Groups of 10 male and 10 female Hoe:NMRKf mice were fed diets containing endosulfan at a concentration of 0 or 18 ppm for six weeks, equal to 0 or 3.7 mg/kg bw per day for males and 0 or 4.6 mg/kg bw per day for females, to determine whether 18 ppm was the NOAEL in this strain, as it was found to be in CD-1 mice in a three-month study
(Barnard et al., 1984). There were no clinical signs attributable to treatment. The mean food intake of mice receiving endosulfan was slightly decreased in males and slightly increased in females. Mean body-weight gain was reduced in treated males during the second half of the experiment but was slightly increased in females throughout the
experiment. Two treated females died, on days 28 and 38; the causes were not established, but no histological changes were found in the mouse that was not autolysed. The absolute and relative weights of the
liver of males and females at 18 ppm were higher than those of controls and statistically significantly so in females (17 and 12% respectively). A NOAEL was not identified, as an increase in liver weights was seen in females at the only dose tested (Donaubauer e al., 1985).