Photoperiodic regulation of reproductive and hormonal rhythms, and litter size in silver foxes (Vulpes vulpes): effects of selection for domestic behavior

Abstract

The silver fox is a strictly seasonal breeder, and photoperiod is the primary environmental cue that regulates reproduction in this species. The aim of the present paper is to study effects of long-term selection of silver foxes for domestic behaviour on photosensitivity in respect of oestrus activity, ovarian hormonal function and the litter size. Adult silver fox females from the commercial and selected population were exposed to artificial photoperiods (9.5L: 14.5D) from September until March in a specially equipped shed. The females of two behaviour types maintained in natural daylight served as a control. The experimental groups received illumination in two fractions, one of 7 and one of 2.5 hours duration. The 7-hour period was natural daylight from 10:00 to 17:00 and the additional light pulse was artificial illumination at night (00-02:30), in the morning (06:00-08:30) and in the evening (17:30-20:00). The results demonstrate that a light pulse at night can induce early oestrus and ovarian hormonal activity in anoestrus fox females and the effect was expressed in most extent in selected than in control females. Additionally, this photoperiod decreased dramatically the litter size in both behavioural groups. Photoperiods with morning and evening additional light pulse did not change the temporal pattern of the reproductive rhythm but the litter size was also decreased in control-combined group but not in selected one. All artificial photoperiods depressed the ovarian hormonal activity during follicular and luteal phases of the ovarian cycle and the group with the night additional light pulse had a most pronounced response. The data obtained suggested that behavior selection resulted in an alteration in the relationship between the endogenous reproductive rhythm and environmental photoperiod and increased resist-ibility to detrimental effects of artificial photoperiods on the litter size

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Osadchuk L.V.