Effect of various photoperiods on testicular weight, weekly sperm output and plasma levels of LH and testosterone over the reproductive season in male turkeys.

The effects of duration and variation in photoperiod on testis weight, testicular sperm production, semen output, and hormone status over the reproductive season in male turkeys were investigated. In Experiment 1, four groups of males raised from 17 to 23 wk of age under a constant short photoperiod were subjected to a constant short (Group 1: 7L:17D; Group 2: 10.5L:13.5D), constant long (Group 3: 14L:10D) or progressively increasing photoperiod (Group 4: 7L:17D to 14L:10D) up to 60 wk of age. In Experiment 2, four groups of males first raised as in Experiment 1 up to 23 wk of age were placed under a constant short (Group 5: 10.5L:13.5D), constant long (Group 6: 14L:10D), or night-interrupted photoperiod (Group 7: 6L:2.5D:1L:14.5D, referred to as subjective 9.5L:14.5D; Group 8: 6L:3.5D:1L:13.5D), referred to as subjective 10.5L:13.5D) up to 60 wk of age. Males in Groups 2-4 had similar reproductive characteristics, whereas sexual maturity was delayed from 29 to 49 wk in males from Group 1. In Experiment 2, males in Groups 5 and 8 had similar reproductive characteristics, whereas sexual maturity was delayed in males in Group 7 in a manner similar to that observed in Group 1. In both experiments, plasma LH and testosterone concentrations were poor indicators of testis development and semen production, irrespective of age and photoperiod. We conclude that a moderately short photoperiod such as 10.5L:13.5D or subjective 10.5L:13.5D may stimulate reproductive characteristics of male turkeys in a manner comparable to constant long or increasing photoperiods. We inferred the existence of a threshold of photosensitivity in male turkeys for photoperiods longer than 9.5L:14.5D, but shorter than or equal to 10.5L:13.5D.

Spermatogenesis in the turkey (Meleagris gallopavo): quantitative approach in immature and adult males subjected to various photoperiods.

The objectives of this study were to identify and quantitate the germ cell populations of the testes in sexually mature male turkeys (Trial 1), determine the duration of meiosis based on BrdU labeling and stereological analyses (Trial 2), and examine the impact of various photoperiods on germinal and somatic cell populations in immature and adult males (Trial 3). In Trial 1, both testes within a male had similar stereological components (P>0.05) for all parameters analyzed. In Trial 2, the duration of Type-1 spermatocytes and round spermatids in turkeys lasted 4.5+/-0.5 and 2.0+/-0.5 days, respectively. In Trial 3, the short photoperiod (7L:17D) delayed testicular growth (in the stereological parameters analyzed). In contrast, the effect of a moderately short photoperiod (10.5L:13.5D) was comparable to the effect of a long (14L:10D) or increasing photoperiod (7L:17D to 14L:10D) on the stereological parameters examined. With the exception of the short photoperiod, all other photoperiods used in this study induced comparable early testicular maturation, with maximum testis weight at 29-35 weeks of age. As the males got older, there was a progressive, linear decline in testis weight through 60 weeks, at which time there were no significant differences among photoperiods. In conclusion, the duration of meiosis in the turkey was similar to that observed in the fowl and guinea-fowl. The existence of a threshold of photosensitivity to gonad stimulation in male turkeys is suggested to be between 7.0 and 10.5 h of light.