Cows are more resilient than you think:

To estimate how far the cows had paddled during their ordeal, journalists seemed to have measured the shortest distance between Cedar Island and the Core Banks using digital tools like Google Maps. Most put the swim at four miles; NBC preferred the precision of 3.39 miles … In fact, Aretxabaleta said, the probable routes taken by the cows, whether living or dead, range from 28.5 to nearly 40 miles. At the low end, that’s considerably greater than the distance across the English Channel. It’s more than ten times what swimmers complete in an Ironman triathlon. By Aretxabaleta’s measure, the absolute shortest period a cow would have been in the water is 7.5 hours; the longest is 25 hours.