Breeding farms are tabs that help you to organize your horses. You must have sixty days seniority to make one. For players with a large number of horses, breeding farms are incredibly useful, as they let you find the horse(s) you are looking for in a short amount of time. On the left is a typical row of breeding farms. You can name each breeding farm whatever you like, as long as it follows the rules of the game.
If you can afford a Pegasus account, you will be given the option of color coding your breeding farms and categorizing them even more! On the right, you can see a row of breeding farms, this time in color.
Clicking on the colored breeding farm leads you to a list of the breeding farms inside that breeding farm! Slightly confusing, though a great help to the game.
In order to create a breeding farm, you need to go to Breeding > My Horses, then scroll to the bottom of the page, where you should see a plus sign and the words 'create a new breeding farm'. Click it, and you will be led to a page where you can name your new breeding farm, give it a description and objective, choose the breed that will be allowed there (or let any horses into that breeding farm), and decide whether it will be for purebred horses only or not. To create more breeding farms, click on the "My horses without a breeding farm" breeding farm and scroll to the bottom of the page. The bottom of other pages will have "Edit breeding farm", which will only modify that breeding farm.
Warning: Your choice of breed and 'purebred only' will be final. You cannot change it later, so make sure you select the right things! You can, however, change the name and description/objective as often as you like.
To edit your already existing breeding farms, go to the breeding farm you wish to edit. Scroll to the bottom of the page, where you should see a pencil and the words 'edit breeding farm'. Click on it, and you will be led to a page where you can edit the name and description of your breeding farm, see which breeds are allowed in that farm, and see the statistics - These include how many horses are in that breeding farm, and how many different people visited it yesterday. You also have the option to delete the breeding farm. Choose wisely, as your decision will be final!
Deleting a breeding farm will allow you to create a new one without waiting. This is good in case a breeding farm becomes empty or you chose criteria, such as purebred only, that you no longer want.
Be careful not to get breeding farms confused with affixes.