202 TECHNICAL BULLETIN 12 



14- Total Days Broody and .liinual J-'rodiicfiuii. 



Degree of broodiness may be measured by tlie total broody days during the 

 pullet laying year. The degree of broodiness is affected by inherited factors 

 so that it may be reduced. The presence of broodiness in any degree has been 

 shown to be inimical to annual egg production (Hays and Sanborn, 1926a) 

 and tlie broody trait itself has been shown to be inherited (Hays, 1924). 



To discover the true relation of degree of broodiness to annual production, 

 the method of partial correlation is applied with age at first egg, winter pause, 

 winter clutch size and persistency made constant. The net correlation between 

 total days broody and annual egg production is — .5630±.0097. This is an 

 important relation and makes clear that degree of broodiness is a vital factor 

 in annual egg yield. Degree of broodiness may be placed on a par with winter 

 pause and intensity as a characteristic affecting annual production (see sections 

 12 and 13). 



The simple correlation between degree of broodiness and annual production 

 is — .1964±.0194 and the simple correlation between broodiness and higher than 

 mean annual production is — .2640±.0132 (Hays and Sanborn, 1926a). This 

 latter constant does not show the presence of broodiness to be as inimical to 

 annual egg yield as is the presence of winter pause. From these observations 

 it appears tliat a very important step has been the reduction in degree of 

 broodiness and that the increased annual egg record from non-broody birds 

 is only significantly greater than that from birds broody but once in the pullet 

 year. 



15. Annual Persistency and Annual Eyy Production. 



Annual persistency in laying (long laying period) at the end of the pullet 

 year has been shown to be very important in relation to annual egg record. 

 The true relation of persistency to egg record may best be arrived at by using 

 the method of partial correlation where age at first egg, length of winter pause, 

 winter clutch size and total days broody are made constant. The net correla- 

 tion between persistency and annual egg yield is -|-.7501±.0063. This is a 

 very intimate correlation and places annual persistency as the greatest single 

 characteristic affecting annual production. 



A breeding program should therefore lay special stress on the high persis- 

 tency characteristic wliich is intimately linked with early sexual maturity 

 (Hays, 1927). 



16. Midtifle Correlation Betzveen Five Fecundity Traits and Annual Eyy 

 Production. ' 



Theoretically, if all influences affecting annual egg yield were brought to- 

 gether and correlated with egg yield, the correlation should be perfect. In 

 this report five of the most important inherited traits are considered. No 

 account is taken of various environmental influences that operate to affect 

 fecundity, because such influences are not breeding problems but rather prob- 

 lems of management. If by this method a high total correlation is discovered, 

 it will be an indication that the breeding program has been directed along 

 constructive lines. 



