PHOTOPERIODISM IN THE FEMALE 

 DOMESTIC FOWL 



R. M. FRAPS 



Agricultural Research Service, United States Department of Agriculture, 



Beltsville, Maryland 



The scope of this paper is perhaps narrower than its title may suggest, 

 being limited to a discussion of relationships between photoperiodicity 

 and certain aspects of reproductive behavior in the hen. Photoperiodic 

 effects on ovarian function, as reflected in rate of production and 

 timing of oviposition are first reviewed. An examination of the role of 

 photoperiodicity in the hen's ovulation cycle follows. 



There is little or no reason to doubt that photoperiodic effects on 

 ovarian function are mediated, in the hen as in other vertebrates, 

 through the central nervous system to the pituitary gland, thence via 

 the gonadotropic hormones to the ovary. The basic relationships are 

 described elsewhere in these proceedings by Professor BuUough (p. 

 641). The mechanism by which the central nervous system, and par- 

 ticularly the hypothalamus, may control and integrate pituitary ac- 

 tivity has recently been thoroughly reviewed by Harris (1955) and 

 cogently discussed by Greer (1957). Except for matters of detail, this 

 important subject will not be referred to further. 



PHOTOPERIODICITY AND LAY BEHAVIOR 



Two differing expressions of lay behavior are associated with photo- 

 periodicity in the hen. One has to do mainly with the onset and rate of 

 Qgg production, the other with the time of day at which eggs are laid. 



Rate of Production 



Pease (in Marshall, 1956) writes that Callus bankiva, when kept 

 in captivity in England, generally lays and incubates a clutch of about 



767 



