Interferon tau (IFNT), a Type I IFN similar to alpha IFNs (IFNA), is the pregnancy recognition signal, produced by the ruminant conceptus. To elucidate specific effects of bovine IFNT and of other conceptus-derived factors, endometrial gene expression changes during early pregnancy were compared to gene expression changes after intrauterine application of human IFNA2. In study one, endometrial tissue samples were obtained on days (D) 12, 15, and 18 post-mating from nonpregnant or pregnant heifers. In study two, heifers were treated from D14 to D16 of the estrous cycle with an intrauterine device releasing IFNA2 or placebo lipid extrudates or PBS only as controls. Endometrial biopsies were collected after flushing the uterus. All samples from both experiments were analyzed with an Affymetrix Bovine Genome Array. Study one revealed differential gene expression between pregnant and nonpregnant endometria on D15 and D18. In study two, IFNA2 treatment resulted in differential gene expression in the bovine endometrium. Comparison of the datasets from both studies identified genes that were differentially expressed in response to IFNA2 but not in response to pregnancy on D15 or D18. Vice versa, genes were found as differentially expressed during pregnancy but not after IFNA2 treatment. In study three, spatiotemporal alterations in expression of selected genes were determined in uteri from nonpregnant and early pregnant heifers using in situ hybridization. The findings of this study suggest differential effects of bovine IFNT compared to human IFNA2 and that some pregnancy-specific changes in the endometrium are elicited by conceptus-derived factors other than IFNT.