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Monthly Distribution of Total Egg Production by Fecundity (lasses--1911-19.
0- 14 8
20 22 11546 14958 21095
23 270 9514 173355
In view of the opinion frequently held that high fecundity is due to the addition to the normal spring reproductive cycle of a winter cycle of production determined by one or a few inherited unit factors, we have compared the seasonal distribution of egg production of the highly fecund fowls (those laying 210 eggs and over) which appear in our data with those of mediocre and low fecundity. The monthly egg production of fowls of each fecundity class is given in Table 10. In Table 11b these figures have been grouped into high medium and low fecundity classes and placed on a percentage basis so that the seasonal distributions may be compared directly. The data in this form are illustrated in Fig 6. Examining at present only the winter months it is found (1) that a lesser proportion of the total egg production occurs in the winter months of the low and medium than of the high producers and (2) that the rate of increase of egg production during these months is much greater for the "low” and “medium” than for the “high" pullets. Egg production by the high producers begins at a high level and reaches seven and a half per cent in December where it remains until March. Egg production by the low and medium producers starts at a low level and increases at a rapid rate in the low and a somewhat slower rate in the medium producers with no semblance of a decrease or pause in either January or February. There is certainly no evidence of a winter cycle in these classes.
The seasonal distribution of egg production in the high producing fowls shows some evidence of a drop in production in February in which (Table 11b line 3) 7.48 per cent of the annual production occurred in February compared with 7.69 in January. This, however, is entirely due to the fewer laying days included in February, for if the February average is corrected to a 31 day basis to make it comparable with January, it becomes 8.01, and shows an actual increase over January production.
Although no definite cycle defined by a decrease in egg production over a period of as long as a month can be discerned in either the high medium or low producers, the winter production of the “high" group is obviously different from that of the lower groups. The superiority of the high over the medium and low producers is in fact greater in the winter than in any
Comparison of Low, Medium and High Producing Pullets on the Basis of Monthly Distribution of Egg Production.
A-Actual Distribution of Eggs.
16889 16432 14119 13056
144 886 102 1132
1.44 1.99 4.64 2.31
2.45 4.36 7.49 4.66
B--Percentage Distribution of Eggs. 3.83 8.55 15.21 15.98
12.11 11.78 10.12
9.12 9.36 9.02 9.30
8,63 8.77 9.05 8.79
6.47 8.18 8.53 8.11
2.19 100.01 5.51 100.00 6.82 100.01 5.47 99.97
(-Percentage Distribution of Eggs in the Four Seasons. Spring Summer Autumn 46.16 28.92 8.66 100.01 36.23 28.25 13.69 100.00 29.50 27.86 15.35 100.01 35.95 28.23 13.58 99.97
other season. Selective breeding for high egg production has obviously changed the seasonal distribution of egg production to a considerable degree. This change has been, however, a gradual one, as may be ascertained from Table 10, rather than by one or a few discontinuous variations. It is probable that numerous, rather than few changes have been concerned, and that these have taken place in rate of growth, speed of maturity and several other elements of vigor contributing to fecundity.
SPRING The spring season is plainly different, although not discontinuous with the other seasons of egg laying activity. It is the season of greatest fecundity in all years and all fecundity classes. It is of course the natural mating season of wild birds, and is the climax of the reproductive activity of the whole year. It is in all groups and all years a period of sustained egg production which remains at a high level through March, April and May, and begins to decline in June. The actual highest production in this breed is reached in March, although the differences between the means of March, April and May are insignificant. In these months practically every pullet in the flocks is laying; the one per cent of non-layers consists probably of birds which are sick or otherwise temporarily subnormal.
TABLE 12 PERCENTAGE OF FLOCK LAYING ZERO EGGS IN THE SEPARATE
67.3 45.6 22.1 8.0 1.2 1.4 1.3 2.0 3.5 4.9 10.7 31.0
In the proportion of annual egg production which occurs in the spring, the several fecundity groups differ somewhat (Tables 10 and 11). The low producers lay the greatest proportion of spring eggs, 46 per cent of their annual production occurring in this period; the next greatest proportion (36 per cent) occurs in the medium group, while the high producers lay only 29 per cent of their eggs in the spring. Whereas nearly half of the eggs laid by the low producers are laid in the spring, less than a third of the total production of the high layers occurs at this time. The low producers resemble in this respect the wild ancestors of the fowl whose egg laying activities were confined to the spring and summer, while the selecte high producing group shows the greatest change from the wild type of fecundity.
The characteristic of summer production in Rhode Island Reds is a gradual decline in egg production. The summer season of fecundity is not sharply marked off from the spring reproductive cycle, but is rather a continuation of it. One factor concerned in the fall of average production is the cessation of laying by a part of the flock; since two per cent lay no eggs
three and a half per cent lay no eggs in July and five per cent lay no eggs in August. The increase in this proportion is not sufficient to account for the drop in per cent production from 58 per cent in May to 43 per cent in August (Table Column 4). The other and probably chief factor in this breed is the onset of broodiness occurring in short periods, which when successfully broken up, alternate with periods of egg laying. The Rhode Island Reds in all contests have shown a higher percentage of broody fowls and a greater proportion of time lost through broodiness than all other breeds (cf. for example Bulletin 89 of this station p. 281).
June production in all years is less than May production (Table 6) and July production is less than June, while in all except three years, August production is less than July. In 1917, 1918, and 1919 egg production in August was the same as or slightly greater than July egg production. Whether this is a chance deviation or whether it indicates a change in the in
qualities of the fowls entered or a change in methods of