Temporal characteristics and incidence of photorefractoriness in turkey hens

We conducted experiments to determine the incidence and temporal components of photorefractoriness (PR) in first-year turkey breeder hens after photostimulation. In turkey hens, PR may be defined as a lack of responsiveness to photoperiods that previously induced or maintained egg production and is characterized by a spontaneous cessation of lay, usually followed by molt, as well as an absence of nesting behavior. In one experiment, groups of hens were photostimulated with 18 h of light (L):6 h darkness (D) for 12, 16, 19, or 22 wk and then were exposed to 13L:11D photoperiods to induce a change in egg laying that allowed an evaluation of the photoresponsive state of each group of hens. In two other experiments individual hens were photostimulated continuously with 16L:8D for 24 or 45 wk, and the onset of PR was evaluated by the spontaneous cessation of lay. Data were collected for time to onset of PR, percentage incidence, duration of PR, and the time required for the transition from the photosensitive to the PR state. The earliest onset of PR occurred 7 wk after photostimulation, and the mean onset occurred at about 18 wk of photostimulation. Hens that expressed PR did so within an 18-wk period ending at 25 wk of photostimulation, but not all of these first-year hens expressed PR. Incidence of PR was variable at 59 and 89% in Experiments 2 and 3, respectively. The transition from a photosensitive state to an overt PR state, and therefore a laying to nonlaying state, occurred abruptly within a 2-wk period. Photorefractoriness was permanent during 45 wk of photostimulation for 11% of the PR hens. In the remaining 89% of hens, PR persisted for at least 14 wk (mean of 20.0+/-0.9) but it was not permanent, because they subsequently spontaneously recrudesced. That is, they spontaneously terminated PR. It was concluded that most, but not all, first-year turkey hens become PR and that the incidence is highly variable; PR may be relative or absolute, and absolute PR occurs abruptly but with a highly variable onset time. In most hens, PR is not permanent.