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What’s hiding in your forages could be harming your cows

Annie Pelletier for Progressive Dairyman Published on 29 March 2019
Cows eating forage

Forage quality is one of the most important factors that determines the level of milk production and profitability of a dairy farm. Traditionally, forage quality has been defined by the nutrient content and digestibility of the nutrients in a forage.

Indeed, the crude protein, acid detergent fibre (ADF), neutral detergent fibre (NDF) and starch content of a forage are critical determinants in how much milk a forage will support.



Over the last several years, dairy producers have made great progress improving the quality of the forages they grow by paying close attention to plant genetics, harvesting crops at optimum maturity, soil fertility, storage, etc.

However, even with these advances in forage production, issues with inconsistent manure, milk quality, gut health, disease and even sudden death of cows still occur.

The presence of “anti-nutrients” or “anti-nutritional factors” in feeds and forages may be the cause of these problems.

Adegbola Adesogan, director of the Feed the Future Innovation Lab for Livestock Systems, University of Florida, defines anti-nutrients as “substances which, by themselves or through their metabolic products, interfere with food utilization and affect the health of production animals.”

John Goeser, director of research and innovation at Rock River Laboratory in Watertown, Wisconsin, has been investigating the impact of “anti-nutritional factors” that may contribute to poor performance of dairy cows.


In recent years, he has found the concentration of anti-nutrients such as yeasts, molds, mycotoxins and bacterial contaminants in feeds fed to dairy cattle to be trending upwards.

To troubleshoot the problem, it helps to understand what we know about these two types of anti-nutrients and their impact on dairy cattle.

Fungal contaminants

Fungal contaminants include yeasts (unicellular organisms) and molds (multicellular filaments) that may grow on the crop before it is harvested and during storage.

The presence of yeasts and molds reveals some deterioration or spoilage, which may be responsible for a loss of dry matter, a decrease in the nutrient content, as well as an accumulation of mycotoxins. They are not always visible or odourous, which makes them difficult to recognize.

Moldy feeds are less palatable, which often results in lower dry matter intake (DMI). This decrease in DMI leads to a drop in milk production and reduced income. A diet containing mold is often less digestible, and the energy content of the diet is lowered.

Molds grow at the expense of proteins, fats and carbohydrates, and can lead to health problems such as abortions or respiratory problems.


When mycotoxins are found in moldy feeds, the losses are even greater. Mycotoxins are harmful compounds produced by molds. Mycotoxicosis can occur when the cow consumes feed contaminated with mycotoxins.

Clinical symptoms include a decrease in DMI, intermittent diarrhea and other digestive disorders, poor general condition, rough coat, reproductive dysfunction, early embryonic mortality (irregular estrus) and a decrease in milk production and milk components.

Mycotoxins can suppress the animal’s immune system, which can lead to an increase in infectious diseases and mortality rates. Thus, opportunistic diseases such as salmonellosis, colibacillosis and necrotic enteritis may very well be at the origin of the clinical signs observed in the context of mycotoxicosis.

Molds and mycotoxins in the diet cause stress in the animal. This stress causes an increase in cortisol that decreases the ability of neutrophils (white blood cells) to migrate from the blood to tissues to kill pathogens.

Their presence may also interact with other stressors the animal is exposed to, resulting in even greater immune suppression.

Proper nutrition is necessary to help maintain the health of the immune system of dairy cows. When cows are stressed by the pressures of production and reproduction, by the presence of molds and mycotoxins, and by the contamination of the environment by pathogens, their immune system starts to fight these “enemies” and weaken.

Bacterial contaminants

The presence of pathogenic bacteria in feed and the potential of these bacteria to cause harm is a growing concern. Toxic bacteria in feed may result in poor performance and disease in cattle.

Pathogenic bacteria in feed can come from soil contamination during forage harvest, application of manure slurry or contaminated irrigation water to growing crops and dirty feeding equipment.

How to control fungal and bacterial contaminants

Prevention and treatment begin in the field by adopting good practices to reduce plant stress, such as the use of mold-resistant plant varieties, timely seeding, adequate tillage, soil fertilization, irrigation, control of insects, fungicides and harvest at the ideal time.

Mold growth and mycotoxin production can be further reduced through harvesting and storage practices that reduce levels of soil contamination (ash) and ensile to higher levels of dry matter, thus reducing risk of feed contamination.

Because molds and mycotoxins can be harmful to the gut and other body tissues, it’s easy to understand they can affect the production and efficiency of cows.

In this context, it is clear producers must adopt management practices that ensure the production of high-quality feeds and minimize the impact of molds and mycotoxins on their cows.

Regardless of the precautions taken at harvest, it is possible to avoid the presence of mycotoxins in high concentrations in the TMR. Given the amounts of hay, silage and grain produced, it is not realistic to discard all feeds that contain mycotoxins.

It is the amount of mycotoxins involved that will justify the importance of choosing the right mycotoxin mitigation strategy.

To limit the presence and effects of mycotoxins, the strategy should include treatments applied to feeds, such as inoculants and propionic acid, to reduce the amount of mycotoxins; use of adsorbents to avoid uptake by animals; immunomodulators to restore immune system function; and the addition of nutrients and incorporation of antioxidants into the TMR.

Reducing bacterial contamination of forages and feeds is likely the best way to prevent the diseases that result from pathogenic bacteria. Take care to avoid contamination of the crop by managing manure applications and irrigation water.

Tillage and harvest practices that reduce the presence of soil in forages may also be beneficial. Keeping feeding equipment clean and free from manure, dirt and other vectors of pathogenic bacteria is another way to help reduce the risk of disease.

The presence of yeast, molds, mycotoxins and pathogenic bacteria in feed and forage could reduce the health, productivity and performance of your herd.

When you consider what is involved in making high-quality forages, don’t overlook the potential impact of anti-nutritional factors.  end mark

PHOTO: Proper nutrition is necessary to help maintain the health of the immune system of dairy cows. Staff photo.

References omitted but are available upon request. Click here to email an editor.

Annie Pelletier
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Common anti-nutritional factors found in feed

Molds and yeasts

  • Aspergillus flavus and Aspergillus parasiticus are molds that can produce aflatoxin, a known carcinogen that can be transferred from feed to milk.

  • Aspergilllus fumigatus is a mold shown to cause disease in humans experiencing immunodeficiency and believed to be the cause of hemorrhagic bowel syndrome (HBS) in cattle. This mold invades and colonizes the respiratory or digestive tracts, then enters the bloodstream to spread to other tissues.

  • Fusarium is a common mold in the northern U.S. and Canada that can grow on crop residue between seasons and is tolerant of a wide range of growing conditions. Fusarium-specie molds can produce mycotoxins including vomitoxin, fumonisin and zearalenone. These fusariotoxins can be found in cereals, mainly corn harvested in grain or stored in silage, but also in grass silage.

  • Wild-type yeasts can grow during feed storage and after feedout. Wild yeasts utilize sugars and fermentation acids in the feed and may lower the amount of energy available to the cow. They may also disrupt the rumen and cause a suppression in milkfat test. In most cases, yeasts are responsible for heated silage.

Pathogenic bacteria

  • Salmonella spp.: A potent pathogen that can survive in the soil for several years. Salmonella can cause digestive upsets, diarrhea, dehydration, anorexia, decreased milk production and, in severe cases, death.

  • Enterobacteria: Can be quite pathogenic and has been implicated as causes of poor gut health and hemorrhaging.

  • Clostridia: Able to degrade proteins and also produce butyric acid. Consuming feed contaminated with clostridia may result in bloating or death.