Semen frozen back in 1968 has been used to impregnate dozens of Merino ewes, resulting in healthy lambs. The Australian scientists who made it happen say it’s the oldest sperm ever used to produce offspring.

A research team led by Simon de Graaf from the Sydney Institute of Agriculture and School of Life and Environmental Sciences impregnated 34 Merino ewes with the thawed out 50-year-old ram sperm, according to a University of Sydney press release. Incredibly, the sperm resulted in birth rates comparable to semen frozen for 12 months.