Effects of photoperiod on annual reproductive and hormonal rhythms and fertility in silver fox females

The silver fox is a strictly seasonal breeder and photoperiod is a main fac tor that regulates reproduction in this species. The aim of the present wor k was to study the effects of different skeleton photoperiods on the induct ion of early estrus, hormonal activity of gonads and fertility in anestrous silver foxes. Adult females (n = 48) were exposed to short days (9.5L : 14 .5D) from September until March. Females (n = 12) kept under the natural da ylight conditions served as the control, The experimental groups received i llumination in two fractions: 7- and 2.5-hour long. The 7-hour period compr ised natural daylight from 10:00 to 17:00 and an additional light pulse at night (00-02:30, group 1) in the morning (06:00-08:30, group 2) and in the evening (17:30-20:00, group 3). There are three types of response in group 1. A half of animals showed signs of estrus in November-December, 2.5-3.0 m onths before the natural reproductive season. The second part displayed no changes until the end of the experiment indicating photorefractoriness. The third part had estrus during the natural reproductive season. Photoperiod 2 and 3 did not affect the temporal pattern of reproductive rhythm. All art ificial photoperiods increased the estradiol level and decreased the proges terone, cortisol and testosterone levels during the anestrous phase and sup pressed the ovarian hormonal activity during the follicular and luteal phas es but photoperiod 1 had the most pronounced effects. Fertility was decreas ed in all experimental groups. Our results suggest that the photoperiod wit h a light pulse at night can induce early estrus and ovarian hormonal activ ity in anestrous females. The data obtained suggest that decreased fertilit y under these conditions could be due to altered ovarian hormonal secretion .