Welfare assessment of fatal methaemoglobinaemia in adult rats (Rattus norvegicus)

This study aimed to assess the welfare of rats poisoned with a lethal dose of a methaemoglobin (MetHb) inducing compound. Twenty rats were dosed orally with either the active compound (treated) or the vehicle only (control). Blood samples were collected post mortem for analysis of MetHb%. Female and male rats received a mean dose of 263 (SD 6) and 199 (SD 13) mg/kg respectively. Mean time to death was 67 (SD 36) and 354 (SD 158) minutes for female and male rats respectively. Control animals did not show any signs of intoxication. The time to death from methaemoglobinaemia in rats was significantly shorter than that previously reported for anticoagulants with no obvious signs of distress or pain.