Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2005
Publication Date: N/A
Citation: Interpretive Summary: There has been little fundamental research looking at the influence of photoperiod (light/dark cycles) on the dynamics of semen production in turkeys. Two experiments were conducted to investigate 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. Our study reveals that turkeys can be brought into semen production by a constant long (14L:10D) or an increasing photoperiod (from 7L:17D to 14L:10D with increasing light weekly). In addition, moderately short or a variable light period of more than 9.5 h but less than 10.5 h/day provided over a 24 h will also lead to semen production. We tentatively recommend that breeder turkey males can be brought into and maintained in semen production under such photoperiods. Our results also indicate that plasma profiles of luteining hormone (LH) and testosterone (T) in male turkeys under moderately short days (10.5L:13.5D) are closer to those observed under short (7L:17D) rather than under long or increasing days. This suggests that the sensitization of the male by photoperiod (and not by variations in hormone levels) can be sufficient to induce testicle development. From a practical standpoint, investigators should not rely on plasma levels of LH or T, as an indicator of semen production.
Technical Abstract: There has been little fundamental research addressing the influence of photoperiod on the dynamics of semen production in turkeys. Two experiments were conducted to investigate 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. In Experiment I, 4 groups (Gr) of males (n=30 males/Gr) initially raised under a constant short photoperiod from 17 to 23 wk of age were subjected to a constant short (Gr 1: 7L:17D; Gr 2: 10.5L:13.5D), long (Gr 3: 14L:10D) or progressively increasing then long photoperiod (from 7L:17D to 14L:10D ; Gr 4) up to 60 wk of age. In Experiment II, 4 groups of males (n=50 males/Gr) first raised as in Experiment I up to 23 wk of age were placed under a constant short (Gr 5: 10.5L:13.5D), long (Gr 6: 14L:10D) or one of two variable photoperiods (Gr 7: 6L:2.5D:1L:14.5D, referred to as variable 9.5L:14.5D; Gr 8: 6L:3.5D:1L:13.5D, referred to as variable 10.5L:13.5D) up to 60 wk of age. In Experiment I, males from Gr 2, 3 and 4 had comparable of reproductive characteristics over the season. However, sexual maturity was delayed from 29 to 49 wk in Gr 1 males. In Experiment II, males in Gr 5 and 8 had similar reproductive characteristics whereas sexual maturity was delayed in males in Gr 7 in a manner similar to that observed in Gr 1. In both experiments, plasma LH and T were poor indicators of testis development and semen production. We conclude that a moderately short photoperiod such as 10.5L:13.5D or variable 10.5L:13.5D may stimulate reproductive characteristics of male turkeys in a manner comparable to long or increasing photoperiods. We also suggest that there is a threshold of photosensitivity in male turkeys to photoperiods longer than 9.5L:14.5D but shorter than 10.5L:13.5D. This information would be useful in the management of the breeder turkey male.