Many dairy producers could save some money, while maintaining milk production, by cutting back on protein.

That's the conclusion reached by Glen Broderick, a research scientist with the U.S. Dairy Forage Research Center, Madison, WI, following a study comparing ration protein levels.

“The optimal percentage of protein in the diet — which minimizes urinary nitrogen excretion without reducing production — is 16.5%,” says Broderick. “That percentage varies from the industry's standard recommendations of 18-19% protein.

“This is a very significant finding, especially in light of today's high prices for protein supplements,” he adds. “If you're feeding over the animal's requirement, that excess nitrogen is running out in the urine — the form that's most likely to cause pollution.”

According to Broderick, if just one percentage point less dietary protein was fed to U.S. dairy cows, urinary nitrogen could be cut by about 60,000 tons/year.

Forty cows were used in his 16-week trial. Five diets were formulated, with protein levels ranging from 16.5% to 19%. Each cow ate four of the five diets over the course of the study.

“I used a Midwest feeding regime,” says Broderick. The main components of the diets included alfalfa haylage, corn silage, high-moisture corn and soybean meal.

Milk production ranged from 80 to 85 lbs/cow/day. There were no statistical differences in production when cows were fed diets with 16.5% protein vs. those with higher protein levels.

“The results were a bit surprising to me, with the protein requirement somewhat lower than I expected,” he says. “But once you meet the animal's requirement for metabolizable protein — the true protein that's absorbed at the intestine in the form of amino acids — there's no reason to think you'll get any more milk production if you feed additional protein.”

In an additional trial, he and his graduate students decreased the protein level from 16.5% to 15.5%. “We actually lost about 2 lbs of milk production/cow/day by feeding the diet with 15.5% protein.”

To optimize production and cut feed costs, he recommends that the forage component of a cow's diet consist of about half alfalfa haylage and half corn silage.

“By doing this, dairy producers will dilute the degradable protein from the alfalfa haylage with the energy from the corn silage, so they're not overfeeding degradable protein. Then I would feed up to 16.5-17% crude protein with soybean meal.”

The switch to feeding less protein should be an easy adjustment; however, Broderick notes that feeding more than 16.5% is practical sometimes, too.

“In our trials, we tracked the protein levels by analyzing feed samples every week. On the farm, producers are often switching silos. They might be feeding a 22% crude protein haylage one day and then haylage with 18% protein the next and they might not be ready to adjust for this change.

“Feeding higher levels of protein is sort of a risk management thing. But, if farmers can stay on top of it, they can back off quite a bit. I think we're overfeeding protein by a fair amount.”