The following quote is from William C. Stringer and Harold B. Hedrick
Don't run or excite the animal prior to slaughter because this may cause poor bleeding and give the carcass a bloody appearance.
Often hogs and beef get very excited when they are taken to the slaughter house. There is other livestock around and it's somewhere they've never been before. And they are not stupid, they know something is happening.
When we come to your farm, we are at your livestock's home. They are calm and relaxed as possible. This helps keep the meat in the best condition possible. The less adrenalin flowing through their bodies, the better. You receive higher quality meat than you would be taking the animal in a highly stressed state to the slaughter house.