ExtractAs a prerequisite to a biochemical investigation into the role of dietary lipids in regulating perinatal fatty acid metabolism, we developed and evaluated a model in which the amount of lipid in the diet can be easily controlled from birth to at least 10 days of age. Neonatal rabbits were fed purified equicaloric diets in which lipid supplied either 14.2% or 77.6% of the total calories. Mortality due to all causes was about 40% in both groups. Some differences in physical development between the two groups were noted. Animals receiving the smaller amount of lipid (LF group) gained weight to 150% birth weight byday 10,whereas the group receiving the larger amount of lipid (HF group) did not gain. In addition, the HF group had lower body temperatures, smaller liver and kidney weights, and greater brain weights relative to body weight. These differences are discussed in relation to the composition of the HF and LF diets. The model promises to provide a direct approach to a more precise evaluation of varied dietary regimens in the neonatal period. In particular, the model lends itself to studies relating diet to developing biochemical functions. In an accompanying paper, we report the results of an investigation comparing fatty acid oxidation in heart and liver of neonates fed the HF and LF diets described here.SpeculationThe model described here overcomes many of the difficulties associated with maintaining neonates on artificial diets in a way that allows precise control of diet composition and environment for at least the first 10 postnatal days. This should provide a new approach to many old questions regarding the specific role of lipids and other dietary constituents in modulating biochemical development.