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Experts discuss risks of feeding moldy hay to livestock

by Wyoming Livestock Roundup

Following a summer plagued with drought conditions, forage harvested this year may be in short supply. Producers feeding hay harvested in years prior or buying hay from outside sources need to keep in mind the risks of feeding livestock moldy hay.

            “Feeding any moldy hay is a risk, but the risk level will change depending on the amount of mold,” notes University of Nebraska-Lincoln Extension Educator Brad Schick. “Any bale of hay can have mold, but the ones with noticeable mold need to be paid special attention.” 


            According to several industry experts, mold makes hay much less desirable and palatable to livestock, but the real concern is the possible presence of mycotoxins, which are created by some fungal molds.

            “Hay can be unfit for livestock due to excessive moisture while baling or exposure to the elements. Molds present in feed may contain mycotoxins, which can cause significant health issues,” says Oklahoma State University (OSU) Cooperative Extension Equine Specialist Dr. Kris Hiney. “While only some molds produce mycotoxins, these are visually unable to be differentiated, and the presence of mycotoxins is difficult to assess.”

            Both Schick and Hiney note consuming contaminated feeds can cause liver and kidney damage, neurological disorders, abortions and estrogenic effects in livestock. While mycotoxins may not always cause clinical disease, the two experts further note they can interact with animal stressors to decrease efficiency and reproduction and increase incidence of disease.

            “Respiratory problems can also be seen,” says Schick.

            Hiney explains a particular mycotoxin, A. fumigatus, is found more frequently in hay, and animals consuming contaminated hay may exhibit symptoms similar to those of protein deficiencies or malnutrition, including poor hair coat, immunodeficiency and poor performance.

            Ochratoxin, another concerning mycotoxin, is typically associated with death in young calves and has been associated with mature cattle deaths and abortions, according to Hiney.

Livestock risk

            “It is important for producers of all forage consuming species, including cattle, sheep, goats and horses, to carefully monitor animal performance when wet weather conditions increase, feeding old hay or feeding hay bought from a wet area,” Hiney says.  

            Hiney and Schick agree while mycotoxins are a threat to all livestock species, special care should be taken with horses.

            “Horse owners should be more vigilant when feeding moldy hay compared to cattle, sheep and goats, as horses are much more susceptible to mold effects than other livestock,” Hiney explains. 

Feeding moldy hay

            In some instances, feeding moldy hay is inevitable. In these cases, producers need to be diligent in observing animal behavior, paying close attention to signs of mycotoxin consumption.

            “If producers have moldy hay they have to use, they need to reduce the risk when fed,” states Schick. “Feed the hay to less susceptible animals such as steers and open cows. Take special care with horses.”

            “Diluting moldy hay by feeding it with good hay is an option,” he continues. “Grinding can be another option, but may eliminate an animal’s refusal to eat bad hay, increasing the risk of severe issues brought about by mycotoxin consumption. For hay of particular concern, roll out the bale and let animals pick out the good parts.” 

            “If moldy hay must be fed, it is important to feed in a well-ventilated area,” adds Hiney. “This is especially true for horses, which are typically fed in more confined areas such as stalls and barns. Mold spores and dust can cause significant respiratory disorders.”

            “More importantly, moldy forage may decrease intake due to its decreased palatability, further reducing performance efficiency,” Hiney says. “Don’t force animals to consume hay by withholding alternative feed stuffs.” 

            Additionally, Hiney suggests sending hay samples to a diagnostics lab for mold spore counts and mycotoxin and nutrient testing.

            “Unfortunately, mycotoxins are not easily verified, as their distribution in feed may be highly variable,” Hiney says. “Samples must be handled carefully prior to analysis. Visual appraisal may not be useful for producers, and the use of black lights is not encouraged as a detection methodology.” 

            She continues, “If the presence of mycotoxins is unable to be verified, producers should carefully monitor herd health regarding reproductive efficiency, feed utilization, gain and overall health status.”

            Hannah Bugas is the editor of the Wyoming Livestock Roundup. Send comments on this article to

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