Ovulation in the Domestic Fowl 



135 



24 hr. Stated differently, lag is simply the difference in times of day at which 

 successive eggs are laid. 



Time of oviposition, particularly in battery-caged hens, may be recorded 

 within almost any desired limits of accuracy. From such records of lay, 

 the time of ovulation of individual follicles constituting the corresponding 

 ovulation sequence may be estimated with fair accuracy. Briefly, each ovula- 

 tion except the first of a sequence occurs at a definite interval, of the order of 

 15-45 min and varying inversely with sequence length, following the pre- 

 ceding oviposition. The first ovulation of a sequence takes place on the day 

 before the second, and earlier than the second by not less than the extent 

 of lag between next to terminal and terminal ovipositions. These relationships 

 have been described in detail elsewhere (17). 



Times of ovulation so calculated for White Leghorn hens, maintained under 

 lights from 6.00 a.m. through 8.00 p.m., and ovulating in sequences of two 

 to six members, are recorded in Table 1. Ovulation of the first member of 



Table 1 . Times of Ovulations in Sequences of 2 to 6 Members, White Leghorn Hens 



UNDER 14-HR PhOTOPERIOD (LiGHTS 6.00 A.M.-8.00 P.M.) 



* From Fraps (17). 



t Light faced figures, morning hours ; bold faced figures, afternoon hours. 



sequences at about 6.00 a.m., the hour of onset of lights, is of no significance. 

 Under relatively lengthy photoperiods (e.g. 18 hr light), the first ovulation 

 takes place well after onset of lights. Under relatively short photoperiods 

 (e.g. 10 hr), it occurs sometime before onset of lights. 



The extent of lag between successive members of the sequences for which 

 actual times of ovulation were given in Table 1 are recorded in Table 2, 

 together with total lag within the sequences — the difference, that is, in times 

 of day between first and terminal ovulations. Total lag obviously increases 

 with sequence length, but to a lesser extent in the longer sequences. In even 

 the lengthiest of sequences, total lag rarely exceeds some nine hours. 



Heywang (33) published extensive data on intervals between lay of succes- 

 sive eggs by White Leghorn hens maintained under natural photoperiods for 

 a year at Glendale, Arizona. Lag in ovulation sequences of 2 to 13 members 

 has been calculated from these intervals and is presented graphically in Fig. L 



10 



