Page images


IN THIS CONTEST (a) Mean production.

The mean annual egg production has varied considerably from year to year. An examination of Table 2 and Figure 2 will demonstrate how large this variation has been. The mean production fell from about 155 eggs in 1911 to the low mean of about 148 eggs in 1913; rose abruptly to the high means of nearly 169 eggs in 1915 and 1917, and fell in the intervening year, 1918, to about 147 eggs, which is the lowest production recorded for any of the nine years. The major changes are not gradual but rather abrupt, indicating distinct differences in either the fowls entered in the contest or the conditions in the different years. It must be remembered that the annual means are computed on a different lot of pullets in each year and that there is probably little relationship between the pullets submitted in different years since they come generally from different breeders. A more important consideration than this is that the numbers of birds from which the records are obtained in any one year are in general too small to constitute a random sample of the breed. Before inquiring into the meaning of these differences in annual production, it will be necessary to determine which differences are statistically significant; i. e. which differences are inherent in the material and not due merely to the ordinary deviations encountered in taking two small samples of a population. In general, only those differences need be considered as possibly real or significant which are greater than three times their probable errors.

When the differences between each pair of years are computed together with their probable errors, it is found that (1) the mean production in 1915 and 1917 was significantly higher than in an other years except 1919 and 1914; (2) mean egg production in 1918 was significantly lower than mean production in 1914, 1915, 1917 and 1919; (3) mean production was significantly lower in 1913 than in 1915 and 1917.(7)

Of the thirty-six possible differences between different pairs of years only these twelve were found to be statistically (7) The table used in determining the significance of these differences is given in Appendix Table III.

significant. The differences between the other years are probably due to the errors of random sampling alone. The differences found suggest a division of the years into three categories as regards mean egg production: (1) the high years 1915 and 1917, (2) the "low” years 1918 and 1913(8) and the intermediate years 1911, 1912, 1914, 1916, and 1919 none of which differs significantly from each other. We have, the efore, to seek explanations only for the low mean production in 1918 and 1913 and the high means in 1915 and 1917.

The reasons for the low production in 1918 are more readily found. In this year, due to conditions brought about by the war, the care of the birds was far from normal. The attendants, in whom interest and experience are requisite to the best results in any poultry enterprise, were continually changing. Trapnesting, cleaning, feeding and care of the health of the birds often had to be entrusted to inexperienced and unskilled help with the result that the records made by all of the breeds in the contest were lower in 1918 than in any other year. We need have little hesistancy in ascribing the low mean production of 1918 to environmental causes. Concerning 1913, the conditions causing low production are less certainly known except that weather and other conditions were apparently abnorinal for the first five months of the contest.

In 1915 and 1917, on the other hand, the environmental conditions were apparently similar to those of other normal years. In general as will be shown later, these were not years of extremely high production in the other breeds. It is probable, therefore, that the reasons for the high mean production of the Wyandottes in these years must be sought in the birds themselves. Since the Wyandottes observed in the contests in these years were significantly superior in fecundity to those submitted in other years, it is probable that they were possessed of innate abilities to lay more eggs. These explanations appear, in the light of the facts cited and others to be considered when the four breeds are compared, to be the most probable ones for the differences noted. They give further indications


(8) Note-From other data it is known that 1913 was a year of abnormally low preduction in all the breeds in the contest. It is included with the low group although its differences from the neans of the intermediate years are not statistically signif. cant.

of what many poultrymen find in their own experience—that although poor management and care and conditions can prevent an average or good fowl from laying as many eggs as she is by nature capable of laying, nevertheless something more than normal or even extraordinary care is necessary to attain high egg production. This something is the innate capacity for high fecundity exhibited by the Wyandottes in the 1915 and 1917 contests, under conditions which did not bring forth the same results in all the other breeds. (b) Variation constants.

The other descriptive constants have like the mean varied significantly from year to year. The range of the standard deviation is roughly from 40 to 50 eggs, although the upper limit was exceeded in 1919 when the standard deviation reached the extremely high value of over 53. The variability of the fowls submitted appears to have no intimate relation with mean production. In the "low” years, 1913 and 1918, the standard deviations are about 46 and 42 eggs respectively, while in the two high years 1915 and 1917, the values of the standard deviation are similar and have a similar difference being about 47 and 40 eggs. The extremes of variability, 53 in 1919, and 39 in 1914 are not marked by abnormally high or low production and one must conclude that the absolute variability and the mean are determined in the main by different sets of factors. The first constant measures the spread or scatter of the distribution. It is an index of the different kinds of birds submitted and is dependent almost wholly on the innate capacities of the fowls. The mean on the other hand is the expression of the egg laying activities of the whole group and may be depressed as we have seen by environmental conditions. The coefficient of variability, representing a percentage relation between the mean and the standard deviation depends of course on both of these values. It varies through a narrower range although giving in comparative terms the same information as the standard deviation. The median, or that point which divides the distribution into equal halves varies through approximately the same range as the mean, from 145 to 173 eggs. The analysis of the general trend of mean production and variation is considered in the ensuing paragraphs.



A question of general interest to poultrymen, to biologists, and to the public at large is whether the general character of egg production is changing. Considerable effort has been expended in the last two decades toward the discovery and application of methods of breeding fowls for high egg production. Is there any evidence that egg production is a character which may be permanently improved by the present methods? Is the average egg production of fowls submitted to this laying contest increasing? Are they becoming more uniform in fecundity? Are the fowls of poor fecundity being eliminated and those of high fecundity being propagated in larger numbers? The present material may be able to throw some light on these questions in regard to one breed of poultry for a short space of time, nine years.

The changes in mean production in the separate years are shown in Table 2. They are in general rather irregular and the significance of the differences between the various years has already been discussed. From the data in such form we cannot determine immediately whether the mean production bas advanced or remained stationary. These data have hence been placed in graphic form in Fig. 2 with mean egg production plotted as ordinates and the separate years as abscissae. By the method of least squares the straight line which most closely fits these various points has been drawn. (Fig. 2 AB) The origin of the line (that is, y ) is taken one year previous to the commencement of the contest. This theoretical origin is 154.316 egers and the equation of the line is y = 154.316 + .815 x; that is, considering the whole nine years the average annual change in mean ego production is +.815 eggs, a gain in nine years of 7.3 eggs or about 4.7 per cent over the theoretical starting point. This average annual gain determines the slope of the line which is gradual but ascending. The line AB then shows the general trend of mean egg production. This is upward, but the amount of advance is relatively small.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small]

Fig. 2. Changes in mean annual egg production from 1911 to 1919.

The solid line AB shows the trend of changes in the mean through the nine year period. The broken line CD shows the trend of changes through the seven normal years designated in italics.

« PreviousContinue »