This creature appears in Welsh folklore and I have never seen any reference to it in any book on cryptozoology. Its name means Gold-Bristle.
It resemble an ox, but was covered with golden bristles. There seems to have been only a single one of these beasts and it was, as its name indicates, covered with golden bristles. Indeed, so bright were these bristles that you could not look upon it. It was so wild that there was no question of drawing near to it. The lake Llyn y Gadair was its haunt, referred to as Gold-Bristle's seat. A hunter was said to have pursued the beast and his dogs slew the unfortunate animal near Bala Denlyn. The cry he uttered re-echoed through the mountains.
The Celticist Sir John Rhys thought the creature entirely mythical, the Celtic god Lugos in animal form.
Source: J. Rhys Lectures on the Origin and Growth of Religion as illustrated by Celtic Heathendom (London, 1892).