Annual Variation of Body Composition, Reproductive Hormones, and Blood Constituents of Red Foxes

Abstract

We tested the hypothesis that there is seasonal variation in the body composition of red foxes ( Vulpes vulpes ) maintained outdoors in captivity and receiving a fixed high-quality ration. We monitored body components (water, fat, protein, minerals) of 12 wild foxes kept at the Jardin zoologique du Quebec monthly from February 1995 to January 1996. We estimated mass of body components using regression models that relied on body mass, linear measurements, and electrical resistance. We also monitored plasma follicle-stimulating hormone, testosterone, and progesterone together with serum phosphorus and albumin. Total body mass increased slightly during the study probably due to limited activity and a constant high-quality diet. Fat reserves exhibited an annual cycle, decreasing by 50% in summer (May–October). In contrast, protein, water, minerals, and phosphorus peaked at that time. Follicle-stimulating hormone reached high levels in December–March and in September–January for females and males, respectively. Progesterone peaked in April for females, and testosterone peaked in January–March for males. Albumin concentration did not exhibit any clear seasonal pattern.