Control of protein intake in the young rat

Both adult and weanling rats are able to control their dietary intake of protein. The purposes of the current study were to determine: the precision of this ability in the weanling rat and when this ability makes its ontogenic appearance. We studied three overlapping age groups spanning the third, fourth and fifth postnatal weeks. Animals chose between two isocaloric liquid diets, one protein-free and the other composed of 50% protein. The intake volume of each diet was measured daily. Three days after introduction to the diets, pups were subjected to short-term tests designed to determine their ability to distinguish between the two diets. All three age groups responded to the protein conditions. However, the youngest group displayed comparatively weaker responses characterized by a prolonged period of reduced protein intake and weaker responses to the protein conditions of the short-term test. We conclude that young rats control protein intake by the end of the third postnatal week and that this ability strengthens throughout the remainder of the weaning period.