Racumin plus , a New Promising Rodenticide against Rats and Mice

Coumatetralyl (Racumin ) has been known since 1957 as a multiple dose anticoagulant and has been used successfully over many decades. In the seventies and especially the eighties, rats developed an increased resistance to anticoagulants in certain regions of Central Europe. Also, the addition of vitamin K to animal feed (especially to chicken feed) has reduced the efficacy against rats and mice in farm buildings. Combinations of anticoagulants with different types of vitamin D are generally described to increase the efficacy of action against rodents. It was found that especially the combination of coumatetralyl with cholecalciferol (vitamin D3) could overcome the above mentioned problems. Cholecalciferol causes hypercalcemia and, therefore, has a different mode of action compared to anticoagulants. The combination of these active ingredients leads to an obvious increase in efficacy against rodents, even under difficult conditions. The formulation with optimal rodenticidal efficacy contains 0.04 % coumatetralyl and 0.025 % cholecalciferol mixed in rolled oats. Proc. 16th Vertebr. PestConf. (W.S. Halverson& A.C. Crabb, Eds.) Published at Univ. of Calif., Davis. 1994. INTRODUCTION Anticoagulants are the most important rodenticides worldwide. Multiple dose anticoagulants have been in use since the early 1950s. In the 1970s the so called "single dose anticoagulants" were evaluated. Besides this mode of action, the hypercalcemia-causing agents calciferol and cholecalciferol came into use, particularly for the control of mice. In the 1970s and 1980s rats developed an increased resistance to anticoagulants in certain areas worldwide (Greaves 1985, 1986; MacNicoll 1982). Also, vitamin K containing feed (e.g., maize and chicken feed) caused severe problems in some places. This paper describes a combination of coumatetralyl and cholecalciferol which overcomes these problems. METHODS Study Animals The tests were carried out with two strains of the Norway rat (Rattus norvegicus) and the house mouse (Mus musculus). The albino strain of R. norvegicus belongs to the WISTAR strain. The wild rats are from a laboratory breeding in our institute. The parental generation of these rats was captured in the environment of Leverkusen (Germany). Choice Tests with Albino Rats Pairs of rats housed together in type III macrolon cages were offered 50 g of the test formulation and 50 g of the premix formulation (e.g., rolled oats or shredded wheat) every day for six consecutive days. The sides from which the food variants were offered were switched daily, to compensate for any "side" influences. The quantities of feed eaten were determined each day by weighing. Drinking water was available ad libitum. Choice Test with Wild Rats Norway rats housed individually in metal cages were offered 30 g of the test formulation and 30 g of the premix formulation every day for four consecutive days. The sides from which the food variants were offered were switched daily, to compensate for any "side" influences. The quantities of feed eaten were determined each day by weighing. Drinking water was available ad libitum. Choice Test According to the Guidelines of the German Registration Authorities (BBA Braunschweig. Germany) with Albino or Wild Rats (BBA 1983) The tests were carried out in small pens which consist of three chambers in tandem arrangement connected by small loop-holes. Each chamber is one square meter in size. One chamber serves as a "living room" for the rats and contains a nestbox with hay and cellulose as nesting material. The second chamber is empty and serves as a runway and the third chamber contains the test bait, the untreated feed and the water source. The drinking water is available ad libitum. The rats were acclimatized to the pens for two days. Over this period they were fed with a standard diet (altromin O). Over the following four days they received 100 g of the test formulation and 100 g of the premix formulation. The sides from which the food variants were offered were switched daily, to compensate for any "side" influences. The quantities of feed eaten were determined each day by weighing. The choice tests with Mus musculus (wild strain) were carried out using similar methods. Active Ingredients and Bait Formulations Coumatetralvl (Table 1) Coumatetralyl has been known since 1957 and belongs to the class of "multiple dose" anticoagulants. Its efficacy is characterized by a highly cumulative effect. In comparison to the so-called "single dose" anticoagulants the LDW of coumatetralyl for rats is high (16.5-30 mg a.i./kg body weight). After consumption over five consecutive days it increases considerably to 5 x 0.3 mg/kg b.w. The house mouse is far less susceptible than the Norway rat to an acute dose of