Responses of modern hybrid laying stocks to changes in photoperiod

Two replicates of each of 4 light patterns were imposed on 4 breeds of laying hen. The light patterns were designed to induce sexual maturity, defined as 50% production, at a range of ages. Within‐room treatments were ad libitum or rationed feeding during rearing and 4 breeds, namely ISA Brown, Hisex Brown, Ross G‐Link Brown and Shaver Brown. A total of 6144 birds were used to test the 32 treatments.

2. Age at 50% production was significantly affected by both lighting treatment and rearing regimen.

3. The light pattern treatments had no significant effect on any cumulative performance variable measured from 20 to 80 weeks of age.

4. Breed had a significant effect on eggs/hen housed, rate of lay, egg weight, egg output and food intake.

5. Rationing feeding during rearing, by holding intake at its 6‐week level from 6 to 14 weeks of age, was associated with significantly lower egg production, but had no effect on egg weight or food intake during lay.

6. Although both rearing and light treatments influenced age at 50% production, this character was not correlated with egg weight or egg production.

7. It is suggested that modern hybrid laying stocks are so genetically predisposed to ovulate that they are becoming refractory towards treatments hitherto regarded as influential.