14 MASS. EXPERIMENT STATION BULLETIN 411 



Four different groups of females were studied to determine the effect of age 

 on egg weight and variability in egg weight. The data are summarized in Table 

 4, and show that a 4 to 5 percent increase in egg weight from the first to the second 

 laying jear is to be expected in a strain of Rhode Island Reds that lay large eggs. 

 Just what would take place in a small-egg strain cannot be ascertained from these 

 data, but earlier records (Hays, 1929) indicate about an 8 percent increase in a 

 strain laying small eggs. There appears to be a slight decline in egg weight 

 with age after the second laying year. 



Atwood (1925) found much lower variabilit>- in egg weight in White Leghorns 

 in the second laying year than in the first laying year. Our data are not in agree- 

 ment with his observations, but the difference may be due to the period of 

 observation and to the method of calculating the standard deviation. Atwood 

 calculated the standard deviation on the individual egg basis, while we have 

 calculated the standard deviation for March on the basis of the individual stan- 

 dard deviation in the month of March. 



Table 4. — Effect of Age on Egg Weight and Variability in Egg Weight. 



Mean Egg Weight and Standard Deviation in Egg Weight, Grams 



Summary 



Variability in egg weight has been studied over a six-year period. Normal 

 variability has been determined by calendar months and for the entire first laying 

 year. The strain of Rhode Island Reds used had been bred for high egg pro- 

 duction for many years and may be considered a large-egg strain since the mean 

 egg weight of the first laying year was 58.4 grams, or 24.7 ounces to the dozen. 



From this study the following deductions seem to be justified: 



(1) Maximum egg weight of the first laying year appeared in March, followed 

 by a slight decline in April and a low summer level in May. In June the egg 

 weight began to increase and increased consistently to September when the 

 March level was again attained. The March and September egg weights were 

 about 3 percent greater than the annual mean. 



(2) Monthly variability in egg weight was greatest in November and Decem- 

 ber, when egg size was increasing at the most rapid rate, and lowest in May. 



(3) The month of March is a good time to evaluate the flock for egg size, 

 because egg size is then at a maximum and variability in egg size is at a low level. 



(4) Inherited variability in egg weight has almost completely disappeared 

 by March. 



(5) Very early maturing pullets showed a high annual variability in egg 

 weight ; but there was no correlation between age at first egg and March variability 

 in egg weight. 



(6) Winter clutch size showed no correlation with annual or with March 

 variability in egg weight. 



