They are as reliable a worker as any boss could hope for, but dairy cows these days are being pushed to the limit.
Demand for milk has never been higher, and neither has its price.
Last year, a gallon of milk on average was just over $3.00. Six months later, it had risen to $3.29. Since then, it has jumped to nearly $4.00 per gallon... a new record.
"I think in some cities around the country, we will certainly see five dollars a gallon in the grocery store," said Scott Brown, a dairy economist at the University of Missouri.
Americans have a love affair with milk, but it's catching on, especially in China and India, where milk consumption is rising as fast as family incomes.
Officials say that, in part, is the problem: There simply aren't enough cows to meet the growing worldwide demand.
The cost of feeding cows is also rising. Alternative fuels like ethanol have made corn - a bovine favorite - a more expensive commodity.