Rather than pin the tail on the donkey, how about kiss the donkey while blindfolded.
You play the game, you take your chances to get the right end.
City kids love those long, yellow, plastic, water slides. How about the green manure pit slide with prizes for those sliding farthest---upright.
Gather the eggs and take them to the house game. One person gathers from a basket of eggs, then teams relay them from person to person to a different point. Team members are spaced about 20 feet apart. Most whole eggs in the basket wins. Perhaps team members should rotate locations.
Clean out the barn pie toss, but I wouldn't let the kids use pitchforks. A team wins by being the first to load a manure spreader.
Archaeology dig. Items buried in grain bins or tubs of grain.
Bull chase. Have kids pretend they are being chased by a bull and see who can jump the highest fence. Kind of like high jump in track and field.
Post hole dig to see which team can get the most post holes dug in 10 minutes. Best use auger type diggers so that no one cuts toes off.
Align the fence to see who can make the straightest fence row. Wooden stakes serve as fence posts.
If you have some really gentle animals, let them dye designs on them. I received a picture of a zebra yesterday that had a bar code imbeded in the stripes. Neat.
Round up time. See who can saddle a barrel the fastest--correctly after being shown once.
Lasso the ?????