Bovine vaginal circulation: changes during estrous cycle.

Vaginal thermal conductance was measured in 12 heifers and 7 cows with a gradient layer heat flow probe. Values rose for 4 to 5 days prior to day of behavioral estrus (day 0), with a peak on days --2 and --1, and then declined from day 0 to +5. Curves for heifers were higher than those for cows although there was no evidence that they were not parallel. Changes during the cycle appear to result from estrogen-induced alterations in blood flow rate in vaginal tissues.