The onset of oestrus in normal and blinded ferrets

Abstract

Because normal anoestrous female ferrets usually become precociously oestrous if exposed to extra artificial light during the winter months, it has been widely assumed that the onset of oestrus in this species in the spring is due to the gradual lengthening of the hours of daylight. Comparison of the dates of onset of oestrus in large numbers of normal and blinded mature anoestrous ferrets, kept under ordinary laboratory conditions and also exposed to added light in the winter months, shows that ferrets blind to form vision, and presumably blind also to light vision, tend to come into heat in the spring of the first year after blinding. If a blinded ferret fails to come into heat in the succeeding spring, it may miss a season and come into heat for the first time in the spring of the year after, or even in the spring of the third year after section of the optic nerves. In so far as blinded ferrets tend to come into heat at the same time as normal animals, it would seem that the timing of the breeding season can hardly be due to the effects of increasing hours of daylight operating through the eyes, even although retinal stimulation can, in certain circumstances, precipitate the onset of oestrus.