Internal organ masses of the red fox Vulpes vulpes: data from the wild

Totally, 330 (125 females, 205 males) red foxes Vulpes vulpes (Linnaeus, 1758), killed during predator control operations (January to April 1992) in central Italy, were dissected. Their kidneys, spleen, heart, liver, and adrenal giands were weighed and related to body mass, age, sex, and kidney fat index. The mass of all organs examined, except for the adrenal glands, was highly correlated with body mass. Sex, age, and fat did not affect liver or spleen mass. Kidney fat was negatively related to the mass of heart and kidneys. Only kidneys and adrenals increased in mass with age. The increases were small, and could not explain an increase of total body mass with age. The hearts and spleens were relatively heavier in wild foxes than in farmed foxes, whereas livers were relatively lighter. Environmental factors (exposure to parasites and physical activity) may explain the differences. The masses of all of the organs were more variable in wild foxes than in farmed foxes, possibly because of a greater environmental and genetic variability.