Heat-damaged hay and silage should be evaluated chemically to determine how much of the crude protein is still available to animals, says Bruce Anderson, University of Nebraska extension forage specialist.
Hay baled too wet or silage chopped too dry may darken and smell sweet like caramel, he says. It's often very palatable, but some of the protein may be indigestible. Tests for crude protein can't distinguish between regular crude protein and heat-damaged protein. So the forage test might show more usable protein than actually is there.
NIR forage tests measure heat-damaged protein, and an adjusted crude protein level is reported if the heat damage is high enough.
“However, I've found that the NIR test for heat damage may not be accurate enough for you if your ration contains a lot of this forage and has little or no extra protein in it for your cattle,” says Anderson.
When heat-damaged protein is suspected, ask the lab to test for it chemically and to adjust the amount of available protein, he advises.