Cows can become pregnant even without embryonal interferon tau

For decades, scientists have believed that a protein called interferon tau (IFNT) is indispensable for pregnancy in cattle. Produced by the early embryo, it was thought to signal its presence to the mother and prevent the hormonal changes that would otherwise end the pregnancy.

Researchers at LMU have now challenged this established model in a study recently published in the journal Nature Communications. Cattle embryos completely lacking IFNT can establish and maintain pregnancies, even resulting in the birth of healthy calves.

Birth of genetically modified calves without interferon tau

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The team, led by Dr. Asghar Ali, postdoctoral researcher at LMU’s Gene Center Munich, and Professor Eckhard Wolf, Chair of Molecular Animal Breeding and Biotechnology and Vice Dean at LMU’s Faculty of Veterinary Medicine, used CRISPR-Cas9 gene editing to eliminate all functional copies of the IFNT genes in bovine cells. Then they generated cloned embryos from these modified cell nuclei and transferred them into recipient animals.

The results surprised the researchers: Despite producing no IFNT, the embryos developed normally during the earliest stages and successfully established pregnancies. On 26 February 2026, two healthy female calves were born, both confirmed to lack functional IFNT genes.

“Our findings challenge a fundamental assumption in reproductive biology. We have demonstrated that cattle embryos can establish pregnancies and develop to term without producing interferon tau, a signal previously considered indispensable,” says Asghar Ali, corresponding author of the study.

How does communication between embryo and mother work?

The researchers also examined how the maternal uterus responded to embryos lacking IFNT. Although the characteristic interferon-driven response was absent, the pregnancies continued. This suggests that alternative signaling mechanisms can maintain the hormonal conditions required for pregnancy.

One potential candidate is prostaglandin E2, a signaling molecule that may help preserve the corpus luteum (or ‘yellow body’), the ovarian structure responsible for producing pregnancy-supporting progesterone. However, its precise role remains to be established.

“These results fundamentally change our understanding of how the embryo communicates with the mother. The next challenge is to identify the alternative signals that allow pregnancy to be established and maintained,” says Eckhard Wolf, corresponding author of the study.

The findings open new avenues for investigating early pregnancy loss, a major challenge in cattle breeding. Identifying the mechanisms that support pregnancy independently of IFNT could ultimately contribute to improved reproductive efficiency in livestock.

Asghar Ali et al.: Pregnancy establishment in cattle without embryonic interferon tau. Nature Communications 2026