166 



MASS. EXPERIMENT STATION BULLETIN 242 



A comparison of the relation between weight at first egg and mortality 

 rate in the laying houses leads to the deduction that the two are independent, 

 because changes in weight at first egg are not accompanied by changes in 

 mortality rate. 



8. Relation of Winter Pcmse to Mortality Rate in the Layinij Houses. 



The individual egg records for the period from 1922 to 1926 have been gone 

 over and all pullets that stopped laying for four days or more between 

 November first and March first are classed as "pause" birds. Thus the popu- 

 lation is divided into the two general classes, pause and non-pause. 



Possibly the ability to lay continuously after November first is an indica- 

 tion of high vigor and, conversely, the presence of winter pause may indicate 

 lack of vigor. With the measure of vigor made use of, namely, mortality 

 rate in the laying houses, some information concerning the relation of winter 

 pause to vigor may be obtained. 



Table 7 — Relation of Winter Pause to Vigor 



Table 7 shows that the proportion of non-pause to pause birds is about 1 

 to 2.7, yet the mean mortality rates in the laying houses for the groups are 

 identical. Records for the five years show no significant differences in mor- 

 tality rates. Furthermore, there is no significant change in five years in the 

 ratio of non-pause to pause pullets. Therefore, table 7 does not indicate any 

 relation between winter pause and vigor. 



9. Relation 'of Mean Winter Clutch Size to Mortality Rate in the Layiny 

 Houses. 



Is high rate of laying associated with high mortality rate? The importance 

 of high intensity is widely recognized in production-bred flocks; therefore, it 

 is desirable to know if this high rate of laying is in part responsible for 

 great mortality in heavy laying strains. 



Satisfactory measures of intensity are difficult to obtain, but the use of 



