Producers warned about the risks of feeding moldy hay to livestock
For many producers across the Cowboy State, the start of the new year is marked by cold, snowy mornings and/or afternoons pitching hay.
Following several consecutive summers of drought and less than ideal haying conditions, as well as a year of devastating wildfires, harvested forage may be in short supply or of poor quality.
Because of this, many experts are reminding producers about the risks associated with feeding moldy hay to livestock this winter.
Mold production
In a Dec. 29, 2024 article published in BEEF Magazine, Mississippi State University (MSU) Extension specialists note there are several ways hay may become moldy.
“Most hay can become moldy when it is baled too wet, left in the field for too long or stored outside in shaded areas where rain or humidity can slow down the drying process and increase the risk of mold,” the experts explain.
Additionally, forage cut and baled in dusty, dirty conditions or in areas where plants show signs of fungal disease may also contain spores which will germinate when exposed to moisture, while hay stored in tall stacks or ensiled at a high moisture content can also become moldy.
MSU notes spores from different mold species can germinate between 24 to 72 hours.
Dangers of moldy hay
While moldy hay is less desirable to livestock, experts note the real concern is the possibility of mycotoxins.
“Hay can be unfit for livestock due to excessive moisture while baling or exposure to the elements such as excessive rain or flooding. 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 in a 2019 OSU Extension publication. “While only some molds produce mycotoxins, these are visually unable to be differentiated, and the presence of mycotoxins is difficult to assess.”
The toxic compounds in mycotoxins can cause a long list of health effects in livestock, including feed refusal, low fertility, increased water consumption, poor hair coat, estrogenic effects, lameness, poor kidney or liver function, respiratory issues like pneumonia, diarrhea and colic in horses.
MSU notes cattle and small ruminants are generally less affected by moldy hay – except during pregnancy – since many mycotoxins can be broken down in the rumen. However, in some cases, these toxic compounds can cause abortion or aspergillosis.
“Lactating dairy cows should never be fed moldy feeds to avoid any trace of mycotoxins in milk,” MSU states. “Across all species, pregnant animals and young animals are at higher risk. Animals in poor condition are more likely to be affected by moldy hay.”
As cecal digesters, mycotoxins present the greatest risk to horses, which may contract Recurrent Airway Obstruction, more commonly known as heaves.
According to MSU, symptoms of heaves include coughing, nasal discharge and labored breathing.
Additionally, the experts note moldy hay may affect producers as well, presenting as a condition called “farmer’s lung,” where fungus grows in lung tissue after breathing in too many spores.
Feeding moldy hay
While avoiding feeding moldy hay is certainly the best way to minimize risk, this isn’t always possible.
Additionally, testing for the presence of mycotoxins in hay isn’t simple and requires a laboratory analysis.
“Visual appraisal – smell and color – might provide cues to determine mold severity but might not provide a complete picture, and the use of a black light is not the best method of detection and assessment,” MSU admits.
When examining hay, MSU encourages individuals to pay attention to the color and texture of mold, as some types may be of greater concern.
According to MSU, the most common types include Alternaria, which is dark green or wooly black; Aspergillus, which is powdery and yellow-green or white; Penicillium, which is fuzzy and green or blue; Cladosporium, which is olive green or black with a velvety texture; Claviceps, an umbrella-shaped mushroom containing a large number of alkaloids; Fusarium, which can come in shades of pink, red and purple and is wooly or cottony in texture; Mucor, which is white, beige or grey and fast-growing and Rhizopus, which is black and highly toxic to horses.
“These molds can produce mycotoxins which can be harmful to animals if ingested in large quantities,” MSU writes. “Members of the genera Alternaria, Aspergillus, Fusarium and Penicillium produce mycotoxins which can cause direct toxicity or suppress the immune system, while the Mucor species do not produce mycotoxins, but in addition with some species of Aspergillus, can cause mycotic abortion in cattle.”
If producers must feed moldy hay and the presence of mycotoxins is unable to be verified, experts encourage individuals to do so in a well-ventilated area and to closely monitor animal behavior and herd health.
“Moldy hay becomes less palatable, which can result in lower feed intake or higher animal refusal. Reduced feed intake can lead to poor weight gain, decreased milk production and diminished animal performance – more susceptible to health issues and nutritional deficiencies,” MSU Extension concludes. “Use commonsense and good observation as your best decision aids concerning feeding or testing moldy hay.”
Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
