Ground blind, or pit? I doubt the farmer is going to want a pit in a field his Holsteins are in! They are so stupid they will fall in.
We have two blind and one in corn and one in grass. Old dried green grass and we refresh it the morning of the hunt with pulled grass from around the field. Depending on the cows, they less you move the better. The more you move, the more they become interested in you. They will come right up behind you and smell you. Then start to smell, drool on and knock over and maybe break the decoys. You can spend enough time chasing away the cows to bust you when birds come.
Every field and group of cows is different. My buddy has a field and the milk cows are just annoying and watch from a distance. Another buddy had a field and you could not hunt in it. They about hassled you just walking through the field to retrieve one that sailed. They would even roll dead geese around like a soccer ball.
Like bored kids.
Bring grass in feed bags if you have to. Extra grass piled around the bottom of the blinds really blends them in even in short grass. Setup in a depression if you can. Bad news is bring new gras into a cow pasture is like waving candy in front of kids.