# Okinawa rail: frozen sperm used for artificial insemination, embryo developed to day 21

- Published: 2026-11-14 18:44 UTC
- Section: Planet › Ecology & recycling
- Tags: Okinawa rail, Hypotaenidia okinawae, frozen sperm, artificial insemination in birds, N-methylacetamide cryoprotectant, endangered species conservation, ex situ conservation, paternity test, avian genetic resources
- URL: https://realtech.media/news/rt-fca270f8f0ada39125544ecf_okinawa_rail_frozen/

**Researchers froze sperm of the endangered Okinawa rail and inseminated a female; one embryo developed until day 21 and died before hatching. The method may help preserve genetic resources.**

![Okinawa rail: frozen sperm used for artificial insemination, embryo developed to day 21](https://realtech.media/media/2026/11/71f3fc9c29d34882.png)
*nature.com*

Researchers from Osaka Metropolitan University reported artificial insemination of an Okinawa rail (Hypotaenidia okinawae) with frozen-thawed sperm, according to a paper on nature.com. The species is endemic to the northern part of Okinawa Island, Japan, and is listed as endangered, with a population of approximately 1,500 individuals. One embryo developed normally until day 21 after egg-laying and then died [1].

The population has declined due to roadkill and predation by feral cats, dogs and mongooses. The authors consider reproductive technology an effective ex situ conservation method, since it can help increase population size [1].

## Sperm freezing and analysis

Ejaculated sperm were collected four times from one male (no. 127), in volumes of 20, 20, 15 and 5 µL. The sperm were frozen in a solution containing N-methylacetamide as a cryoprotectant. According to the authors, sperm frozen with this agent can be used without removing it before insemination [1].

The samples were thawed slowly in water at 4 °C and analyzed with a computer-assisted sperm analysis system. Motility of frozen sperm in samples 1–3 was 42.2%, 46.1% and 25.1%, while fresh sperm of samples 1 and 2 showed 61.3% and 62.6%. Normality of the sperm membranes in samples 1–3 was 78.8%, 62.0% and 67.3% [1].

Sperm from four other individuals were not used for insemination, to maintain genetic diversity. They were stored in liquid nitrogen for future use [1].

## Insemination and embryo

Artificial insemination was performed three times. Eggs were laid in the first and second trials; the egg from the first trial was unfertilized, and the one from the second was fertilized. No laying was observed in the third trial [1].

The fertilized egg was placed in an incubator. The embryo was unable to pip on the scheduled hatching day (21 days) and died. It was then removed from the egg for genetic analysis [1].

The female had earlier been inseminated with fresh sperm from another male (no. 152), so a paternity test was carried out. Fragment size analysis showed that male no. 127 shared alleles identical to those of the embryo, confirming that it derived from the frozen sperm [1]. The authors conclude that frozen Okinawa rail sperm could potentially fertilize oocytes via artificial insemination, and that the protocol may also help maintain populations of other endangered bird species [1].

## Sources

1. [nature.com](https://www.nature.com/articles/s41598-026-67828-9)
2. [science.mail.ru](https://science.mail.ru/news/60486-okinavskij-pastushok)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-fca270f8f0ada39125544ecf_okinawa_rail_frozen/