I am not sure I agree with Bright Raven's handling of this, but I may be misinterpreting his response. Breeding stock is usually considered a capital expense and is depreciated. I would download IRS Publication 225 and read the information that begins on page 35.
https://www.irs.gov/pub/irs-pdf/p225.pdf
In many cases you can chose to deduct the whole cost as a section 179 expense in the year of purchase. You can also chose to depreciate over 5 years using the recovery period from the General Depreciation schedule under "cattle, dairy or breeding" listed on page 42. When you sell that bull you must recapture any gain over book value at the time of sale. You will report the sale on schedule 4797. If you paid $1500 for the bull and he was depreciated down to a value of $500, but you sold him for $1500 you need to recognize the $1000 depreciation as a gain. If he sold for more than $1500 you would carry the balance of that gain to schedule C where it will be recognized as a capital gain and may be taxed at a lower rate. If you deduct all of the cost under section 179 you will need to recognize the entire sale price, less any costs of the sale, on schedule 4797 as a gain. The easiest way to deal with this is to buy a tax program like Tax Cut and be sure to follow instructions. The advantage of showing sales of breeding stock on schedule 4797 rather than as income on schedule F, is that you won't pay Social Security Taxes on those gains. I realize that for many that post here, this may not be an issue, as they may be reporting a loss on Schedule F. If you are close to retirement and looking for high income years to boost SS earnings, this may also not be to your advantage.