Variations in the plasma levels of luteinizing hormone and androstenedione and their relationship with the adult daily sperm output in cockerels raised under different photoschedules.

Circulating levels of LH and androstenedione were measured in 4 groups of 30 cockerels from 3 to 26 weeks of age. Each group was submitted to a different programme of artificial lighting, either a long (16 h) photoperiod, a short (8 h) photoperiod, an increasing (8 h to 16 h) photoperiod or a night-interruption regimen. Measurements were also made of the numbers of spermatozoa ejaculated on a daily basis between 22 and 24 weeks of age, and these data were then compared with data on the hormone levels in plasma. Certain differences in mean plasma hormone levels between groups subjected to different photoperiodic treatments were observed. Adult plasma levels of LH were lowest in birds exposed to 16 h of light per day while they were attained later in animals exposed to only 8 h of light per day. Similarly, adult plasma levels of androstenedione were attained at a later age in birds subjected to 8 h light per day than in the other treatment groups while the highest peak values, around the time of puberty, were found in cockerels receiving 8 h light in two blocks of 7 h and 1 h. Although some differences in hormone parameters were found between the best and the poorest sperm producers under certain of the lighting programmes, no relationship could be found between either the mean plasma level of LH, the duration of the pre-pubertal plateau of LH, the age at the pre-pubertal rise in LH or the age at the pre-pubertal rise in androstenedione and the level of adult fertility.