Acceptance and efficacy of ready-to-use coumatetralyl paste and freshly prepared cereal bait based on coumatetralyl against Rattus rattus

The feeding of ready-to-use Racumin paste (RP) containing 0.0375 % coumatetralyl for 2, 4, 6, 8 and 10 days in choice with untreated plain bait (PB) consisting of WSO mix (cracked wheat, groundnut oil and powdered sugar in 96 : 2: 2 ratio) to Rattus rattus resulted in 20, 30, 30, 70 and 90 per cent mortality, respectively. The median lethal feeding period (LFP 50 ) of RP was found to be 5.55 days and the median lethal feeding dose (LFD 50 ) was found to be 2.41g/100g b.wt. with 1.15-5.65 as 95% confidence limits in bi-choice with PB for R. rattus. The mean daily intake of RP was found to be significantly (p<0.05) lower than PB and freshly prepared cereal bait (FB) of 0.0375 % coumatetralyl. Per cent acceptance of RP was found to be very much less than FB. The zero feeding response of rats towards RP was much greater than towards PB and FB whose frequency of eating 1g or more bait daily was many times more than that of RP. These differences in feeding were mainly due to the type of bait formulation. The RP is generally considered safe to the user and less hazardous to non-target species, but the bait formulation and the number of feeding days are the crucial factors affecting performance of any rodenticide.