You can use either Schedule C or F. They are both taxed the same; it's only the income and expense headings that are different. You can always use miscellaneous income or expenses entries. Generally, Farm Income is for crops and livestock raised and Business Income is more for services provided. If you have been using schedule C, I'd stay with it and add your farm income and expenses to your business return. This is the easiest option, however, you have other options as well.
There is no transferring of a Schedule C to a Schedule F. You do have the option of creating a Schedule F for 2017 that covers both, and also closing out your horse business on the Schedule C. Or you can keep both (C for horse business and F for farm business); the important thing is not to duplicate or overlap any income or expenses. If you want to have everything on a new Schedule F, the Schedule C business will need to be closed out. Here is more information on how to close out a Schedule C business.
Closing a Business - TurboTax Blog
IRS - Closing Your Business
