182 



TECHNICAL BULLETIN 8 



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

 laying, wliich 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 jjause 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 sucli 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 together. In breeding 

 for high annual intensity, winter pause nnist certainly be reduced in duration. 



20. Correlation Betxaeen Annual Kate or Intensity Below the Mean and the 

 Presence of Winter Pause for the Total Population. 



Coefficient of correlation -)-.6649 ±: .0081 



The sul^stantial magnitude of the 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 

 while 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- 

 nificantly to lower tlie annual rate of laying. 



21. Correlation Betwetn Annual Persistencif and Len(jth of ]\'inter Pause. 



Annual persistency represents the nimiber of days of laying from tlie 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 the biological laying year. 



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

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

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

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

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

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

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

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

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

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

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

 constants: 



