[Photoperiodic control of gonadal endocrine function in silver-gray foxes and its alteration during domestication].

Studies have been made on the level of estradiol and progesterone in domesticated and nondomesticated female silver foxes under different photoperiodic regime. The duration of the "light--darkness" cycle was equal to 24 h. Total duration of the light period was equal to 9 1/2 h; illumination was natural for 7 h, being artificial for the rest 2 1/2 h in a dark part of a day. It was demonstrated that additional illumination affects the hormonal level and sexual activity, the effect being dependent on the particular time of illumination. Nocturnal illumination significantly increased the level of sex hormones in the blood, domesticated animals being more sensitive as compared to nondomesticated ones.