Aspergillosis in Cows: Respiratory and Abortion-Related Fungal Infection

Aspergillosis is a fungal infection caused by Aspergillus species, most commonly Aspergillus fumigatus. These molds are widespread in soil, decaying plant material, hay, silage, bedding, and barn dust. In cattle, the disease is usually opportunistic, meaning infection is more likely after heavy mold exposure or when normal defenses in the respiratory or digestive tract are overwhelmed.

In cows, aspergillosis is most often discussed as a cause of mycotic abortion rather than a classic herd-wide respiratory outbreak. The fungus is thought to enter through the oral or respiratory tract, spread through the bloodstream, and localize in the placenta. This can lead to severe placentitis and abortion, usually in the second half of pregnancy, often from about 4 months to term.

Respiratory aspergillosis can also occur, especially when cattle inhale large numbers of spores from moldy forage or dusty, poorly ventilated environments. Signs may include cough, increased breathing effort, fever, and reduced feed intake. Because these signs overlap with bacterial pneumonia, viral respiratory disease, and other causes of abortion, your vet usually needs lab testing to confirm the diagnosis.

Aspergillosis is caused by exposure to Aspergillus fungal spores in the environment. These molds thrive in decaying organic material and are commonly associated with moldy hay, spoiled silage, damp bedding, dusty barns, and poorly stored feed. Cattle are exposed by inhaling spores or ingesting contaminated material.

In abortion cases, the fungus is believed to enter through the respiratory or digestive tract and then spread through the bloodstream to the uterus and placenta. The placenta becomes severely inflamed and damaged, which can cut off support to the fetus. Merck notes that Aspergillus species account for a large share of bovine mycotic abortions, with septate fungi such as Aspergillus involved in roughly 60% to 80% of cases in this category.

Risk goes up when pregnant cows are housed in damp, poorly ventilated areas or fed visibly moldy forage. Sudden use of poor-quality stored feed during winter can also increase exposure. Not every exposed cow becomes sick, so herd management, spore load, pregnancy status, and overall health all matter.

Your vet usually diagnoses bovine aspergillosis by combining the history, exam findings, and laboratory testing of the fetus and placenta. In abortion cases, the placenta is especially important because fungal lesions are often most obvious there. Merck describes diagnosis based on finding fungal hyphae associated with necrotizing placentitis, dermatitis, or pneumonia, with confirmation through culture, histopathology, or direct examination of placental tissues.

If possible, your vet may recommend submitting the entire fetus and placenta to a veterinary diagnostic lab. Useful samples can include placenta, fetal stomach contents, lung, skin lesions, and other tissues. This matters because fungi can contaminate tissues after abortion, so culture results need to be interpreted alongside microscopic lesions rather than used alone.

For respiratory disease, diagnosis may involve a farm exam, lung evaluation, response history, and selected testing to rule out more common causes of pneumonia. Your vet may also investigate feed and bedding quality, ventilation, and whether other cows have aborted or developed respiratory signs. A careful workup helps separate aspergillosis from listeriosis, leptospirosis, neosporosis, IBR, and other important differentials.

Prevention focuses on reducing mold exposure, especially for pregnant cows. Avoid feeding visibly moldy hay, spoiled silage, or damp byproducts. Store forage correctly, protect bales from moisture damage, and discard feed that smells musty, heats excessively, or shows deep mold growth. Clean, dry bedding and good barn ventilation also help reduce airborne spore load.

Pregnant cows deserve extra attention because bovine mycotic abortion is often linked to fungal exposure from feed or the environment. If an abortion occurs, remove and contain the fetus and placenta promptly, clean the area, and ask your vet whether additional biosecurity steps are needed while test results are pending. Even though aspergillosis itself is usually considered sporadic rather than highly contagious, other abortion causes can spread within a herd or pose human health concerns.

A practical prevention plan may include routine forage inspection, better storage practices, reduced dust, and quick correction of leaks or damp housing. If several cows abort or respiratory signs appear after a feed change, involve your vet early. Early investigation can protect the rest of the herd and help you avoid ongoing losses.