Rat control strategies in organic pig and poultry production with special reference to rodenticide resistance and feeding behaviour

Abstract

Once rats have invaded farm buildings, efficient rat control usually requires the application of rodenticides. Efficacy of control measures may be lost by physiological resistance to anticoagulant rodenticides and by behavioural reactions of the target rat population. On a farm within the area of anticoagulant resistance in north-west Germany, two consecutive rodenticide treatments were carried out against rats, using different anticoagulant bait preparations. Bait consumption was monitored in combination with direct individual video-monitoring of bait uptake behaviour. Almost half of the rats survived the first three-week treatment using coumatetralyl bait. This result was ascribed to the high overall degree of anticoagulant resistance prevailing in the rat population. The second treatment of the same population using difenacoum bait totally failed to reduce population numbers. Dietary preferences, neophobia, social interactions and habitat structure are important behavioural parameters determining bait uptake. They are discussed in relation to the results of the treatment and a conceptual model for the factors determining rodent control efficacy is presented. The combined results of the two monitoring techniques applied demonstrate the significance of resistance and bait uptake behaviour for the efficacy of rat control measures and suggest the need for adapted rat-control strategies to reduce hygienic problems and the risk of non-target poisoning hazards for livestock and wildlife. This can be achieved if the choices of bait base and active ingredient as well as the methods of bait positioning are adapted to the behavioural peculiarities of the rats and the specific structural conditions on each farm.