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Moldy hay can be utilized on cattle operations with special considerations

by Wyoming Livestock Roundup

Casper – This fall, many producers around the state experienced rain on their forage after it was already cut. The result, said UW Extension Livestock Specialist Steve Paisley, was moldy hay.

“We were very fortunate to have a wet fall, but third cutting hay got the downside of that,” he said. “There was a lot of black hay in the field, but there are ways we can manage it.”

Paisley discussed how producers can utilize their moldy forage during the Progressive Rancher Forum, held at the 2013 Wyoming Stock Growers Association Winter Roundup at the beginning of December.

Mold issues

Paisley commented that fields remained wet through the fall and forage didn’t dry quickly enough.

“Many of our producers don’t have covered storage either, so what hay that was baled got more rain,” he continued. 

In attempting to utilize forages that have mold, Paisley noted that the type of mold can be determined, as can the toxicity of the mold.

“What is the black dust we are seeing?” Paisley asked. “The mold is a fungus and in most cases, the black dust is spores.”

Some of it, he said, is also decomposing plant material.

Hot bales

Paisley also noted that occasionally reactions happen in the bale that can turn the bales dark brown or caramel colored.

“This is known as a Maillard Reaction, explained Paisley. “This is a reaction between the amino acids and the sugars that causes the darkening.”

The resulting hay releases more sugar and has a sweeter flavor, so cattle like the taste, but it is not as nutritious.

“If we did a regular analysis of the hay, it would show normal protein and energy,” Paisley said. “The issue is that they are altered and unavailable. If the protein is not available, the animals are not getting the benefit of eating the hay.”


A variety of mycotoxins can be found in moldy forages.

“The mycotoxin is a secondary metabolite produced by mold or yeast organisms,” Paisley explained. “There are seven different varieties that show up. Aspergillus, fuserium, penicillium and rhizopus are the most predominant in hay.”

Laboratories can test for molds and which varieties are present in samples, but may labs test for primarily grain molds, rather than those associated with forages.

“If we do an overall mold and yeast count, it will give the producer an idea of the severity of the mold in their hay so they can get an idea of how carefully the forage should be handled,” Paisley commented. 

In sending in samples for testing, he encouraged producers to sample several bales, noting that there may be a wide variety in the severity of a mold infestation.

Along with testing, Paisley asked producers, “How can we manage moldy hay to mitigate the impact of the mold?”


“There are also some issues with feeding dusty hay,” he said. “One of the biggest responses we see in feeding hay with mold spores is a reduction in intake.”

The bitter taste of the moldy hay spores reduces intake, and the resulting impacts should be considered in developing the cattle diet. 

“This is not to say we can’t feed some moldy hay, we just need to adjust our rations,” he added.

Some research shows that cattle can adapt to eating moldy hay over a period of time, and cattle can tolerate higher levels of mold than other species. Paisley noted that horses and swine are most susceptible to mold complications. 

Though some cattle can tolerate moldy hay, Paisley cautioned against feeding moldy hay prior to breeding or to pregnant cows. 

Producers should also not feed hay to immune compromised animals, newly weaned calves or stressed cattle.

Side effects

“Animals do not only ingest the mold, they inhale the spores as well, so there is a combination of impacts,” he said. “We have a lower risk in feeding moldy hay to yearling steers or non-pregnant animals.”

“Cattle can have an allergic response, and there may also be endocrine effects,” he explained. “Many of these mycotoxins can have hormonal impacts.”

Heat suppression or deficient rebreeding may occur or a result of feeding moldy hay.

 Mitigating impacts

Paisley noted that moldy hay can be blended with non-moldy hay to further decrease the risk.

“The first two ways to manage moldy hay include diluting and blending when possible,” Paisley said. “If the producer is able to grind hay or sell the hay to a local feedyard, they can blend in a small percentage of moldy hay and get the benefits of the roughage but minimize the negative effects of mold.”

Paisley also recommended feeding the hay in well-ventilated areas to minimize inhalation of spores.

“There are also recommendations to feed with wet feed or silage to minimize the dust,” he said. “It is also important to monitor intake when possible.”

Monitoring cattle can alert the producer when intake is reduced. 

“When producers have to feed moldy hay, avoid abrupt changes in the diet,” Paisley added. “Cattle will adapt and adjust their rumen from a microbe standpoint. They can adapt better if we work moldy hay into the diet slowly.”

“When we try to minimize our costs, especially feed costs, we try to utilize whatever feeds we do have,” Paisley said. “We need to balance the fine line between the type and quality of forage and manage in moderation.”

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at

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