I don't know very much about this subject at all, but in 1984 I took a photo of this graphic in Tierpark Hellabrun (Munich Zoo) which illustrates Heinz Heck's backbreeding to the Aurochs.
http://www.zoochat.com/136/backbreeding-graphic-1984-a-52597/
They had some aurochs on display http://www.zoochat.com/136/aurochs-1984-a-52596/ and - although a bad photo - you can clearly see these are of the form with wide-spreading upward-pointed horns.
A couple of weeks before I was in Antwerp, and their Aurochs had the forward-pointing horns. http://www.zoochat.com/35/aurochs-1984-a-51660/

Hix
http://www.zoochat.com/136/backbreeding-graphic-1984-a-52597/
They had some aurochs on display http://www.zoochat.com/136/aurochs-1984-a-52596/ and - although a bad photo - you can clearly see these are of the form with wide-spreading upward-pointed horns.
A couple of weeks before I was in Antwerp, and their Aurochs had the forward-pointing horns. http://www.zoochat.com/35/aurochs-1984-a-51660/
Hix