Crossbreeding proposal: Chianina-Watussi

Chianina are famous for their large body size with sometimes long legs, Watussi are for their very large and thick horns. Now we know that the original aurochs phenotype was very large with mostly large to very large horns (go here for a post on particularly large-horned aurochs). I think the combination Chinaina-Watussi bears potential for achieving cattle that are both large and large-horned and even more than that. 

The problem is that Chianina is large but very small-horned, and Watussi is large-horned but small. Both horn size and body size are quantitative traits which are controlled by many different genes that all have a more or less large or small impact on the final phenotype. That means that if one wants the result of cattle that have the Chianina body size but not horn size, and the Watussi horn size (or slightly smaller) but not body size, the breeding must use the second Mendelian law, otherwise the breeding takes forever. And most likely a larger number of individuals is required, not only a couple of individuals but rather herds of 20-30 (which happens to be the natural Bos primigenius herd size). So at first, a herd of Watussi x Chianina should be produced, as many individuals as possible. The phenotype of the F1 individuals is completely irrelevant as it is the result of maximum heterozygosity, thus combinations of alleles that will not be present anymore as the population becomes genetically stabilized. Both horn size and body size will be somewhat intermediary between the parental breeds, but that is not really relevant yet. It’s the second generation, the F2, where the phenotype of the animals becomes relevant. So a herd of F2 Watussi x Chianina should be produced. Some will have an indicine hump (probably), some will not. Some will have smaller horns and smaller body size, some will have large horns but small body size et cetera. As the focus is on creating a population of large cattle with large horns, only those F2 that have large horns and body size should be chosen for further breeding. 

It is even possible that the combination Watussi-Chianina has potential for a correct wildtype colour with at least some degree of sexual dichromatism. This may sound counterintuitive when two breeds are crossed that both have no visible sexual dichromatism and one is completely white and one is homogeneously reddish-brown. But one should consider the genetics of the two breeds. Chianina has the wildtype allele on the Extension locus, but the colour is diluted by at least two dilution alleles. Watussi does not have these dilution genes, otherwise it would not have that strong expression of red pigment – it has a mutation on the Extension locus that disables the production of black pigment. So a F2 combination of both has the potential for individuals that have the Extension wildtype allele and the production of both black and red pigment enabled. A hint for that is the colour phenotype of the Watussi x Chianina cow of the Auerrind project: 

 

© Claus Kropp 

It clearly has the wildtype Extension allele expressed (it is dominant over the recessive mutation disabling black pigment) and the colour is barely diluted if at all (possibly because some of the dilution alleles of Chianina are recessive). So a F2 of this combination could potentially result in, among other colours, wildtype colour that is not diluted. Sexual dichromatism is possible as well because Chianina might have some degree of sexual dichromatism or even a very strongly expressed one, masked beneath the dilution factors resulting in a white colour in both sexes. That possibility is there since some Sayaguesa x Chianina bulls produced in the Lippeaue had a perfectly black wildtype colour while the cows are always lighter in colour. Therefore, there is at least the chance to achieve aurochs colour from two breeds which do not have aurochs colour at all, because of the genetic background of the colours of the parental breeds. 

In the F2 Chianina x Watussi generation, I would pick those that are large with large horns for further breeding. Some of them might have indicine traits such as the fleshy indicine hump or hanging ears, and the body morphology might not be completely taurine because of the more or less high portion from Watussi. That is why I would backcross the F2 with good Chianina again. And, as you can surely guess by now, create an F2 of this backcross generation. Creating true F2s is the most important step for genetic reasons. The backcross generation might look quite good already, but it will have a full set of Chianina chromosomes. That means they are heterozygous for all the optically good traits and will pass on the alleles for small horns and various colour dilutions. By using the second Mendelian law that applies to a true F2 generation, these alleles can be selected out much more easily than by conventional breeding. So, in the F2 of the Chianina x F2 (Chianina x Watussi), I would only continue to breed with those individuals that are large, have a taurine morphology and large horns, and – as far as possible – also a correct colour. From this selection event on, I would continue to breed with the suitable individuals from that combination in a conventional fashion otherwise the gene pool might become too narrow. It is even possible that not only body size, horn size, colour and morphology of this population is good but also the horn shape, as Chianina often have forwards-facing horns with sometimes a useful curvature. 

 

This scenario takes four generations (8-10 years) and might result in very satisfying individuals that will pass on the desired traits more or less reliably. 

 

 

Would it be crazy to use hybridization in "breeding-back"?

As my readers will know, I suggested cautious hybridization with extant wild bovines that would add traits hardly achievable using domestic cattle only in “breeding-back” in a couple of my posts, after I initially opposed that idea. In this one for example, I suggest using wild yaks in “breeding-back”. But the Java banteng would add value as well, and using both in cautious doses would be add all of the traits that are difficult to achieve with domestic cattle only. The kouprey, which would add all the desired traits both the wild yak and banteng would add and has a slightly more aurochs-like morphology, unfortunately is not available for hybridizing as it is most likely extinct. To give a quick summary of the benefits the wild yak and the Java banteng would add to “breeding-back”:

Wild yak: 

- Very large, up to 205 cm withers height in bulls what equals the large size of European aurochs; difficult to achieve with domestic cattle only, where the upper height limit might be roughly 180 cm; well-marked size dimorphism between the sexes 

- Perfectly aurochs-like horns in both sexes. The horns of the wild yak are really identical to those of the European aurochs in terms of size, curvature, orientation to the skull and even colour. They have a very pronounced inwards-curve which is lacking in most aurochs-like cattle 

- They have a large shoulder hump and a long snout, two traits which are rarely as expressed as in the aurochs in domestic cattle 

- The physiological fitness is higher than in domestic yak and most likely domestic cattle 

- The food choice overlaps with that of cattle/aurochs, they are predominantly grazers 

Java banteng:

- A very well-marked colour difference between the sexes that is always present. This is extremely rare in domestic cattle as domestication reduces sexual dimorphism

- Aurochs-like body size (up to 190 cm which is not quite as large as wild yaks but still significantly larger than most domestic cattle) 

- Roughly aurochs-like morphology (hump, short trunk) 

- It ecologically overlaps with cattle/aurochs, although they browse more, including fruits 

 

Cautious hybridization and wise selection might thus speed up the process of achieving an aurochs-like animal significantly and might have a better end result. But there are, as one can imagine, objections against hybridizing with other species, which I shared until recently. Those objections are two main ones: 

 

Argument #1. A different species would add many undesired, non-aurochs traits, some of which are practically invisible and thus hard to select against, which might distort the authenticity and ecologic suitability of the results. 

There is valid truth to that argument. For example, wild yaks are adapted to higher altitudes than the aurochs, which was a lowland animal, and have larger lungs. They are also adapted to more severe cold, having fewer sweat glands and a different pelage. Also, there are skeletal differences, such as a different vertebrae count. Wild yaks also browse less than cattle/aurochs as they are more strict grazers. Banteng are adapted to a much hotter climate and browse more than cattle. There are also behavioural differences in both species. Yaks, for instance, have a different aggression display behaviour by presenting their large tail tuft, while banteng rely more on display in intraspecific competition than fighting head to head like cattle/aurochs and wild yaks. 

However, it is not impossible to get rid of these undesired behavioural, ecological and morphological traits. The solution might be absorptive breeding while running a strict selection regime. That means that each hybrid generation would be backcrossed with taurine cattle, but only those hybrids that still have retained the desired traits added by the species would be kept for further breeding. After eight generations, for example, the genealogical portion from the other species would be as low as 0,3%, therefore there would be a high chance that the undesired traits are washed out while the desired ones remain in the population when selected appropriately. 

 

Argument #2. “Breeding-back” cattle with a tiny but important bit of introgression from wild yak and Java banteng would not be pure domesticated aurochs anymore. Thus, the argument that “breeding-back” cattle are a native species in European nature would be gone, as they would more or less be hybrids. 

There are two problems with this objection. On a more general note, introgression between closely related species at some point of time has been found everywhere it was looked for in mammals, including our own species Homo sapiens, so it seems that hybridization (or more precisely, introgression) is a very widespread phenomenon in the process of speciation and evolution in general. In the case of wild bovines, Cambodian banteng have introgression from the kouprey, wisent have homeopathic introgression from aurochs and there may be more cases which we are currently not aware of. So introgression per se is not “unnatural”, quite the contrary. Furthermore, it is not technically true that domestic cattle are “pure” albeit domesticated aurochs. Domestication itself is an anthropogenic process, resulting in organisms that differ from the wildtypes that were shaped by nonhuman evolution. A wild aurochs’ genome is 100% wild aurochs. A domestic cattle genome is 100 - x % wild aurochs, x being the portion of the genome that is made up by alleles that mutated after domestication. I do not even dare to speculate how large or small that portion is, and it is certainly different from breed to breed to a certain degree. Thus, domestic cattle are not “pure” aurochs, but rather partly wild aurochs and partly a domestic mutant. So, the originality of the aurochs is gone as a result of domestication anyway. If another species is bred in, the non-aurochs portion would increase dramatically in the first couple of generations, but decrease in the advanced generations as a result of absorptive breeding. It is even possible that, when selected wisely, the aurochs portion could actually increase by introgression from wild yak and banteng. I say that because I consider it likely that, as long as the aurochs-like traits in wild yak and banteng are not the result of convergent evolution (which I do not consider particularly likely), these traits are caused by the same wildtype alleles as in the aurochs. For example, the identical horn curvature between aurochs and wild yak might be caused by alleles shared from a common ancestor. Introgression might reintroduce these alleles into the domestic cattle population. The same could be the case for the sexual dichromatism in the Java banteng. In this case, introgression would reintroduce wildtype alleles found in the aurochs which are absent or at least very rare in domestic cattle. So the “genetic purity” argument is not convincing to me. Apart from that, the introgression might also introduce physiological fitness-related alleles from banteng and wild yak which are superior to those of domestic cattle in terms of physiological fitness, thus providing an advantage for “breeding-back” cattle compared to the domestication-induced disadvantage that domestic cattle usually might have. 

 

Therefore, I think small doses of controlled hybridization/introgression from the two wild bovines most suitable, and subsequent wise selection, is not a crazy idea at all and could be very beneficial for the ecologic and phenotypic goal of “breeding-back”. What would be crazy, on the other hand, would be hybridization without a plan and without strict selection.