Growth in iron-deficient rats.

Poor growth in iron deficiency is commonly observed in animal studies. Previous studies from our laboratory showed that iron-deficient rats are metabolically inefficient and have less body fat than controls and proposed that iron deficiency was related to increased metabolic rates and heat loss. To examine these points more completely, we examined growth and metabolic rate of iron-deficient rats at two environmental temperatures, 25 degrees C and 32 degrees C, and feed efficiency in separate groups of rats during a period of rapid growth. Iron deficiency (hemoglobin [Hb] approximately 60 g/liter) was associated with a systematic elevation of metabolic rate over the 24-hr day with animals at 25 degrees C. This did not occur in animals living in thermoneutrality. Iron deficiency affected growth of animals at 25 degrees C but not at 32 degrees C. Feed efficiency (kcal retained/kcal absorbed) was 25 +/- 4.2 and 31 +/- 4.9 kcal (P < 0.0001), respectively, in iron deficient rats and animals were not anorexic. Use of food-restricted animals allowed the direct calculation that iron deficiency was associated with a 10%-15% increase requirement for growth. We conclude that iron deficiency anemia is associated with a poor feed efficiency and that it is attenuated when nonshivering thermogenesis is minimized by a thermoneutral environment.