Influence of Level of Energy Demand on the Ability of Rats to Compensate for Diet Dilution

Mature, weanling and lactating rats, which had energy demand levels of 150, 225, and 555 kcal/Wkg0.75, were fed a commercial diet diluted 0, 10, 20, 30, 40, 50, 60 and 70% by weight with perlite. Caloric density of these diets ranged from 5.17 to 1.55 kcal/ml. Feed dry matter and digestible energy intakes were determined on an individual basis during 4 days when a basal commercial diet was fed and during 12 days when a diluted diet was fed. Results showed that the mature and weanling rat (42 days of age by the end of the experiment) maintained energy intake by increased feed consumption through the equivalent of a 45% and 40% dilution (or a diet containing 2.65 and 2.86 kcal of digestible energy per milliliter for mature and weanling rats, respectively). Diets of higher dilution, or lower caloric density, caused a linear decrease in food and energy intake. Lactating rats, on the other hand, were unable to compensate on an energy basis for even the 10% diet dilution (4.47 kcal/ml). Food consumption increased slightly at the 10 and 20% dilutions and then decreased linearly with dilution. There was an overall decrease in digestible energy intake (Y = kcal/Wkg0.75) as the caloric density of the diet (X = kcal/ml) decreased: Y = 151.14X - 174.2; r = 0.993. Since digestive tract capacity is maximal in lactating rats it is suggested that this relationship describes the maximal energy intakes for rats fed diets of varying caloric densities.