In experiment 2, six healthy, sexually mature mixed-breed beef heifers (1.5-2 yr of age; 520 ± 31-kg bodyweight) showing a cycle length of 1920 days were randomly assigned to control (n = 3) or IFN-т treatments (n = 3) and treated midcycle with Estrumate (500 mg cloprostenol, Sch-ering Canada Inc., Pointe Claire, QC, Canada) to synchronize estrus. Animals were observed at least twice daily for estrus throughout the experiment. In the morning of Day 14 after estrus (Day 0), each heifer received either vehicle (5 ml, 0.1% BSA in PBS) or recombinant ovine IFN-т (5 ml, 0.25 mg, equivalent to 2.5 X 107 antiviral units) transcervically into the uterine body. Infusions were repeated three times at 12-h intervals.
The animals were slaughtered in the afternoon of Day 16, 7 h after the last infusion. Both uterine horns, ipsilateral [ipsi] and contralateral (referring to the corpus luteum), were collected and dissected into 1.5-cm3 crosssectioned blocks. Fixation in 4% paraformaldehyde was allowed to proceed for 4 h. Samples were then dehydrated and embedded in paraffin and stored at room temperature until processed.