Effect of Early and Late Weaning on Learning in Adult Rats

AT the time of weaning the mother rat ceases to be a necessary part of the external environment ensuring, among other things, a stable body temperature 1 , micturition 2 , etc. In addition, milk is the only food supplied before weaning. Quantitative 3 and qualitative 4 changes in the food supplied, at a time when milk is normally the only source, may have late effects that become apparent only in the adult animal. The time at which rats are weaned is also of importance. Thus premature weaning (when the infant rat can survive without the mother, but normally still lives predominantly on milk—about day 15–18 postnatally) causes impairment of spermiogenesis in male rats 5 and also decreases fertility in female rats 6 .