1. Pullets of 2 high-producing commercial stocks (both brown-egg layer
s) were exposed to 5 different lighting patterns between 18 and 72 wee
ks to test the hypothesis that photoperiods used in commercial lightin
g programmes early in the laying year may be unnecessarily long and, b
y accelerating the development of photorefractoriness, may contribute
to the decline in egg production observed after the initial peak. Two
rooms of 288 pullets were allocated to each treatment. 2. The rate of
lay observed with a Step-Up treatment which gave increases in photoper
iod from 8L:16D at 18 weeks to 15L:9D at 27 weeks of age was not signi
ficantly different from that of treatments which held the birds on 11L
:13D during peak egg production but gave increments up to 15L:9D later
in the laying year. 3. A control group maintained on 11L:13D from 20
to 72 weeks laid 295 eggs per bird housed and a further group held on
8L:16D from 0 to 72 weeks laid 284 eggs per bird. These yields were lo
wer than the Step-Up treatment (299 eggs) but show the potential of mo
dern hybrid stocks to lay prolifically even without light stimulation.
4. It is concluded that the stocks tested in this experiment showed n
o advantage when given lighting programmes in the first laying year wh
ich were designed to minimise the adverse effects of photorefractorine
ss.