Could your silage kill cows? “It's quite possible,” says Oregon State University nutritionist Steve Puntenney.

Last February, Puntenney reported that a common mold found in grain and silage, Aspergillus fumigatus, may be the cause of hemorrhagic bowel syndrome (HBS), a deadly dairy cattle disease.

Based on research he conducted with colleagues Yongqiang Wang and Neil Forsberg, Puntenney suggests that dairy cattle can contract HBS if they eat fumigatus-infected feed when they're stressed or have suppressed natural immunity.

Previously, the exact cause of HBS in cattle was unknown.

“Tens of thousands of cows across the country are affected by HBS,” Puntenney says. “An estimated 1-2% of the adult cow deaths in North America are caused by this.”

Clinical signs can include depressed appetite, decreased milk production, diarrhea, fresh or clotted blood in feces, abdominal distension and extreme weakness, according to Sandra Godden, a University of Minnesota veterinarian.

“Medical or surgical treatments are typically ineffective, so HBS is usually fatal,” Godden says. “Eighty-five to 100% of affected animals die within 24 to 36 hours of the onset of clinical signs.”

Necropsy of HBS-infected cattle typically reveals blood clots or bloody fluid in the jejunum (middle portion of the small intestine), Godden notes.

With sound management, HBS can be prevented, Puntenney says.

“For starters, follow best management practices for proper storage and rotation of feed ingredient and ensiled forage inventories,” he says. “Compromising hygiene at feed bunks and water troughs often leads to explosive growth of molds, including Aspergillus.”

Attention to detail when ensiling forages is paramount to the prevention of mold growth, Puntenney emphasizes.

“Maturity is important when harvesting forages,” he begins. “Goals for moistures should be 68-72% for corn silages and 64-68% for legume haylages going into bunker or drive-over silos.”

Bunker silos should be continuously and rapidly filled, and immediately packed with a heavy-wheeled tractor for best results, Puntenney continues.

“Avoid interruptions in the filling process, if possible, to prevent layers of spoilage from forming,” he says. “Properly fermented corn silages should reach a pH of 4.0 or less and legume forages will come in below pH 4.5. Inoculants have been beneficial in more rapidly lowering silage pH's and the savings in dry matter losses will more than pay back your investment.”

Once filled, bunker silos should be immediately covered with quality plastic. The plastic should be weighted down with tires to ensure that it will remain in place.

Collaborating with Prince-Agri, Quincy, IL, Puntenney and his Oregon State colleagues developed a feed additive that is said to reduce the incidence of HBS by suppressing growth of A. fumigatus. Marketed as OmniGen-AF, the product, a powder added to TMRs at a rate of ⅛ lb/head/day, made its commercial debut in May this year.

Doyle Waybright started using it in July. He's been dealing with HBS at his 2,300-cow dairy near Gettysburg, PA, for the past seven years. Death loss due to HBS is currently about eight head per year, but has been as a high as 25 head per year.

Waybright has never had his feed tested for the presence of A. fumigatus, so he isn't sure it's the cause of HBS in his herd.

“Hopefully, the product will provide immunity and stop breaking cases of HBS,” he says.

For more information about OmniGen-AF, contact Puntenney at 503-784-8691 or