These unlock once you get to Empire. You have to ride out to the ranch to participate in them.

Herding
Ride out to The Rancher - he's got a cute little piggie. He says he'll teach you to herd, and first you need to get a horse from the barn. The horses have various names like storm and cinnamon. First, herd the calves into the pen. Stay behind them so they go in the right direction. When get all 3 in - well done. OK, now you have to follow him. You look down on the cows in the field. You have to get them all to the steer, and he'll guide them properly. The Vs on your compass are cows, below you. Herd them all to the steer. Follow them all and if one leaves the group, get them all to stay together. They just run off one by one so it's not too hard.
Reward: horse +5, $10

These next unlock after the first Hoodoo mission.

Mustangs
Mustangs were stolen from his ranch. Follow the creekbed and chase them back. You herd them like cattle, start by getting a horse in the barn. Just do as he says - ride down the creekbed and herd them back, chasing after any runaways.
Reward: horse +5, $10

Wolves
The rancher has a problem with wolves. You have to check up on the herd, and make sure theyre safe. It's dark instantly, neato! There are really pretty stars and a moon too. In any case, use a small calibur weapon. If a cow dies, you get mission failed. Kill all the wolves by being alert and watching out for them.
Reward: horse +5, $10

Gun Walkthrough