Lots of good discussion and food for thought here. In my overall engineering free body diagram approach, any cow, bred or open, costs in excess of $500/year (1.40/day) to maintain, according to several upper midwest university’s numbers. A good cow with a 280 day gestation period, a 45-60 day rest period and rebreeds on the first or second cycle that has a calf every 365 days is doing her job to be a profitable cow worth keeping. The farther from 365 day calving interval she gets, the less profitable a cow she is. Costs to maintain that cow stay the same, annual income from her calves declines. When the bull is in full time it’s hard to identify your profitable, 365 day calving interval cows and gradually herd fertility goes downhill along with profitability.