EFFECTS OF INBREEDING ON FECUNDITY 3 



that were freest from undesirable weaknesses as far as known characters affect- 

 ing egg production are concerned. The foundation stock used in this experiment 

 was made up of the highest class of birds available with respect to known fecundity 

 characters. 



A standard for sslecting pullet breeders was drawn up and followed as closely 

 as possible throughout the experiment. Since the standard deals with the 

 entire pullet laying year, it was necessary to place pullets in the breeding pens 

 that had qualified up to the breeding season and to retain offspring from those 

 that met the standard when their laying year closed. 



Frevious experience has shown that pullets and cockerels are more satisfactory 

 for breeding in restricted projects where specific matings are desired. This is 

 especially true for males where the death rate is very high, and to no small extent 

 for females also. This explains why young untested males and females were 

 used for breeding in this experiment, and why offspring were retained from but 

 a small proportion of the pullet breeders used. 



The standard for selecting each year was as follows: 



Sexual maturity — 215 days or less. 



Weight at first egg — 5 pounds or more. 



Winter pause — not over 4 days. 



Winter clutch size — 2.6 or over. 



Broodiness — none during the pullet year. 



Persistency — 315 days or more. 



Hatchability — 85 per cent or more. 



Egg size — a minimum average of 52 grams to January 1. 



Range mortality — not above 10 per cent in family. 

 In selecting breeding stock for a considerable number of characters, more 

 difficulties exist than might be anticipated in an improved flock. Rather earlv 

 in this experiment, it became necessary oftentimes to use birds for breeding that 

 most nearly conformed to the standard. When, however, breeding females 

 deviated widely from the standard set up for breeders, progeny was no longer 

 maintained. 



EXPERIMENTAL RESULTS 



Character of Female Breeders 



Table 1 shows the degree of conformity to the standard, by inbreds, checks, 

 and birds from the inbred lines crossed as the experiment progressed. 



Range mortality represents the death losses in families from the age of one 

 day up to September 1. Hatching dates range at weekly intervals between 

 March 25 and May 15 each year. All chicks were taken from the incubators at 

 one day of age and placed in 10 x 12 portable brooder houses on the chick range. 

 The chicks in this experiment were brooded along with other pedigreed Rhode 

 Island Red chicks of the same age, in units of about 200. It is evident from the 

 data obtained that the mortality rate was increasing in the inbred lines as the 

 inbreeding became more intense, and that crossing lines A and C reduced the 

 mortality rate in the last generation of breeding females. 



Age at sexual maturity has been observed to increase under inbreeding by 

 Dunn (1923), Dunkerly (1930), and Jull (1933); but Hays (1929 loc. cit.) failed 

 to discover a consistent increase in age at sexual maturity when inbreeding Rhode 

 Island Reds. This study, however, shows a rather consistent increase in the 

 age at sexual maturity in the inbred mothers as the experiment progressed. The 



