Impact of contraceptive hormones on the reproductive potential of male and female commensal black rats (Rattus rattus)
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Date
2021
Journal Title
Journal ISSN
Volume Title
Publisher
International Society of Zoological Sciences
Abstract
The black rat is considered one of the world’s top pests. With increased restrictions on rodenticides, new alternatives
to manage rats are urgently needed. Research on the use of contraceptive hormones, levonorgestrel (LE), and
quinestrol (QU), have been evaluated against some rodent species, and this research is the first study to assess
these on black rats. Hormones were incorporated into rodent bait at 10 and 50 ppm concentrations singly and in
combination (EP-1). Groups of 10 animals of each sex were fed the baits over 7 days. Lower bait consumption was
observed with slight body mass reductions. On dissection, it was observed that the uterus was in a state of edema
and male reproductive organs weighed less with reduced sperm counts/motility. The 2 most promising baits, 50 ppm
QU and EP-1, were used to assess impact on pregnancy and litter size. Pregnancy was reduced from 70% success
when both males and females consumed untreated bait, down to 30% when males had consumed contraceptive
bait but females had not, and down to 0% when females had consumed contraceptive bait, regardless of whether
they had paired with a treated or untreated male. Litter size in the untreated pairs was 8 pups, but only 4 pups in
those cases where the male only had consumed the contraceptive. Further studies should investigate how long the
effect lasts and its reversibility. Field studies at the population level may also shed light on the practicality of using
contraceptive baits for black rats in different habitats.
Description
Integrative Zoology 2022; 17: 991–1001
Keywords
contraceptive bait, ecologically based rodent management, fertility control, levonorgestrel, quinestrol
Citation
doi: 10.1111/1749-4877.12563