these are the export settings I used for the lowpoly obj, the model had only 2 smoothing groups, 1 for the body and 2 for the bottom of the hooves
On another forum it was suggested to use a cage in xnormal, which fixed the artifacts.
There is a 2 pixel padding, I 'll increase that for the next bake
I am gonna do some more experimentation with using a seperate smoothing group for each uv island.
@ jimonions: I made it in max 2014, using box modelling, the entire mesh should be one (no seperate element) and only have 2 different smoothing groups in the version I uploaded.
@ surfa: baking in max isn't really an option, since it performs very sluggish with a highpoly mesh of 5 million polygons :/
edit 10000: when I apply the normal map as a diffuse it also shows the seam in the viewport