The lot
The season
What it actually costs
All-in cost of gain
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Breakeven
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Margin per head
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Days on feed
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What this model does that a spreadsheet doesn't
A death forfeits the animal and every dollar already spent on it, so mortality is the most leveraged number here — and it's usually carried as a flat guess. Move death loss a single point and watch the breakeven move.
Heavy cattle bring less per hundredweight than light cattle. The added pounds have to beat that slide plus your costs before a pound of gain is worth anything.