Differences Between Rats and Rabbits in their Response of Feed and Energy Intake to Increasing Dietary Fat Content
It is common practice to use an ad-libitum feeding regimen in rat studies, even when experimental diets with different energy densities are used; a prerequisite is that the diets have identical nutrient:energy ratios. It is assumed that the rats will maintain a constant energy intake so that nutrient intake will not differ between the dietary treatments. The concept that energy requirement determines feed intake is supported by the study with rats that is described in this paper. Increasing the amounts of dietary fat (coconut fat or corn oil), and thus increasing the energy densities of the diets, caused decreasing feed intakes so that energy intakes remained unchanged. However, feeding the same diet recipes to rabbits led to increasing feed intakes, and even further enhanced energy intakes, in response to increasing concentrations of corn oil in the diet. Secondly, when the diet contained coconut fat, an increase in fat content also raised feed intake, but at higher inclusion levels there was no further increase or rather a decrease in feed intake by the rabbits. It is suggested to apply restricted feeding in rabbit studies using diets with different energy densities in order to avoid additional variables such as differences in weight gain and nutrient intake.