Introduction Predation of wildlife by the introduced red fox (Vulpes vulpes) is considered a major threat to the conservation of a range of terrestrial wildlife species in Australia (Mansergh and Marks, 1993; Saunders et al., 1995; Anon, 1996). Currently, management of fox populations is limited to the use of poison baiting with 1080 (sodium fluoroacetate), shooting, trapping and killing, exclusion fencing and den fumigation. Concerns over the potential impacts of 1080 baiting on domestic and wildlife species such as quolls (Dasyurus maculatus) (Soderquist and Serena, 1993; Belcher, 1998), although not confirmed in some field studies (King, 1989; McIlroy, 1993), currently limits the broad-scale use of baiting in some habitats. The conservation of some Victorian wildlife populations, including eastern barred-bandicoots (Perameles gunni), little penguins (Eudyptula minor) and mountain pygmy possums (Burramys parvus), is compromised by foxes that inhabit adjacent urban developments that are not easily managed with current methods (Mansergh and Marks, 1993; Marks and Short, 1996; Marks et al., 1996). Control of foxes by manipulating fertility may prevent population increase after lethal control (Bomford, 1990; Bomford and O’Brien, 1992), as well as the dispersal of foxes from urban habitats to rural areas containing susceptible wildlife species (Marks and Short, 1996; Marks et al., 1996). Methods to reduce prolactin secretion induce abortions in domestic dogs (Canis familiaris) when administered after week 6 of pregnancy (Conley and Evans, 1984; Post et al., 1988; Concannon et al., 1989; Jöchle et al., 1989; Olson et al., 1989). In red foxes, inhibition of prolactin secretion is thought to cause luteal regression and abortion during the second half of pregnancy (Hartley et al., 1994). Cabergoline (1-[(6- allylergolin-8β-y1)carbonyl]-1-[3-(dimethylamino)propyl]-3 ethylurea) is a dopamine agonist with an extremely high affinity for the dopamine receptor sites on the anterior pituitary lactotrophs (Benedetti et al., 1990), and its capacity to inhibit prolactin secretion is more potent than that of bromocriptine (Pontiroli et al., 1987; Dall’Ara et al., 1988; Post et al., 1988; Caballero-Gordo et al., 1991; Rolland et al., 1991; Ferraro et al., 1992). Cabergoline Control of red fox (Vulpes vulpes) fertility with cabergoline: dose response and timing of intervention C. A. Marks 1 , L. Jalkanen 2 , R. Savolainen 2 and R. V. Short 3 1 Vertebrate Pest Research Department, Victorian Institute of Animal Science, PO Box 48, Frankston, Victoria 3199, Australia; 2 Department of Applied Zoology and Veterinary Medicine, University of Kuopio, Kuopio, Finland; and 3 Department of Obstetrics and Gynaecology, University of Melbourne, Parkville, Victoria 3052, Australia Reproduction (2001) 122, 147–154 Research Cabergoline, a potent dopamine agonist and inhibitor of prolactin secretion, was investigated as a potential fertility control agent in the red fox (Vulpes vulpes). Sixty silver fox vixens were selected randomly and artificially inseminated. Cabergoline was fed to groups of 12 vixens in a minced beef ration either as a single dose of 25, 50 or 100 μg kg –1 , or a dose of 50 μg kg –1 that was repeated 2 days later (2  50 μg kg –1 ). Four foxes from each group of 12 were given cabergoline at day 28, day 35 or day 48 after artificial insemination, and a control group of four foxes was used as a comparison for each dose day. In a separate trial, two groups of five foxes were selected randomly from the farm population and fed 100 μg kg –1 of either cabergoline or a placebo each day from day 42 to day 46 of pregnancy. Foxes that received single doses of cabergoline of 100 μg kg –1 or 2  50 μg kg –1 aborted at day 28, but the same doses did not result in abortions when administered on days 35 and 48. Although lactation was not terminated in groups that received a single or double dose of cabergoline, increased post-natal cub mortality was associated with cabergoline administration. Growth of cubs between 4 and 8 weeks of age was not inhibited in vixens that received cabergoline. Doses of 100 μg cabergoline kg –1 administered each day from day 42 to day 46 resulted in abortions and terminated lactation. The capacity of single doses of cabergoline to cause abortions in the red fox during mid- rather than late pregnancy is contrary to reported observations for the domestic dog. This finding indicates that luteotrophic support of the corpus luteum by prolactin may be more important at mid-pregnancy in the red fox. The results of this study support previous field observations that cabergoline delivered in bait affects the reproductive success of vixens and may be a practical adjunct to the lethal control of wild red foxes in Australia. © 2001 Journals of Reproduction and Fertility 1470-1626/2001 Email: camarks@attglobal.net