Prelay Light Restriction of Turkey Hens: Daylength Versus Exposure Time ,

Abstract

A 3 x 3 factorial experimental design was used to examine the relationship between the duration of short daylength (10, 8, or 4 h light/day) during prelay light restriction and the length of time (12, 8, or 6 wk) that young turkey hens were exposed to light restriction and subsequent photoinduced reproductive performance. Data were collected for time to first egg, egg production, percentage of fertility, and hatchability, and poult weight. Light restrictions consisting of 10, 8, or 4 h light/day were equally effective in terminating photorefractoriness and preparing hens for subsequent photoinduced reproductive performance. A 6-wk exposure to light restriction did not prepare hens for egg laying as effectively as 8 (P less than .05) or 12 (P less than .10) wk of exposure, both of which were similarly effective. A lack of interaction between the light restriction daylength and exposure time suggests that the requirements for effective light restriction are rather specific and cannot be beneficially manipulated by various combinations of daylength and weeks of exposure.

Photostimulated Expression of Type 2 Iodothyronine Deiodinase mRNA is Greatly Attenuated in the Rostral Tuberal Hypothalamus of the Photorefractory Turkey Hen

“…Another group of photosensitive hens in their first or second reproductive cycle were kept as above, but then exposed to long days (LD 16 : 8 h) for 48 h (long‐day group). A third group of hens in their first or second reproductive cycles were placed on 35–46 weeks of long day exposure (photorefractory group), then transferred to short days for 2 weeks, which is not sufficient to terminate photorefractoriness (24), and finally returned to long days for 48 h before sacrifice. Ovarian regression was confirmed by necropsy to ensure these hens were photorefractory.…”

Tuberal hypothalamic expression of the glial intermediate filaments, glial fibrillary acidic protein and vimentin across the turkey hen (Meleagris gallopavo) reproductive cycle: Further evidence for a role of glial structural plasticity in seasonal reproduction

“…Turkeys ( Melagris gallovapo ) also use long photoperiods as a proximal cue for reproduction (Siopes, 1994). As with many other avian photoperiodic breeders, female turkeys (Siopes, 1994) develop a state of photorefractoriness in which previously stimulatory day lengths become insufficient to maintain reproductive activity and the HPG-axis shuts down in anticipation of unfavorable environmental conditions (Nicholls et al, 1988); exposure to short days for several weeks is necessary to reestablish photosensitivity (Siopes, 1989). In sharp contrast to reproductively inactive short-day but photosensitive hens, as well as photorefractory hens, the rostral and central ME of reproductively active long-day turkey hens express high levels of type 2-iodothyronine deiodinase, a glial derived enzyme that increases thyroid hormone activity (Steinman et al, 2008).…”