Breeding-back: How I would do it

In this article, I want to outline how I would execute “breeding-back” myself if I had the chance to breed a herd. There are multiple ways to Rome of course, and I am not saying that I would do it better than anyone else, it is just how I would do it. 

1. The goal

My goal would not be to breed yet another “breeding-back” herd, but to produce a high-quality line that is as genetically stable as possible even if genetic diversity has to be sacrificed. Of course genetic diversity is important, but the purpose would not be to fill the entire European continent with this herd exclusively, but to produce high-quality individuals that can improve the quality of other herds and therefore the gene pool of “breeding-back” cattle as a whole. This is similar to the line bred by Walter Frisch (the Wörth line), who produced a herd of Heck cattle with the best horns found in this breed, which are also comparably stable in inheritance, what contributed a lot to the improvement of horns in other Heck cattle herds. This was also achieved by the use of inbreeding in order to stabilize traits. 

2. The starting herd 

Of all the primitive breeds and “breeding-back” herds on this world, what would I compose my starting herd of? I would take a number of good Taurus cattle from the Lippeaue because I think they represent the top quality of contemporary “breeding-back”. I would select individuals that have the right colour, are large, have a good body shape and proportions and take care that the choice of individuals also includes genes for large and correctly curved horns. Maybe one or two Auerrind crossings with Watussi genes would be included as soon as they are available. This starting herd would include all genes for the desired traits that domestic cattle have: large size, aurochs-like proportions, aurochs-like horn curvature and dimensions, wildtype colour and sexual dimorphism. 

3. The breeding 

I would use a large chef bull that would cover all the cows. In order to speed up the process, I would not use the same individuals/generations for too long but instead replace them quickly with the subsequent generation. If the first filial generation has produced a good bull and good cows that are at least as good or better than their parents, I would sell the parental generation (or at least the chef bull), the offspring taking their place. In the subsequent generation, I would do the same and so on and so on. When selecting I would try to continuously increase the level of quality. Due to the inevitable (and in this case, wanted) use of siblings mating as well as selection, the gene pool would continuously narrow. The result would be a quality line that is comparably stable for the desired traits. It has worked with the Wörth line, it should also work with Taurus cattle. 

4. The selection 

Every breeder has his own priorities concerning selection criteria. I would pay a lot of attention to body shape, proportions and size because these traits are controlled by a large quantity of genes, surely dozens and possibly hundreds, while colour is regulated only by about a dozen of genes. I would also prioritize inwards-curving horns because they are comparably difficult to breed as this trait is rare in primitive cattle. Due to the use of Chianina, alleles for colour dilution might be present quite frequently in the population. I would try to eradicate those two or maybe three alleles, even if it might take a while as they are recessive. It has worked in the Neandertal and Wörth line, it should also work here. I would select against bulls with a colour saddle, as the European aurochs probably did not have this trait and it might be a sign of reduced colour dimorphism. However, I would not always select out black cows, as historic evidence reports the existence of black aurochs cows in Europe. For the horn size, we have quite a large spectrum indicated by fossil and subfossil bones. However, I would not permit horns that are only the size of Sayaguesa horns or smaller. Horn size is most likely regulated by a large number of genes, and it might be that genes for small and thin horns are sometimes recessive. In the Wörth lineage, small-horned individuals still might appear occasionally. Recessive alleles are very difficult to breed out and also requires luck. 

Breeding works with luck and by coincidence. One would need patience, especially when using the method as described in section 3. In the Lippeaue, many individuals are half-Sayaguesa. Half-Sayaguesa will always look good in some way because Sayaguesa is a very good breed. But it becomes more difficult when you mate crossbred individuals among each other, because inheritance works by chance. The result might have the large horns of Heck cattle, or the small body size. It might have the large size of Chianina and long legs, or the diluted colour. Londo, the Taurus bull, was the result of two siblings mating. He looked a lot like his father Lamarck, but was smaller and short-legged. However, due to its genotype there was the chance that he was more stable than its father (which is not stable at all as it is a cross), and indeed he seemingly passed on the short legs with stability. This shows that using siblings mating for stabilization can work quite fast. In the case of Londo it was simply bad luck that he was stable for short legs and not for his good traits.