Checking bulk tank levels might be the quick-and-easy way for dairy producers and their nutritionists to determine whether a recent ration change accomplished what was intended.

But to get a more accurate picture of how effective the change has been, you’ll want to supplement bulk tank monitoring with other tools, says Iowa State University Extension dairy specialist Lee Kilmer.

“The bulk tank can give you a rough estimate of what’s going on with the herd,” he says. “But you don’t want to use it as your primary barometer. It just isn’t reliable enough.”

The key factor, says Kilmer, is that dairy herds aren’t static.

“Some cows are in early lactation and still increasing in daily milk production, while some are coming up to the end of the lactation and tailing off on production,” he says. “At the same time, other cows are calving or going dry.”

Also coming into play is the fact that not all of the milk produced daily will wind up in the bulk tank. “Some of it might be thrown out because a cow was being treated with antibiotics, some of it might get fed to calves.”

DHI testing services are one of the tools producers can use to supplement bulk tank monitoring when evaluating the effectiveness of ration changes. Examples include the standardized 150-day milk test from Dairy Records Management Systems (DRMS) and the herd summary report from AgSource.

“The value of these reports is that they adjust production for each cow in the herd to the same point in the lactation,” explains Kilmer. “The numbers allow you to evaluate the impact of a management change from one test day to the next.”

One drawback to the testing-service results is that they’re only available once a month.

“If you’re adding an ingredient to the ration to correct a glaring deficiency, results of the ration change could start showing up in just three days or so,” says Kilmer. “On the other hand, if you’re doing some minor tweaking (adjusting levels of non-degradable protein, bypass amino acids, added fat, etc.), it might take seven to 10 days for significant changes to occur.”

Electronic metering in the parlor will give producers a variety of other tools they can use to evaluate the success of a ration change. “But again, you want to take into account the stage of lactation the cow is in,” he says. “Is she at a point where production should be going up or down anyway?”

Kilmer adds that the job of evaluating ration changes will be easier if you stick with products that are backed up by a fair amount of scientific testing. He points to products like Rumensin and sodium bicarbonate as examples of products meeting that criterion.

“Because there’s a fair amount of science behind them, you’ll have a pretty good idea of the potential outcome of the change you’re making,” he says. “On the other hand, there are a lot of additives out there that are only backed up by testimonials. Trying to figure out what kind of effect they’ve had on a change in production or performance can be a major challenge. I’m a big fan of sticking with the science.”

As a final point, Kilmer encourages producers to use their own observation skills as a tool for evaluating what’s going on in the herd. Pay attention to body condition, locomotion and manure scores, Monitor bunk weighbacks, milk urea nitrogen (MUN) levels and fat and protein tests. Keep close tabs on rates of metabolic disorders and milk production levels.

“Your cows are talking to you all the time,” he says. “Take a little more time to listen to them.”

See “Use Numbers To Monitor Progress.”