A flock of wild sheep that has been running in the hill country of inland Hawke’s Bay since the 1880s is down to roughly 300 animals, and the first straws of frozen semen have now been banked in an attempt to keep the breed alive.
The Mohaka sheep are small and robust, with large curling horns and black and white wool. They take their name from the Mohaka River country where they have lived without a farmer, a fence or a drenching gun for around 150 years. RNZ reported on 11 August that semen from three Mohaka rams has recently been collected, frozen and stored, and that the people behind the work are now hunting for ewes.
Michael Willis of the Rare Breeds Conservation Society told RNZ the Mohaka are one of the oldest wild breeds in the country, and that nobody knows their history with any great accuracy.
“They date back so long and were recognised as being there about 150 years ago,” he said.
“We had to step up and get some semen. We still need to get some embryos because they are the last of them so we are really fighting a bit of a downhill battle to preserve these animals.”
The difference between semen and embryos matters more than it sounds. Frozen semen lets a breeder cross a Mohaka ram over ewes of another breed and then work back towards the original type across several generations, diluting whatever made the flock distinctive along the way. A frozen embryo carries both parents, so it can be implanted in a surrogate ewe and produce an animal that is Mohaka on both sides. With ewe numbers as low as they are, collecting embryos is the harder half of the job and the half still outstanding.
The storage itself is handled through the Rare Breeds Gene Bank, a project the society runs with Xcell Breeding Services in Canterbury and Rare Breeds International. The bank holds mostly semen straws, along with embryos and tissue that DNA can be taken from later. The stated aim is up to 100 straws from each animal and up to 10 unrelated sires for each breed, with a third of the material locked away in long term storage, a fifth set aside for approved conservation programmes and the rest available for breeding. The society was founded in 1988 to record and promote rare livestock and to hold onto genetic diversity that commercial farming has no immediate use for.
Feral flocks like the Mohaka have a particular appeal to breeders. Generations of living without shepherds tends to select hard for hardiness, foot health, resistance to internal parasites, the ability to do well on rough or poor country and, in many feral lines, wool that sheds by itself rather than needing a shearer. Those are exactly the traits a warming, labour short, wool depressed sheep industry keeps saying it wants. The catch, as anyone who has taken one home discovers, is that the wild gene does not switch off. Tame or not, they need good fencing.
How much genuinely novel genetic material is sitting out there in the Mohaka hills is a fair question, and it has been tested. A study by McKenzie and colleagues published in Genetics Selection Evolution in 2010 sampled 878 feral sheep from 10 New Zealand flocks, including Arapawa Island, Pitt Island, Chatham Island, Campbell Island, Hokonui, Herbert, Woodstock and Mohaka. The researchers looked at four genes linked to wool traits, lamb survival in cold conditions and immune function. They found no new allele in any of the sheep for any of those genes, which means the feral flocks were not going to hand the industry a variant it did not already have.
What the same study did show was how thin the Mohaka line already was 16 years ago. Only six Mohaka animals could be sampled, the fewest of any flock in the survey, and those six returned two to three alleles per gene and the lowest average heterozygosity of the 10 populations at 0.43. Low heterozygosity is the statistical fingerprint of a closed population breeding among itself. The authors were careful about reading too much into six animals, but the number is a warning either way, and it was recorded long before the flock fell to its current estimate.
The decline is not new either. When the scientist Tony Whitaker surveyed the country’s feral sheep in 1976, he put the Mohaka at fewer than 1000 animals scattered across more than 30,000 hectares between the Te Hoe and Waipunga rivers, in several groups that may or may not have been connected. Even then the pressure was not culling but land use, with habitat lost to agricultural development. Half a century on, fewer than 1000 has become about 300.
The society counts around a dozen self maintaining feral sheep populations on the mainland and the outlying islands, from Campbell Island in the subantarctic to the Hokonui hills in Southland. Most have never had the scientific attention given to Campbell and Arapawa, which is part of why so much of what is said about them is anecdote rather than data.
Three hundred sheep barely register against the national flock. Stats NZ counted 23.6 million sheep at June 2024, and that figure is itself a long way down from the peak of more than 70 million in the early 1980s. New Zealand has been shedding sheep by the million for four decades through land going into dairy, forestry and towns. Losing another 300 would not move a single line on a production chart. It would, though, close off a lineage that has been solving the problem of staying alive on that particular piece of country, unaided, for about 150 years.
Willis is asking farmers with the time and the paddock space to take on a few and breed them. That is the part no freezer can do. Cryopreservation buys time and insures against a fire or a disease outbreak, but a breed only survives as a breed if there are live animals in a live paddock producing lambs. For the Mohaka, the shortage now is not straws in Canterbury. It is ewes.
Have you come across the Mohaka sheep or any of New Zealand’s other feral flocks, and should we be putting more effort into keeping them going? Leave a comment below and tell us what you think.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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