7.00+.11
153.36+5.82 Dec. 8.18+.20 8.70+.14
106.42+3.05 Jan. 10.40+.18 8.10+.13
77.82+2.21 Feb. 12 62+.15 6.70+.11
53.11+1.05 Mar. 17.77+.13 5.98+.09
33.66+ .59 Apr. 18.00+.13 5.66+ 09
31.42+ .55 May 18 00+.14 6.22+.10
34.58+ .61 June 16.25+.14 6.33+.10
38.97+ .70 July 14.63+.15 6.62+.11
45.24+ .85 Aug. 14.92+.15 6 58+.10
44.12+ .83 Sept. 14.01+.16 7.07.11
50.52+ .98 Oct. 10.07+.18 8.05+.13
1. Low November production (relative).
In this month occurs the minimum production for the Wyandottes studied. They laid in November only 2.87 per cent (Table 6) of the mean number of eggs for the year, compared with 3.59 per cent for Barred Rocks (Pearl & Surface 1910), and 3.58 for Leghorns (Ball et al 1917).
These last figures are for birds in station flocks, bred and raised in the same place in which they made their egg records. The pullets submitted to egg laying contests, on the other hand are raised at a distance from the site of the contest and must be transported in cramped quarters and for long distances, in some cases across the ocean or across the continent, immediately prior to the beginning of the laying year. The low November production is to be regarded in part as an effect of this circumstance. It is characteristic of contest records in general and is not peculiar to any one breed. This departure of the seasonal' curve in Wyandottes from the usual is, therefore, probably not a breed characteristic but is inherent in the conditions surrounding the making of the record.
2. A second peculiarity of this curve is more probably a breed characteristic. This is the absence of a drop in the curye or even of a slackening of the rate of increase of egg production at the end of the winter months. Such a drop in February was
noted by Pearl and Surface for Barred Plymouth Rocks and interpreted as indicating a rest period following the winter production cycle. By them it was stated to be a characteristic of fowl fecundity in general. The general form of the Wyandotte curve at this period indicates that this generality probably does not apply to Wyandottes. This point is discussed at greater length in a later section.
3. There is no single month of maximum production. Egg production is almost exactly the same in March, April, and May, the season of natural fecundity in all wild and domesticated birds in this latitude.
A comparatively high level of egg production is maintained through June, July, August, and September; the mean falling only gradually in these months. The slight increase in mean production in August, while probably not significant, is a general feature of six out of the nine years, and indicates at least that there is no drop in egg production in August.
5. Egg production declines sharply in October, but is comparatively high. It is about equal in the present data to January production and exceeds both November and December production. These Wyandottes laid a larger percentage of
eggs (6.30%) in October than did the Barred Rocks referred to above (4.27%).
In general then, the distribution of Wyandotte fecundity through the months of the year follows the general scheme as established for Barred Rocks; departures from this scheme are most apparent in the difference in the month of minimum production, the practical equivalence of egg production in the three maximum months, March, April, and May; the absence of a drop in production in February; the maintenance of high production in the summer and the relatively high October pro
(b) Variation in Production.
viation. (Table 7).
Variability in egg production as measured by the standard deviation changes through the months of the year in a manner almost exactly opposite to the changes in the mean. It is high in November, reaches its highest value in December, falls steadily to a minimum in April and increases again slowly to reach a second maximum in October. It does not again attain a value as high as that for December, the October absolute variability being like the mean equivalent to that for January. The general aspects of variability and even the values themselves resemble so closely those obtained for Barred Rocks as to confirm the generalities and conclusions drawn by Pearl and Surface. It is not necessary, therefore, to depict graphically or to discuss further, the monthly changes in absolute variability.
2. Relative variability as measured by the coefficient of variation. (Table 7).
Almost the same remarks may be made concerning the changes in relative variability. Its changes when plotted form a mirror image, more or less exact, of the changes in the mean. The month of greatest absolute variability is November, when mean production is lowest. From November it falls rapidly to March, drops slightly to reach a minimum in April and then rises to a second maximum in October, when the egg production is only about a half as variable as it was in November. The graph of the monthly changes in this coefficient likewise resembles closely that plotted for Barred Rocks. It differs in these few particulars. (1) The Wyandottes are absolutely more variable in November, December, and January due possibly to the larger number of zero producers in the contest birds. (2) There is no abatement to the rapid decrease in variability between February and March. This was a marked irregularity in the seasonal variability curve for Barred Rocks, connected with the completion of the winter cycle in February. From February on variability in the Wyandottes is considerably less than in Pearl and Surface's Barred Rocks, and the increase in variability is more rapid for Rocks than for Wyandottes in the summer and fall months.
These are the main features of monthly changes in egg production in the contest Wyandottes. An evaluation of their sig. nificance will be made when statistics on all the breeds in the contest are collated. At present they may be used as standards descriptive of Wyandotte production.