INHERITANCE OF EGG SIZE AND EGG CHARACTER 



By F. A. Hays, Research Professor of Poultry Husbandry 



INTRODUCTION 



Egg size and external egg character studies involve a considerable number of 

 problems that have been considered by many investigators. Curtis (1914) 

 studied egg weight in 22 Barred Rock females during the first two laying years. 

 During the first year there was an increase in egg weight up to April and a new 

 high level appeared in September. Hadley and Caldwell (1920) reported on 

 38 White Plymouth Rock females. In these birds egg weight reached the 

 highest level of the pullet laying year during April and attained a new high 

 level the following December. Atwood (1923) pointed out that the mean egg 

 weight of White Leghorns not bred specifically for high egg production in- 

 creased each month of the first laying year. Jull (1924a) reported the mean 

 monthly egg weights on 40 Barred Rock females during their first laying year. 

 Maximum egg weight occurred in February and a new high level in egg weight 

 appeared the following November. Jull (1924b) further showed that egg 

 weight was intimately related to production and that the time when laying 

 began had a very significant effect on egg weight. Hays (1930) presented data 

 on 222 Rhode Island Red pullets, also observing maximum egg weight during 

 February and a rapid increase in egg weight during September at the end of 

 the laying year. 



The data of all of the above workers stress the fluctuations in egg weight 

 from month to month in the first laying year and indicate that caution is 

 needed in classifying birds for egg weight when weighings are made only a few 

 times during the year. 



Commercially an individual egg weight of 56.7 grams or 24 ounces to the 

 dozen is considered standard. It is probable also that a mean egg weight of 

 56.7 grams for all the eggs laid during the first laying year is a satisfactory goal 

 for poultrymen to attain especially in flocks bred for high fecundity. 



A number of workers have studied the relation of the weight of the first pullet 

 eggs to mean annual egg weight in order to obtain a physical basis for selecting 

 laying pullets at the beginning of the year. Maw and Maw (1932) reported 

 that White Leghorn pullets whose first ten eggs averaged less than 47.5 grams 

 each were not likely to attain standard egg weight the first year. The mean 

 weight of the first ten eggs laid by these pullets in the fifth laying month corres- 

 ponded closely to the mean egg weight for the entire year. Jull and Godfrey 

 (1933) found that White Leghorns that will show a mean annual egg weight 

 of 56.7 grams must have an average weight of the first ten eggs between 48.86 

 and 50.00 grams. Wilson and Warren (1934) presented data on White Leg- 

 horns, Rhode Island Reds and Barred Plymouth Rocks. These workers found 

 that pullets starting with an egg weight of less than 46 grams in October, 50 

 grams in November, or 52 grams in December or later generally failed to attain 

 standard egg weight the first year. Hays (1929) reported that Rhode Island 

 Red pullets must lay 52-gram eggs in November and 55-gram eggs in December 

 if they are to lay standard weight eggs by March 1. 



