Mycotoxins are poisons produced by molds and occur frequently in a variety of feedstuffs. The high frequency of occurrence as well as the concentrations suggest that mycotoxins are routinely consumed by dairy cattle, causing subclinical symptoms which result in production losses. In fact, it may be more likely for cattle to consume contaminated feeds than clean feeds. Mycotoxins are most often found at low levels which may result in subclinical decreases in milk production, increases in disease incidence and severity, and decreases in reproductive performance. In some cases, mycotoxin concentration in feedstuffs is high enough to cause more severe problems. The effects on the cow are dependent on the level of mycotoxin in the diet, the duration of feeding, and the interaction of the mycotoxin with other mycotoxins or stresses that may activate or accentuate these responses. Such stresses may include disease, calving stress, heat stress, nutritional deficiency or excess, acidosis, and production stress.

There are more than 400 different known mycotoxins. Aflatoxin (AF), deoxynivalenol (DON), zearalenone (ZEN), T-2 toxin (T-2), and fumonisin (FB) are of greatest concern in animal agriculture. The presence of these mycotoxins is checked more frequently because they are the most commonly occurring mycotoxins associated with production losses. The presence of DON, ZEN, T-2, and FB may also be indicative of the presence of other Fusarium produced mycotoxins and in that way serve as markers for feeds contaminated with an array of Fusarium produced mycotoxins. Some other mycotoxins may be more toxic, but are less likely to be encountered. The lack of simple and inexpensive analytical methods limits the routine analyses of other mycotoxins, although screens for a larger array of mycotoxins are available.

Mold growth and mycotoxin production are related to:

• Weather extremes (causing plant stress or excess hydration of stored feedstuffs).

• Inadequate storage practices.

• Low feedstuff quality.

• Faulty feeding conditions.

Molds can grow and mycotoxins can be produced pre-harvest or during storage, processing, or feeding. The Fusarium species are generally considered to be field fungi and may be more likely to proliferate prior to storage. Since both Aspergillus and Penicillium grow at low water activities, they are considered to be storage fungi. Aspergillus species are more likely to grow in warm climates, while Fusarium and Penicillium species prefer cooler climates.

Following is a discussion pertaining to frequently occurring molds that have been associated with mycotoxicosis in dairy cows.

Mold Species

Aspergillus Molds
Aflatoxin (AF) is produced primarily by Aspergillus flavus and is commonly found in the Southern U.S., but may occur in other regions in years when weather conditions are conducive. For example, in 1988 which was a drought year, 8% of Midwestern U.S. corn grain samples contained AF. Aspergillus flavus does not grow well in hay or silage; however, AF has been measured at levels as high as 5 ppm in forage. Concentrations of AF in corn silage and alfalfa are usually below 100 ppb. The FDA limits the level of AF in corn grain according to its intended use, which for lactating dairy cattle is 20 ppb. AF is excreted into milk in the form of aflatoxin M1 (AFM1) with residues approximately equal to 1.7% of the dietary level. The FDA limits AFM1 in milk to no more than 0.5 ppb.

Aflatoxin levels of 300 to 700 ppb are considered toxic for beef cattle. While weight gain has been reduced when cattle consume 700 ppb AF, cattle may still be affected at lower levels. At levels as low as 100 ppb, liver weights are increased. With lactating dairy cattle, concentrations above 100 ppb have produced numerous symptoms, including a decline in reproductive efficiency, birth of small weak calves, and a loss in milk production. As with other mycotoxins, impure AF provided from a culture is more damaging than equal amounts of the pure mycotoxin which makes it difficult to predict the effect of specific concentrations of mycotoxins.

Aspergillus fumigatus has been found in both hay and silage and can produce several toxins (fumitremorgens including fumigaclavine A and C). Animal symptoms include generalized deterioration typical of protein deficiency, malnutrition, diarrhea, irritability, abnormal behavior, retarded growth, histopathological changes in the liver and kidneys, and occasional death. Aspergillus versicolor produces sterigmatocystin which has been observed as a primary mycotoxin produced by Aspergillus on cereal grains in Western Canada. While it is thought to be infrequent at toxic levels in the U.S., it has been associated with bloody diarrhea and cow deaths in a field case in Tennessee.

Aspergillus ochraceus has been implicated as producing ochratoxin that was associated with abortions in cattle consuming moldy alfalfa hay. Ochratoxin is also produced by Penicillium molds.

Fusarium Molds
Fumonisin B1 (FB1) was isolated in1988 and has been shown to be a cancer promoter. Fumonisin B1 causes leukoencephalomalacia in horses, pulmonary edema in swine, and hepatoxicity in rats. Fumonisin B1 occurs frequently and primarily in corn grain. A survey by the USDA found about 7% of the1995 crop corn sampled from Missouri, Iowa, and Illinois contained more than 5 ppm FB1. While FB1 is much less potent in ruminants than monogastrics, it is known to be toxic to sheep, beef cattle, and dairy cattle if fed at high concentrations. Mild liver damage has been seen in beef calves consuming 148 ppm of FB1 for 31 days, but with no significant affect on feed intake or weight gain. Studies at North Carolina State have shown FB1 toxicity in dairy cattle. Fed for approximately seven days prior to freshening and for 70 days thereafter, dietary FB1 at 100 ppm significantly and dramatically reduced dry matter intake and milk production (16 lb/cow/day) and increased serum enzymes which are indicative of liver disease. While more definitive information is needed on mycotoxin destruction in the rumen, the meager data which are available suggest that only 10% of fumonisin may be destroyed in the rumen. FB1 carryover from feed to milk is thought to be negligible and only trace amounts have been detected in milk.

Deoxynivalenol (DON) is the proper name for a commonly detected Fusarium produced mycotoxin that is often referred to as vomitoxin. DON is thought to be a primary mycotoxin associated with swine problems including feed refusals, diarrhea, emesis, reproductive failure, and deaths; however, it appears that the presence of fusaric acid greatly enhances these symptoms. DON may serve as a marker for problem feeds. It has been noted that DON provided from naturally contaminated feeds produced more severe symptoms in swine than does the pure mycotoxin added to feeds at similar levels.

In controlled research studies with dairy cattle, DON has been associated with reduced feed intake, less weight gain, lower milk fat test, but not statistically with milk production losses. Although fat corrected milk production has been reduced by about 13%, there have not been enough cows in such studies to demonstrate statistical relationships. North Carolina State clinical studies have shown a significant association of reduced milk production with DON. Field observations by others help substantiate that DON is associated with losses in milk production; however, some work has failed to see effects of DON on dairy cattle consuming up to 14 ppm on a short-term basis. Beef and sheep appear to tolerate relatively large amounts (up to 20 ppm) of DON without obvious deleterious effects.

In 1982 the FDA issued an advisory which recommended a level of concern for DON at 1 ppm in finished wheat products for human consumption, 2 ppm for wheat entering the milling process, and 4 ppm for wheat byproducts used in animal feeds. This advisory was updated in 1993 to 1 ppm in finished wheat products for human consumption; and for grains and grain products to 5 ppm for swine not to exceed 20% of the diet; 10 ppm for poultry and ruminating beef and feedlot cattle older than four months not to exceed 50% of their diets; and 5 ppm for all other animals not to exceed 40% of their diets.

Zearalenone (ZEN) is a Fusarium produced mycotoxin that elicits an estrogenic response in monogastrics. Zearalenone is much less toxic to ruminants than to monogastrics probably because ZEN is rapidly detoxified in the rumen. Ruminal degradation of ZEN has been estimated to be 30% within 48 hours, suggesting that some of the parent compound passes the rumen intact.

Controlled research with ZEN has resulted in some very different observed effects than when the toxicity has been observed in the field. In controlled studies, cows fed up to 22 ppm ZEN showed no major effects except that corpora lutea were smaller in treated cows. In heifers, conception rate has been significantly reduced with the consumption of 13 ppm of ZEN. Several case reports have related ZEN to an estrogenic response in ruminants. Symptoms have included abortions, vaginitis, increased vaginal secretions, poor reproductive performance, and mammary gland enlargement of virgin heifers.

In combination with low levels of DON (500 ppb), ZEN at 750 ppb has been associated with poor feed consumption, depressed milk production, diarrhea, and total reproductive failure. Work in New Zealand has related low levels of ZEN (< 1 ppm) to reproductive disorders in sheep and dairy cattle.

Symptoms in sheep included lower conception, reduced ovulation, and increased twinning rates. In dairy cattle herds, zearalenone at about 400 ppb has been related to low fertility and anestrus.

T-2 toxin (T-2) is a very potent Fusarium produced mycotoxin. Data with cattle are limited, but the toxicity of T-2 in laboratory animals is well documented. In cattle, T-2 has been associated with gastroenteritis, intestinal hemorrhages, gastrointestinal lesions, feed refusal, poor production, and death. A hemorrhagic syndrome is not always seen. In calves, serum immunoglobulins, complement proteins, white blood cells, and neutrophil counts may be lowered. Calves may also have severe depression, hindquarter ataxia, knuckling of the rear feet, listlessness, and anorexia.

In the field, T-2 has been associated with milk production losses. In one case, milk production was reduced in excess of 15% in association with T-2 at 350 ppb. Production losses coincided with diarrhea. At similar levels in other herds, we have associated T-2 toxin with an increased incidence of disease in early lactation, poor adjustment of fresh cows to the lactation ration, excessive weight loss, increased death loss, and a loss in milk production. Diacetoxyscirpenol is a Fusarium produced mycotoxin. It may occur along with T-2 toxin and is thought to cause similar symptoms of toxicity.

Penicillium Molds
Ochratoxin is produced primarily by a Penicillium mold, but is also produced by certain Aspergillus molds. Ochratoxin has been reported to affect cattle, but it has been shown to be rapidly degraded in the rumen and thus thought to be of little consequence unless consumed by young pre-ruminant calves. In some cases, ochratoxin has been found in the milk of dairy cows suggesting that some of the ochratoxin must escape the rumen undegraded. It is thought that high-concentrate diets which reduce rumen pH and reduce numbers of viable protozoa will reduce ruminal degradation of mycotoxins, including ochratoxin.

Patulin is produced by Penicillium, Aspergillus, and Byssochlamys molds. Patulin has been incriminated as a possible silage toxin in Europe and New Zealand.

PR toxin, produced by Penicillium roquefortii, has been found in silage and has been suspected of causing abortion and retained placenta in field observations.

Penicillium or Aspergillus molds growing on sweet clover or sweet vernal grass can cause a conversion of natural compounds in the plant to dicoumarol. Dicoumarol interferes with the function of vitamin K, resulting in a hemorrhagic syndrome.

Other Molds
While it is thought that other mycotoxins affect ruminants, lack of information prevents conclusions to be drawn regarding species and symptoms. Stachybotrys toxicosis has been observed in some countries when mold occurs on hay and straw, but it is thought to be rarely associated with dairy cattle problems in the U.S. This mold was associated with deaths of thousands of horses in Russia during the 1930’s. The mold produces a large number of spores, resulting in sooty black spots on the forage.

Mold Growth and Mycotoxin
Formation Molds are fungi which grow in multicellular colonies, as compared with yeasts which are single cellular fungi. They grow over a temperature range of 50-104°F, a pH range of 4 to 8, and above 70% humidity. Molds can grow when moisture exceeds about 12% to 13%. Higher moisture levels support mold growth up to the point where water excludes adequate oxygen. Almost all molds are aerobic (require presence of oxygen to survive). Molds can grow on a dry surface, while yeasts require a moist surface or water layer.

The Aspergillus species grow at lower water activities and at higher temperatures than do the Fusarium species, which require higher water activities and grow at much lower temperatures. Aspergillus flavus growth is favored by heat and drought stress associated with warmer climates. Most mold growth is enhanced by insect damage before and after harvest. Penicillium species grow at relatively low water activities and low temperatures and are fairly widespread in occurrence. Fusarium molds commonly affect corn and small grains. In corn,

Fusarium molds are associated with ear rot and stalk rot. In small grains, they are associated with diseases such as head blight (scab). In wheat, excess moisture at flowering and afterward is associated with an increased incidence of mycotoxin formation. In corn, Fusarium diseases are more commonly associated with insect damage, warm conditions at silking, and wet conditions late in the growing season.

The conditions most suitable for mold growth may not be the optimum conditions for mycotoxin formation. Mycotoxins may be produced when the mold is stressed. For example, some Fusarium molds which produce T-2 have been reported to grow prolifically at temperatures of 77 to 86°F without producing much mycotoxin, but at near freezing temperatures, large quantities of mycotoxins are produced without much mold growth. Field applications of fungicides may reduce mold growth and reduce production of mycotoxins; however, the stress or shock of the fungicide to the mold organism can also increase mycotoxin production. In a like manner, mold inhibitors added to a feed after mold growth has started, can induce mycotoxin production.

The primary storage methods for forages are drying (hay) and ensiling (silage). These methods of storage utilize the principles that growth of undesirable organisms is retarded in hay by low moisture content and in silage by a low pH and absence of air. In poorly stored forages, molds are potential spoilage organisms, which not only cause deterioration but can also produce mycotoxins. Therefore, maintaining proper preservative conditions are critical for ensuring quality forages.

Mycotoxin Effects
Mycotoxins exert their effects through three primary mechanisms:

• Alteration in feed nutrient content, nutrient absorption, and nutrient metabolism.

• Effects on the endocrine system.

• Suppression of the immune system.

Mycotoxins can increase the incidence of disease and reduce production efficiency. Symptoms are often general and may be the result of a cascade of events which makes diagnosis difficult. Diagnosis is complicated by a lack of research, especially with dairy cattle, by nonspecific symptoms, by interactions with other stress factors, and by the lack of feed analyses. Regardless of the difficulty of diagnosis, mycotoxins should be considered as a possible cause of production and health problems in the dairy herd. A process of elimination of other factors, coupled with feed analyses and responses to treatments can help identify a mycotoxin problem.

Dairy herds experiencing a mycotoxicosis that is severe enough to reduce milk production will usually display other symptoms. Deoxynivalenol, T-2 toxin, and fumonisin may result in digestive disorders while zearalenone is more likely to be associated with reproductive problems. Because of possible interactions with opportunistic diseases, symptoms may be general and variable. Symptoms may include some of the following: intermittent diarrhea, reduced feed intake, feed refusal, unthriftiness, rough hair coat, undernourished appearance, subnormal production, increased abortions or embryonic mortalities, silent heats, irregular estrus cycle, expression of estrus in pregnant cows, and decreased conception rates. Fresh cows under the stress of calving may show the most pronounced symptoms. There may be a higher incidence of displaced abomasum, ketosis, retained placenta, metritis, mastitis, and fatty livers. Cows may not respond well to typical veterinary therapy. A definitive diagnosis cannot be made directly from symptoms, specific tissue damage, or even feed analyses; however, experience with mycotoxin affected herds may increase the probability of recognizing a problem.

Mycotoxin Testing
Mold spore counts may not be very useful and are only a gross indication of the potential for toxicity. Mold identification can be useful to suggest which mycotoxins may be present. Analytical techniques for mycotoxins are improving, with a reduction in cost and a decrease in turnaround time. Testing feeds for DON, ZEN, and T-2, is recommended and their presence may be an indication of contamination with an array of Fusarium produced mycotoxins. Feeds should be tested for other mycotoxins if symptoms suggest specific mycotoxins. Aflatoxin should be analyzed if the feed is produced in a warm and humid environment.

Collection and handling of representative feed samples are a problem. Since molds grow in spots, mycotoxins are not uniformly distributed within a feed, which makes it difficult to obtain a representative sample. This is further complicated if the feed is a whole seed or coarsely ground or chopped. Obtaining representative samples of hay and silage is extremely difficult. Best samples may be taken from a lot of feed that has been recently blended, otherwise many sub-samples should be taken and composited. Once collected, samples should be handled properly to prevent further mold growth in the sample container. Wet samples may be frozen or dried prior to shipment and time in transit should be minimized.

Prevention and Treatment
Dry matter loss during hay storage can be huge, especially for large round bales stored unwrapped and without shelter in the Eastern U.S. Heat tolerant molds account for much of the spoilage occurring in wet hay. With excessive moisture (>20%) molds can grow prolifically, dry matter and nutrient losses can be large, and heating can be significant. Large bales that are not properly protected may have spoilage in the outer four to eight inches, and sometimes with browning throughout the bale. General recommendations suggest that large round bales should contain no more than 18% moisture, large rectangular bales <16% moisture, and small rectangular bales <20% moisture. Even at these levels of moisture, some mold growth can occur if moisture levels remain high for an extended period of time, or if spots of higher moisture are present. Preferably, hay should be protected from rain and stacked off the ground. Preservatives may also be used to help prevent mold growth.

In silage, molds may grow during the early aerobic phase, but as the oxygen is depleted and the lactic acid producing anaerobes prevail, pH and oxygen levels become too low for mold growth to continue. Some mold growth may continue near the silo surfaces, that are exposed to air and in air pockets within the silage mass. A dry silage (>35% dry matter) is more prone to mold growth than is a wet silage (<30% dry matter). A wet silage has less air infiltration and is more likely to support production of butyric acid, which contributes to aerobic stability and retards mold growth. A dry silage may allow more air to infiltrate, resulting in a prolonged aerobic phase, less production of lactic acid, and a higher final pH.

After the primary fermentation phase, continued air infiltration and a higher than optimum pH may allow renewed aerobic activity and depletion of organic acids. Acid tolerant yeast may proliferate if silage with adequate residual sugars is exposed to air. In this case, yeast will utilize lactic acid and then raise the pH enough for molds to grow. High yeast counts in excess of 10⁵ organisms per gram, may be indicative of aerobic instability. Other organisms also contribute to aerobic instability.

Molds may be especially prolific within areas of the silage where air is allowed to infiltrate. Problems may occur in all types of silos, for example in tower silos that may have poorly fitting doors, in bag silage where the silage is not tightly packed or plastic is not properly sealed or maintained, and in horizontal silos not properly packed or sealed. Once the silo is opened, the feeding face of the silage becomes aerated. Oxygen can penetrate to a depth of two feet within a day. Therefore, it is important that silage be fed at a rate which allows exposed silage on the feeding face to be fed before excessive deterioration occurs.

Recommended feeding rates vary from four to twelve inches daily with the higher feeding rates recommended in warm weather. Horizontal silos offer a special challenge. Large horizontal silos may have feeding faces too large to allow for a feeding rate sufficient to prevent deterioration. In this case, preservatives such as propionic acid may be used on the feeding face to reduce daily deterioration and mold growth. The feeding face should be disturbed as little as possible and that silage which is removed should be fed soon after removal. Fissures opened when the loader bucket is raised against the feeding face can introduce air to a depth of several feet; therefore, the silage should be cut with a downward motion. Dry matter loss in horizontal silos is twice as great when using a front-end loader in comparison to a block cutter.

Excessive heating in the feed bunk is an indication of unstable silage and deterioration. Practices to reduce deterioration and heating in the feed bunk include, immediate feeding of silage after unloading, use of propionic acid on the silage or TMR at feeding, increasing the frequency of feeding, and properly cleaning and maintaining feed bunks.

Some additives may be beneficial in reducing mycotoxins because they are effective in reducing mold growth. Short-chain fatty acids, such as propionic acid, are excellent mold inhibitors and are used on high-moisture grains, “at risk” grains, silage, and on hay to reduce mold growth and mycotoxin formation. Ammoniation of grains can destroy some mycotoxins, but there is no practical method to detoxify affected forages already in storage. In silage, ammonia, propionic acid, microbial, and enzymatic silage additives have all shown some effectiveness as mold inhibitors. Additives to enhance fermentation may be added at ensiling. Mold growth inhibitors, such as propionic acid, may be helpful as a surface treatment when capping off the silo or daily after silage feedout to reduce molding of the exposed silage-feeding surface. If unacceptably high levels of mycotoxins occur, dilution or removal of the contaminated feed is preferable; however, it is usually impossible to completely replace major forage ingredients. While dilution is sometimes a viable practice to reduce mycotoxin exposure to the cow, reduced silage feeding rate could increase mycotoxin concentrations because silage is exposed to oxygen for a longer time period.

When mycotoxins are known to be in the feed and the feed must be used, certain practices can reduce the effects of mycotoxins. Increasing nutrients such as protein, energy, and antioxidant nutrients may be advisable. Dietary additions of sorbent materials, such as clays (bentonites), activated charcoal, and esterified glucomannans, have helped reduce the effects of mycotoxins. These sorbent materials bind with the mycotoxins in feed and prevent digestive absorption by the animal. In most cases, clay has been added to the diet at about 1%, activated carbon at 1% to 2% of the diet, and glucomannans at 0.05% of the diet. Results may depend on the specific mycotoxin(s) and level(s) in the diet, the interaction with other factors, and the type and amount of sorbent used. Using aflatoxin as a model and based on the carryover of aflatoxin to milk, we have estimated the more effective products may bind as much as 60 to 65% of the mycotoxin consumed.

Summary
Mycotoxins are frequently found in grain and forages at low levels causing subclinical losses in performance. Sometimes concentrations of mycotoxins are encountered in feeds which are high enough to cause severe performance and health problems. Although, mycotoxicosis is difficult to diagnose, mycotoxins should be considered as a possible causative factor when unidentified problems exist. Methods for detection of mycotoxins have improved in accuracy and cost. To help reduce production losses, certain feed additives can be used to reduce mycotoxin exposure to dairy cattle when a known mycotoxin exists in the feed supply. While the potential for effective treatments has improved, prevention practices should be the primary management tool used to minimize mycotoxicosis.

If mycotoxicosis is suspected, check with your local ADM Alliance Nutrition Dairy Specialist for recommendations on the alleviation of symptoms.