An experiment was conducted to determine whether a commercial strain of turkey hens exhibits relative photorefractoriness (rPR) during a reproductive cycle and to ascertain whether plasma levels of certain hormones early in the reproductive cycle might be associated with subsequent expression of rPR or absolute photorefractoriness (aPR). Twenty-seven percent of hens maintained on a stimulatory photoperiod of 18L:6D for 19 wk and then given a shorter, but still stimulatory, photoperiod (13L:11D)

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... ceased to lay and their ovaries regressed within 4 wk. These hens were considered rPR. Subsequent exposure to the 18L:6D photoperiod resulted in ovarian recrudescence in 41.7% of these PR individuals, confirming the presence of rPR at 19 wk after photostimulation. Absolute PR was observed in 15.1% of hens during (Abbreviation Key: aPR = absolute photorefractoriness; GnRH-I = chicken gonadotropin-releasing hormone-I; LH = luteinizing hormone; PR = photorefractory, photorefractoriness; PRL = prolactin; PS = photosensitive, photosensitivity; rPR = relative photorefractoriness; T3 = triiodothyronine; T4 = thyroxine.