Vaginal opening and early estrous cycles in rats raised at a low ambient temperature

Abstract

Rats raised from day 2 of life at an ambient temperature of 10° showed delayed vaginal opening when compared to controls raised at 22°. Coldraised animals were also lighter in weight at the time of vaginal opening and had significantly longer estrous cycles. Low temperature may cause these effects either by suppressing prolactin secretion or, more probably, by elevating thyroid hormone levels which in turn suppress serum gonadotropin concentrations.