You should consider reporting your horse breeding business
on Schedule F (farming business), click
here for 2016 IRS publication
225 Farmer's Tax Guide (which provides valuable information on the taxation of horse
breeding), also if both you and your husband own the business, you can treat it
as a qualified joint venture and prepare two Schedule F's, each claiming 50% of income, expenses, and depreciation.
For a horse breeding business the horses can be assets that are
depreciated (see page 42 in IRS publication for specific lives and depreciation
methods). The tractor and trailer would also be assets that may be depreciated,
or in some cases expensed. Registration fees and testing are generally expensed.