10 MASS. EXPERIMENT STATION BULLETIN ill 



appearance of 5 families of non-broody daughters from broody mothers 

 is probably due to inadequate numbers of daughters and to deferred 

 broodiness in the daughters. In general the data in table 4 indicate that 

 few sires used were homozygous for either dominant gene. There is also 

 evidence that the sires used were freer from broody genes than were the 

 broody dams whose daughters were included in table 5. 



Table 5. — Phenotypes of Daughters from Broody Hens. 



Percentage of Number of 



Broody Daughters Families 



(Class) 



5 



25 14 



38 6 



50 



56 4 



100 12 



41 



SUMMARY 



Breeding tests on the inheritance of the broody instinct in Rhode Island 

 Reds were carried through a ten-year period using 72 sires and 210 dams 

 which produced 1767 daughters. Evidence was secured on inherited de- 

 grees of broodiness, on the problem of deferred broodiness, and on pos- 

 sible sex-linked inheritance of broodiness. A number of deductions were 

 made from this study. 



1. Degree of broodiness as measured by the number of broody periods 

 in the first laying year is inherited. 



2. Broodiness depends in inheritance on two complementary dominant 

 genes A and C; neither appears to be sex-linked. 



3. Dams exhibiting the broody character in their first laying year had 

 about twice as many broody daughters as dams in which the broody 

 instinct did not appear until the second or third laying year. 



4. In the data presented, 57.45 percent of the broody dams were broody 

 in their first year, 34.04 percent were not broody until their second year, 

 and 8.51 percent were not broody until the third year. 



5. Deferred broodiness greatly retards progress in breeding to elim- 

 inate the broody trait. 



6. The complete elimination of the broody instinct appears to be very 

 unlikely, at least in the American breeds. 



7. No evidence was found to indicate sex-linked factors in the inher- 

 itance of the broody instinct. 



REFERENCES 



Burrows, W. N., and R. C. Hyerly. 1936. Studies on prolactin in the 

 fowl pituitary. 1. Broody hens compared with laying hens and males. 

 Proc. Soc. Expt. liiol. and Med. 34:841. 



