Hemoglobin values and organ weights in fast and slow growing rats at the time of weaning

Three experimental groups of newborn rats were formed according to the number of animals suckled by one dam: fast growing animals (4 per litter), normally growing animals (8 per litter) and slow growing animals (16 per litter). All the animals were killed on the 21st day of life and the following data were collected: hemoglobin and hematocrit values, body weight and the weights of heart, kidney, liver and spleen. The results were statistically analyzed according to experimental group and also in relation to body weight with all rats treated as a single group. Hemoglobin concentration was highest in the smallest animals, gradually declining towards the lowest values around the normal body weight with a subsequent increase in the heaviest animals. The relationship between the organ weights and body weight followed an allometric formula. The slopes of the lines alpha were close to 1 in case of the heart, kidney and liver, indicating the growth of these organs proportional to the growth of the total body. The spleen grows faster than the total body in this experimental situation (alpha = 1.6).