Wet weather last summer in some locales caused much hay to be baled too wet, says Bruce Anderson, University of Nebraska Extension forage specialist. Now that hay has heated and turned brown. Are there special considerations to bear in mind with this feed?

Anderson explains that hay baled too wet or silage chopped too dry can get excessively hot and cause certain chemical reactions to occur. These chemical reactions and the heat that produces them will darken the forage and make it smell sweet like caramel.

While livestock often find such hay or silage very palatable, the chemical reaction that caused this heat-damaged forage also makes some of the protein indigestible, Anderson says. “Unfortunately, tests for crude protein (CP) can’t distinguish between regular CP and this heat-damaged protein. As a result, your forage test can mislead you into thinking you have more usable protein in your forage than actually is there.”

If your forage test is done using NIR (near infrared reflectance), heat-damaged protein is one of the analyses reported, he points out. If the heat-damaged protein is high enough, the test also will report an adjusted CP that is different from the regular CP.

“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 your ration has little or no extra protein in it for your cattle,” Anderson says.

He suggests producers request a chemical analysis for heat damage when heat-damaged protein is suspected. “Then have them use this test to correctly adjust the amount of CP your forage will provide to your animals.”

Forage tests can tell us a lot about the nutrient supplying ability of our forages. But we need to make sure we conduct the right tests and then use the results wisely, he adds.
-- Bruce Anderson, University of Nebraska