When you remove a horse from a pasture and another horse becomes upset, bobbing the head and calling to the other horse, the upset horse is what's called "buddy sour." Buddy sour horses can be dangerous. Training your horses to feel secure around you, and practicing separation exercises, can cure buddy sour horses.
Fine-tune your horses' ground manners to help them feel secure around you. Walk one horse away from the pasture, but still in sight of the other horses, while keeping his ears in line with your body. Don't allow him to walk in front of or behind you, and make certain he follows your pace and does not pull at the lead rope. Give your horses praise for good ground manners.
Return the first horse to his pasture and work on ground manners with the second horse in the same manner. This procedure helps each horse to bond better with you so each one will not be stressed when leaving pasture mates behind.
Leaving the Pasture
Put a lead rope on one horse who is buddy sour, while he is in his pasture. Lead him toward the exit gate. Stop at the gate and praise the horse while giving him a tasty treat such as an apple slice. Lead this horse back toward the other or others in the pasture, and allow him to graze for a few minutes. Lead him back to the gate and open it. If your horse balks or tries to turn and look at his pasture mate or mates, walk through the open gate and stand to one side of the horse while giving him treats. Lead him back to the herd and allow him to graze after he calms down. Return to the gate and lead him through it. Turn the horse around so he is facing the others, and give him a treat and praise.
Separation Training Tips
Gradually increase the distance you lead a buddy sour horse away from the others, and give him treats only when he is calm. If you have two buddy sour horses, train both to be independent of the other. Practice separation training with your horses once in the morning and once in the evening, just before mealtime -- you're rewarding your horses with a meal for their cooperation.
If your horses are broken for riding, train them on a lead rope first by walking away from the other horses until they are no longer buddy sour before attempting to ride one or more horses out of the sight of the others.
Until your training is complete and your horses are no longer buddy sour, do not remove a horse from the pasture for injections, teeth floating or a farrier appointment so they will not associate being led away from their pals with an unpleasant activity.
Never stand directly in front of an agitated horse. He may kick, rear up or bite you when he is trying to return to his pasture mates.
If a horse suddenly becomes buddy sour, call your veterinarian for an appointment to rule out any type of illness causing the behavior.