Growth, food intake and cold exposure in mice. 1. Cold exposure of adolescent mice

Abstract

ABSTRACT1. Adolescent mice were exposed from 33 to 84 days of age to a warm (30°C) or to one of four cold (15°C, 10°C, 5°C or 1°C) environments. Before and after exposure the mice were kept at a normal mouseroom temperature of 23°C. Controls remained at this temperature throughout. Voluntary food intake, live weight and growth efficiency were individually monitored before, during and after exposure, i.e. from 19 to 112 days of age.2. Food intake during exposure was linearly related to temperature, ranging from 4 g/day at 30°C to 14 g/day at 1 °C. Intakes differed only slightly between males and females. Food intake at 10°C was 70% above controls. Oxygen consumption in adults at 10°C was 74% above controls.3. Male growth was unaffected by temperature. Superiority over females (56% at 30°C) diminished at lower temperatures (12% at 1 °C) because females grew 41% faster at 1 °C than at 30°C. Females whose growth was depressed at 30°C, showed compensatory growth on returning to 23°C.4. Growth efficiency was strongly, but not entirely linearly, related to temperature, and increased approximately three-fold between 1°C and 30°C. Efficiency was maximal at 30°C in males and at 23 °C in females. Males grew 76% more efficiently than females at 30°C and only 12% more efficiently at 1°C.5. Increased food intake in the cold satisfied energy requirements and allowed females to grow faster.6. Individual differences in appetite persisted throughout life, but rankings in growth and efficiency changed with age. Food intake was strongly correlated with growth rate in weanlings, but growth rate was always the main determinant of growth efficiency.7. The variance of adolescent growth rate was unaffected by the treatments.