Photoperiodic Response of Chickens

PHOTOPERIODISM was established as the principal environmental stimulus for reproduction in birds many years ago. Wetham’s (1933) suggestion that light stimulates the anterior lobe of the pituitary gland to produce gonadotrophins resulted in many experiments with the domestic fowl to determine how reproduction could be controlled and enhanced by artificial illumination. Reproduction (flowering) in plants was shown to be stimulated by dark periods rather than light periods by Hamner and Bonner (1938). Plants are now classified as short-day if they flower when the dark period is longer than critical value, and long-day if they flower in cycles containing dark periods shorter than critical value (Bonner, 1959). Wild bird s (bob-white quail, slate colored juncos, and white-throated sparrows) have been the object of research to learn the relationships of light and dark in controlling gonadal stimulation. Kirkpatrick and Leopold (1952), Jenner and Engles (1953) and Wolfson (1959) have demonstrated that light…