Photoperiodic regulation of reproduction in the male silver fox (Vulpes vulpes)

• Published in: Journal of reproduction & fertility Vol. 87; no. 1; pp. 115 - 123
• Main Authors: Forsberg, M, Fougner, J A, Hofmo, P O, Madej, M, Einarsson, E J
• Format: Journal Article
• Language: English
• Published: England Society for Reproduction and Fertility 01-09-1989
• Subjects: Animals; Foxes - physiology; Light; Luteinizing Hormone - blood; Male; Pituitary Hormone-Releasing Hormones - pharmacology; Reproduction - physiology; Testis - cytology; Testis - metabolism; Testosterone - biosynthesis; Testosterone - blood
• ISSN: 1470-1626; 0022-4251; 1741-7899
• DOI: 10.1530/jrf.0.0870115

Six silver fox males were exposed to short days (6L:18D) from February, when the testes were fully developed, until June
1986 (Group 6L). Eight males maintained in natural daylight served as controls (Group N). Histological sections from the testes
of 2 males in Group 6L killed in June indicated full spermatogenic activity. Three blue fox vixens inseminated the following
year with semen collected and frozen in June from 3 males in Group 6L failed to produce litters. One possible explanation
for the reproductive failures could have been that the high environmental temperatures in June influenced semen quality. There
was no significant difference ( P > 0·05) in LH release in response to GnRH stimulation in June, but testosterone response to LH release was significantly
higher ( P < 0·01) in animals subjected to a restricted photoperiod, demonstrating that testicular testosterone production was maintained
longer than in control animals. Two males in Group 6L were retained in 6L:18D from June until December 1986 and then exposed
to natural daylight until the end of the study in May 1987 (Group 6L:6L:N). These males started to shed their winter coat
and showed clinical signs of testicular regression in December, i.e. after ∼11 months exposure to 6L:18D. The 2 remaining
males in Group 6L were moved to cages with natural daylight in June 1986, where they were kept until the end of the experiment
(Group 6L: N:N). These males displayed testicular regression soon after the change in photoperiod but maintained their capacity
for testicular redevelopment during the following breeding season.
Five males from Group N were moved from natural daylight to 6L:18D in June 1986, when the testes were fully regressed. The
animals were kept in 6L:18D until December 1986 and then exposed to natural daylight until the end of the study (Group N:6L:N).
The 3 remaining males in Group N continued to serve as controls (Group N: N:N). Six blue fox vixens inseminated in the natural
breeding season with semen collected and frozen in December 1986 from 4 males in Group N:6L:N conceived with an average litter
size of 8·8 ± 1·7. Plasma concentrations of LH in response to GnRH stimulation in October and November 1986 indicated no variation
of the pituitary to respond by LH release. In contrast, total testosterone release was twice as high in animals subjected
to a restricted photoperiod compared with control animals, indicating that short days had a stimulatory effect on testicular
redevelopment.
The results demonstrate that artificial illumination can be used to increase the reproductive capacity of silver fox males. Keywords: light; reproduction; silver fox; male; semen; testes