7 74 TECHNICAL BULLETIN 8 



constant is subject to error, however, in that any increase in length of winter 

 cycle reduces the possible pause interval before March first. The coetticient 

 of correlation as calculated is of value in that it gives the actual relationship 

 between length of winter cycle and duration of pauses within the winter 

 season. These data furnish very good evidence that the length of winter 

 pause does not depend upon the length of the winter cycle of laying. 



In this report consideration is given to the winter pause from three gen- 

 eral standpoints, namely, (a) Environmental factors affecting duration of 

 the pause; (b) Inherited characteristics concerned with fecundity in relation^ 

 to winter pause, and (c) The absolute relationship of winter pause to egg 

 production. 



(a) Environmental Factors Alfectiny Duration of Pause. 



Much concern should be given to the relation of environmental factors 

 affecting the duration of the winter pause since these conditions are more or 

 less under the control of the poultryman. In the group of environmental 

 factors the following have been placed: hatching date and time of beginning 

 to lay in the fall. The time of year when pullets begin to lay is clearly de- 

 pendent both upon management and inheritance. Management is a factor 

 when the hatching date remains constant because housing, range, and feeding 

 may either retard or accelerate sexual maturity. Just how significant these 

 environmental influences are on time of beginning to lay in comparison with 

 inherited early or late sexual maturity remains to be determined. At any 

 rate, hatching date can be definitely controlled and time of beginning to lay 

 may be considered as partially controllable. 



7. Correlation Between Hatching Date and Length of ]Vint(r Pause. 



A very common observation among poultrymen is that early-hatclied pulletg 

 arc more likely to exhibit winter pause than are late-hatched birds of the same 

 dock. In other words, the belief is prevalent that the earlier the hatching- 

 date, the longer the winter pause. Such observations have naturally led to 

 the assumption that the pullet possesses capacity to lay a certain number of 

 eggs in the fall and winter and if this number is laid early there will be a 

 cessation of laying until the spring season. That hatching date is only one 

 of several conditions operating to aifect the onset and duration of winter 

 pause has been shown by Hays (1924) and Hays, Sanborn, and James (1924). 

 Age at sexual maturity has been pointed out as an inherited characteristic, 

 and as a characteristic having greater effect than hatching date upon winter 

 egg production. Furthermore, winter pause of seven or more days' dura- 

 tion is an inherited characteristic. The importance of knowing just how 

 intimate a relationship exists between date of hatching and duration of 

 winter pause becomes apparent and may be discovered by means of the 

 coefficient of correlation. 



A total of 2134 birds exhibited a pause of four or more days and are in- 

 cluded in these calculations. The winter pause class interval is ten days in 

 all cases. Constants obtained from this study follow: 



