THE RELATIONSHIP BETWEEN THE WEIGHT OF EGGS 
AND THE WEIGHT OF CHICKS ACCORDING TO SEX 1 
By M. A. Jull, Poultry Husbandman , and J. P. Quinn, Chief Scientific Aid f 
Bureau of Animal Industry , United States Department of Agriculture 
INTRODUCTION 
In the domestic fowl the relationship between the weight of eggs 
and the weight of chicks according to sex at hatching time is an in¬ 
teresting problem, inasmuch as the mature male is normally heavier 
than the mature female. If the chicks of both sexes weigh prac¬ 
tically the same at hatching time, then there remains an interesting 
study of different rates of growth of the sexes. On the other hand, if 
the weights of the sexes are significantly different at hatching time, 
it is of importance, then, to try to discover why the weights are 
different and whether the sexes of standard-bred chicks can be 
separated according to differences in weight. 
This study was undertaken to determine, first, the relationship 
between the weights of chicks of the two sexes at hatching time; and, 
second, the relationship between the weights of the eggs and the 
weights of the chicks hatched from them. 
PROCEDURE 
The eggs used in this study were obtained from four different 
sources: 53 Rhode Island Red yearling hens, 30 Rhode Island Red 
>ullets, 50 Barred Plymouth Rock yearling hens, and 113 Barred 
Plymouth Rock pullets. All the females were mated to Rhode 
island Red cockerels. The eggs were saved from March 15 to 
March 23, when the incubators were set. Only a portion of the 
Rhode Island Red eggs laid during the period mentioned were used 
in this study. All the eggs laid by the Barred Plymouth Rocks were 
used. In this paper no account is taken of the infertile eggs, em¬ 
bryos which died during the period of incubation, and chicks which 
died in shell at hatching time. The eggs were weighed daily as laid, 
the weights being recorded to hundredths of a gram. The chicks 
were weighed at hatching time, the weights also being recorded to 
hundredths of a gram. 
The sex of the chicks from the Barred Plymouth Rock females 
was recorded at hatching time, and that of the Rhode Island Red 
chicks when the chicks were 9 weeks old. Distinguishing the sex of 
chicks from the Barred Plymouth Rock females mated to Rhode 
Island Red males was an easy matter, since the sex-linked barring 
pattern of the barred females is transmitted to the sons only. The 
male chicks always have the white spot on the top of the head and 
yellow shanks, characteristic of purebred Barred Plymouth Rock 
male chicks, while the female chicks of this cross lack the white spot 
and have black or very dark shanks. 
1 Received for publication Oct. 25, 1924; issued September, 1925. 
Journal of Agricultural Research, 
Washington, D. C. 
( 223 ) 
Vol. XXXI, No. 3 
Aug. 1, 1925 
Key No. A-97 
