A breath test for spotting ketosis is not accurate. “You may miss up to 80 percent of cows with clinical ketosis,” says Sheila McGuirk, veterinarian at the University of Wisconsin’s School of Veterinary Medicine.

Instead, use a urine test or milk test to detect ketones. The cost of a urine test is only a few cents per cow, so try that first, McGuirk says. If you can’t get urine, use a milk-ketone test. It’s more expensive — about $2 per cow — but, if the test is positive, you can be sure that she has ketosis.