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 rate s 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 se parate groups of rats during a period of rapid growth. Iron deficiency (hemoglobin [Hb] approximate to 60 g/liter) was associated with a sys tematic elevation of metabolic rate over the 24-hr day with animals at 25 degrees C. This did not occur in animals living in thermoneutralit y. 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 defici ent rats and animals were not anorexic. Use of food-restricted animals allowed the direct calculation that iron deficiency was associated wi th a 10%-15% increased requirement for growth. We conclude that iron d eficiency anemia is associated with a poor feed efficiency and that it is attenuated when nonshivering thermogenesis is minimized by a therm oneutral environment.