Early identification of bovine pregnancy status and embryonic mortality†.

Bovine interferon-tau (bIFNT) is produced by the trophectoderm cells in the bovine conceptus as early as Day 12 following fertilization. It was hypothesized that IFNT detection in blood, milk, and/or cervical secretions could be used to diagnose pregnancy in lactating cows. Recombinant bovine (rb) IFNT was generated to produce goat and rabbit anti-rbIFNT polyclonal antibodies, and an enzyme-linked immunosorbent assay (ELISA) was developed for bIFNT using these reagents. The IFNT ELISA did not cross-react with other type I or II IFNs and had a limit of detection of 50-100 pg/ml. The IFNT ELISA detected IFNT in external ostium (os) cervical swabs from Days 15 to 25 post-AI, but did not detect IFNT in serum, plasma, or milk. The time for most accurately detecting IFNT in cervical fluid was Days 16-19 after AI. A custom bovine swab device used to collect cervical secretions reduced false-negative rates to 5.5% (94.5% sensitivity) in dairy cows on Day 17 and 0% to 3.4% (100% and 96.6% sensitivity) in beef cows on Days 18 or 16, respectively. In summary, the detection of IFNT in cervical fluid by ELISA provides an accurate indication of pregnancy status in lactating dairy cows. Early identification of the non-pregnant cow allows re-insemination on Day 21 compared to waiting until ultrasound (US) on Day ~32-39. In addition, the detection of IFNT on Day 17 followed by the loss of pregnancy detected by US on Day 32 provides a novel research tool for studying pregnancy loss caused by embryonic mortality.