GONADAL-FUNCTION IN MINK UNDER ARTIFICIAL PHOTOPERIODS

Exposure of juvenile minks to artificial light conditions imitating ea rly autumn (additional illumination from 20 June to 20 July followed b y 8 h daylight from 21 July to 10 October - photoperiod I; 8 h dayligh t from 21 July to 10 October - photoperiod II) induced the prolonged m odification of sex steroid concentrations. The increase in plasma test osterone concentrations during the prepubertal period was followed by a decrease before and during the mating period in experimental males. The concentration of oestradiol in plasma increased just before the st art of the mating period (January and February) in females under photo period I, and these hormonal changes were accompanied by an increase i n fertility. The conditions of photoperiod II (involving fewer hours o f daylight) had less effect on the sex steroid concentration in the bl ood of females, and fertility was not changed. The response of gonads to hCG injection at the beginning of puberty (November) was higher in males exposed to photoperiod I conditions and in females exposed to bo th photoperiods than in control animals.