« PreviousContinue »
As indicated by its equation y 13.073 .168x the line describing the trend of changes in the relative frequency of love producers is nearly horizontal, with a slight tendency to slope downward. The equation for high producers is y 10.108 + .245x and the slope of this straight line is upward. This proportion gained about 2.02 per cent in the nine years. Neither of these changes is very marked and it is doubtful whether either indicates a significant tendency. The data are moreover complicated by the inclusion of two years of abnormal conditions.
In the annual changes in both of these percentages an extreme deviation is noticeable in 1918 and 1913. In these years the percentage of pullets laying 210 eggs and over was lower than in any other year, while the percentage laying 104 eggs and less was abnormally high. If, in order to measure the changes in the performance of the birds in different years under uniform conditions, we omit the years 1918 and 1913, it is found that the straight line describing the changes in the percentage of low producers has a more marked downward slope. Its equation is y = 14.719 - .668x, and the total theoretical decrease in the frequency of low producers in the eight years is about 5.3 per cent.
Under the same treatment the equation to the line most nearly describing changes in the percentage of high producers becomes y =8.159 + .948x. The slope is distinctly upward and the total theoretical increase in the frequency of high producers in eight year: is about 7.6 per cent. The straight lines htted to the data when 1918 and 1913 are omitted are shown as the dotted lines (1) in Figs. 4 and 5. In interpreting this line, the seven absciss: e labelled in italics should be used as references lines.
Before drawing co iclusions from this evidence, it will be well to reconsider our definitions of high and low egg producers. We have classified these arbitrarily as laying more or less than a given number of eggs in any year. It is possible, however, that the number of eggs which distinguish a high or low producing pullet is different in different years, particularly since the mean production varies considerably from year to year. Thus of two birds each of which lays 225 eggs, one may The propor
belong to a population with a mean production of 146 eggs,
The importance of these data for our present purpose. however, is for their bearing on the changes in the proportions of high and low producers in the nine years. We have titted straight lines to the proportions of fowls laying 33.3 per cent less than the mean number of eggs (low producers) and to the corresponding proportions of high producers so defined. The
equation to the line for the low producers for the nine years is
= 12.919 – .175x indicating a slight but probably insignificant tendency toward decrease in this proportion. For the high producers this line is described by the equation y=11.871 - .060x which indicates no tendency toward change. The proportions of high and of low producers, relative to the mean, have tended to remain stationary through the nine years.
We may summarize our findings in respect to changes in the proportion of extreme variates as follows:
(1) When arbitrarily deined the proportion of high producers has tended to increase very slightly during the nine Tears while the proportion of low producers has remained stationary or declined slightly.
(2) When only the seven normal years are considered, it is found that the proportion of fowls laying 210 eggs and more has increased significantly while the proportion laying 107
eggs and less has declined. The rate of increase in the proportion of high producers has been greater than the rate of decrease of the low producers, thus accounting to some extent for the absence of any decrease in variability as the mean has increased. On the whole it is probable that there is a tenclency toward increase in the proportion of high producers and toward decrease in the proportion of low producers as measu red by arbitrary standards among the Wynadottes submitted to the contest from year to year.
Progress in these directions has been neither extremely rapid nor steady: nor are changes in the two proportions closely correlated. A decrease in the proportion of low producers is not necessarily followed by an increase in the proportion of high producers or vice versa, since both groups are relatively small. It is probable that environmental changes have different effects on these two proportions. The number of birds laying 210 eggs or over is determined chiefly by innate factors and although this number may be decreased by unfavorable conditions, it can probably not be increased by conditions above the average. It
represents usually a minimum. The number of birds laying 104 eggs or less on the other hand, usually represents a maximum since in addition to the hereditary low producers it probably contains a variable number of potentially high producers which because of illness and environmental variations fail to attain their real capacity. It is less likely that any potertially low producers may be included either in the mediocre or high classes. The somewhat greater annual variation in the proportion of low producers is perhaps to be explained by the considerations just cited.
(3) When defined as those fowls which deviate above or below the mean of the flock by a given percentage of the mean, the high and low producing classes have shown no significant tendency to change during the nine years. The proportion of fowls entered which are superior t. the average of all competing fowls has shown no tendency to increase, such as the increase, in mean production might have led us to pect. The significant generalization from all these lines of evidence appears to be that low producing individuals, however defined, are being only very gradually eliminated from the fowls entered and still constitute the chief impediment to progress in increasing egg production.
CHANGES IN EGG PRODUCTION AT OTHER PLACES.
We have partial data at hand for the English contests which are reported by individual birds. The three years already quoted (p 44 and Table 3) for the Harper Adams Contest show much more striking changes in mean, variability, and percentage of high and low layers. The rising mean there is accompanied by a falling variability, the cause for which is found in the almost complete elimination of low producers from the competing pens. The percentage of birds laying 104 eggs and less fell from 5.4 in 1912, to 5.2 in 1913 to slightly less than 1.1 in 1918 while the percentage of birds laying over 210 eggs rose rom 15.7 in 1912, to 36.3 in 1913 and fell to 31.0 in 1918. Percentages of high layers such as these last two have never been approached in this contest. On the whole, they indicate that the English Wyandottes have become more and more uniform, as witnessed by the falling variability, and that the modal frequencies of egg production have been raised as a whole. It is possible that the birds now submitted to such a contest as that at Harper Adams Agricultural College are extremely homogeneous in blood and in egg producing ability due to the dissemination of breeding stock which placed high in the early contests and the subsequent return of progeny of these birds to make up a large portion of the entries in later contests. Our general conclusions must be limited to these:
(1) Egg production in Wyandottes submitted to contests all over the world is probably on the increase.
(2) This increase in the Northeastern United States which supplies most of the birds in this contest is in general smaller than that indicated by incomplete figures from Enir
(3) The American birds are both absolutely and relatively more variable in respect to egg production than the English
Breeders in this country do not appear to have climinated the low producing pullets from the birds entered in the
These facts should contain food for thought for the Ameri-
English and probably colonial breeders have, as is well known, departed from the standards which influence the breeder in this country. They are breeding for egg production and have sacrificed the standard or conformational type which is still maintained in this country. Uniformity in appearance has been replaced by uniformity in performance. The wisdom of this must be judged according to the individual
SEASONAL DISTRIBUTION OF EGG PRODUCTION
1. General Character of Egg Production in the Separate
Months. The foregoing sections have described by reans of statistical constants the general facts regarding the annual egg production of Wyandotte pullets. These facts alone do not give a complete idea of the character fecundity in this breed, for the year is a large and coarse unit of measurement. Fowls differ Teatly in seasonal, as well as in annual egg production, and these seasonal variations are of great importance to the poultryman and the student. We propose, therefore, to describe for