VARIABILITY IN EGG WEIGHT IN RHODE ISLAND REDS 



By F. A. Hays 

 Research Professor of Poultry Husbandry 



Introduction 



In recent years the problem of egg size as measured by weight has been of vital 

 concern to poultry breeders. Since weight plays a major role in the development 

 of market grades of eggs, it is easy to understand that both breeder and con- 

 sumer are concerned. Grades of eggs are built around the two-ounce egg as a 

 standard. Before the present era, when most flocks were not bred for high egg 

 production and when the average annual egg production was below 75 eggs for 

 each hen, a mean egg weight of 24 ounces to the dozen prevailed. 



During the past two decades there has been an immense increase in the num- 

 ber of flocks that are selectively bred for high egg production. Ten years ago the 

 average egg production for the United States was 85. In 1942 this average had 

 been raised to 113, and this year the average will probably be higher. As might 

 be anticipated, there has been a tendency for egg size to decline as the number of 

 eggs increased. At the present time this undesirable decrease in egg size has 

 been overcome by selective breeding, but egg size still remains an important 

 character to be watched by the breeder. 



Studies on egg size by many investigators including Atwood (1923), Jull 

 (1924), Jull and Godfrey (1933), Marble (1931), Hays (1930), Funk and Keinp- 

 ster (1934), Jeffrey (1938), Clark (1940) and many others have shown that egg 

 size fluctuates widely during the pullet laying year. This is particularly impor- 

 tant because most of the eggs produced come from pullet layers. In carrying 

 on a breeding program for egg production it becomes very important that the 

 breeder be able to regulate egg size by breeding and by hatching date to satisfy 

 market demands. 



The study presented in this report was undertaken for the purpose of de- 

 termining normal variability in egg weight for Rhode Island Reds bred for high 

 egg production. 



Available Data 



Rhode Island Red birds that had been bred for high egg production were used 

 exclusively in this study. Six generations hatched from 1936 to 1941 and con- 

 sisting of 790 individuals are included. These birds exhibited far superior egg 

 size to those used in our 1930 study. 



Changes in Egg Weight During the Pullet Laying Year 



In 1930, data on Rhode Island Reds were reported from this laboratory show- 

 ing that egg weight in the first laying year increased at a nearly constant rate 

 from October through February. It was shown at that time that the maximum 

 egg weight of the first laying year was attained in February when the average 

 age of the birds was from ten to eleven months. During the summer months 

 there was something of a decline in egg size, which persisted until near the end 

 of September when mean egg weight approached the February level. These data 

 are illustrated graphically in Figure 1 taken from the original report. 



