This Slaughter House offers an Indoor cattle pen where you can breed your cows, then move them over to the killing area, as many as you'd like(area is about 3w x 7L), Then hit the button until their dead, then lower the door, and pick up your meat and leather. Rinse and repeat.

Additional Notes

The schematic contains a lot of ground under the building, this was done to preserve the Red stone wires that operate the front door of the building as well as the controls to raise and lower the killing area door.

Any suggestions please voice them as a comment.