By Fae Holin, Managing Editor, Hay & Forage Grower

A consistent feed – whether it's hay or silage – translates to consistent milk production. Yet just a small amount of variation in feed quality can immediately affect milk production, according to Dave Mertens, who spoke at the recent Getting More From Forages conference in Madison, WI.

"For high-producing cows, we have a conflict between trying to maximize the nutrient density in the ration and also meeting a minimum fiber requirement. If you look at a range of diets feasible for (high-producing) dairy cows, you find that, as milk production goes higher, the range of diets you can feed to those animals that allow them to produce that much milk becomes very narrow.

"These cows are just like racecars," said Mertens, a dairy scientist with the U.S. Dairy Forage Research Center (USDA-ARS) near Madison, to a room full of nutritionists and scientists. "In the racecar you are pushing everything to its maximum for power and traction. Almost anything that you do affects performance, and an abrupt change, such as a blown tire, is going to cause a disaster. Dairy cows that are performing at their maximum need consistency in the ration, and abrupt changes can cause problems."

Even a small change, such as rain or snow on an open silo face, can affect the amount and proportion of dry matter from forages in a dairy diet. In Mertens' recent research on dry-matter variation in forages, a one-day change resulted in a 2.2-lb/cow loss in dry matter intake and a 1.8-lb milk production loss the next two days. The dairy scientist concluded that a certain amount of day-to-day variation is unavoidable, but that daily on-farm, rapid analysis of forages for dry matter – along with good feed management – can help control some of that variation.

"When measuring moisture, we have to have a rapid return of results so the ration can be adjusted immediately. We can’t wait for three days for results to come back, because feed is gone at that point. We have to have accurate methods that are very rapid."

Koster tests and microwave analyses don't produce the instantaneous results that near-infrared technology can, Mertens said. He doubted many farmers would bother testing moisture on a daily basis using those methods because they require several drying and weighing steps with calculations that all take time. Properly calibrated, portable sensors using diode array NIR provide immediate results; Mertens used the Deere & Co. HarvestLab moisture sensor in his study (this information for description only, because USDA does not endorse or recommend a specific product).

"It is a very rapid scanning machine. It uses a very large bowl so you can have a reasonable farm-level sample taken. The bowl spins so the entire surface underneath the sample can be scanned," he added.

Additional work would be needed to integrate the information gained from the NIR technology into feed-mixing software, the dairy scientist warned. "Just getting the number is only part of the problem. The next part is that the number has to be put in software to calculate the proper mixture to make a new ration for that single day."

He brought up another valid concern about just how difficult it is to keep rations consistent: "I often point out that there are four different diets on a farm. There is the one that the nutritionist puts together using the information he gets from the lab analysis and nutrient requirements. He gives it to the farmer. Typically, the farmer makes changes that he may not even tell the nutritionist about. For example, Silo A is empty, so he uses Silo B. Then he gives that to the feeder and the feeder makes some adjustments and this is what he puts in the bunk. Finally, the cow selects what is in the bunk and that is what she eats.

"Moisture sensors cannot solve the problems of the nutritionist or farmer in formulating the proportion of dry matter from each ingredient that is needed in the ration. Neither can they solve the problem of the cow selecting the diet she eats,” Mertens said. ”But they can help the feeder get the correct amounts of forages in the daily ration. When the dry matter of a forage decreases, the feeder is weighing less forage dry matter and more water, which affects the amount and composition of the ration that is fed. We now have on-farm technology to measure moisture that can help the feeder minimize the effects of variation in forage dry matter on the ration that is fed to those high-producing dairy cows.”

For additional articles on dairy feeding, watch for Hay & Forage Grower's September Dairy-Forage Nutrition issue that goes to dairy producers in mid-September. The issue will be accessible online at in text form under our Most Recent Issue heading. It will also be available In a digital format; just click the Introducing Our Digital Edition button and complete registration information.