Soft-diet feeding during development enhances later learning abilities in female rats

We investigated whether a decrease in masticatory work affected not only jaw bone growth but also radial eight-arm maze learning, and whether there was a sexual difference in this effect, if any. Male and female rats, weaned at 3 weeks of age, were fed either pelleted or powdered chow until 16 weeks of age and learning experiments were conducted at 10-13 weeks of age. Almost all of the five dimensions of the jaw bones were greater in rats fed pelleted chow than in rats fed powdered chow in both sexes. The number of correct choices in the last five trials was significantly greater in female, but not in male, rats fed powdered chow, and the number of trials to attain at least seven correct choices in the first eight choices in five consecutive trials was greater in female rats fed pelleted chow than in female rats fed powdered chow and in male rats fed either powdered or pelleted chow. These results suggest that 1) a decrease in masticatory work due to soft-diet feeding during development enhances later learning ability preferentially in female rats, and 2) the reported sexual inferiority of female rats in learning and memory functions is due to hard-diet feeding as the standard laboratory condition.