182 



TECHNICAL BULLETIN 8 



The mean annual rate of laying is lower than the mean winter rate of 

 laying, which is 65.69. This difference may be attributed largely to the fact 

 that in calculating annual rate no account is taken of winter pause or of 

 broody pauses. In the winter rate calculations, winter pause days are not 

 included and very few birds become broody before the end of the winter 

 season. The standard deviation in annual rate is relatively small and suggests 

 uniformity in annual rate of laying. 



The coefficient of correlation is negative and of such magnitude as to indi- 

 cate a significant relation between rate and length of pause. In other words, 

 low annual rate and long winter pause tend to move togetlier. In breeding 

 for higli annual intensity, winter pause nuist certainly be reduced in duration. 



W. Correlation Bettaeeii Annual Rate or Intensity Below the Mean and the 

 Presence of Winter Pause for the Total Population. 



Coefficient of correlation 



-I-.6649 It .0081 



The substantial magnitude of tlie above coefficient of correlation points to 

 a pronounced tendency for low annual rate to occur with winter pause. The 

 table above also sliows that 80 per cent of the low-rate birds are pause birds 

 wliile only 45 per cent of the high-rate birds are in the pause group. The 

 conclusion, therefore, seems justified that winter pause operates very sig- 

 nificantlv to lower tlie annual rate of laving. 



21. Correlation Betzi'ein Annual Persistency and Lenyth of ]Mnter Pavse. 



Annual persistency represents the number of days of laying from the first 

 egg to a pause of thirty or more days after March first. If no thirty-day 

 pause occurs between March first and the date 364 days after the first egg, 

 the bird is given a persistency of 365 days on ordinary years and 366 days 

 on leap years. A cessation of laying for a period of thirty days or more 

 during summer is a rather dependable indication of the onset of complete 

 molt, which always signifies the conclusion of tiie biological laying year. 



Persistency as indicated by time of molting has long lieen recognized as 

 affecting egg yield, and poultry investigators have recommended the use of 

 late molting birds for i)reeding purposes. Hurst (1921) was the first to 

 offer a definite hypothesis concerning its mode of inheritance. He believes 

 high persistency is transmitted as a single factor recessive. If a rest period 

 111 winter enables the bird to lay later in the fall than does the bird without 

 the rest period, then persistency must depend in part upon the previous 

 physiological activity of tlie reproductive organs, or possibly there is linkage 

 between winter pause and liigli persistency. The same group of 1348 birds 

 used in the two previous sections is studied below. Persistency range lies 

 between 67 and 366 days with class intervals of 15 days. Following are tlie 

 constants: 



