When should you test your hay?

When Should You Test Your Hay?

It’s that time of year when we fill our haylofts with freshly cut hay. If you are able to store enough hay to merit testing, don't rush to pull a forage sample. Wait 3–4 weeks after baling before sending it to the lab.

Testing too early can give you results that don't accurately represent the hay you'll actually be feeding. Why? Because freshly baled hay goes through a natural process called "sweating." This is when living plant cells continue to respire for a short time after baling, while bacteria and fungi naturally present on the hay also respire and break down plant sugars. Both will cause the temperature inside the bale to rise. During the sweat, your hay is still changing. Moisture, sugars, fiber, and protein availability are all in flux. Once the hay stabilizes — usually around 90% dry matter — your test will finally reflect what your horses are actually eating for the rest of the year. This process can last from several days to a few weeks, depending on the moisture content at baling.

Here's how this process can affect the results of your hay analysis:

Sugars (ESC/NSC/WSC) are used up through plant and microbial respiration, so carbohydrate levels gradually decline. All you metabolic horse owners take note!
As sugars are lost, fiber (NDF and ADF) becomes a larger percentage of the forage, making the hay less digestible.
If hay gets too hot (generally above 140°F because it was baled too wet), a Maillard reaction can occur. This is when free sugars and amino acids (proteins) chemically bind together under the high heat. While this "caramelized" hay often smells sweet or like tobacco and is readily eaten by horses, the bound protein becomes completely indigestible to the horse.

Here's the important part: A standard crude protein test may still report normal protein levels even though some of that protein is no longer digestible. If your hay overheated, ask your forage lab to include a Heat-Damaged Protein (HDP) or Acid Detergent Insoluble Crude Protein (ADICP) analysis to determine how much protein is available.