By definition, molds are filamentous fungi that occur in feedstuffs, including roughages and concentrates. They date back to biblical times; however, molds have been gaining more attention in recent years due to their increased presence in feeds and their effects on dairy cattle.

Dr. Lon Whitlow, professor emeritus of North Carolina State University – Raleigh, recently spoke about mold and mycotoxins during his 2017 World Dairy Expo seminar, “Limiting Mold and Mycotoxins Problems in Dairy Herds.” Whitlow’s research on molds and mycotoxins has proven that “mycotoxins do occur routinely and do affect dairy cattle.”

Mold, by nature, is either toxic or nontoxic. Whitlow said about half to two-thirds of the molds seen on feeds are non-toxigenic. Nontoxic molds do not produce a poison and are not harmful to the animal. Examples of nontoxic molds include mucor, trichoderma, rhizopus and cladosporin. Mucor, in particular, is a white mold that can be seen in silage and sometimes on the outside of hay bales or wet grain.

Even though many of the molds are non-toxigenic, it is important to recognize and manage toxic molds due to their potency and their effects on dairy cattle.

“Toxic molds are important to dairy producers because they lower the performance of the herd, they cause poor health and they reduce profits,” Whitlow said.

Toxic molds include aspergillus, penicillium and fusarium. Each of these molds produce mycotoxins that are poisonous to the animal. Toxic molds are often associated with ear and stalk rot in corn, and head scab in small grains.

Toxic molds affect dairy cattle either through mycosis or mycotoxicosis. Mycosis is when the mold itself causes a fungal infection in the animal by infecting its skin, lungs (pneumonia), digestive tract, mammary gland or reproductive tract (fungal abortions).

“The fungal infection that a lot of people have heard about and maybe dealt with in more recent years has been hemorrhagic bowel syndrome [HBS],” Whitlow said. “This is where the mold, Aspergillus fumigatus, infects the lining of the gut and causes a hemorrhage, the formation of a blood clot and sudden death.” HBS involves not only mold, but mold and bacterial toxins.

Mycotoxicosis is a disorder where the poisonous effects of mycotoxins produced by the fungi affect the animal. There are hundreds of different mycotoxins, but some of the most common ones are: aflatoxin, gliotoxin, fumonisin, deoxynivalenol (DON), zearalenone, T-2, PR toxin, roquefortine C and mycophenolic acid.

“Aflatoxin is the ‘big one’ because it is carcinogenic and is secreted into milk,” Whitlow said. “Therefore, it is regulated by the FDA to very low levels; you cannot tolerate more than 20 parts per billion of aflatoxin in feed.”

Dairy cattle infected with mycotoxins can experience lower feed intake, production loss, ruminal and digestive upset, diarrhea, nervous disorders, organ damage, reproductive disorders, poor fresh cow transition or suppressed immunity.

“Mycotoxins have a big effect on the gut and on immunity,” Whitlow said. “The animal consuming contaminated feed is not going to have the ability to resist disease.”

A further problem is that mycotoxins are never found in isolation. In 2013, researchers studied 83 different feed samples from around the world where at least one mycotoxin was present. The results showed that, most commonly, each feed contained anywhere from 20 to 30 different mycotoxins.

“This shows that it is difficult to look at one toxin and say, ‘Well, this is the effect of that one toxin,’ because generally you have multiple mycotoxins that interact and cause symptoms to the dairy cow,” Whitlow said.

Occurrence

The occurrence of mycotoxins depends on the local situation as well as seasonal effects, weather and plant stress. During droughts, aflatoxin and fumonisin are more common, while DON, zearalenone and T-2 are more common during wet conditions.

“Historical incidents in your region are a good indicator that you may have a problem in the future,” Whitlow said. “Mold and mycotoxins vary from year to year, but overall, they have increased over the years.”

Environmental conditions conducive to the production of molds and mycotoxins include damage to feedstuffs, a pH between 4 and 8, temperatures between 40ºF to 110ºF, moisture greater than 13 to 15 percent, relative humidity greater than 70 percent, water activity greater than 0.75 and oxygen greater than 0.5 percent.

“Molds need a little bit of oxygen, but they don’t need a lot,” Whitlow said. “In many cases, there is enough oxygen in silage to get molds to grow.”

Spore distributions, plants lacking genetic resistance to fungal diseases, monoculture (corn on corn), minimum tillage, plant stress and a too mature or late harvest are all environmental factors that affect fungal growth.

In 2005, Penn State University compared corn grown with moldboard plowing, mixed tillage, minimum tillage and no till. The level of DON went up fourfold going from moldboard plowing to no tillage.

“We see more mycotoxins with no-till practices, and this is true for corn, wheat and small grains,” Whitlow said.

Prevention

Mold production can occur in the field preharvest, during harvest or during crop storage. Establishing prevention and treatment methods is helpful to lessen the effects mold and mycotoxins have on the animal.

Prevention methods include cropping management, proper harvest and storage of feeds, and the removal or dilution of contaminated feeds.

In terms of cropping management, it is best to use hybrids that are less susceptible to disease and insect damage. It is also important to minimize plant stress and to plant and harvest at proper times. Using products such as fungicides and non-toxigenic competitive molds is also effective.

“Fungicides are increasing in use, and data shows they are very effective,” Whitlow said. “They are expensive though, so you will want to look at cost benefit.” Control of fungi can reduce mycotoxins and increase crop yields.

Cotton production is utilizing non-toxigenic competitive molds. The non-toxigenic mold is sprayed on the crop, which inhibits the growth of the wild-type mold and therefore prevents mycotoxin production.

“Non-toxigenic competitive molds are also being used on peanuts, and it is moving into corn,” Whitlow said.

At harvest time, crops need to be harvested at the proper stage of maturity and moisture. Dry feeds, such as hay or grain, need to be harvested dry and kept dry. Grains, in particular, should be handled at less than 14 percent dry matter. Wet feeds, such as silage and byproducts, need to have good moisture control, which will exclude the air and allow for a good pack.

Proper feed storage management is also important. Grain bins need to have proper air movement to prevent moisture migration. The bins and storage sheds need to stay clean and dry. Moisture barriers on floors are also helpful as well as rotating inventory.

Acidifying wet and dry feeds with chemicals is also helpful in achieving proper pH levels in feed.

“Keep in mind that penicillium can still grow at a low pH in silage,” Whitlow said. “In the silo, a low pH will stop the growth of fusarium and aspergillus, but with a small amount of air, penicillium will continue to grow. Therefore, penicillium is one of the most prevalent toxigenic molds found in silage.”

Silages need to be packed well, have good moisture control and they need to be covered properly. “Oxygen-limiting plastics do a tremendous job of keeping the air out of silage,” Whitlow said. “Air is the enemy of silage.”

Silages should have 1 foot per day fed off of its feeding face. If mold is found, it is best to remove it and discard it, or in other situations, dilute it.

“Farmers do not throw away feed,” Whitlow said. “In these situations, it is best to dilute it and feed it to less susceptible animals, such as steers.”

Treatment

Diagnosing a mold problem can be tricky since some molds are not visible to the naked eye; however, if the cows are signaling that there is a problem with the feed, then it may be time to take a feed sample in for analysis or simply treat the cows.

Treatments – which will lessen the effects mold and mycotoxins have on the animal – include mold inhibitors, nutritive additives, antioxidants, rumen fermentation aids, immune modulator products and binders.

Whitlow said the two most important treatment products are immune modulator products and binders. Immune modulator products are based on yeast cell wall components, and research shows that, in the normal or stressed animal, you can improve immunity with these products.

“It takes four to six weeks to get the immunity level at the maximum, so you need to be feeding this in the dry cow group,” Whitlow said. “They will then be ready to resist any problems that they may encounter upon freshening.”

Examples of mycotoxin binders or adsorbents are silicate products, chemically treated silicates, carbon products, yeast derived products, chitin products and inorganic polymers or resins. These products grab and hold on to the mycotoxins and, during digestion, they prevent the animal from absorbing the mycotoxins.

“The FDA has not approved any mycotoxin binder products for this purpose, but there are a lot of these products being fed internationally,” Whitlow said. “Research shows that they can be effective.”  

Jenny Binversie is a freelance writer from Wisconsin.

PHOTO 1: Toxic molds include aspergillus, penicillium and fusarium. Each of these molds produce mycotoxins that are poisonous to the animal. Toxic molds are often associated with ear and stalk rot in corn, and head scab in small grains.

PHOTO 2: “We see more mycotoxins with no-till practices, and this is true for corn, wheat and small grains,” said Dr. Lon Whitlow, professor emeritus of North Carolina State University – Raleigh. Photos provided by Dr. Lon Whitlow.