Nothing is more constant than change. And changes in your TMR can impact dry matter intake, rumen health and milk production.

“The day-to-day variation in dry matter in some feeds can be substantial. If you don't correct for it, you end up feeding an unbalanced diet,” says Bill Weiss, dairy scientist at Ohio State University.

“It's not uncommon for moisture to vary in wet ingredients by 3-5 units/day. If you measure and make adjustments, then you're always ahead of the cows.”

A day or two after a TMR has been formulated, silage can become wetter or drier and the amount of dry matter you're feeding can change.

“For a couple of hundred bucks you can get set up to moisture-test your wet feed ingredients,” he says. “Once you see how much the moisture changes in a day and how it affects your cows, it's pretty convincing.”

Frank VanGenugten of Stardust Dairy, South Solon, OH, is convinced. His nutritionist, Dolf Slagter, tests the wet ingredients in the ration — haylage, corn silage and wet brewers' grain — at least twice every week. And he'll check them every day if he's seeing big moisture differences.

“If the ration's too wet, it heats up in summer, the dry matter content goes down, and the cows don't eat as much,” says VanGenugten, who milks 800 cows. “The goal is a TMR that's 50% moisture. If we need the ration drier, we take out some corn silage and wet brewers' grain; if we need it wetter, we add water.”

The easiest way to check moisture is with a cooker-type tester or a microwave oven, says Weiss.

“Most studies show that a Koster-type tester is within 1-2 percentage points. It's not quite as accurate as a lab, but the fact that you're getting real-time results is what's important,” he says.

It takes 30-40 minutes to do a Koster test, but it can be left unattended. The microwave method is faster — it takes about 10 minutes — but it's more involved and takes more training, says Weiss. He says probe-type testers are less accurate.

Stardust Dairy uses a Koster tester.

“It's really easy. You just throw the ingredient into the cooker and you do your other jobs,” says Slagter. “Then when you're done with your chores, and just before coffee, you check the dry matter and you're done with it.”

Slagter uses an Excel spreadsheet he designed to adjust the ration. He plugs in the dry matter number and the spreadsheet quickly tells him what ingredients need to be adjusted.

“Ideally, you want exactly the same ration 365 days a year,” he says. “You can have a lot of variability in ingredients. I just plug in the dry matter content of the silage and it tells me how many pounds of water to add to compensate.”

Slagter also checks the ration's particle size using a Penn State forage particle separator every week. And he checks manure to make sure the cows are digesting the corn. But he notes that moisture testing has proved to be an accurate indicator of what cows need. He also watches for other clues.

“An hour or two after feeding, at least 50% of the cows should be lying down and cud chewing,” says Slagter. “If they're not one day, that's not a problem. But if it's consistent, we do have a problem.”

If that happens, Slagter makes sure there's enough forage in the ration, checks the particle length, and looks at his moisture tests.

“One of the biggest effects for dairies that start checking their moisture is just better overall rumen health,” says Weiss. “They have more consistent feed intakes, fewer foot problems and more consistent milk production.”

So by checking moisture changes, your cows will deal with fewer diet changes and you will see fewer changes in their output, says Weiss.