Egg production in turkeys is regulated by photoperiod. Long days stimulate egg production, followed by broodiness and a photorefractory stage in which long days are no longer stimulatory and egg production ceases.
Understanding the photoperiodic regulation of reproduction is critical for developing strategies to increase production efficiency. Recent studies have implicated a specific area of the brain, the premammillary nucleus of the hypothalamus (PMM), as the site of photoperiodic timekeeping. The effects of PMM lesions on egg production have been examined in order to test the hypothesis that this brain area mediates the development of photorefractoriness in hens. Sexually mature hens, held on short photoperiods (8:16 light:dark), were divided into two groups: a photostimulated group (n=45), and an unstimulated group (n=45). Birds in the photostimulated group were transferred to long photoperiods (16:8 light:dark) prior to PMM lesion surgery. Egg production was monitored by trap nesting, and photostimulation was confirmed in individual birds prior to surgery. Birds in the unstimulated group received PMM lesions while still being held on short photoperiods, prior to photostimulation. Following surgery, birds in all groups were held on long, photostimulatory photoperiods.
The photostimulated group will allow to determine whether or not the PMM plays a role in regulating broodiness and/or photorefractoriness, because these birds were already laying eggs prior to PMM lesion. The unstimulated group will permit to determine whether or not the PMM plays a role in regulating the photostimulation of egg production, as these birds received PMM lesion prior to photostimulation.
Egg production is monitored by trap nesting: 32 trap nest boxes are checked every 2-3 hours over the course of the 16-hour day and individual egg laying recorded. Data are collected on the number of eggs laid for individual birds, as well as broody behaviors (going into nest boxes in the absence of egg production). Now egg production is being monitored and will this will last for a total of 6 months, or until birds cease laying eggs. Data will be analyzed for total egg production, weekly egg laying frequency, latency to initiate lay following photostimulation, daily nesting frequency, and latency for initiation of broodiness and/or photorefractoriness. After monitoring egg production, brains will be histologically examined to qualify the extent of PMM damage. Results from this study will illuminate the role of the PMM in the photoperiodic control of egg production.
From the Necad Proceedings