^"ARIABILITY IX EGG PRODUCTION 5 



Age at First Egg 



Line A had the lowest variabihty in age at sexual maturity in the first gen- 

 eration. The coefficients of variation in the three lines for the first generation 

 were 6.72, 12.09 and 8.63 per cent, respectively. The variability in age increased 

 in subsequent generations in line A and was greater in the fourth generation than 

 the normal of 10.64 per cent shown by the check group. 



Line B showed a wider variation in age at first egg than the check group in 

 all generations, e.xcept the second. It is clearly evident that neither the method 

 of selecting breeders nor the degree of relationsliip reduced the age variability 

 in this line. In fact, 19 of the 22 daughters in the fourth generation actually 

 came from full brother-sister matings. 



Line C exhibited a very significant reduction in variability of age at sexual 

 maturity in the last two generations. This line actually had a variability in the 

 fourth generation about half as great as the check group. The low variability 

 was evident in the third generation resulting from unrelated matings as well as 

 in the fourth generation from a brother-sister mating. 



In general, these data indicate that non-heritable influences are constantly 

 operating to reduce or increase the age at sexual maturity in genetically early 

 pullets so that a reduction in age variability below 10 per cent by breeding 

 methods does not seem feasible. ]\Iore carefully controlled environmental con- 

 ditions are likely to reduce variability but the possibilities here are limited. 



Intensity 



Intensity is here measured by mean winter clutch size. The first generation 

 of females in lines A and B show a variability of intensity of about 60 per cent. 

 Line C has a variability of about 47 per cent in the first generation and is com- 

 parable with the check group. The results of breeding are shown in generations 

 two, three and four. 



Line A was selected each year for imiform high intensity. It will be observed 

 that the clutch size showed a consistent decrease in variability with each genera- 

 tion and the last three generations are lower in variability than the check group. 



Line B exhibited a high degree of uniformity in intensity in the second gen- 

 eration; but withoiit specific selection for uniformity generations three and four 

 show decreased uniformity. 



Line C gave a highly significant decrease in variability in each succeeding 

 generation. The number of birds concerned in the last generation is too small to 

 give the zero value significance, however. Results in this line illu.strate that in 

 the selection of very high producers for breeding, the variability of winter in- 

 tensity is reduced. It is probable that almost every bird in the first generation 

 of this line carried both genes I and I' for high intensity and such a genetic make- 

 up should produce increased uniformity in succeeding generations. 



The data point in general to the effect of inheritance upon uniformity of 

 intensity and demonstrate clearly that breeding is more important than environ- 

 ment in controlling variation in intensity. 



Duration of Winter Pause 



In duration of winter pause only birds ceasing to lay for four or more days in 

 the winter season are considered. Such birds presumably carry the dominant 



