8 MASS. EXPERIMENT STATION BULLETIN 364 



weights taken twelve months later. Individuals that lost more than .25 pound 

 during the year were placed in the first class. Individuals whose weight did not 

 change more than .25 pound during the year were in the second class. . Individuals 

 that had a weight increase of more than .25 pound were placed in five subclasses 

 in the third class, depending upon the amount of weight increase. 



All eggs laid by these birds up to January 1 were weighed and the mean egg 

 weight for each individual was designated as the winter egg weight. Table 3 

 is presented to show the relation between body weight increase or decrease in the 

 first laying year and mean winter egg weight. 



The group of birds that lost weight during the year and the group that showed 

 no change in weight throughout the year laid small eggs. In the class of birds 

 that showed a weight increase, there was a rather consistent increase in winter 

 egg size with each half pound increase in body weight during the year. 



Table 3. — Weight Increase or Decrease from Housing to the End of 

 THE Year, and Winter Egg Weight 



Hays (1937) pointed out that, for the flock being studied, the mean winter 

 egg weight must be about 23 ounces to the dozen if the bird is to produce eggs 

 averaging 24 ounces to the dozen for the first laying year. On this basis the data 

 in Table 3 show that a pullet must average to gain not less than one pound in 

 body weight in her first laying year if she is to produce eggs that average 24 

 ounces to the dozen for the first laying year. Those individuals that had a greater 

 weight increase produced heavier winter eggs. These data point rather strongly 

 to body weight increase as being correlated with egg weight. 



4. Body Weight on March 1 and Annual Egg Weight 



Data presented in Table 1 indicate that, with the stock used, maximum body 

 weight of the first laying year appeared when the pullets were between 11 and 

 12 months of age, or about March 1 when the stock was hatched in eight weekly 

 hatches between March 4 and April 27. Since mature weight is probably de- 

 pendent largely upon inheritance, it is apparent that body weight taken about 

 March 1 would be the best measure of weight obtainable during the pullet laying 

 year. 



Annual egg weight was calculated by determining the mean of all eggs laid by 

 each bird for 365 days, beginning with her first egg. Data on egg weight are 

 available on 486 birds in the various experiments being carried on. These birds 

 were housed in house 1 and represent one of the three units used in the weight 

 studies. 



From a tabulation of body weight on March 1 against mean annual egg weight, 

 the following constants were derived: 



