PREDICTING EGG PRODUCTION IN WHITE LEGHORNS 267 



r t en who feel that they cannot trap-nest for the whole year may be able to 

 o so for a period of one, two or three months. Furthermore, another 

 :ethod of determining the record of individual birds for a given period 

 then a knowledge of the maternity of the individual eggs is not necessary 

 !is recently been suggested by ALDER and EGBERT (1918). 

 , In selecting the months to be used in the calculation of prediction equa- 

 pns for practical use one should of course be guided by the experience 

 id needs of commercial poultrymen. It has generally been maintained 

 lat culling should not be undertaken until the period of summer pro- 

 action. The price of eggs is highest during the winter and early spring 

 \onths. If birds have been left in the flock during these months in the 

 ope that they will produce some eggs in the period of generally low pro- 

 uction and high price, it would be unwise to discard them just at the time 

 &quot;hen some return will most probably be made for maintenance rations 

 uring a preceding period, unless the price of eggs is too low to pay for 

 ic cost of the feed during the period of spring production when most ot 

 le birds are laying heavily. Possibly this opinion is partly based on the 

 [adequacy of criteria for eliminating the probably less productive birds 

 irly in the season. 



Furthermore, the physiological laws underlying egg production should, 

 i so far as possible, be taken into account in selecting the periods upon 

 hich prediction equations are to be based. Previous students of fecun- 

 ity in the domestic fowl have been inclined to recognize certain standard 

 eriods. For example, the division of the year adopted in the many papers 

 ublished by PEARL, SURFACE and their collaborators at the MAINE STA- 

 ION is the following: 



Period of winter egg production: November, December, January and 

 ebruary. 



Period of spring egg production: March, April and May. 



Period of summer egg production: June, July and August. 



Period of autumn egg production: September and October. 



This is also the division adopted by CARD (1917, p. 67). 



These periods will be used in the present paper, and other combinations 

 dded so that there may be a wide range of periods from which selection 

 lay be made. 



While fully recognizing the foregoing principles we have felt it a part 

 f the biologist s task to furnish a comprehensive series of measures of 

 iterrelationships of the egg production of various periods from which 

 ny desired equation may be selected. It has, therefore, seemed to us 

 est in this publication to base prediction equations upon a large number 



ENETICS 6: My 1921 



