INTENSITY OR RATE OF LAYING 

 IN RELATION TO FECUNDITY 



By F. A. Hays and Ruby Sanborn 



INTRODUCTION 



Intensity or rate of laying was first cited by Goodale and Sanborn (1922) 

 as of vital importance in relation to total number of eggs laid. The sig- 

 nificance of intensity in relation to winter fecundity' has been further 

 stressed bj' Hays (1924) and a theory concerning inheritance of winter 

 intensity proposed. The probabilities are that higli winter rate behaves 

 as a dominant in inheritance and that two Mendelian factors are concerned. 

 Possible measures of intensity are numerous and diverse. A number of 

 .such measures will first be considered. 



Meaisures of Intensity. 



Since rate can only be obtained on a time basis, it becomes necessary to 

 <nake use of some definite time interval. Furthermore, the time element 

 must be based either on calendar months or upon a specific period in the 

 laying year of the individual bird. From the biological standpoint the 

 second method of assigning time in calculating rate might be preferable, 

 yet diverse weather conditions throughout the year may partially nullify 

 effects of biological differences. 



Goodale and Sanborn (loc. cit.) suggest as time units the month, the 

 initial cycle, the inter-broody periods, the summer period and the spring 

 period. These workers also mention length of clutch as a possible meas- 

 ure and make the statement that the calendar montli may be employed for 

 flock comparisons though unsuitable for individual comparisons. 



A rather common measure of intensity is the greatest number of eggs 

 laid by a bird during any calendar montli of the pullet year. Such a 

 criterion of intensity is certainly very crude, as Harris and Goodale (1922) 

 have shown for Rhode Island Reds. Probably a long time interval, gov- 

 erned in part by the individual date of first pullet egg and terminated at 

 a definite calendar date, offers the most reliable period for calculating 

 intensity. 



In these studies four measures of intensity liavc l)een used: 



i. First si.vti/ daiftt' prodiirtion. 



The number of eggs laid from the first pullet egg for a period of sixty 

 days was tabulated. This figure represents a definite interval in the lay- 

 ing year and furnishes a clue as to the rate at winch the birds begin lay- 

 ing. In this instance the actual calendar date varies both with hatching 

 date and with age at which sexual maturity is attained. In other words, 

 the production of the first sixty days is not comparable with production 

 tor two specific calendar months. 



