Regular

Every horse on your ranch with a score less than 45 can be trialed for money. You can easily do this while breeding horses. Every foal born you trial for 10k.

Foal Method

To gain a lot of money fast and easy you can pick out a mare or many to breed for the purpose of having foals u can trial for 10k each. Basically you just keep breeding the mare trialing the foals and either releasing them or donate them.

Rescue Method

This is more profitable than the foal method, though a tad bit more complicated. You search rescue for the lowest base statted horses as these will be $250 and up and you rescue the untrialed ones. You then trial them and either release or donate them.

Selling

An easy way to make money is selling horses or tack. Do remember that it takes time to sell horses as many players are also selling horses and most are either full or may not have the money to buy your horses. You have to be patient and not get mad at people who don't happen to buy your horses not everyone can or can use it.

Studding

Another easy way to make cash if you have a very high statted stallion or one that is very high up in his breed.

Competing

This isn't the best way to make cash since your horse has to place 1-5 and it costs money to enter events.

Betting

Can be good can be bad. To win any money betting someone has to bet on another horse in the event otherwise you just get your bet money back.

Training

This one can make you money but is slow. You can train other players horses for money if they lease them to you to train. To be sure to have read over all my training guides before doing this so you have a good grasp of how to train. And do remember that training costs you money as well so set your pricing accordingly.