Fat appetite in rats: the response of infant and adult rats to nutritive and non-nutritive oil emulsions.

Fat appetite was studied in rats using corn oil and mineral oil emulsions. In Experiment 1 ingestive responses to intraoral infusions were measured in rat pups 6-15 days of age. By 12-15 days of age pups responded more to oil emulsions (10% and 30%) than they did to water or emulsifier solution. The corn and mineral oil emulsions were almost as effective as milk but less effective than sucrose (0.3M) in stimulating ingestion. Experiments 2 and 3 examined the acceptance and preference for oil emulsions in adult rats. The corn oil and mineral oil emulsions were equally acceptable to non-deprived rats, as measured by 3-min and 30-min one-bottle tests. Food deprivation increased the one-bottle intake of both emulsions. In two-bottle tests, rats displayed a slight corn oil preference when non-deprived, but developed a strong preference when food deprived. Taken together, the results suggest that rats have an unlearned attraction to the orosensory qualities of emulsified oils and they learn to prefer corn oil based on its postingestive nutritive effects.