Bait-delivered pimozide causes precocious embryo implantation in mink: a fertility control option for the exotic stoat?
Clive A. Marks A D , Heli Lindeberg B and Judy Van Cleeff CA Nocturnal Wildlife Research, PO Box 2126, Wattletree Road RPO, East Malvern, Vic. 3145, Australia.
B Institute of Applied Biotechnology, University of Kuopio, PO Box 1627, FIN-70211, Kuopio, Finland.
C Animal Sciences Laboratory, 1207 West Gregory, MC630 University of Illinois, Urbana, IL 61801, USA.
D Corresponding author. Email: camarks@attglobal.net
Reproduction, Fertility and Development 18(6) 703-708 https://doi.org/10.1071/RD05015
Submitted: 4 February 2005 Accepted: 9 April 2006 Published: 10 July 2006
Abstract
Stoats (Mustela erminea), an exotic pest in New Zealand, threaten the conservation of several ground-nesting bird species and broad-scale methods for their control are sought. Females are seasonally monestrous, show a 9-month period of obligatory diapause and usually do not breed more than once in their lives. A bait-delivered agent that terminates diapause and results in a non-viable embryo may have a significant impact on their reproductive success. Prolactin (PRL) is hypothesised to be the only gonadotrophin required for renewal of luteal activity and blastocyst implantation in some mustelids. We investigated the effects of bait-delivered dopamine (DA) antagonists (which stimulate the release of PRL) using a mink model (Mustela vison), a species that maintains a short period of diapause. A bait dose of 0.8 mg kg–1 of pimozide was more effective in elevating PRL levels than equivalent doses of fluphenazine, sulpiride (P < 0.01) or haloperidol (P < 0.05). Bait doses of 1.6 mg kg–1 pimozide given at Days 0, 3, 9 and 11 after mating caused a significant reduction in the length of pregnancy compared with a positive control and placebo (46 days v. 51 days), indicating early termination of diapause (P < 0.01). Pimozide doses caused higher elevations in PRL concentration relative to the oral placebo by Day 12, but mean PRL levels fell below all other groups by Day 18. A borderline significant increase in progesterone (P4) secretion compared with the oral placebo was detected at Day 18. These results suggest that bait-delivered pimozide can elevate PRL outside of the normal breeding season and doses of 1.6 mg kg–1 are effective in terminating embryonic diapause in mink. The implications and limitations of these data are discussed with reference to the use of bait-delivered DA antagonists as a possible means to affect the reproductive success of wild stoats.
Extra keywords: pest control, vertebrate pest.
Acknowledgments
The authors wish to thank Anitta Helin and Elina Reinikainen from the University of Kuopio for their expert technical assistance, enthusiasm and good humour during this trial. This study was funded by the Department of Conservation (New Zealand). All experimental procedures were carried out in accordance with the 1997 Australian Code of Practice for the Care and Use of Animals for Scientific Purposes. The research protocol was approved by the Primary Industries Animal Ethics Committee as protocol number 2513 and the University of Kuopio Ethics Committee. We thank Lyn Hinds and Roger Short for constructive suggestions and advice that improved the manuscript. Comments from two anonymous referees improved the earlier manuscript.
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