Wednesday 6 July 2022

Which horses should be used for a reintroduction in Europe's nature?

The discussion which horse breed or type is closest to the European wild horse and which horses should be used for a reintroduction of the species into European nature systems is sometimes carried out rather controversially and is sometimes needlessly emotionalized. In recent years, a variety of horse landraces have been used for “rewilding”, including the Konik pony, the Exmoor pony, the Garrano pony, the Hucul, Retuerta, Sorraia and the Bosnian Mountain horse. Some of them have popular background stories that claim they are, respectively, the most recent descendants of the European wild horse – none of these popular background stories are scientifically tenable. That does not make those breeds any more, or any less, suitable for natural grazing projects or even establishing truly feral populations. The Konik pony and the strongly Konik-influenced Heck horse are most frequently used in natural grazing and “rewilding” projects, probably due to their scientifically untenable reputation of being wild horses, recent wild horse descendants or phenotypic copies of the European wild horse. However, the range of pony or horse breeds used in “rewilding” is slowly diversifying. Currently, the only place in Europe where horses live completely free of human influence (except for poaching, unfortunately) is the Chernobyl exclusion zone, where a population of about 100-200 Przewalski’s horses thrives. They also happen to be true wild horses instead of domesticates. But which type of horse should be used for a reintroduction of Equus caballus into European wilderness?

One of the problems we face when trying to resolve that question is, apart from all the confusion that the mythologized breed origin stories of certain landraces have created, that we do not know how the wild horses in Europe exactly looked like. Not a single complete skeleton of a Holocene, predomestic European wild horse has been described so far. It is likely that it had the robust pony morphology with a thick head, as this morphotype is found in the closely related Przewalski’s horse and Pleistocene wild horse skeletons from Europe. But we do not know the morphology for sure. What is much more certain is the colour phenotypes, as the colour loci of ancient DNA samples from European wild horses have been tested for the respective alleles. It turns out that during the early and middle Holocene, both bay dun (the colour of the Przewalski’s horse) and black dun (the colour found in Koniks, Hucule and Sorraias) were found in European wild horses. During the later Holocene, however, black dun became the prevalent phenotype as a//a is the prevalent genotype found in the ancient samples [1]. It is also possible that non-dun wild horses existed in Europe, but the Dun locus has not yet been tested in European wild horse samples. I believe that it is likely that dun was prevalent (go here). A tricky question is the mane of Holocene European wild horses. All wild equines today have a standing mane, while hanging manes are found exclusively in domestic horses and donkeys. Nowadays I think it is much likelier that European wild horses had a standing mane as all other living wild equines do (go here for a post). 

It is also important to note that there was not one European wild horse during the Holocene, but at least two subtypes: Iberian wild horses and wild horses on the rest of Europe. It turns out that, genetically, Iberian wild horses are less closely related to the ancestors of domestic horses than the Przewalski’s horse [2]. Furthermore, it is important to note that the range of wild horses was likely continuous from Europe to Asia and that there was a continuum between European wild horses and the Asiatic Przewalski’s horse, as introgression from the latter subspecies has been found in a European wild horse stallion’s DNA sample [3]. 

 

Combining these facts, there are two concepts for horse reintroduction in Europe that I prefer. I cannot decide which one of the two concepts I favour as both have pretty strong pro-arguments. I see that there are diverse options for “rewilding” horses on this continent and that each project is free to pick those types of horses they prefer, but I think there should be a somewhat consistent baseline for why choosing a particular breed for a true reintroduction into European nature, at least in my opinion. By true reintroduction I mean the establishment of self-sustaining, unregulated horse populations in a nature system or wilderness area. 

 

1. Using pure Przewalski’s horses 

 

There are two very obvious arguments for choosing Przewalski’s horses exclusively for the reintroduction of horses into Europe’s nature. For once, they are the only wild horses left. It is true that the Przewalski’s horse is the Asiatic subspecies, and therefore not the native subspecies, but it has to be considered that it is closer to European wild horse subspecies outside Iberia than the Iberian wild horse was, and that there apparently was a continuum between both subspecies. Furthermore, it is very likely that the Przewalski’s horse would have recolonized the European continent after the man-made extinction of wild horses in Europe if it had not been for human influence. It is true that the habitat of the Przewalski’s horse was restricted to the steppe in historic times, but we do not know the natural plasticity of the ecotype as it might have also inhabited other biomes previously. Przewalski’s horses do very well in grazing projects in Central and Western Europe and also wild in the European wilderness as the Chernobyl population demonstrates. The second argument for using Przewalski’s horses exclusively is that it would be a very valuable contribution to the preservation of this endangered last remaining wild horse subspecies. The Konik population in Oostvaardersplassen numbers around 1000 individuals – image Przewalski’s horses would have been chosen for that initiative. It would have grown to the largest single Przewalski’s horse herd on the continent (or perhaps even the entire world). There are dozens of grazing projects in Germany alone, if all of them chose Przewalski’s horses instead of domestic horses it would not take long until the last wild horse on this world is not endangered anymore. 

The question then is, why are not all “rewilding” and grazing projects using the Przewalski’s horse? This has two very practical reasons. First of all, the Przewalski’s horse is not just another domestic breed, but a genuine wild animal with the behaviour of a wild animal. They can be very aggressive, particularly the stallions, and may attack humans. Przewalski’s horses are very difficult to handle. The other reason is that Przewalski’s horses are not as easily available as domestic breeds are. 

 

2. Using hybrids of Przewalski’s horses and robust landraces 

 

The second concept is using hybrids of Przewalski’s horses and robust landraces that are adapted to the climate and vegetation of the respective region. The reason for that is that European domestic horse breeds are the descendants of the European wild horse, and thus there is a chance that they preserve at least some of the wildtype alleles that were unique for this wild horse type. The Przewalski’s horse should be in the mix because it is a wild horse with a wildtype morphology, genetics and behaviour. This would also create a greater genetic diversity than using Przewalski’s horses only, as they have a limited genetic diversity due to their genetic bottleneck during the 20thcentury. As a continuous range of free-roaming horses from Iberia to Asia is illusional in modern times, there is no danger of intermixing between pure Przewalski’s horses that have been released back into the wild and the hybrids in isolated European reserves. 

Creating hybrid populations of Przewalski’s horses and robust domestic landraces is also the chance to mimic the phenotype of the European wild horse. As mentioned above, the exterieur of that wild horse type during the later Holocene likely was the pony morphotype coupled with a standing mane and the black dun coat colour. The Przewalski-Konik hybrids living in the Lippeaue (go here or here) bear great potential for achieving that with selective breeding. The recessive standing mane and the recessive black dun coat colour can be fixed rather easily by breeding. I do not necessarily suggest that the combination Przewalski-Konik is the way to go for entire Europe. Many local landraces could be crossbred with Przewalski’s horses for “rewilding”. For example, the already established populations of Garranos, Sorraias, Exmoor ponies, Hucule and Bosnian mountain horses could be supplemented by single Przewalski’s horses, most ideally stallions. Surplus animals from zoos could be used so that the population of Przewalski’s horses that is used to preserve the subspecies is not depleted. And as the Lippeaue horses have shown, the introgression of one single animal can have a great impact on the phenotype of the entire herd without affecting Przewalski’s horses preservation efforts. I would pay attention that the genes for a black dun coat colour are always in the mix, as this was the original colour of the late Holocene European wild horse. In the case of the Sorraia, Hucule and Bosnian mountain pony, these alleles would be in the mix. In the other breeds, it might be best to introduce black dun stallions with a standing mane from another location to produce the desired phenotype. 

 

I think Przewalski’s horses should always be in the mix because they represent the last wild horse and the populations in Chernobyl and grazing projects have shown that they do well in the European biome. Alas, most projects will likely pick domestic horses only, because they are easier to handle, easily available, cheaper and there are no legal restrictions. 

 

Literature

 

[1] Sandoval-Castellanos et al.: Coat colour adaptation of post-glacial horses to increasing forest vegetation. 2017.

[2] Fages et al.: Tracking five millennia of horse managment with extensive ancient genome time series. 2019. 

[3] Wutke et al.: Decline of genetic diversity in ancient domestic stallions in Europe. 2018. 

 

 

13 comments:

  1. I think that the genetics of the mustang horse could be very interesting in the reconstruction of the wild horse. Mustangs are horses that have shown that they can survive and multiply without problems, better than other breeds.

    ReplyDelete
  2. Hey Daniel Foidl can you do the one blog about Aurochs in Bosnia and Herzegovina ? I have the many examples .In the Cazin region, wild cattle are called Garonja (Slavic name for black bulls) , which actually resembles a real Aurochs ( Bos Primigenius ) . In Bosnia and Herzegovina there are toponyms for Aurochs. For example, Turija in Bihać (Una river), Turijak village near Višegrad (Drina river), Turjak near Banja Luka, Vrbas river, Turić near Pelagićevo (Sava river). Aurochs as animal is very common in Bosnian mythology as giant black bull who holds the whole world . In Bosnia it is very common for person who is strong to be said " Jak si kao bik " ( translated as You are strong as bull ). In National Museum of Bosnia and Herzegovina there are few fossils of Aurochs found in Northern Bosnia in coast of Sava river .

    ReplyDelete
  3. Don’t you think it could be useful to have, in the second option, also Przewalski ‘s mares to have more Wild horses blood?

    ReplyDelete
    Replies
    1. Ideally yes, but critics could point out that this would deplete the pure Przewalski's population. Having a pure wild stallion as the only sire in a population will change the gene pool quite fast.

      Delete
    2. What is the difference between using Przewalski's that are unmixed and those that are crossed with robust landraces from a legal point of view? Do the ones that are mixed have to be treated like domestic animals and have to be tested for disease and require husbandry like a horse? Do their carcasses have to be removed from reserves or can they be left out for scavengers? Can either be hunted and eaten (it numbers of both types grow so that all available reserve space is filled as there are no living predators in Europe that can dent their numbers)?

      Delete
    3. Good questions, that would depend on the legal situation of each country. I was told that in Germany, the Przewalski's hybrids are treated as Przewalski's. I think the law dictates that carcasses always have to be removed, even in Oostvaardersplassen they remove carcasses. I don't know what they do with dead wisents in Bialowieza. That would depend on the legislation of each country. I fear that a true wilderness is "not allowed" in most cases in Europe, unfortunately.

      Delete
  4. I definitely agree that at least some Przewalski influence would be beneficial for european projects. I believe I've asked something similar in the past, but I'm wondering what varieties of horse I should use here in the southeast (if I can start a breeding-back project someday). I'm pretty sure there's at least two herds of Heck Horses (which look promising) here in the US, one being Dixie Meadow Tarpans, and the other somewhere in Oregon. But, would one of the coastal southeast breeds (like Cracker Horses, Marsh Tackies, or Banker Horses) be more suitable?

    ReplyDelete
    Replies
    1. In North America, I would go with pure Przewalski's. There are no descendants of American wild horses, so I'd use rewilding in North America as an opportunity to contribute to the preservation of this endangered wildtype.

      Delete
    2. Good point. But, how well can Przewalski's horses adapt to the hot and humid weather of the southeast?

      Delete
    3. Probably well, it gets hot in the steppe as well and Przewalski's do well in wet climates (it has been tried with success, see grazing projects in Germany or the Chernobyl exclusion zone). But it would have to be tried.

      Delete
  5. There is no tougher horse for cold weather than the Icelandic horse, which is also an intelligent and resourceful breed. Thousands of years naturally selected to survive the vegitatively meager, snow and frost ravaged landscapes of One of Europea most life-hostile landscapes, Iceland. Whilst simultanously have been selected based om fitness for use of human.
    Also closely related to primitive horse breeds.

    There is no overall more healthy breed than the Criollo horse, naturally selected in the nature of Argentina, resistent to parasites, healthy build, can maintain physique and health om meager food supplementation.

    Often when rewilding, people obsess with finding horses closely related to the previously wild horses of Europe, simply because they're phenotypically similar, even though they're really domesticated breeds that have been taken care of and fed by humans, and not been hardened by natural evolutionary pressure, when in fact some other breeds, have retained and improved qualities specific to wild earlier horses maybe not in appearance, but in behavior and sturdyness.

    I say Icelandic and Criollo horse are two of the very best candidates for rewilding based on fitness and resilience!

    ReplyDelete
  6. I think the fjord horse would be a better choice than the Icelandic pony. It's used to a tough climate, has good coloration and only the original gaits. The tölt and skeið found in many icelanders are quite recent.

    ReplyDelete
  7. Can you talk about breeding back north american horses that went extinct during the last ice age?

    ReplyDelete