![]() Rats are common in rural habitats, in particular on livestock farms, where rat colonies settle and individuals actively disperse over long distances (Herden 1992 Taylor and Quy 1978 Taylor 1978 Telle 1966). The Norway rat ( Rattus norvegicus) is known as a commensal rodent pest, coping with a wide range of environmental conditions. When the use of highly toxic compounds is required in resistance management, addition of cholecalciferol to these baits may reduce the transfer of residues to the environment. ![]() All treatments resulted in control levels exceeding 90%, despite a high proportion of anticoagulant-resistant rats. Bait ingestion was reduced by almost fifty per-cent when cholecalciferol was added to the bait with no impact on control success. 78.8% of 183 rats were confirmed Y139C resistant. On farms treated with brodifacoum only, the ratio of total bait consumption to pre-treatment census was significantly higher (6.6 and 4.8 times) than on farms treated with the combination (2.7 and 2.9 times). On all farms, control success exceeded 90%. DNA of each rat was genotyped to determine the resistance status conferred by the VKORC1 gene. Rats were radio-tagged, and carcasses were searched for during the treatment period. Infestations were assessed pre- and post-treatment. ![]() On two field study sites each, bait containing either 25 mg kg −1 brodifacoum or 25 mg kg −1 brodifacoum and 100 mg kg −1 cholecalciferol was applied to treat infestations of Norway rats. ![]() Cholecalciferol caused a strong stop-feed effect after two days in the laboratory study. Additionally, the efficacy of both baits was determined against resistant Y139C rats. ![]() We examined the effect of a low concentration of cholecalciferol in brodifacoum bait on bait consumption by Norway rats ( Rattus norvegicus Berkenhout 1769) and on the control success in a laboratory study and in field trials. Second-generation anticoagulant rodenticides potentially build persistent residues in animals and accordingly pose a risk of secondary poisoning. ![]()
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