Once the deer get used to the cows it will not be a problem. In fact, it can work to your advantage. I used to hunt a lease that had cows. One of the cows had a cowbell on and you could hear that thing ringing from a mile away at all times of the day and night. One year, one of my buddies decided to carry a cowbell when he walked in to his stand in the morning because he had been spooking deer every morning. I thought he was crazy but he went into to town and bought a cowbell and used it the next morning. The rest of us could hear him when he was walking, but he walked right up on several deer that were near his stand and just stood there and waited for first light without climbing up. When he could see well enough he saw that there was no shooter there, but there was a small buck and a couple of does standing 25 yards away and looking in his direction.
So consider belling one of those cows and try it yourself after the deer have listened to it for a year.