Photoperiodism in quail: testicular growth and maintenance under skeleton photoperiods.

Testicular growth was induced in quail which were exposed to a skeleton photoperiod that included a pulse of light given during the dark period (night-interruption). The minimum duration of the pulse inducing testicular growth was 3.75 min per day. Longer pulses induced greater rates of growth, and of LH and FSH secretion; maximum rates occurred with a night-interruption of 60 min. Pulses even shorter than 3.75 min maintained testicular function in previously photostimulated quail. A night-interruption of 14s maintained full testicular size and hormone secretion in four out of six quail, and with 56s no regression whatsoever occurred. The rate of testicular growth was largely independent of the duration of the main light period used in the skeleton treatment. The light intensity within the night-interruption also affected the degree of testicular development and gonadotrophin secretion.