Horn shape evolution in Oostvaardersplassen

I already covered my suspicion that Heck cattle are morphologically changing in the Oostvaardersplassen reserve due to natural selection in a number of posts, see here, here or here. Each of these posts provide photos of individuals endorsing my suspicion. 

And so does this post. A number of individuals in the Oostvaardersplassen reserve show horns that are definitely curving inwards and facing more or less forwards in an aurochs-like manner. Here are photos that I recently discovered via google search: 

- Photo 1 
- Photo 2
- Photo 3 (cow in the front, left)

I am convinced that these three photos all show the same individual and I think it is quite likely that it is the same as on older photos like this one, just fully mature. On photo 2 linked above you also see a cow in the background that also has remotely aurochs-like horns. On photos available in the web, there is also another individual on older photos that shows the same colour morph and horn shape as the cow in the background on photo 2 but more mature, so there are at least 3 individuals born in Oostvaardersplassen that show an aurochs-like horn shape. 

What is striking is that I haven't ever seen any Heck cattle in real or on photos (contemporary or historic) outside of Oostvaardersplassen that show this horn shape, indicating that this phenotype might be unique to the population within the Heck cattle gene pool. While body shape and to a certain degree maybe also proportions can be influenced by phenotypic plasticity, I see now plausible way how phenotypic plasticity may influence horn shape that visibly. Therefore, I think that we see a true shift of allele frequency due to selective pressure, and thus evolution, in the Oostvaardersplassen that is at the same time also a regression towards the wildtype. This is an assumption that endorses a concept of dedomestication as outlined in the dedomestication series. 

A puzzling question is why we see this tendency only in cows, and not in bulls so far.