The paper addresses all feasible applications of long ahemeral light cycles in breeding flocks and reviews the limited published studies. Long cycles are likely to be most beneficial towards the end of the production cycle – when eggshell quality is often poor – and at the beginning of lay to increase the proportion of eggs exceeding the minimum weight for incubation. Published reports show an improvement in both fertility and hatchability of breeding flocks under long cycles.

The possible influence of age at change in cycle length and differences in effective photoperiod (Δp) on the response of layers to ahemeral light cycles have been examined. A brief account of the physiology of pattern of lay in the hen is given.

When an ahemeral light cycle is applied, mean rate of lay in relation to a normal 24-h cycle changes. The change in mean rate of lay depends upon the rate of ovarian follicular maturation of the individuals in the flock at the time of change to an ahemeral cycle. Early in lay, when rate of follicular maturation is rapid, changing to a long light cycle reduces rate of lay, whereas changing to a short cycle could increase rate of lay. As rate of follicular maturation declines with age, changing to a long cycle late in lay leads to an improvement in rate of lay. Based on published reports, a theoretical curve of the response to a 28-h cycle is given showing the significance of age at which application is made. From the available literature it appears that, provided Δp ≥ 0, response to ahemeral light cycles is not affected.