Vaginal oestrus during the non-reproductive period in European ground squirrels

Author(s)
Anna Strauß, Ilse Hoffmann, Manfred Walzl, Eva Millesi
Abstract

Most hibernating animals are thought to be monoestrous because reproductive activity is subject to strong time constraints. In previous studies, female European ground squirrels (Spermophilus citellus) turned out to have elevated oestradiol levels during late lactation and after weaning, indicating ovarian activity during summer. Therefore, we monitored vaginal cytology, endocrine changes, and vulval development in semi-free-living female European ground squirrels throughout one active season. Vaginal oestrus, defined by the predominance of cornified cells in smear samples, was found during the mating period shortly after vernal emergence. This phase was followed by metoestrus, characterised by the appearance of leukocytes, and a subsequent anoestrous phase. During weaning or postlactation, a second vaginal oestrus was documented in all experimental females, again followed by a metoestrous and an anoestrous phase lasting until hibernation. In line with the second vaginal oestrus, plasma oestradiol concentrations peaked during postlactation. Progesterone levels were elevated from gestation to postlactation, and titres were marginally higher during vaginal oestrus in summer than in spring. Vulval swelling was more pronounced during the first than the second vaginal oestrus. The second oestrous cycle was non-reproductive, as males were sexually inactive with regressed testes during summer. We assume that the second oestrous cycle and the accompanying endocrine changes have beneficial effects on prehibernatory fattening and reproductive performance in the subsequent season. This might allow females to become oestrous immediately after emergence from hibernation in spring.

Organisation(s)
Journal
Animal Reproduction Science
Volume
112
Pages
362-370
No. of pages
9
ISSN
0378-4320
DOI
https://doi.org/10.1016/j.anireprosci.2008.05.068
Publication date
2009
Peer reviewed
Yes
Austrian Fields of Science 2012
106054 Zoology
Portal url
https://ucris.univie.ac.at/portal/en/publications/vaginal-oestrus-during-the-nonreproductive-period-in-european-ground-squirrels(b161aa0c-a39c-45d3-a7d2-c06eb48111d9).html