Lions prefer killing piebald cattle

In my dedomestication series from 2015 I speculate on the selective pressures acting upon the genetic structure of feral domestic animals that will eventually turn the feral animals into wild animals adapted to their environment. I made the prognosis that the animals will show a regression towards wildtype traits because these provide a greater evolutionary fitness since they are the product of past natural selection. Colour would be one of the examples. I speculate that predators would influence the colour of the animals, because some variants are well-camouflaged and others are not, such as piebald individuals. This would, after a sufficient amount of generations in the wild, lead to an eradication of alleles producing piebald colours which are typical of domestic animals and to a genetic fixation of non-piebald (wildtype) alleles. 

My dedomestication hypothesis has empirical problems, as there is no feral population of domestic animals in the same habitat as their wildtype under the same ecologic circumstances that has been reproductively isolated for a sufficient amount of time. But recently there was a study that might provide empirical support for some of my prognoses postulated in the dedomestication series. 

The prey behaviour of lions preying on cattle in Botswana has been analyzed in 2020 by Weise et al.. What they found was not only that lions prefer to kill cattle that are easier prey such as hornless individuals (which is not surprising, as hornless cattle have a much harder time defending themselves against predators than horned cattle), but also that piebald cattle have a higher risk of being attacked by lions. Lions seem to prefer piebald cattle over solid coloured cattle [1]. The authors speculate that a piebald colour makes identifying movement easier for the lions, and therefore they are attacked more often than solid coloured cattle [1]. I think that it is also possible that it is simply the fact that piebald patterns stand out more than solid colours, so that these individuals are attacked more often.  

The authors also found that short-horned cattle were preferred over long-horned cattle, which were mostly avoided by the lions. 

These findings are very interesting. In my view, they clearly suggest that at least some wildtype traits (solid colour, long horns) provide a selective advantage over domestic traits (piebald colour, short or no horns). The authors indirectly say the same by pointing out that cattle lost adaptions of the aurochs against predators [1] (this is a generalization that is not actually true, as there are cattle which still have large forwards-facing horns, significant body size, an athletic long-legged stature and wildtype colour et cetera). This implies that in a heterogeneous cattle population, where some individuals have these wildtype traits and others do not, this will lead to an increase in the frequency and eventually the fixation of the wildtype alleles, and therefore a regression towards wildtype traits, when exposed to selective pressure caused by large predators. 

This shows that the selection criteria of "breeding-back" are not pure cosmetics as some critics repeatedly claim, but actually contribute to the survival of the population of the animals once returned into an ecosystem with predators. 

Literature 

[1] Weise et al.: Lions Panthera leo prefer killing certain cattle Bos taurus types. 2020. 

Transforming Lerida the Taurus cow to an aurochs cow

A while ago I did a post on the Taurus cow Lerida in the Lippeaue, Germany. She is a Sayaguesa x Heck cow, and has always been among my favourite Taurus cattle individuals. Recently I used a photo of Lerida and used the program GIMP to modify her morphology so that she fits a European aurochs cow. The result is down below. The photo was provided by Matthias Scharf from the ABU. 

original photo (bottom) © Matthias Scharf

The changes I made include: 

- horn size increased 

- horns slightly elevated viewed from frontal view 

- visible udder removed 

- trunk shortened 

- dewlap size decreased 

- hump size increased

A real aurochs cow would probably be slightly more muscular, as wild bovines usually are. But apart from that, I think the manipulated photo compared to the original shows the differences and commonalities between Lerida and an aurochs cow very well. The differences are reflected by the changes on the photo that I made, the commonalities include the colour, which is flawlessly wildtype, the skull shape, the leg length, the horn shape except for the fact that they could be more raised in frontal view producing that < >-shape, and also the body size is probably right as Taurus cows are usually around 150 to 155 cm in withers height. 

Australian scrub bulls and their aurochs-like morphology

There are feral cattle in Australia called scrub bulls. Those scrub bulls are noteworthy for their morphology. They are long-legged, slim but not too gracile. They are part zebu, and I think the zebu influence is responsible for their morphology, as primitive zebus are very short-trunked with long and slim legs. It is also possible that the fact that they live feral contributed to the morphology of the scrub bulls, but I do not know if they have been living feral for enough generations so that natural selection influenced their skeletal morphology.  

Here you have a video of some interesting scrub bulls in Australia: 

The morphology of scrub bulls, in my opinion, endorses the idea of using primitive zebus for achieving aurochs-like proportions in "breeding-back". An F2 of well-selected Taurus x (Taurus x primitive zebu) could be very interesting. 

Is "breeding-back" too much looks-based?

Originally, when the Heck brothers started their breeding experiments, their intent was merely to show what the aurochs looked like, i.e. they only cared about the animals’ looks. Nowadays, “breeding-back” aims to produce animals that are fit to ecologically fill the empty niche of the extinct aurochs. Cattle that work ecologically like aurochs are a valuable contribution to conservation and rewilding, as they represent a species once native in Europe. 

This is the modern purpose of “breeding-back”. But isn’t it too much looks-based for this purpose? Shouldn’t the breeding focus on the animals’ ecology, health, natural instincts and ability to defend themselves against predators if the cattle are supposed to survive without human help in nature? Wouldn’t existing feral cattle populations be a better substitute for the aurochs, because they proved to survive without human help? 

 

These objections against the concept of “breeding-back” occur from time to time, and I do not consider them valid. To avoid this kind of criticism, “breeding-back” projects emphasize that they do care about the cattle’s ecology. But that seems to be unheard by those who consider “breeding-back” too much looks-based. 

I think that those who criticise “breeding-back” as too superficial imagine that the desired aurochs traits are evenly distributed among the cattle world, so that aurochs-like traits desired are coincidentally found in breeds that might or might not be robust in ecological terms, and that the breed choice of “breeding-back” is based only on those optic criteria, so that the selection of breeds used might consist of breeds that have the desired optic traits but may lack the ability to survive and thrive in nature and the subsequent breeding focuses only on those optic traits, so that the robustness of the cattle would fall by the wayside while feral cattle prove to be robust and able to survive in nature. 

This, however, is a wrong assumption. In fact, optically aurochs-like cattle are always at the same time robust, hardy landraces because they are less-derived as a whole, and often live free all the year round. That means that the animals that “breeding-back” works with are hardy and robust right from the beginning. Heck cattle are a very good example for this. As mentioned above, the Heck brothers only cared about the looks of the cattle. Yet the resulting breed turned out to be healthy, hardy and robust, because the breeds it was created from were healthy, hardy and robust. Heck cattle proved to be able to survive without human help in the Oostvaardersplassen reserve. If the assumption of those considering “breeding-back” too much looks-based was correct, Heck cattle – originally only selected for looks – would not have ended up as a hardy and robust breed that is able to survive in nature. The same inevitably goes for more aurochs-like “breeding-back” cattle like Taurus cattle, because those projects also exclusively work with hardy and robust breeds. I have to admit that I do not know of a single breed that is truly aurochs-like but is susceptible to diseases, not able to cope with weather or to live free all year round and can only live on easy-digestible food provided by humans. 

It is also not true that “breeding-back” does not care about the ecologic capacity of the animals. For example, “breeding-back” cattle in Central, Northern and Eastern Europe need a thick insulating winter coat in order to cope with harsh winters. Watussi is used in some “breeding-back” projects which is a subtropical breed and not very winter-resistant, and the winter coat of Chianina is not the longest and thickest either. The breeders are aware of that and included breeds which have a thick insulating winter coat, f.e. Hungarian Grey cattle in Hungarian Taurus or Auerrind cattle. Yes, “breeding-back” focuses on a lot of optic traits, but the ecologic capacity of the animals is an additional criterion in all modern projects. 

Regarding the behaviour of the cattle, I think that many people underestimate the natural instincts of cattle. Cattle of any breed redevelop a natural shyness after a few weeks in the wild [3]. Heck cattle are known to form defensive circles around their offspring when they consider it threatened, they will defend calves and cows retreat to a shelter when giving birth, where they hide the calf during the first days of their life [1,2]. All free-roaming cattle populations show herding behaviour, this also goes for “breeding-back” cattle. No additional breeding for natural instincts is necessary, cattle still have the natural behavioural repertoire required by a life in nature. 

 

Furthermore, the assumption that feral cattle are more qualified as an aurochs substitute than “breeding-back” cattle is not really logical when the fact that many feral cattle populations descend from ordinary farm cattle is considered. For example, the exterminated population on the Ille Amsterdam which thrived in the wild for about 150 years, descended from the following breeds: Jersey, Tarentaise, Grey Alpine and Breton Black pied [4]. If just any cattle can build up and sustain feral populations in nature and redevelop wild traits, then so will “breeding-back” cattle. 

 

Another important aspect to consider is that an aurochs-like morphology also provides fitness advantages for the cattle. Small, hornless or short-horned cattle have a harder time defending themselves and their offspring from predators than large cattle with aurochs-like horns. Also, a short dewlap and a small udder mean less heat loss during winter. And as already mentioned, “breeding-back” cares about the winter coat. Wildtype colour is probably more suitable for a life in nature than a piebald colour, piebald calves are detected much easier by predators than the chestnut colour of wildtype-coloured calves. 

 

All in all, I do not think that “breeding-back” is too much looks-based and I am 100% confident that “breeding-back” cattle will fulfil the ecological niche of the aurochs very well if they were released into nature. 

 

Literature 

 

[1] Frisch, W.: Der Auerochs – das europäische Rind. 2010. 

[2] Poettinger, J.: Vergleichende Studie zur Haltung und zum Verhalten des Wisents und des Heckrinds. 2011. 

[3] Bunzel-Drüke et al.: Praxisleitfaden für Ganzjahresbeweidung in Naturschutz und Landschaftsentwicklung -  “Wilde Weiden”. 2008. 

[4] Rozzi & Lomolino: Rapid dwarfing of an insular mammal – the feral cattle of Amsterdam Island. 2017. 

 

 

 

Second generation Auerrind calves

Today, Claus Kropp posted new photos of second-generation Auerrind calves. They are the offspring of Alvarez, the Sayaguesa x Watussi bull. 

© Claus Kropp

This photo shows a young (Sayaguesa x Watussi) x (Sayaguesa x Chianina) bull. His colour is flawless as he is black with a dorsal stripe. I think he looks promising, he is quarter Watussi but does not have any of the obvious negative Watussi traits (zebuine hump, long dewlap etc.). If his horns get good and he grows large, he will make a prime new breeding bull. 

© Claus Kropp

This photo shows a (Sayaguesa x Watussi) x Chianina cow calf. It seems that she will be of a correct cow colour, and thus not too dark (as both Sayaguesa and Watussi do not have sexual dichromatism, this is a strong hint for the suspicion that Chianina has sexual dichromatism masked beneath the colour dilutions). Based on her breed combination, she would be the ideal cow to mate with the young bull linked above, as the result would have the potential to not only have a qualitative phenotype but also to be homozygous for some of the desirable traits inherited from the three founding breeds. 

Wild horses: getting the taxonomy right

I used to refer to the European wild horse as Equus ferus ferus, which may be wrong. This post deals with the issue of the taxonomy of the European wild horse(s), the domestic horse and the Przewalski’s horse. 

 

Some consider the domestic horse and the Przewalski’s horse different species, mainly because of the different chromosome number and morphological differences. However, we find differences in the karyotype also in other species, such as the Banteng (the Cambodian banteng has a chromosome number different from the other subspecies), and morphological differences are also found between subspecies, and both horse types interbreed without fertility problems. Thus, it is not unjustified to consider the domestic horse and the Przewalski’s horse members of the same species. The western subspecies of the Eurasian wild horse, which was the predecessor of the domestic horse, was definitely part of this species too, for once as many consider wildtypes and their domestic derivates members of the same species, and because they most likely could interbreed without fertility problems too and the morphological differences were likely smaller than between domestic horses and Przewalski’s horses. How to name this species, then? Wikipedia, and I too in the past, uses Equus ferus ferus for the western wild horse subspecies, Equus ferus przewalskii for the Przewalski’s horse and Equus ferus caballus for the domestic horse. I consider this problematic. 

At first we have to consider the priority rule of the ICZN. Equus caballus was described in 1758, Equus ferus in 1784 and Equus przewalskii in 1881. Following the priority rule, Equus caballus would definitely be the senior synonym and thus the name that should be used for the species. However, in 2003 a number of names of wildtypes that are synonymous with their domestic derivates, have been conserved by the ICZN, including Equusferus (and also Bos primigenius, by the way). Thus, the name to be used would be Equus ferus. But the main problem is: what type of horse is Equus ferus based on?

The original description of Equus ferus is a short description by Boddaert from 1784, lacking a holotype, but referring to free-ranging horses of the Russian steppe. According to most recent research as well as the fact that these horse populations included many individuals that might have been feral domestic horses or hybrids, these free-ranging horses (called “tarpan” by other contemporaneous authors), were most likely hybrids between native wild horses and domestic horses. Thus, Equus ferus is not based on the predomestic western Eurasian wild horses, but on hybrids with domestic horses. Hence, it does not describe the wildtype. Therefore, the reason to preserve this nomen in the ICZN falls apart. Also, the description lacks a holotype and is based on hybrids of two subspecies, thus the legitimacy of the taxon is to be questioned. 

Considering this, I no longer use Equus ferus as the name for the species of the western Eurasian wild horse, the eastern Eurasian wild horse (Przewalski’s horse) and the domestic horse. Rather, Equus caballus should be used: Equus caballus caballus for the domestic horse, Equus caballus przewalskii for the Przewalski’s horse and the western subspecies of the Eurasian wild horse is yet not scientifically described. 

The western Eurasian or European wild horse thus needs a proper description in the scientific literature. Someone should describe this subspecies, using a type specimen that is definitely a member of the Holocene western wild horse subspecies, f.e. bone remains predating domestic horses (so that they are predomestic for sure) found in Europe. I know of no such specimen that are mounted and on display, but there are remains that have been found. 

Another important aspect is that the Iberian wild horses probably deserve a subspecies status on their own. They are a genetically independent lineage that is less closely related to the domestic horse (and their predecessors) than the Przewalski’s horse and Equus (caballus) lenensis, respectively [1], and thus should not be regarded as a part of the western subspecies that gave rise to domestic horses and was found on the rest of Europe, because that subspecies is younger than the Iberian wild horse. As the European wild horse, the Iberian wild horse subspecies needs a proper description with a reliable type specimen. 

 

Literature 

 

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

 

 

 

 

Why is the aurochs extinct while the wisent survived?

As everybody reading my blog will know, Holocene Europe was originally home to two native bovines, the wisent and the European aurochs. But only the wisent survived, while the aurochs eventually died out in the 17^thcentury, as a result of anthropogenic influence. But why did the aurochs die out while the wisent survived human activity until today? 

 

It was two anthropogenic factors that drove the aurochs to extinction: one was hunting, the other one habitat limitation due to the expanding civilization. Both factors also apply in the case of the wisent. The wisent was also hunted, and its habitat was also limited increasingly as the human population in Europe grew continuously. So why did the wisent survive and did not die out at the same time the aurochs did? 

One of the reasons might be that aurochs were hunted more intensively than wisent. Aurochs had larger, more impressively shaped horns and a colour that was more aesthetically appealing than that of the wisent (Sigismund von Herberstein wrote: “…the wisent is not as beautifully black as the aurochs…” in the 16^th century), so that it is possible that trophy hunting focused more on the aurochs than on the wisent. Julius Caesar wrote in De bello gallico that the Germanic people liked to hunt the aurochs for its horns, while he made no mention of the wisent, although this species must undoubtedly have lived in the Hercynian forest as well. 

Another possible reason why the wisent survived human activities while the aurochs died out lies in the ecology of both species. I outlined the ecologic differences between the two bovines in my post The ecologic niche of the aurochs. The aurochs was likely in direct competition with domestic cattle (and likely also horses) for feeding grounds. The aurochs was predominantly a grass eater, as are cattle and horses, and it is historically documented that aurochs grazed on the same places as the livestock of farmers, who chased the aurochs away if they encountered one on the pastures (see Anton Schneeberger’s report in Gesner 1602). During the last millennia and centuries of its existence, the aurochs retreated to wet habitats, such as swamps and marshes as isotope analyses show [1]. But also these areas were cultivated increasingly. The last historically documented population of aurochs, which lived in the forest of Jaktorow in Poland, disappeared because the space available to them became ever smaller and smaller as farmers continuously let their cattle and horses graze in the forests, so that the aurochs had to retreat even further and could not thrive [2]. 

The same problems also applied to the wisent. It, on the other hand, had the advantage that it could retreat to more mountainous regions (while the aurochs lived in even lowlands), which was less invaded by farmers or their domestic cattle and horses. Also, the wisent is more adapted to a forested habitat than cattle (and consequently likely also the aurochs), as they consume more wooden vegetation and need less grass in their diet [3]. The ecology of the wisent is probably the main reason why the extinction of the species in the wild occurred three centuries after the extinction of the aurochs, in 1919 [4]. We should not forget that the wisent survived the extinction in the wild only due to the fact that it was bred in captivity. Without the captive population, there would be no wisents today. The Caucasus wisent, B. b. caucasicus, did not have that luck and was fully exterminated in 1927. 

 

Literature 

 

[1] Lynch et al.: Where the wild things are: aurochs and cattle in England. 2008. 

[2] van Vuure: Retracing the aurochs - history, morphology and ecology of an extinct wild ox. 2005. 

[3] Bunzel-Drüke et al.: Praxisleitfaden für Ganzjahresbeweidung in Naturschutz und Landschaftsentwicklung – “Wilde Weiden”. 2008. 

[4] Krasinska & Krasinski: Der Wisent: Bison bonasus. 2008. 

 

How to breed for the right sexual dichromatism?

The sexual dichromatism, the difference in colour between the sexes, is one of the most defining characters of the wild aurochs. A reduced or absent dichromatism is a typically domestic trait. Thus, “breeding-back” definitely has to try to achieve a well-marked sexual dichromatism.

 

Aurochs calves were born of a reddish chestnut brown colour, and grew their adult colour in their first year. The reddish brown base colour becomes superseded by black hairs that steadily increase in number. This darkening of the coat starts on the head and neck, the legs and ventral side of the trunk. I call this darkening of the coat the process of eumelanisation (eumelanin is the black pigment in mammals). When the eumelanisation is completed, the whole body is black except for a lightly coloured dorsal stripe and mouth. This was the colour of the bulls. Bulls with a colour saddle did very likely not exist in the European subspecies (go here). In cows, the eumelanisation is stopped earlier. Depending on the degree of eumelanisation, cows can display a wide range of colours which I illustrated in the drawing down below: 

 

I am not so sure about the top left phenotype, but the other phenotypes are proven for aurochs cows based on cave paintings and historic records. It has to be noted that bull-coloured cows are reported to have been very rare. 

 

In wildtype coloured cattle (cattle with a phenotype caused by the E⁺ allele on the Extension locus) we have the same mechanism. The difference is that in most breeds domestication has caused a chaos regarding the degree of eumelanisation: some breeds are bull-coloured in both sexes, such as Sayaguesa where the cows are bull-coloured in many cases, or the dichromatism is at least reduced by bulls having a colour saddle, such as in Alistana-Sanabresa, or both sexes have a very reduced eumelanisation, such as Cachena and Barrosa, for example. Only some breeds have retained the dichromatism we see in the aurochs, such as Maronesa (the bulls are always black, and most cows are less eumelanised than the bulls), or the old lineage of Corsican cattle, which is almost extinct due to crossbreeding with more productive breeds. In those two breeds, all the alleles involved in the production of the colour are very likely the original alleles of the aurochs otherwise we would see a different phenotype. 

The genetic background of the sexual dichromatism found in Bos primigenius is not resolved yet. The genetic program of the eumelanisation process can be located anywhere on the genome. The degree of eumelanisation is said to be dependent on the testosterone level. Bull calves that get castrated before they grow their adult colour grow the colour of cows. This explanation, that eumelanin is only dependent on testosterone level, cannot be the whole story, however, as this would mean that a Sayaguesa cow (which usually is more or less fully eumelanised) has more testosterone than a Barrosa bull (which is barely eumelanised), which is very implausible. Consequently, it must be the alleles that regulate the degree of eumelanisation that mutated in these cattle, with some alleles needing a higher level of testosterone (resulting in less eumelanised sexes) and some alleles needing a lower level of testosterone (resulting in bull-coloured cows) to become active. This is a speculation, but the only plausible one to me. 

 

How to breed for a well-marked sexual dichromatism as in the aurochs? Crossbreeding shows that trying to reduce the eumelanisation of bull-coloured cows by crossing in a less eumelanised breed does not increase the degree of sexual dichromatism. This has been shown in the Sayaguesa herds of Peter van Geneijgen, who incorporated individuals influenced by Alistana-Sanabresa, a less eumelanized breed. The results were less eumelanized cows (thus with “cow colour”), but also in some bulls having a colour saddle. Thus, the sexual dichromatism did not increase, even though some cows are now correctly coloured. 

This tells us that working with two breeds which have a reduced sexual dichromatism cannot result in an increased sexual dichromatism. One would have to take a breed with the right alleles having the right sensitivity for testosterone, if my assumption above is correct. Thus, the right sexual dimorphism can only be achieved if there is a breed that already has it. Luckily, this is the case as there are at least two breeds in Europe with that trait (Maronesa and Corsican cattle). 

 

There are “breeding-back” herds that have a satisfying degree of sexual dichromatism. For example, the Hellabrunn Heck herd has a excellent colour and dichromatism (go here). I evaluated the sexual dichromatism in the Lippeaue population using a photo archive (go here). The result was that more than 80% of the individuals have the right degree of eumelanisation for their sex. Of course some individuals that are correctly coloured might pass on individuals with no sexual dichromatism, f.e. bull-coloured bulls that pass on bull-coloured cows or cow-coloured cows that pass on bulls with a saddle. In order to increase the sexual dichromatism, it would have to be possible to discriminate between those individuals and those that pass on sexual dichromatism, which is hitherto impossible as the genetic background of this trait is not resolved. 

Heck cattle have their sexual dichromatism from Corsican cattle, and Taurus cattle has it from Heck cattle (Chianina might contribute an at least moderately developed dichromatism as well, it could be masked beneath the dilution alleles producing the white colour). 

 

Achieving a well-marked sexual dichromatism might become problematic for the Tauros Programme and perhaps also the Auerrind project. Many Tauros cows are rather dark and bulls often have a saddle, and most of the founding breeds have a more or less reduced sexual dimorphism (Maremmana, Highland, Sayaguesa, Podolica, Boskarin, Pajuna), they use Maronesa only on a small scale in the form of four cows and a few bulls in Dutch herds as far as I am informed. For the Auerrind project, all of the founding breeds have a reduced sexual dichromatism (Sayaguesa, Watussi, Maremmana, Hungarian Grey, Pajuna, perhaps Chianina). So far, not enough crossbred animals have been produced to judge the sexual dichromatism in the Auerrind herds. 

 

The last free-ranging horses in Europe were hybrids

EDIT: The individual examined in the study is actually the Shatilov tarpan, a specimen which was also caught in the Cherson region but died in 1868. 

The nature of the horses described in contemporaneous literature from previous centuries, such as by Gmelin, Pallas, Smith and others, has long been dubious. It was unclear if those horses were genuine wild horses, feral domestic horses or hybrids. In the Russian steppe, these free-ranging horses of the 18th to the early 20th century were called "tarpans". 

The fact that a black dun colour prevailed in these historic reports may suggest that these horses were at least partly wild horses, because black dun or black was the prevalent colour of late Holocene European wild horses. However, the fact that also non-wildtype colours were mentioned in these reports suggests admixture. The mane of the last free-ranging horse of the Russian steppe was described as being semi-erect, as to be expected from a hybrid between a horse with an upright mane and a falling domestic mane. 

The Cherson Tarpan, photographed in 1884

Librado et al. 2021 examined the genome of the so-called Cherson Tarpan, the only "tarpan" to be photographed. It revealed that at least this individual has a hybrid origin of western wild horses and domestic horses. To be precise, the authors write: "The tarpan horse came about following admixture between horses native to Europe [...] and horses closely related to DOM2". A hybrid origin for the free-ranging horses described in historic references makes sense. That they were pure wild horses was unlikely due to their phenotype (domestic colour variants et cetera). That they were merely feral horses was also unlikely because black dun prevails in these reports, and it would be a big coincidence if feral domestic horses also were mainly black dun in colour. Also, I have always considered it the most likely scenario that the pure wild horse did not die out as a whole but got continuously genetically influenced by feral domestic horses. So it seems that this scenario is confirmed, at least under the assumption that not only the Cherson tarpan but all the other free-ranging horses of Europe during the 18th to 20th century were hybrids. 

The information that the horses historically called "tarpans" might help to stop the inappropriate synonymization of the word "tarpan" with the original European wild horses. 

The study's main purpose was the origin of the domestic horse. They conclude that the domestic horse most likely originated in the lower Volga-Don region, and that mutations on two genes were of particular importance for the domestication of the horse: one on the GSDMC gene, probably improving the horses' ability for bearing weight on their back, and one on the ZFPM1 gene, probably reducing the fear response and increasing the docility of the horses. 

The study, however, completely ignores the work of Taylor et al. 2021 that concluded that the Botai horses were not domestic. 

Literature: 

Librado et al. 2021: The origins and spread of domestic horses from the Western Eurasian steppes. 2021. 

Five common myths about Heck cattle

I already did a post on myths about Heck cattle in 2013 (go here). But that post fails to address the most prevailing myths or misconceptions about Heck cattle that I want to outline with this post. 

 

Myth #1: Heck cattle are aggressive. This is a very annoying myth, because it simply is not true. I made a post on that a few weeks ago. It is based on one incident that is repeated over and over, yet that incident is the only documented case of some Heck cattle individuals behaving aggressively. Heck cattle are used in numerous grazing projects, are bred on private farms and zoos, and there have been no further incidents of Heck cattle attacking people without a reason. Heck cattle is generally described as a rather unproblematic breed by breeders [1,2]. I can confirm from my personal experience that Heck cattle are not an aggressive breed. 

 

Myth #2: Heck cattle were bred using the Spanish fighting bull. I made a post on that common misbelief years ago. Many people that are only half-educated on this breed believe it was bred using the Spanish fighting bull. That false claim is even made in otherwise very well-researched sources [2]. While it is true that Lutz Heck has used Toro de Lidia in his crossbreeding experiments, it is also true that none of his stock survived past 1945, so that modern Heck cattle exclusively go back to the stock of Heinz Heck, who did not use that breed. 

 

Myth #3: Heck cattle were created by the Nazis. This is another very annoying myth. The claim that it was Nazi officials that ordered the creation of Heck cattle is just plain wrong. The Heck brothers started breeding in the 1920s and their motivation was purely zoological. It is true that Hermann Göring sponsored Lutz Heck’s experiments and allowed him to spread his cattle among German game parks, but it is also true that Heinz Heck, whose stock is the basis of modern Heck cattle, was opposed to the Nazi regime. That’s the whole story. Yet a lot of people make a huge deal of it, because “Nazi cows” is simply too entertaining for some individuals. 

 

Myth #4: Heck cattle look like the aurochs, just smaller. This is a claim that is objectively wrong. I reviewed the quality of Heck cattle as a “breeding-back” result in this 2013 post. Heck cattle are noticeably different from aurochs on many aspects, not only the size. See down below for a drawing that illustrates the optical differences between aurochs and cattle: 

 

Myth #5: The Berlin lineage and the Munich lineage looked identical, proving the success of the Heck brothers’ experiments. This myth also occurs from time to time and was created by the Heck brothers themselves. They claimed their results looked the same, although they used different breeds, what, according to them, proved that they did their work right. This is far from the truth because Lutz and Heinz Heck’s cattle did not look very similar. Lutz Heck’s cattle were greatly influenced by the Spanish fighting bull, while the cattle of Heinz Heck were heavier and also the horns were different. I do not know why the Heck brothers thought their cattle looked identical, it clearly was wishful thinking. 

 

Literature 

 

[1] Frisch, W.: Der Auerochs – das europäische Rind. 2010. 

[2] Poettinger, J.: Vergleichende Studie zur Haltung und zum Verhalten des Wisents und des Heckrinds. 2011. 

 

 

The wild zebu, B. p. namadicus

I did a couple of posts on the Indian aurochs, B. p. namadicus, the ancestor of the zebu, previously. Go here or here. 

Recently I did another artwork for the Indian aurochs or wild zebu. I think this new artwork is the most accurate for this subspecies I have done so far. 

The head and horns are based on the cranial material you can see in the second post I linked above. The horns are proportionally large, and more wide-ranging than in the European subspecies. The skull is narrower with less prominent eye sockets. 

As to the body, I was unable to find any information on the postcranial anatomy of B. p. namadicus. But it is very likely that it had a standard wild cattle anatomy, such as a short trunk, long legs and a hump formed by tall processus spinosi. I speculate that the dewlap of the wild zebu was longer than in the European aurochs B. p. primigenius, because of thermoregulation and its possible display function. The ear shape is based on zebus. And it is not unlikely that it lacked the curly hair between the horns that the European aurochs had, since tropical bovids usually do not have hairy ornaments and no zebu has curly hair on the forehead. The colour is speculation, for this artwork I assumed that it had the same colour as the European aurochs. 

It is not totally impossible that the Indian aurochs or wild zebu had a zebuine hump made of muscles and fat just like zebus. There are no osteological correlates between the zebuine hump and the skeleton, so that we cannot deduce its presence or absence based on the bones. Furthermore, there are no artistic depictions of B. p. namadicus that could provide a clue. For this artwork, I assumed that it did not have a fleshy zebuine hump. 

How much introgression from wild aurochs was there in Europe?

Taurine cattle were domesticated in the Fertile Crescent in the Near East. As “breeding-back” focuses on the European aurochs, it is an important question how much introgression from local aurochs populations into the domestic gene pool there was in Europe. Especially as some claim “breeding-back” is doomed to fail because it focuses on the European type while domestic cattle descend from the Near Eastern aurochs. 

 

To assess the question if there was local influence from European aurochs into the modern taurine cattle population, the genetic evidence has to be taken into account. The mitochondrial DNA tells us about the possible matrilineal introgression from local aurochs. There were two separate mitochondrial groups of European aurochs, Bos primigenius primigenius. Southern European and Near Eastern aurochs share the mitochondrial haplotype T, which is also found in most domestic cattle, while Central, Northern and Eastern European aurochs have the haplotype P [1]. The P haplotype was discovered in Holstein cattle and the Korean Hanwoo [1,2], what suggests introgression from wild cows of the northern type. Some Italian breeds also have the haplotypes R and Q, which are unique among domestic cattle [3,4]. This suggests local introgression or even domestication of wild aurochs in Italy [4]. 

Regarding the patrilineal evidence, it has been suggested in 2005 that introgression from aurochs bulls into domestic cattle was common in Europe [5], which was refuted later [6]. 

It has to be kept in mind that mitochondrial and Y-chromosomal haplotypes only tell half of the story. The mitochondrial genome is passed on by the mother exclusively, and the Y chromosome only by the father. Thus, looking only at mitochondrial or Y-chromosomal haplotypes can be misleading. If aurochs bulls mated with domestic cows, which is not unlikely as cattle were kept free all year round in earlier times (and still are today in some regions of Europe), which is also historically documented to have happened (Anton Schneeberger mentioned that occasionally wild aurochs bulls covered domestic cows in the 16^th century), and if only the female offspring was kept for further breeding (which is also not unlikely because the behaviour of the hybrid bulls was certainly more problematic than that of the cows), the wild influence would be undetectable by mitochondrial and Y-chromosomal haplotypes. The aurochs would not pass on aurochs mtDNA, and the Y-chromosome would be selected out in the first generation. Thus it is possible or even likely that introgression from local wild aurochs was more common in Europe than suggested by mitochondrial and Y-chromosomal haplotypes. Therefore, not only these parts of the genome should be considered to look for local aurochs introgression, but also the autosomal genome. 

Not surprisingly, when the first nuclear aurochs genome was fully sequenced [7], it was found that British aurochs significantly influenced British and Irish landraces [7,8]. 

 

Therefore, hybridization between local aurochs and domestic cattle not only happened occasionally, but the offspring was actively included into the breeding by ancient farmers. It is possible that the influence of local aurochs contributed alleles useful for the breeding, f.e. adaptions to local climate and diseases that were beneficial for the cattle from the Near East. Consequently, modern European taurine cattle are not only the descendants of the Near Eastern aurochs, but also of the European aurochs. The European aurochs left living descendants. 

 

 

Literature 

 

[1] Mona et al.: Population dynamic of the extinct European aurochs: genetic evidence from a north-south differentiation pattern and no evidence of post-glacial expansion. 2010. 

[2] Zhang et al.: Evolution and domestication oft he Bovini species. 2020.

[3] Park et al.: Genome sequencing of the extinct Eurasian wild aurochs, Bos primigenius, illuminates the phylogeography and evolution of cattle. 2015.

[4] Bonfiglio et al.: The enigmatic origin of bovine mtDNA haplogroup R: Sporadic interbreeding or an independent event of Bos primigenius domestication in Italy? 2010. 

[5] Götherström et al.: Cattle domestication in the Near East was followed by hybridiziation with aurochs bulls in Europe. 2005. 

[6] Edwards et al.: Mitochondrial DNA analysis shows a Near Eastern Neolithic origin for domestic cattle and no indication of domestication of European aurochs. 2007. 

[7] Orlando, L.: The first aurochs genome reveals the breeding history of British and European cattle. 2015. 

[8] Park et al.: Genome sequencing of the extinct Eurasian wild aurochs, Bos primigenius, illuminates the phylogeography and evolution of cattle. 2015. 

 

Is Oostvaardersplassen a "new wilderness"?

I covered Oostvaardersplassen multiple times on this blog, but never the ecologic dimension of the reserve as a whole. Oostvaardersplassen is often praised as a new wilderness, f.e. in the documentary “De nieuwe wildnernis” from 2013. Others have claimed it is a failed case of rewilding. 

 

Oostvaardersplassen, located in the province of Flevoland in the Netherlands, is a fenced area of 56 square kilometres. In 1983, 35 Heck cattle were introduced, followed by 27 Konik ponies in 1984 and 54 red deer in 1992. The number of the animals was not regulated and there also was no supplementary feeding. In the early 2000s, the number of cattle reached its peak of about 1000 animals, and after that, started to decrease again while the number of horses and red deer started to increase further. As of October 2017, there were 230 Heck cattle, 1040-1060 Koniks and incredible 3910-3990 red deer in the reserve (go here). It has to be noted that the largest carnivore in the reserve is the fox, while there are no lynxes, bears, wolves and of course no lions which would be the natural enemies of grown bovines and equines. 

What is very interesting is the drop in the number of cattle. It is very likely that the cattle are outcompeted by geese [1] and possibly also horses, because both can graze a few centimetres deeper than cattle [1,2]. I would not rule out that the cattle may one day disappear from the reserve because of that. If that is the case, how did aurochs coexist with these animals? One possible explanation would be so-called predation-mediated coexistence. Adult aurochs were possibly less easy to kill for wolves and even lions than horses or deer. Thus, these predators would reduce the population of these animals more than that of the aurochs, and therefore enabling coexistence between these species. 

Roe deer already disappeared from the reserve, perhaps outcompeted [3] (that’s what the literature says; however, I recently saw a video from OVP that shows a roe deer in the reserve). 

 

The original natural population density of large herbivores in Europe without human influence is unknown. But the fact that the avifauna in the OVP has declined by 36% since 1997 [3], as well as the drastic reduction of cover from woody vegetation from 30% to less than 1% from 1996 to 2011 [4] may suggest overgrazing in OVP. 

 

The OVP should be regarded as an artificial system rather than a nature area, in which some of the native large herbivores are present (red deer, cattle, horses) and others are not (roe deer, wild boar, elk, wisent) [4] and, more importantly, no predators for adult deer, cattle and horses. Because the area is fenced, the large herbivores are unable to migrate and the area is basically an island – an island devoid of predators. The reduction in avifauna diversity and decrease of habitat diversity in the reserve as a consequence of the intense grazing pressure caused by the very high density of the herbivores as a consequence of the lack of predators, as well as the disappearance of roe deer from the reserve suggest that the OVP anything but a “natural” ecosystem. It is as if one would fence an area in the Serengeti, kill off all the predators, watch some herbivore species reaching very high densities while others disappear, and a loss of habitat types and an accompanying loss of species diversity in that area. 

In the Yellowstone reserve, the reintroduction of wolves has shown to have an impact on herbivore activity and population density, which in turn influences the vegetation [5]. A reintroduction of predators in the OVP is unfortunately out of question, as the surrounding area is densely populated and farmers would have to fear for their livestock. 

 

Some consider the OVP because of all that a “failed case of rewilding”. Regardless of if this is true, it is still very valuable as a dedomestication experiment. There are hints that the Heck cattle population in the OVP, which has been exposed to selective pressure for 40 years now, is evolving (go here or here). 

 

Literature 

 

[1] Cornelissen et al.: Rewilding Europe: Early dynamics of a multispecies grazing ecosystem.

[2] Bunzel-Drüke et al.: Praxisleitfaden für Ganzjahresbeweidung in Naturschutz und Landschaftsentwicklung – “Wilde Weiden”. 2008.  

[3] van Vuure: On the origin of the Polish Konik and its relation to Dutch nature management. 2014. 

[4] Cornelissen et al.: Effects of large herbivores on wood pasture dynamics in a European wetland system. 2014.

[5] van Vuure: Retracing the aurochs – history, morphology and ecology of an extinct wild ox. 2005. 

 

 

 

Why were the last aurochs less impressive than earlier ones?

Species change over time, evolution is inevitable. Apparently the European aurochs, Bos primigenius primigenius, on which the guideline of “breeding-back” is based on, also changed over time. It got continuously smaller towards the end of its existence, and also its horns became smaller and less curved. Basically, these changes made the last European aurochs less impressive than those of the early Holocene. But why is that, and which type of aurochs (the impressive Early Holocene aurochs or the not so impressive aurochs of the Jaktorow forest) should “breeding-back” focus on? 

 

The size decrease 

 

Late Holocene aurochs were smaller than Pleistocene and Early Holocene aurochs. Some authors assumed a dramatic size decrease so that the last aurochs were merely as large as domestic cattle [1]. This is certainly incorrect. There is no evidence for aurochs bulls considerably below a withers height of 160 cm. The shortest withers height for a male aurochs described in the literature is 154 cm [2]. Considering the fact that soft tissue and hooves would add to the height in the living specimen, it might have been 159 to 165 cm tall in life. There are several Holocene aurochs specimen that exceeded a height of 170 and 180 cm in bulls and reach 165 cm in cows [2], and also historic reports from the 16^th century describe the aurochs as “much larger than cattle” (Schneeberger) or “huge” (Swiecicki) [3]. Van Vuure (2005) summed up all credible references for aurochs size and concluded that Holocene bulls were 160 to 180 cm tall at the withers, and cows 150 cm, and Pleistocene specimen were on average 10 cm taller [3]. 

Nevertheless, aurochs got smaller during the Holocene. Pleistocene remains suggest aurochs of a very large size, such as the oldest aurochs skull found or a huge skull with a length of 91,2 cm [4], which suggests a specimen that easily surpassed 200 cm withers height (sounds huge, but some wild yaks also reach 205 cm). The Prejlerup bull skeleton from Denmark from the early Holocene reaches 190 cm withers height, what means that in life the bull probably was between 195 to 200 cm tall. That means that early Holocene northern European aurochs at least occasionally reached heights this large. Later finds do not reach this size anymore. 

How large the last aurochs at Jaktorow were is unknown, since there is no height data for them. But Schneeberger mentioned that they were still much larger than domestic cattle. 

 

The decrease in horn size 

 

Pleistocene aurochs not rarely had huge horns. The earliest aurochs skull found has horn cores of a length of 112 cm (external length of the horn core) [5]. In the living animal, the horn sheath would add to the length, a few centimetres at least, a few decimetres maximum. A Pleistocene skull from Germany has a horn core length of 92 cm, another skull from Italy a horn core length of 120 [4]. Again, the sheath would have added to the horn length. Holocene bulls still had occasionally large horns, such as the Sassenberg specimen, but smaller-horned bulls began to appear, such as the Prejlerup, Himmelev or Önnarp specimen. 

The horn of the last reported aurochs bull which died in 1620, however, is rather meagre in comparison. It measures only 46 cm, is slim and not as curved as earlier horn sheaths. The age of the bull is not recorded, so that it could have been not fully grown at the time of its death, but to me it looks like a fully grown horn (horns that are not fully grown yet often look a bit compressed in length, while that horn is very slim and stretched). 

So the horns diminished from lengths of possibly 1,5 metres maximum to not even half a metre at the very end of its existence. 

 

So it seems that the very last aurochs from the 16^th and 17^th century were much less impressive than Pleistocene and early Holocene specimen. They were smaller, and their horns not even nearly as huge. It is not unlikely that the trend would have continued till today, so should “breeding-back” focus on the less impressive aurochs, since the aurochs of today would not be 2 metres tall with one meter long horns but much smaller and with comparably meagre horns? Well, let’s have a look at the reasons for why the aurochs got less impressive in historical times. 

 

The reasons for the decrease of body and horn size 

 

When animals change in body size, climatic changes are often the first explanation that comes to mind. The controversial Bergmann’s rule proposes that animals in colder regions are larger than those of warmer regions, because the surface to mass ratio allows larger animals to preserve energy easier than smaller animals. However, the Bergmann’s rule is not undisputed, there are as many examples against this “rule” as there are in favour of it [6]. Nevertheless, the Pleistocene was colder than the Holocene, so maybe this (assuming the Bergmann’s rule is correct) is the reason why Pleistocene aurochs were that large. However, this is not a valid argument, because the distribution of the aurochs changed with the climate. During the cold glacials, the aurochs retreated to the south and was mainly found in Southern Europe and North Africa. Large aurochs were found there, f.e. the large-horned large skull of the oldest aurochs found so far is from Tunisia. Pleistocene Tunisia probably was not colder than Holocene Denmark, for example. Also, climate cannot explain why the size of the aurochs’ horns decreased. 

EDIT: I did not address the role of predators enough. The aurochs evolved under the pressure of predators such as big cats and hyenas in the Pleistocene. These predators died out in Europe at the end of the Pleistocene. It is thus tempting to assume that the lack of large predators that could take down adult aurochs was a factor in the decrease of body and horn size. However, aurochs in North Africa and India were smaller than those of Northern Europe, despite being preyed on by big cats in these ecosystems. Thus it is not likely that the lack of big cats and hyenas was an important factor in the size decrease of the European aurochs. 

If climate did not cause the decrease of the aurochs’ body and horn size, it is important to look at other factors that might have influenced a large European herbivore in the last 10.000 years. These factors are caused by man: habitat limitation and hunting. 

 

It is likely that hunting might have negatively influenced the horn size of the aurochs. Julius Caesar mentions in De bello gallico that the Germanic people hunted aurochs for their horns. Probably trophy hunting was not restricted to ancient Germanic people. Aurochs horns were often used as ornament or drinking horns for the nobility. The larger the horns, the more impressive the trophy. Therefore, it is possible that large-horned aurochs were hunted more intensely than smaller-horned aurochs. It is also known that trophy hunting has lead to a considerable size decrease of the size of tusks of African elephants [7]. The so-called “great tuskers” have become rare, and the portion of tuskless African elephants has increased significantly. 

Habitat limitation also very likely influenced the body size and horn size of aurochs. The habitat of the aurochs was increasingly replaced by agricultural fields and pastures for domestic cattle. The aurochs had less space to live the more the human population grew. The habitat of the aurochs was lessened and fragmented. This leads to the island effect: large species shrink in size because less space and food is available, what increases the evolutionary fitness of smaller individuals. Go here for my post on the aurochs and insular dwarfism. Aurochs were pushed into hideaway regions which were not ideal for the species. Also, the lack of space for the aurochs to thrive might have further increased the reduction of horn size. Growing horns costs energy and minerals, and while horns certainly have a fitness advantage, on a confined space were food and minerals are scarce, smaller horns are more economic than large horns. 

Another factor that might have influenced the genetic structure of the aurochs that should not be forgotten is hybridization with domestic cattle. As the habitat for the aurochs became increasingly limited by pastures for cattle and horses, the wild bovine and its domesticated descendants lived side by side. Recently it has been found that the last aurochs bull had a domestic mitochondrial haplotype, what shows that there was maternal introgression from domestic cows into the last aurochs population [8]. Seemingly, domestic cows either escaped or were stolen from the pastures by wild aurochs bulls, and reproduced with aurochs in the wild. This might have contributed to a decrease of body and horn size, and could have also influenced the horn curvature (what might explain why the horn of the last bull is only weakly curved). 

 

To sum it up, trophy hunting as well as habitat limitation and hybridisation with domestic cattle likely are the cause for the aurochs becoming less impressive, i.e. smaller and with only comparably meagre horns. As to the question on which type of aurochs “breeding-back” should focus, the answer is clear to me: “breeding-back” wants to mimic the extinct ancestor of domestic cattle in its original form as it would exist today if it had not been for human influence. Hunting, habitat limitation and hybridisation with cattle are clearly anthropogenic factors. Without human influence, the aurochs probably would not have changed that much during the 9.000 years since the Prejlerup aurochs died, just as the difference between an aurochs from 100.000 years and one from 110.000 years ago would not have been dramatic if even noticeable in the morphology that is accessible to us. Therefore, I think it is definitely legitimate if “breeding-back” aims for 1,9 or even 2 metre tall cattle with 1,2 meter long or larger horns (if that goal is achievable with domestic cattle only is another story). The size goal for the bulls in the Auerrind project, for example, is 170 to 180 cm as Claus Kropp stated on Facebook, and that is perfectly in line with the evidence. 

 

Literature 

 

[1] Poettinger, J.: Vergleichende Studie zur Haltung und zum Verhalten des Wisents und des Heckrinds. 2011.

[2] Rene Kysely: Aurochs and potential crossbreeding with domestic cattle in Central Europe in the Eneolithic period: A metric analysis of bones from the archaeological site of Kutna Hora-Denemark (Czech Republic). 2008.

[3] van Vuure: Retracing the aurochs – history, morphology and ecology of an extinct wild ox. 2005. 

[4] Frisch: Der Auerochs – Das Europäische Rind. 2010. 

[5] Martinez-Navarro et al.: The early middle Pleistocene archaeopaleontological site of Wadi Sarrat (Tunisia) and the earliest record of Bos primigenius. 2014. 

[6] Wright: The history of the European aurochs (Bos primigenius) from the Middle Pleisotcene to its extinction: an archaeological investigation of ist evolution, morphological variability and response to human exploitation. 2013. 

[7] Nowak et al.: Trophy hunting: bans create opening for change. 2019. 

[8] Bro-Jorgensen et al.: Ancient DNA analysis of Scandinavian medieval drinking horns and the horn of the last aurochs bull. 2018.

The problem with fixing traits through conventional breeding

Today comes a rather theoretic post on the obstacles of breeding, which is relevant for “breeding-back”. One of the biggest challenges for “breeding-back” is to genetically fix the desired traits. By fixing traits I mean achieving that all the individuals of the population have the desired trait. For example, the E+ allele is fixed in Taurus cattle because all individuals are homozygous for this allele. Fixing a trait requires consequent selection and to consider the difference between genotype and phenotype. 

 

As an example: Heck cattle of the Wörth/Steinberg lineage have very large thick horns that match those of the aurochs in absolute and relative dimensions. However, their curvature does not curl inwards enough in most individuals (see this individual). Maronesa sometimes have a very narrow, aurochs-like horn curvature, but lack the desired volume (see this individual). Something intermediate would be ideal. And considering that those traits are very likely regulated by more than one gene, the results of crossing Wörth/Steinberg Heck cattle with Maronesa would likely be intermediate, and hence show the desired phenotype: horns with the right volume and right curvature. Is the work done with that? Not even nearly – the desired phenotype would have to be genetically stabilized in the individual and to be fixed in the population. Simply backcrossing the offspring with the individual with the desired phenotype again and again will not be able to do that, and here is why: 

The cross individual might have the desired phenotype, but that phenotype is the result of maximum heterozygosity between the parental breeds. It has the alleles for the horns that are not curled enough and the alleles for the narrowly curled horns on the same loci, and it has the alleles for the very large horns and the not so large horns on the same loci, resulting in a phenotype that is intermediate and hence “perfect”. When the animal produces offspring it either passes on the alleles for the very large horns, the not so large horns, the not very curved horns or the narrowly curled horns, but it will never pass on the desired phenotype because it is the result of a heterozygous state. Thus backcrossing with the F1 individual with the desired phenotype will be pointless because it is genetically unable to stabilize the phenotype. By stabilizing in this case I mean that the individual always passes on the desired phenotype to its offspring, which is the case when the alleles producing the desired phenotype are present homozygous. When the phenotype is the result of heterozygosity, stabilizing it is impossible. However, since both horn volume and perhaps (or: hopefully, for this example) horn curvature are quantitative traits that are regulated by more than one locus, there is the chance to genetically stabilize the desired phenotype. As a simplified example, let us assume that horn size is controlled by only two loci, A and B, (unlikely, but only an example) and that Wörth/Steinberg Hecks are homozygous for alleles producing very large horns on both locus A and B, and that Maronesa are homozygous for alleles producing not so large horns on A and B. Thus, they only pass on very large horns or not so large horns, it is stabilized in their genome. What we want is a stabilized intermediate phenotype by crossing those breeds. The F1 individual will have the right phenotype because it is heterozygous for both very large horn alleles and not so large horn alleles, producing the intermediary phenotype desired. But, as mentioned above, it is impossible to stabilize this phenotype with this genotype, the genotype is not right yet. The right phenotype in this individual is actually only an “illusion”. The only way to stabilize the intermediary phenotype is to produce offspring that is homozygous for alleles producing very large horns on either locus A or B, and that is homozygous for not so large horns on the other locus. This way, the intermediate (= desired) phenotype can be passed on in a stable fashion. If horn curvature is a polygenic trait too, it works the same with horn curvature. It is impossible to have that in a first-generation hybrid. Breeding this F1 individual to another breed or one of the parental breeds will not stabilize the desired phenotype, even if you backcross it with the F1 again and again and again. This is why “breeding-back” herds are still heterogeneous and not genetically stable even if the same breeding bull has been used for multiple generations. The most efficient way to stabilize the desired phenotype is to breed the F1 individual to another F1 individual of the same combination (if you have only breeds A and B, in this example Wörth/Steinberg Heck and Maronesa). This way it is possible that an individual is born that has only alleles from Heck on one locus and only alleles from Maronesa on the other locus, if the goal is to stabilize the intermediary phenotype of a quantitative trait (f.e. body size or horn size). If you have such a true F2 individual with the right genotype (the more individual of this combinations you produce the less luck you need, the less individuals the more lucky you have to get for that), it is possible to fixate the trait in the population by backcrossing its offspring with it. 

Summa summarum: If you cross two breeds because a phenotype intermediary between both breeds is the phenotype you desire, the F1 individual will not have the right genotype for stabilizing the trait in the population, no matter how long you use it as a sire. If you produce a true F2 of this combination, the offspring has at least the chance to have the right genotype. 

If you are looking at a monogenetic trait, and you want to stabilize the intermediary phenotype that is the result of a heterozygous state, you will never ever be able to stabilize the intermediary phenotype in the population. To use Wörth/Steinberg Heck cattle and Maronesa as an example again: the former have horns that often are too upright for what is average in the European aurochs, while the angle of the horns is too narrow in most Maronesa. Let’s say the parental individuals have horns of an angle of 90° (Heck, too upright) and 35° (Maronesa, too narrow angle) and you want something intermediary to produce phenotype like in the European aurochs. If horn orientation relative to the snout is a monogenetic (Mendelian) trait, and the heterozygous state produces something intermediary like 60° as in the aurochs, it is impossible to stabilize this in the population, because the F2 will either have the 90° phenotype, the 35° phenotype or the desired 60° phenotype. You may be happy about the individuals having the right phenotype, but will never be able to fixate this trait in the population using these two breeds if horn orientation was regulated only by one locus. You would have to find a breed that has the right allele, as long as the right allele was not lost during domestication. I do not think that horn orientation is a Mendelian trait, but just to illustrate what I am saying, it would be impossible to fix a desired phenotype using two parental breeds that are homozygous for a phenotype that is not the desired phenotype. 

It gets more complicated if there are more than two alleles, f.e. three: let us say we have only one locus with three alleles, allele A producing the right phenotype when homozygous (60°), allele B producing very upright horns (120°) when homozygous, and allele C producing a very narrow angle when present homozygous (20°). Now let us assume that we have two parental individuals, one with horns having a 90° orientation and a genotype A//B (intermediary between the phenotypes A//A, the desired one, and B//B, the very upright horns), and one with a horn orientation of 35° with a phenotype A//C. By crossing these two animals, which both do not have the right phenotype, you would produce the following genotypes and phenotypes: 50% would be A//A, the right phenotype of 60° and right genotype, B//C would have a phenotype intermediary between 120° and 20° so perhaps the desired 60° but the wrong genotype, A//B with 90° as in one of the parents and A//C with 35° as in the other parent. If you produce only one offspring individual, the genotype will come about by chance. Either you have an individual that has the wrong phenotype and will be discarded, or you have the right phenotype but do not know if the genotype is right (A//A) or wrong producing the same or a similar phenotype (B//C). You can only know by producing further cross generations and analysing the offspring, when it is already too late if you picked the wrong individual. Thus, either the genetic background of traits is resolved (the individual alleles and the phenotypes produced are known, which is currently only the case in colour traits), or you have to accept that you also need a lot of luck or in some cases, stabilizing the trait is impossible with the breeds chosen because it is the result of a heterozygous state in a monogenetic trait.

Summa summarum #2: In a monogenetic trait, you need to have the one right allele in order to stabilize the fix phenotype. If the allele has been lost during domestication, it is not possible to stabilize the desired phenotype. 

 

Another problem for fixing desired phenotypes is genetic linkage. It is very likely that some domestic (= undesired) alleles are genetically linked with wildtype alleles (= desired) on the same chromosome. This can be a problem for “breeding-back” in two ways. For once, it might be the case that some desired phenotypes are genetically linked with domestic phenotypes in some breeds, f.e. the right colour might be linked to a wrong horn shape or other examples. In this case, a breed would have to be found in which this is not the case or you must hope to get very lucky with recombination. Another problem could be if a number of wildtype alleles for wildtype traits that are not morphologically visible (f.e. physiological traits) are genetically linked with visible mutations such as “wrong” colour variants or deviant horn shapes, the selection for aurochs-like morphology or looks might eradicate other wildtype traits for physiology, genetic fitness or immunology. This would be a case of bad luck, but cannot be ruled out completely. 

 

This is why it is a huge pity that there is currently no project that is trying to execute “genetic breeding-back” (go here for a post on that issue). For “genetic breeding-back”, the resolved full genome of that one British aurochs bull could be used as a template in order to accumulate wildtype alleles responsible for all aspects of the organism (physiology, morphology and life appearance, immunology, development, genetic fitness etc.), and produce something that is as aurochs-like as possible with living animals (not only in morphology, but also all other organismic traits). This would require a lot of extra research that has not been done yet, and it is problematic that we only have the genome of only one aurochs, which bears the danger of selecting against other wildtype alleles not found in that one particular genome.