VARIABILITY IN EGG PRODUCTION 7 



These data give evidence that in selection for uniformity in persistency in the 

 three Hnes, environmental forces appear to be more potent than heredity in 

 affecting variability in strains where most individuals carry gene P for high 

 persistency. 



To sum up, the data presented in Table 1 concerning the variability of five 

 inherited characters affecting fecundity indicate the following: Age at first 

 egg in pullets is modified by environmental influences in a genetically early 

 maturing population so that there is a variation of about 10 per cent that is 

 not produced by hereditary differences. Winter intensity is highly variable, 

 and the response to selection for low variability in all three lines indicates that 

 the observed high varial)ility is largely due to genetic differences. The data 

 further point to the possibility of reducing the variation of intensity to a figure 

 comparable with age at sexual maturity. Winter pause duration is modified 

 but little by selection. Some evidence that degree of broodiness is governed by 

 hereditary factors appears. High persistency behaves like early sexual maturity 

 in that a moderate degree of variation occurs that does not appear to be genetic. 



VARIATION IN WINTER PRODUCTION 



Winter production depends largely upon the three inherited characters; age 

 at sexual maturity, winter pause and intensity. Line A was constantly selected 

 for uniformity in the above characters along with non-broodiness and high 

 persistency. Lines B and C were not selected for uniformity in these inherited 

 characters. \'ariation in winter egg records was not consistently reduced in any 

 of the lines, but all three lines were less variable than the check group. 



VARIATION IN ANNUAL PRODUCTION 



Annual egg records depend upon five inherited characters already indicated 

 as well as upon many environmental influences both controllable and otherwise. 

 Line A was selected for uniformity in inherited characters affecting fecundity, 

 line B was selected for uniformity of annual egg records, and line C was selected 

 for high egg records. All three lines were carried under the same environmental 

 conditions. 



The data in Table 1 show that line C alone decreased in variability with 

 each generation. This fact would indicate that selection for high annual records 

 decreased the variation in annual records. The data as a whole show that both 

 heredity and environment are operating to affect variation in annual egg records. 



ENVIRONMENTAL FACTORS IN RELATION TO VARIATION IN 

 ANNUAL PRODUCTION 



Hatching Date 



Birds used in this experiment were regularly hatched in eight weekly hatches 

 beginning JMarch 25. It is conceivable that these rather restricted hatching dates 

 may affect the variation in annual egg production because unequal numbers of 

 birds in the three lines were hatched on the same date. 



In Table 2 the three lines are combined and the number of individuals hatched 

 on each date in each generation is recorded. The coefficients of variation of the 

 mean production records of each hatch are recorded in the four generations to 

 serve as a rough measure of variation in production attributable to differences 

 in hatching dates. 



