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.