A TEST FOR PHOTOREFRACTORINESS IN HIGH-PRODUCING STOCKS OF LAYING PULLETS

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.