Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2005
Publication Date: 8/15/2005
Citation: Noirault, J., Brillard, J.P., Bakst, M.R. 2005. Spermatogenesis in the turkey (meleagris gallopavo): quantitative approach in immature and adult males subjected to various photoperiods. Theriogenology. 65:845-859. Interpretive Summary: Like birds in general, turkeys respond to increasing duration of light (photostimulation) in many ways, one is the onset of sexual maturation. In the male turkey, the age of photostimulation, can influence the quality of the semen produced and the duration of semen production. This is of great important to managers in the turkey industry concerning with the production of fertile eggs. In this study we determined the effects of increasing photoperiods on the onset of testicular development, on testicular growth, semen output and on the histological characteristics of the cells forming the seminiferous epithelium ( the cells associated with the testicular production of sperm) during the turkey's reproductive season. We determined the duration of the initial phases of spermatogenesis in the turkey and also showed that a short photoperiod, that is 7hr of light with 17 hr of darkness result in little growth and maturation of the testes. We also showed that as little as 10 hr of light can initial and maintain spermatogenesis. While the shorter duration of light may save energy costs, we observed that it was harder to collect semen from makes on the 10 hr of light when compared to males on 14 hr of light. This work will be useful to other scientist working in the area of turkey breeding . We also provide evidence that while a moderately long photoperiod, less than 11 hr, is capable of initiating and sustaining spermatogenesis, the male's response to manual stimulation at semen collection is not sufficient to elicit a good ejaculation.
Technical Abstract: 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 the main stages of meiosis based on BrdU labeling and stereological analyses (Trial 2) and, to examine the impact of various photoperiods on germinal and somatic cell populations in immature and adult males (Trial 3). Results in Trial 1 indicate that both testes within a male have similar stereological components (p > 0.05) for all parameters analyzed. Trial 2 revealed that the duration of Type-1 spermatocytes and round spermatids in turkeys lasts 4.5 ' 0.5 and 2.0 ' 0.5 days, respectively. In Trial 3, turkeys 23 to 60 wk of age were subjected to either a constant short (7L:17D, Group 1; 10.5L:13.5D, Group 2), long (14L:10D, Group 3) or progressively (+1h/wk) increasing photoperiod (from 7L:17D to 14L:10D, Group 4). The short photoperiod (7L:17D) resulted in a delayed response of testicular growth as measured 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, the photoperiods used in this study induced comparable early testicular maturation with maximum testis weight at 29-35 wk of age. Furthermore, as the males increased in age we observed a progressive, linear decline in testis weight through 60 wk of age. At 60 wk, testicular weights, stereological estimates and germinal components showed no significant differences (p > 0.05) between photoperiods. In conclusion, we found that the duration of the stages of meiosis in the turkey is similar to that observed in the fowl and guinea-fowl. Our observations also indicate that immature male turkeys subjected to a moderately short photoperiod over the entire reproductive season have similar testicular development and histological characteristics as those observed in males submitted to a long or increasing photoperiod. The existence of a threshold of photosensitivity to gonad stimulation in this species is therefore hypothesized to occur between 10.0 hr and 10.5 hr of light.