Animals and Tissue Collection
All procedures performed were in accordance with the guidelines of the Canadian Council on Animal Care and were reviewed and approved by the Nova Scotia Agricultural College Animal Care and Use Committee. In experiment 1, 12 sexually mature, healthy mixed-breed beef heifers were slaughtered at government-inspected abattoirs on Days 0 (estrus), 7, 16, and 18 of the estrous cycle (n = 3 per day). To confirm the stage of the estrous cycle, animals were observed for estrous behavior, and blood samples taken at estrus and slaughter were assayed for progesterone (P4) by RIA with a Coat-A-Count kit (Diagnostic Products Corporation, Los Angeles, CA).
Ovarian dating was also performed at collection according to the criteria of Ireland et al. Another group of 18 heifers was observed for at least one natural estrous cycle before breeding by artificial insemination. Reproductive tracts were collected on Days 7, 16, 18, 21, 24, and 30 of gestation (n = 3 per day). These days were chosen based on the IFN-т timeframe (d16P, d18P, d21P, and d24P), with d7P and d30P respectively serving as controls before and after the major output of IFN-т. Pregnancy was confirmed by examination of the ovaries and the presence of embryonic tissue. Uteri from all animals were dissected into 1.5-cm3 cross-sectioned blocks, frozen in liquid nitrogen ( —179°C) at the collection site, and transferred to an ultra-low-temperature freezer (—80°C) for storage.