Eighteen pregnant cows were individually housed and allowed to calve normally. None of the cows retained fetal membranes. Tissues were obtained for study on Days 1, 3, 5, 7, 11, 15, 19, 23, 27, 31, 45 and 60 post partum. Because the exact time of calving of each animal was not known, the term `Day 1' represented an approximated period of 24 hr beginning from the time of observation of the calf with its dam in the maternity stall.
Following exposure of the internal genitalia as described by Schultz, Fahning & Graham (1966), caruncular and intercaruncular uterine samples were obtained from an area at the base of the uterine horn by an in-vivo serial surgical technique (Archbald, 1969). Uterine