An international research team led by Arne Bielke and Elmira Mohandesan of the University of Vienna, working with colleagues in Sweden, Wales, the United States and New Zealand, generated genome-wide single nucleotide polymorphism data from Kaimanawa Horses and integrated these results with previously generated mitochondrial and Y-chromosome markers. The comparison set comprised 22 domestic breeds, allowing the researchers to place the feral population within the broader landscape of global horse genetic diversity. The study was conducted in collaboration with the Kaimanawa Heritage Horse society and with the informed consent of horse owners who provided hair samples, photographs and background information on individual animals.

The genetic story that emerged is one of multiple founding contributions layered on top of one another. Admixture analyses showed that Kaimanawa Horses share genetic components mainly associated with British pony lineages, Thoroughbreds, Arabians and draft breeds, a pattern consistent with historical records describing the varied stock that contributed to the population during the colonial era and afterwards. Rather than descending from a single narrow source, the herd represents a living archive of the mixed breeding practices of nineteenth and twentieth century New Zealand, when working horses of many types were moved across pastoral land and often left to fend for themselves.

Yet the same analyses also documented the genetic costs of isolation. The population exhibits reduced heterozygosity, elevated inbreeding and an effective population size estimated at fewer than 50 individuals, a threshold widely regarded by conservation geneticists as dangerously low for long-term viability. The researchers traced this erosion of diversity to the population’s isolation and to recent demographic contraction, driven in part by management interventions. Kaimanawa Horses are subject to periodic musters, in which animals are rounded up and removed from the ranges to keep the population within an officially mandated ceiling, a practice that inevitably influences which genes persist in the free-ranging herd.

One of the most technically revealing aspects of the study involved runs of homozygosity, the long stretches of the genome where an individual inherits identical DNA segments from both parents, signaling recent or ancient inbreeding. By measuring the inbreeding coefficient derived from these runs and stratifying them by length class, the team could distinguish between older inbreeding events and more recent mating among relatives. The results confirmed that Kaimanawa Horses carry a substantial burden of homozygous segments relative to many domestic breeds, underscoring how founder effects, small population size and restricted gene flow have combined to shape the population’s genomic landscape.

Population structure analyses identified two distinct genetic subgroups within the herd, suggesting that geography and management history have produced detectable internal differentiation. Horses captured in different zones of the Kaimanawa Ranges, including the Argo Valley, southern zones and a designated capture zone, showed patterns consistent with limited movement between groups. Linkage disequilibrium decay, a measure of how quickly genetic variants lose their statistical association with physical distance along chromosomes, provided further evidence of the population’s demographic trajectory, while historical estimates of effective population size reconstructed over roughly the last seventeen generations revealed a declining trend that has accelerated in recent generations.

Perhaps the most striking discovery came from the paternal line. Analysis of the male-specific region of the Y-chromosome in 26 stallions revealed private paternal haplotypes that are absent from modern breed reference panels, indicating that the Kaimanawa population has retained unique paternal diversity that has disappeared, or was never present, in the registered breeds used for comparison. Mitochondrial DNA analysis of the maternal side complemented this picture, placing Kaimanawa maternal lineages within the broader spectrum of global horse diversity while highlighting the population’s distinctiveness. Together, these uniparental markers demonstrate that feral populations can serve as reservoirs of genetic variation lost from managed breeding programs.

The implications for conservation and management are considerable. An effective population size below 50 places the herd in a category where loss of genetic variation and inbreeding depression, including reduced fertility and foal survival, become realistic concerns. The authors argue that genomic approaches of the kind used in this study can directly inform management strategies, for example by guiding which animals are retained or relocated during musters to preserve the two genetic subgroups and maximize the retention of the population’s rare alleles and unique haplotypes. Without such informed intervention, the very management practices designed to control the population’s ecological footprint could inadvertently erode the genetic legacy that makes it scientifically and culturally valuable.

Beyond New Zealand, the study offers a template for understanding how founder history, demographic processes and human management jointly shape the genomes of free-ranging animal populations around the world. Feral horses occupy a contested space between pest and heritage icon, and their management is often decided in the absence of genetic data. By demonstrating that a feral population can harbor both documented vulnerability and irreplaceable diversity, the Kaimanawa work makes a compelling case that conservation genomics belongs at the center of such debates. As the researchers conclude, these findings not only illuminate the past of one of New Zealand’s most iconic wild animals but also support future research and evidence-based stewardship of feral horse populations wherever they roam.

Subject of Research: Genomic analysis of demographic history and genetic diversity in New Zealand's feral Kaimanawa Horses

Article Title: Demographic history and management practices shape the genomic landscape of New Zealand’s feral Kaimanawa Horses

Article References: Demographic history and management practices shape the genomic landscape of New Zealand’s feral Kaimanawa Horses. (n.d.). https://doi.org/10.1186/s12864-026-13345-y

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13345-y

Keywords: Kaimanawa Horses, feral horses, population genomics, conservation genomics, inbreeding, New Zealand, genetic diversity, Y-chromosome, effective population size, runs of homozygosity, horse breeds, population structure