POTENTIATION OF WARFARIN TOXICITY TO ROOF RATS (RATTUS-RATTUS) BY L-HISTIDINE AND BY VITAMIN-K ADSORBERS

The efficacy of warfarin alone or with various additives was tested against roof rats (Rattus rattus). Warfarin alone at 50 mg kg−1 of bait killed 37% of the roof rats where‐as the additives, L‐histidine (40 mg kg−1 of bait), activated‐clay, charcoal and carbon (10 g kg−1 of bait), tested individually, produced no mortality. However, when warfarin wascombined with each of these additives in turn, only the L‐histidine combination resulted in 100% mortality while the other combinations killed 88, 75 and 63% of the test rats respectively. Further trials of paired comparison tests were carried out in order to evaluate the efficacy of the warfarin/L‐histidine combination under different environmental conditions. All the rats succumbed to this combination in both cage and rattery conditions when there was no alternative food. Mortality decreased to 60% in cage and 70% in rattery when alternative food was provided alongside the poison bait. Rats tended to die more quickly with the L‐histidine combination than with warfarin alone. Field trials also confirmed that this combination was effective in reducing roof rat infestations as shown by the yield of corpses, the post‐poison bait intake and post‐operational surveillance. Copyright © 1979 John Wiley & Sons, Ltd