Exposure duration to long day lengths associated with the expression of photorefractoriness in turkey breeder hens

Abstract

In addition to inducing egg production, exposure to long days concomitantly activates processes that eventually result in photorefractoriness (PR) and cessation of egg production. Experiments were conducted to evaluate the duration of exposure to long days that result in these processes. In each of 3 experiments, we subjected Large White turkey breeder hens to long days (16 or 18 h per day) for differing lengths of time from initial photostimulation and then returned them to a photoperiod (12L:12D) that provided sufficient, but decreased, photoperiodic drive to support egg production but not induce PR. Photoresponsiveness was then evaluated by egg production after a return to a longer day length (20 h per day) late in the lay period and beyond the mean onset of PR typical for these turkey hens. Hens that have undergone any reduction in photoresponsiveness should not increase egg production in response to the increased photoperiod. From experiments 1 and 2, exposure to long days for as little as 1 d and as much as 9 wk from initial photostimulation did not result in an alteration in subsequent photoresponsiveness. This was based on an increased egg production response to a change in photoperiod from 12L:12D to 20L:4D after 20 wk of photostimulation that was similar to controls held continuously on 12L:12D and opposite to the response of controls held continuously on 18L:6D. It was clear that PR had been fully programmed by 20 wk of exposure to long days. Exposure to long days for 12 wk (experiment 3) resulted in a partial alteration of subsequent photoresponsiveness. It was concluded that programming of PR during late spring-summer season occurs after 9 wk of long day exposure, is not fully expressed by 12 wk of long days, and can be fully expressed by 20 wk of photostimulation.

Ovarian steroid withdrawal results in GABAA receptor upregulation in the photoperiodic neuroendocrine pathways of the turkey hen

“…In seasonally breeding temperate zone birds, including the domestic turkey hen, the changes in the reproductive neuroendocrine pathway and the subsequent manifestation of photorefractoriness terminate the reproductive season (MacDougall-Shackleton et al, 2006;Siopes, 2001;Siopes and Proudman, 2009). In the present study, we observed that the expression patterns of genes in this neuroendocrine pathway including GnRH-I in the nCPA (Kang et al, 2006;Thayananuphat et al, 2007), TH (DA synthesis), OPN4x (deep brain photopigment) (Kang et al, 2007;Kang et al, 2010), and circadian clock genes (Per2, Per3, Cry1) in the PMM where DA-Mel neurons are localized (Leclerc et al, 2010) were all downregulated in the steroid withdrawal hens as in photorefractory hens.…”