THE INHERITANCE OF INTENSITY OF LAYING IN 

 RHODE ISLAND REDS 



By F. A. Hays, 

 Research Professor of Poultry Husbandry 



Internal factors affecting egg production have been studied by various investi- 

 gators since their value was first stressed by Goodale in 1918. Attention has 

 been directed toward the possible modes of inheritance of several of these charac- 

 ters and especially to their interrelationships and importance from the standpoint 

 of fecundity. More recently attempts have been made to account for the wide 

 variability in egg production so characteristic of high-producing flocks (See Lerner 

 and Taylor, 1943 and Hays, 1944a). 



As the level of egg production goes higher, breeding operations become more 

 difficult. It is well known that operating with large numbers is a very great 

 advantage from the standpoint of selection, yet much is still unknown regarding 

 the genetic nature of particular characters. There is a great need for information 

 regarding the possibilities and limitations of selective breeding under carefully 

 controlled environmental conditions. Any information concerning the inheritance 

 phase of the problem should be of value to the breeder. 



REVIEW OF LITERATURE 



Dryden (1921) used the best two months' record as a measure of intensity and 

 concluded that intensity is an inherited trait. 



In a study of the mode of inheritance of winter rate of laying. Hays (1924) sug- 

 gested that tw^o complementary genes R ana R' were concerned. Gross winter 

 rate was calculated by dividing the number of eggs laid from first egg up to March 

 1 by the number of days concerned. A rate of 50 percent or more in this period 

 was considered high. 



Intensity in Rhode Island Reds was given further consideration by Hays and 

 Sanborn in 1927. Four measures of winter intensity were employed: first 60 

 days' production, mean winter clutch size, net winter rate, and annual rate. 

 Mean winter clutch size was found to be a satisfactory measure of winter in- 

 tensity and its mode of inheritance was studied. Again two complementary 

 genes I and I' w'ere suggested as governing the inheritance of large clutch size. 



The problem of intensity was further examined by Hays and Sanborn in 1932. 

 Mean clutch size in winter, in spring (March, April, and May), and in summer 

 (June to end of year) was studied and interdependence determined. Important 

 associations were reported between intensity of lading at different seasons of the 

 year. No important association was observed between winter pause duration 

 and clutch size. Winter, spring, and summer clutch size were all rather intimately 

 correlated with annual egg production. 



Jull (1924) used gross winter rate as a measure of intensity. In his calculation 

 of rate he divided the number of eggs laid from first pullet egg up to March 1 

 by the total days concerned. Jull did not consider winter pause a separate entity 

 as has already been suggested. He found the correlation in winter rate between 

 mothers and daughters to be .154 in Rhode Island Reds and .108 in White Leg- 

 horns, but considered them of little biological significance. 



Lerner and Taylor (1936) used two measures of rate in White Leghorns: net 

 winter rate and net spring rate. The net winter rate was calculated from Novem- 



