Mycotoxicosis in Rabbits: Moldy Feed and Hay Poisoning

Mycotoxicosis is poisoning caused by mycotoxins, which are toxic compounds made by certain molds. These molds can grow on stored hay, pellets, grains, straw, or mixed feeds when moisture, warmth, and poor storage conditions allow fungal growth. In rabbits, the problem is not the mold alone. It is the toxin left behind in the feed, and that toxin may still be present even if the feed no longer looks obviously moldy.

Rabbits are especially vulnerable because they depend on steady food intake to keep the gut moving. When a rabbit eats contaminated feed, the toxin may irritate the digestive tract, damage the liver, suppress the immune system, or trigger appetite loss. Once a rabbit stops eating, GI stasis can develop within hours, which can quickly turn a toxic exposure into an emergency.

Different mycotoxins can cause different patterns of illness. Aflatoxins are best known for causing liver injury, while other mold toxins may lead to feed refusal, diarrhea, weakness, or poor growth. Because signs overlap with many other rabbit illnesses, your vet usually has to piece the diagnosis together from history, exam findings, lab work, and sometimes feed testing.

Mycotoxicosis happens when a rabbit eats feed contaminated with toxins produced by molds. Risk is highest with damp or poorly stored hay, pellets kept in humid areas, grain-based treats, straw bedding, or feed that has been stored too long. Warm temperatures, moisture, condensation, and poor airflow all make mold growth more likely.

Aflatoxins are among the best-known mycotoxins in animal feeds and are associated with liver damage. Other toxins from molds such as Fusarium or related fungi may cause feed refusal, digestive upset, or more general illness. One tricky part is that feed can contain toxin even when mold is not obvious, and contamination may occur in "hot spots" within a bag or bale rather than throughout the whole batch.

Rabbits may be at higher risk if they are young, stressed, already ill, pregnant, or eating a lower-fiber diet that makes the gut less resilient. In many homes, the trigger is not dramatic. It may be a new bale of hay, a bag of pellets stored in a garage, or feed exposed to humidity after opening.

Your vet will start with a careful history. That includes what your rabbit eats, when the current hay or pellet bag was opened, whether the feed smelled musty, and whether any other pets were exposed. Because mycotoxicosis can look like many other rabbit problems, diagnosis is often based on a combination of exposure history and supportive test results, not one single test.

A physical exam may show dehydration, abdominal discomfort, reduced gut sounds, low body temperature, jaundice, or signs of GI stasis. Your vet may recommend bloodwork to look for dehydration, electrolyte changes, and evidence of liver injury. X-rays can help rule out obstruction and assess gas buildup or stasis. In some cases, fecal testing or other diagnostics are used to look for competing causes such as parasites or infection.

If moldy feed is suspected, save a representative sample in a clean sealed bag. Feed testing can sometimes identify a specific toxin, but sampling is imperfect because contamination may be uneven. That means a negative feed test does not always rule out mycotoxicosis. In severe cases, diagnosis may become clearer through repeated bloodwork, response after feed removal, or necropsy findings if a rabbit dies despite treatment.

Prevention starts with storage. Keep hay and pellets in a cool, dry, well-ventilated area and off concrete floors where moisture can collect. Use breathable hay storage rather than sealed damp containers, and keep pellet bags tightly closed in a dry bin. Do not store rabbit feed in garages, sheds, or porches if humidity swings are common.

Check every new bag or bale before feeding. Hay should smell fresh, not musty or sour. Pellets should be dry and intact, not clumped, dusty, or discolored. Throw out any feed that looks damp, has visible mold, or has an off odor. Because toxins can exist even when mold is not obvious, it is wise to avoid old feed, buy manageable bag sizes, and rotate stock so nothing sits for months after opening.

A hay-based diet also helps protect rabbits by supporting normal gut movement. Offer unlimited good-quality grass hay, measured pellets, and rabbit-safe greens as advised by your vet. If your rabbit ever refuses food after a new batch of hay or pellets, stop that batch immediately and call your vet. Quick action can prevent a mild exposure from turning into a much more serious problem.