Genetic testing reveals that the current breeding population of Holsteiner horses originated from at least eight ancestral founder mares.
The Holsteiner horse, which originated in the marshlands of Schleswig-Holstein in northern Germany, is one of the most popular horse breeds, and is especially known for its showjumping ability.
The maternal lineages receive special attention and are considered important for the breed’s success.
The documentation of maternal lines had already started in the early 1800s. At that time, each mare with unknown parents was defined as a founder mare for a new lineage.
Originally, five different breeding districts existed, each with its own breeding organization, but they later merged.
Today, 437 maternal lineages have been preserved, but there are large differences in the number of mares per maternal lineage. The breeding population currently comprises 5729 active broodmares.
Laura Engel and her fellow researchers, in a German study published in the journal Frontiers in Genetics, have described their work exploring the origins and relatedness of maternal lines within the breed through analysis of mitochondrial DNA.
Mitochondrial DNA is particularly suitable to examine maternal lineages, given that it is passed down through female lines.
The study involved molecular-based testing of hair samples from 271 mares made available by 207 different breeders. Documented pedigrees for all the mares could be traced back up to 10 generations. They represented 75 lineages – that is, 17.4% of all registered maternal lineages of the current breeding population.
Altogether, 78 distinct haplotypes were identified that have not yet been described in other breeds. A haplotype is a group of genes inherited together from a single parent. Six of these occurred in two or three different lineages, indicating common ancestry.
In nine lineages, mares had a common female ancestor one to seven generations ago, but in four lineages no common female ancestor could be found in the previous 10 generations.
The study team said their testing revealed pronounced mitochondrial variability within the population, with the findings indicating very accurate pedigrees within the examined lineages.
The lineages, they said, can be divided into eight clusters, corresponding to the haplogroups identified in 2012 research and based on the genetic distances between their mitochondrial DNA sequences in the current study.
No geographical pattern could be observed within the haplogroups, supporting the assumption of an early maternal gene flow across the former breeding districts.
The researchers said more than half of all active broodmares within the Holsteiner breed can be assigned to the maternal lineages examined in the study.
“The results,” they said, “indicate that the 75 lineages of the current breeding population included in the dataset have developed from at least eight ancestral founder mares.”
An investigation of the entire population would possibly reveal further founder mares, they said.
“Based on our findings, the lineages that were studied could be assigned to consolidated groups. In principle, further studies of the mitochondrial DNA sequences of Holstein horses would enable a complete re-definition of the maternal lineages resulting in a much smaller number of female lineages.”
The study team comprised Engel, Georg Thaller and Nina Krattenmacher, all with the Institute of Animal Breeding and Husbandry at Christian-Albrechts-University in Kiel, Germany; Doreen Becker, with the Institute of Genome Biology, part of the Leibniz Institute for Farm Animal Biology; Thomas Nissen, of the German Holsteiner Association; and Ingolf Russ, with Animal Breeding Research e.V. in Munich.
Engel L, Becker D, Nissen T, Russ I, Thaller G and Krattenmacher N (2021) Exploring the Origin and Relatedness of Maternal Lineages Through Analysis of Mitochondrial DNA in the Holstein Horse. Front. Genet. 12:632500. doi: 10.3389/fgene.2021.632500