What a "breeding-back" zebu could look like

All current “breeding-back” projects focus on the European subspecies, but that one is not the only that left living, domesticated descendants. There probably was introgression into African taurine cattle from B. primigenius mauretanicus, and the Indian aurochs was domesticated as well, the results being called zebus. A “breeding-back” initiative for zebus would be very interesting, as they still exhibit some of the autapomorphies of the Indian aurochs. 

However, since the Indian aurochs, also called Narbada ox or as I also like to call it, wild zebu, is less well-documented than the European form, the breeding objectives for such a zebu “breeding-back” project would be less clear. I did a number of posts on the Indian aurochs, the most recent being this one. 

To sum up what the Indian aurochs most likely roughly looked like: 

- smaller than the European form, possibly between 150 and 160 cm withers height in bulls

- proportionally larger, slightly more upright and more wide-ranging horns 

- narrower skull with less prominent eye sockets 

- probably very similar postcranial anatomy, with long legs, short trunk and a shoulder hump (not to be confused with the fleshy indicine hump) 

- perhaps a slightly larger dewlap than the European aurochs 

- a colour possibly similar to that of the European aurochs, perhaps with some minor differences as zebu colours suggest

- very likely sexual dichromatism comparable to the European aurochs and Java banteng 

All of these traits can be achieved or approximated by breeding with less-derived zebu landraces. I would include: 

- some Deshi variants (wildtype colour, useful anatomy) 

- Kankrej (sometimes horns of a useful curvature and size, large-bodied) 

- Deoni (very short trunk and long legs, small udder and slender body) 

- Watussi (horn size and partly curvature)

This set of breeds can result in a zebu that looks more like what their wild ancestor looked like than many or all other zebus breeds. However, it would not yet seize the complete potential to mimic Bos primigenius namadicus as the horns would probably be more or less too upright, the zebus would still have an indicine hump which is unlikely to have been present in the Indian aurochs, they would have little to no sexual dichromatism as this trait is barely present in zebus. The solution to that is, in my opinion, to include: 

- Sayaguesa: for the overall aurochs-like morphology, for the lack of an indicine hump and the presence of a well-developed shoulder hump as in the aurochs 

- Java banteng: for the sexual dichromatism. Many cow-coloured zebus have a colour that is virtually identical to that of the Java banteng minus the white socks and buttocks (reddish-brown colour, dark brown dorsal stripe etc.), suggesting that female Indian aurochs had this colour. Of course it would be possible to include a taurine breed that reliably has sexual dichromatism such as Maronesa, but in these the cows are not nearly as lightly-coloured as in zebus and Java banteng. 

Some might think now that I am crazy suggesting a taurine breed and another species for “breeding-back” focusing on the Indian aurochs. But for once, I am not afraid of using less-derived zebu landraces for “breeding-back” focusing on the European aurochs, since they share some alleles with the European aurochs that taurine cattle have lost and contribute some phenotypically desired traits that taurine cattle do not have. So the reverse is legitimate to me as well, using a taurine landrace to acquire a trait that cannot be achieved with zebus alone, in this case, the lack of an indicine hump and the overall aurochs-like morphology. As for the banteng, I suggest using wild yaks and Java banteng for “breeding-back” focusing on the European subspecies, but only in very small doses and only in experimental herds, used very wisely with efficient selection (and not rampant hybridization in order to see what happens). The wild yak is unnecessary for a zebu project and possibly even counterproductive considering its climatic adaptions, so I’d only go with small doses of Java banteng to breed for the right colour dimorphism. I would backcross the hybrids as often as possible with “pure” zebus until the taurine and banteng influence is reduced to virtually nil genealogically, but always keeping those individuals that display the desired traits. 

I did a painting with GIMP what such a “breeding-back” zebu bull could look like, and this is the result: 

Overall, while the result would still be a domestic animal, it possibly resembles what we know of the Indian aurochs quite well on certain traits, and would be suitable to fill its ecologic niche in Southern Asia.