Nobody knows how they came to do this. It's been assumed that somebody or something chased them off the cliff, and the immediate suspect was a bear, of which there are two on the Spanish side of the Pyrenees, neither of whom the farmers are fond of. But the bears have been ruled out as suspects, seeing as their movements are monitored.
Or mostly ruled out, depending on which paper you read. El Periódico de Aragón is a Zaragoza paper, while Diario del Alto Aragón serves Huesca province, where the ganaderos, the cattle farmers, live. As do I.
It's been described as the biggest disaster in the history of Pyrenean cattle farming, which it no doubt is, though the disaster would be smaller if more than twenty of the sixty-one dead cows had been insured. Insurance costs, apparently, a little more than four Euros per head of cattle.
The ganaderos are demanding the regional government solve the mystery, insisting that you couldn't chase sixty-one cows off a cliff with twenty men. Or with forty dogs. Meanwhile the carcasses are lying at the bottom of a cliff, where their most likely fate is to be food for the vultures. A common theme in contemporary Spain.
Cows do not normally do this even if you have forty dogs