Photoperiodicity in the Female Ferret

Abstract

ABSTRACT Evidence accumulated during two years’ work and experience in photoperiodicity in ferrets suggests the following conclusions: Oestrus or anoestrus may be induced by influencing the activity of the pituitary gland; this is effected through a contrast-sensitive mechanism which is stimulated by light:dark sequences. The total daily quantity of light is not the controlling factor. In order to obtain the long-light : short-dark ratio necessary for an oestrusactivating sequence, the ratio should be in the proportion of two parts or more of light to one part darkness and reversed if it is desired to induce a state of anoestrus. Slowly increasing or decreasing planes of light are not an essential part of an oestrus-activating sequence. Because ferrets can be brought into anoestrus quicker than they can be brought into oestrus it is considered that the sexual season curve is more acute when entering anoestrus than when entering oestrus. Doubling the number of light–dark contrast stimuli from one every 24-hour period to two every 24-hour period produced no acceleration of the onset of oestrus nor any indication of a ‘tetanus effect’.