If you’re going to feed a residue forage to add effective fiber to rations, cornstalks and wheat straw are about equal. The one you choose may depend on what you need it to do,” says Mary Beth Hall, USDA-ARS dairy scientist at the U.S. Dairy Forage Research Center in Madison, WI.

Adding a small amount of residue forages to dairy rations provides a good source of physically effective fiber, which is a key to healthy rumen function, she points out. Those forages can also help dilute the energy and starch from high-corn silage diets and protein in rations high in legumes.

Hall wanted to find out if wheat straw is more beneficial for rumen function than cornstalks. For her study, she used chopped, ensiled cornstalks to gain additional insight into how corn silage fiber functions.

“Dairy producers only have so much room to work in a ration, so if they know how ingredients work, they can choose which ones will best fit,” she says.

She also varied the starch sources within the rations. High-moisture shelled corn, a rapidly fermenting starch and dry, ground corn, a slowly fermenting one, were used.

She formulated four diets: wheat straw with high-moisture shelled corn; wheat straw with dry, ground corn; chopped and ensiled cornstalks with high-moisture shelled corn; and chopped and ensiled stalks with dry, ground corn. Other ration components included alfalfa haylage, corn silage, soybean meal, roasted soybeans, soy hulls and a vitamin and mineral mix that contained monensin.

Each ration was 31% NDF, with 25% of ration dry matter coming from forages, 26% starch and 17.5% crude protein. Cows rotated among the diets and ate at least three of them over the two-month trial.

Daily dry matter intake per cow was 50 lbs, with over 6 lbs of that total coming from straw or stalks.

“Producers wouldn’t normally feed that much straw or stalks,” says Hall. “We fed that much to be able to clearly see how they acted as physically effective fiber sources.”

Here are her findings:

All cows stayed healthy during the trial; daily milk production averaged 82 lbs/cow with 3.8% butterfat and 2.9% protein.

“There was no difference across the diets in dry matter intake or in the amount of time cows spent ruminating,” she reports. “However, cows on the dry, ground corn diets spent a little bit more time eating than those on high-moisture corn diets.

“Milk and protein yields were slightly higher on diets with cornstalks.” Milk-urea-nitrogen (MUN) levels were higher on the wheat-straw diets.

“Cows gave 0.1 lb/day more fat on high-moisture corn, whether it was combined with stalks or straw.”

The scientist looked at how the two residue forages behaved in the rumen and digestive tract by measuring pH levels. The cornstalks appeared to increase the rate of passage, whereas the wheat straw held feed in the rumen longer.

“If you need to add fiber to rations, wheat straw might be the better option if you’re feeding a diet high in corn silage and are looking for a fiber source that will act differently than the stover in corn silage,” she says. “But if you just need a straight-out forage fiber, either straw or stalks will do the trick, as long as the ration is well-balanced.”