And they really, really love it.
Most observers of this awesome video have said that it is likely they were kept indoors to protect them from the winter. Cows can slip on ice and break their hips, which can harm their ability to walk forever, so it's important that they are protected from the extreme cold.
These cows are well fed, well groomed and their hooves are taken care of. It is certainly a situation where they were protected for an undisclosed amount of time (though the video posters say 6 months).
It is common for cows to romp and play when they are first let outside. It's their natural environment and who doesn't like going outside on a warm day after being cooped up through the winter?
Many people that have cows say that they get excited about pretty much anything cool. New grass? They'll go to town, jumping around.
It's great to see them so happy.