Too Many Cattle Breeds and Not Enough Horse Breeds in the Back-breeding Effort

            Back-breeding, wherein domestic breeds are crossed and selected in order to more closely resemble their wild ancestors, is a major component of the Rewilding effort in Europe. Back-breeding is of particular importance for cattle and horses, the European ancestors of which are now extinct. In general, the morphological and behavioural changes that have occurred in the process of domestication are much more substantial for cattle than for horses, thus necessitating a more intensive selection process. As a consequence, there are multiple back-breeding projects for cattle, and essentially none for horses, the idea being that certain breeds of domestic horses (caballus)  are close enough to the original European wild horses (ferus) to sufficiently emulate their ecological function. This is essentially true, but there are drawbacks to favouring certain breeds and allowing them to become overrepresented. Conversely, there is an issue in the back-breeding of cattle, where perhaps too many breeds are incorporated, making a uniform appearance less attainable.

            Beginning with horses, one thing which needs to be addressed is the tendency for people to exaggerate the relatedness or similarity between certain breeds and the original ferus-type horse. Examples include Sorraias, Exmoors, Koniks, and Yakuts, all of which have been touted as the result of recent hybridization events with true wild horses. There is, however, no reason to believe this is true in any of these cases. Sorraias and Koniks are the results of very recent breeding efforts using local farm horses. Exmoors do have a long history as a feral animal, but their current phenotype is also the result of a recent selection process, and their origin likely postdates the extinction of ferus in Britain. Yakuts have been shown genetically to be the very recent and intensively selected descendants of horses from Mongolia. None of this is to say that these breeds have no value for rewilding projects, as they all most certainly do, However, none of them are intrinsically more valuable than the others, and indeed there are numerous primitive horse breeds with rewilding potential. What is more than that, we should be abandoning the idea of using a single breed in any given area, as no one breed presents the entirety of the known ferus phenotype nor the genetic diversity typical of a wild population.

            It would be a mistake, for example, to use exclusively Konik ponies in Central/Western European Rewilding areas. However, the availability and general suitability of this breed have led to it being massively overrepresented in these areas. There is nothing wrong with Koniks, but they could use some improvement. For example, Koniks are near-universally Black-Dun, which is one of the colours displayed by ferus, but only one of at least four. Bay, Black, and especially Bay-Dun would also have been prevalent, in addition to the occasional Leopard-Spotted variant of these colours. Consequently, in order to make Konik populations, which necessarily possess the Black and Dun alleles, more closely resemble their ancestors, it would be beneficial to cross in breeds that possess the Bay and Non-Dun alleles. The Exmoor displays these alleles exclusively, so if you were to form herds made up primarily of Exmoor-Konik crosses, then it would contain the necessary alleles for all of the ferus base-coats right from the start. If you added in a couple of individuals from a suitably primitive breed containing the Leopard-Spotting allele, then the full range would be present for nature to select upon. It is likely that, due to Bay and Dun being dominant over Black and Non-Dun respectively, Bay-Dun would emerge as the most prominent colour in the population, which is likely as it was in the past.  A more heterogeneous wild horse population is desirable, both in appearance and in genetics. So long as certain genetic diseases and domestic colours are avoided (Chestnut being the only undesirable recessive), almost any primitive European breed could be used. Emphasis on local adaptations and primitive appearance is important, but beyond that, we should be forming as broad a genetic base as possible. Taking Central/Western Europe as an example, while Koniks and Exmoors are an excellent start and may form the bulk of the eventual ancestry, there are numerous other breeds from temperate/continental Europe that would be appropriate contributors to the gene pool. Some passive artificial selection might occur after these populations are formed, but little would be necessary.

            Just as homogeneity is currently an issue with rewilded horses, heterogeneity is a problem for rewilded cattle. The traits that defined the aurochs are so much more spread out in modern cattle, that to get them all in one population is difficult. To get them all in one animal is even harder. I think the issue we run into is that the impulse is to try and breed for multiple traits at once. Larger, more curved horns, more athletic bodies, more shoulder height, correct colour and sexual dimorphism, longer skulls, and the list goes on. Though some might find it counterintuitive, I think the best results could be achieved by using fewer breeds, and selecting for these traits one at a time, in order of most to least difficulty. If we started with a herd of a single breed, incorporating as much of the desired traits as possible, then we could begin to make gradual changes. What seems to be the hardest thing to get right is the horns, so start with that. Select for larger, properly oriented horns until you have a small population that reliably displays that trait. If you hit a wall where the horns cannot be improved past a certain, insufficient point, then you consider adding new blood, but in a minimal, controlled way which will bring in the necessary variation without introducing too many undesirable traits. When and only when this process is complete do you move on the next step, which would probably be body size and conformation. Variation in size and proportions are often highly variable within a population, and offspring often have the potential to be larger than their parents. Consequently, given time, it would be possible to gradually increase shoulder height and improve upon skull length, leg length, and spinal curvature. Again, if new blood is needed, incorporate it in a very purposeful and careful way. All of this could be done while essentially ignoring other, less difficult to breed for traits, such as behaviour and colouration. If your end-result was a population of cattle that look like aurochs in every possible way except that they were all snow-white, you would be closer than anyone has gotten yet. Colour is determined by a very finite number of loci and the wildtype could be integrated and bred for much more easily than the other traits.  Once you have a successful back-breeding attempt that displays a satisfactory aurochs phenotype, it is a simple matter to create more genetic diversity. This is where expulsion breeding comes in, wherein other breeds are crossed into the gene pool, and the resulting offspring are repeatedly crossed back to the gene pool, such that the desired phenotype is preserved while at the same time avoiding inbreeding depression. It would also be important to keep the animals in a semi-wild setting throughout the process, allowing a degree of behavioural and natural selection.

            I think that while the back-breeding of horses will overall be a rather simple process, the procedure for cattle will take a very long time. Certain genetic technologies may expedite the process in the future, but for now, we can only work with what we have. What we have is a lot of different projects with a different idea of the best way to do this and the best breeds to use. I am glad to see that some of these projects are now collaborating, but there is a risk that this may only contribute to the heterogeneity problem. While using multiple breeds has the advantage of putting all the desirable traits in one population, it can do the same for undesirable traits, making their removal that much harder. Time will tell what the best method is, but for now, the long generational turnover of cattle and the expense of keeping them limits our ability to experiment. If it were just about ecological function, then any sufficiently hardy breed would do, but I think it is more than that. We are trying to restore the aurochs niche as a management tool yes, but it is also of cultural and economic importance for these cattle to look, act, and be treated like wild animals. This is equally true for domestic horses and water buffalo, though people tend to accept them as wild animals much more readily. Clear separation in the appearance of back-bred and regular cattle would perhaps make it easier to see the rewilded animals as something separate. The more imposing nature of such an animal, and the novelty of its creation, would hopefully also make it a bigger draw for tourism, an important stream of revenue in the rewilding sector. As I have said before, to do this right we need to abandon or alter some of our ideas on what exactly we are trying to protect. Our concepts of “what is native?” and “what is a species?” may eventually need to take a backseat in order to promote the more immediately important ideas of ecological function, evolutionary potential, and socio-economics.