Effect of age of release from light or food restriction on age at sexual maturity and egg production of laying pullets

I. Lohmann Brown pullets, in one trial, and Hylinc Brown pullets in another , were reared from day 2 on short day lengths, and from week 8 in trial 1 ( week 16 in trial 2) on food restriction. These restrictions were lifted at various times during the rearing period as a means of determining the relat ive importance of the day length and food restriction stimuli on the attain ment of sexual maturity and subsequent laying performance. 2. A total of 2304 pullets were used in each trial. The birds were reared i n light proof rooms, and subjected to 8L:16D until they were moved to a lay ing facility where a light stimulus of 16L:8D was applied. In trial the sur ages at which light stimulation was applied were 115, 112, 129, 136, 143 a nd 171 d. Within each light treatment, food restriction of pullets, which c onsisted of feeding 72 g of food/bird d, was lifted at six different ages, namely 115, 129, 143, 157, 171 and 185 d. In trial 2 both the light stimula tion and the lifting of food restriction occured at 111, 125, 139, 153, 167 and 181 d of age, producing 6x6=36 treatments in both trials. 3. The first trial was terminated when the pullets were 28 weeks old, soon after all the birds had commenced laying, because of an outbreak of Egg Dro p Syndrome. However, because age at maturity was the variable of major inte rest, data from this experiment could be used in the analysis. The second t rial ended when the birds reached 40 weeks of age. Variables measured were age at maturity, food intake and body weight gain subsequent to the lifting of restrictions and, ill the second experiment, rate of lay, peak rate of lay and egg weight at various ages. 4. The mean age at sexual maturity was influenced by the date of release fr om light restriction (P<0001) and from food restriction (P<0.001) in both t rials. III addition, the interaction between the age at release fi om light and from Food restriction was significant. Regression Equations were produ ced for each trial to describe the relationships between the age at sexual maturity and the age at release from light restriction and food restriction . 5. There was an effect of both light restriction (P<0.001) and of food rest riction (P<0001) on the increase ill food intake (g/bird d) in the week fol lowing release from food restriction in both experiments. These effects wer e not independent: the effect of the interaction of light and food restrict ion on this increase in food intake was also highly significant. The longer the birds were subjected to light restriction, the less dramatic the incre ase in food intake when food restriction was lifted. The more sustained the period of food restriction, the higher the increase in food intake in the week following release from the restriction. 6. Mean egg weight was 4 g heavier at 22 weeks of age in birds released fro m food restriction at 16 and 18 weeks, than from those released at 24 and 2 6 weeks of age. However, by 30 weeks of age, birds restricted for longer pr oduced heavier. eggs than their earlier-maturing counterparts. This effect continued to the end of the trial at 40 weeks of age, at which time there w as a 2.3 g difference in egg weight between these treatments. 7. Both light and food restriction have an effect on the age of maturity in laying hens. The length of time between the release from light Or fi om fo od restriction to the onset of laying depended on the age of the pullets wh en the release occurred. Egg weight at a given age was significantly affect ed by the age at release from food restriction, but not from light restrict ion.