I'll summarize how we figure it:
We run mother cows on some of our ranches in California and Nevada.
We plan on using a bull for 5 seasons. An annual 35/head breeding charge is billed to each cow in the CA operation and a charge of $36/head (less cows exposed to each bull in NV) is assigned to each cow in the NV operation. While we would like to see that charge closer to $30/head, we aren't operating in a vacuum and failed semen tests, broken penises and other things arise that prevent a small percentage of bulls from seeing 5 productive seasons. Keeping that per head allocation in the mid 30's accounts for that.
So we are in the midst of buying bulls for our Spring calving NV operation right now. The high desert operation sees one bull turned out for every 18 cows. 18x36x5=$3,240 in lifetime breeding charges that bull will recoup. Secondly we factor in salvage value. as we are replacing bulls leaving the program, we use the salvage on the bulls that are leaving to assist in forming a budget for their replacements. The truckloads of cull bulls off the NV ranches were recently contracted to Laura's Lean for an average of $90/cwt. weighing 1,900 or $1,710/head. that along with the $3,240 gives us a figure of $4,950 that we will use as our target average to be at or below on the bulls we need to buy for the NV operation. When fall bullsale season rolls around for our fall calving CA program, we will use the same equation but plug in the different variables. assuming a similar cull bull market we would see 35x20x5=$3,500 (our CA bulls are turned out at a rate of 1:20) plus a salvage of 1,900x90=$1,710 (while bulls mature to a slightly bigger size on CA foothills than on NV sagebrush I'll leave it constant) for a budget of not to exceed $5,210 for the bulls purchased to enter our CA operation.
We have found this to be the best method of coming up with what a bulls honest top end value is to us in relation to where he will break-even and salvage in a fashion to replace himself after a useful life while keeping our annual breeding expense per mother cow at a level where we are comfortable with the charge she is being asked to carry while remaining profitable.