PHOTOPERIODISM IN FEMALE DOMESTIC FOWL 769 



Dobie et al. (1946) state that the first reported use of artificial light- 

 ing for poultry houses appeared in 1889. 



In practice, artificial photoperiodicities are commonly used to 

 stimulate egg production during fall and winter months, when produc- 

 tion is normally low. Under prolonged photostimulation, production 

 declines, much as it does after the period of high production during 

 the spring months. The usual effect of lights is therefore to advance 

 the "curve" or peak of production, just as "the breeding season" may 

 be advanced in wild birds. Total annual production is not greatly in- 

 creased in high-producing strains by the use of lights. 



(a) Length of light day. A long-standing and still common prac- 

 tice in stimulating winter egg production is to use fights from 4:00 

 A.M. into daylight. Kennard and Chamberlain (1931) and Penquite 

 and Thomson (1933) reported equally good production under 24-hr 

 lights. 



A critical and extensive investigation of the effect of length of light 

 day on production was carried out by Roberts and Carver (1941).* 

 Artificial light was used (daylight excluded) on White Leghorn 

 pullets selected as high-producing birds. At light intensities of 7.5 

 ft-c, 13 hr of light daily resulted in practically maximal production. 

 Daily light periods of less than 13 hr led to decreased production. 

 Light periods greater than 13 hr (to 19 hr) failed to increase produc- 

 tion appreciably, and production under continuous light was some- 

 what less than under 13- to 19-hr photoperiods. 



Dobie et al. (1946) tested the effectiveness of supplementing win- 

 ter daylight (ca. 9 hr) with 15 hr light (1 ft-c) or 4 hr light (3 ft-c) 

 before, following, or as 2 hr before, 2 hr following, the hours of day- 

 light. Their results indicated no significant differences in egg produc- 

 tion. Dobie et al. concluded that the only condition for maximal 

 photostimulation is that a total of 13 hr light be supplied. 



Piatt (1953), supplementing dayfight with "dim red light," re- 

 ported the effect on production to be equivalent to that from white 

 light, 3:00 a.m. to daybreak. As used by Piatt, some of the stimulating 

 effect of red light may have been due to the "carry-over" effect noted 

 below. 



* The results of Roberts and Carver (1941) were apparently republished, 

 with results of other studies, by Dobie, Carver, and Roberts in 1946. 



