With the harvest behind us, some producers, nutritionists and veterinarians may think their bumper crop and supply of feed went unscathed from the initial reports of possible molds and mycotoxins in this year’s moist yield.

However, while the crop can look completely clean to the naked eye, the potential for mycotoxins is still there.

Mycotoxins are harmful compounds produced by molds or fungi. They are found in soil and can grow on vegetable matter such as grains, forages and silages. Molds and mycotoxin production can occur in the field pre-harvest, during harvest and post-harvest.

While ruminant animals are the most resistant (due to the rumen microorganisms capable of degrading mycotoxins before they ever enter the bloodstream), there can still be harmful consequences. Adverse effects such as reduced feed intake, reduced nutrient utilization, altered rumen fermentation, suppressed immunity, altered reproduction, tissue irritation and cell death have been reported in dairy cows affected by mycotoxin contamination.

The Fusarium problem

One family of mycotoxins that producers should be more attentive to is the Fusarium toxins. While Fusarium molds normally thrive in temperate climates and are more common in the Cornbelt and Southern Canada, mycotoxins produced by this species can make its way south and to both coasts through interstate commerce.

Fusarium mycotoxins are broadly classified into trichothecene and non-trichothecene groups. More than 100 trichothecene mycotoxins have been chemically identified. The most common is DON which is also known by the chemical name deoxynivalenol and sometimes referred to as vomitoxin. DON and the other trichothecenes affect dairy cows in three ways:

• Influencing behavior, causing reduced feed intake that results in reduced milk production.
• Causing bleeding and ulcers in the digestive tract, resulting in reduced nutrient absorption.
• Causing immunosuppression and greater susceptibility to diseases, including mastitis and higher somatic cell counts in milk.

With research continuing each year, scientists are finding more and more harmful effects that can be linked to the Fusarium mycotoxins. According to the 2007 Journal of Dairy Science article by Korosteleva, Smith and Boermans, feeding a combination of Fusarium mycotoxins in naturally contaminated feed can increase the immunosuppression and reduce the utilization of nitrogen. This study consisted of 18 mid-lactation Holstein dairy cows (six cows per diet) fed TMR containing naturally-contaminated corn, wheat, hay and silage with 3.6 ppm DON for 56 days. Bodyweight, milk production, somatic cell count, blood chemistry, hematology and immunoglobulin were measured.

The results of the study showed that dry matter intake and bodyweight, as well as milk production, milk composition, and SCC, were not affected by diet. However, total serum protein and globulin levels increased significantly in cows fed the contaminated TMR as compared to cows fed the control diet, whereas the albumin:globulin ratio decreased. Serum urea concentrations were significantly elevated throughout the experiment in cows fed the contaminated diet compared with those fed the control diet. Serum IgA concentrations decreased significantly in cows fed the contaminated TMR. It was concluded that Fusarium mycotoxins can alter protein metabolism and intestinal immunity in dairy cows.

Korosteleva, Smith and Boermans further continued their research to study some of the immune functions in detail (Korosteleva et al., 2009). The experimental details were the same as Korosteleva et al. (2007) with around 3.5 ppm DON. The immune parameters included specific antibody response to ovalbumin and neutrophil phagocytosis. Feeding of contaminated grains significantly reduced neutrophil phagocytosis, but increased primary antibody response to ovalbumin (Table 1).

Neutrophils serve as phagocytes and play an important role in nonspecific immunity. Depending on the concentrations of Fusarium mycotoxins, they either stimulate or suppress antibody-mediated immunity.

The results from both the studies concluded that feed naturally contaminated with Fusarium mycotoxins can adversely affect metabolic and immune parameters of dairy cows. The greatest cost arising from feeding these materials is reduced disease resistance, failure of vaccination programs and lack of response to medications.

The Penicillium problem

A recent survey of molds and mycotoxins in corn silage, alfalfa haylage and hay has shown that TMR can be contaminated to varying degree with Penicillium molds and mycotoxins. Due to the lack of commercial facilities to analyze Penicillium mycotoxins, much of the emphasis has been made on mold count and identification. Penicillium mycotoxins can harm rumen micro organisms, thereby affecting fiber digestion (Tapia et al., 2002, 2005).

In Korosteleva et al. (2007, 2009), cows in both control and mycotoxin groups were fed the same corn silage and hay produced under the University-controlled conditions. In the field conditions, the quality of these ingredients can vary considerably and therefore, the presence of Penicillium mycotoxins along with Fusarium mycotoxins may also reduce the performance parameters, such as milk production and milk composition, along with metabolic and immune parameters. More studies are needed wherein all the sources of mycotoxins are evaluated.

Synergistic effects

A further problem is that mycotoxins are never found in isolation. The mycotoxin mentioned above and much more can be present together in the feed ingredients and complete feed. When they are present together, they exert additive or synergistic interactions and cause significant adverse effects on livestock and poultry. DON has been shown to interact with T-2 toxin, and fusaric acid, while fumonisins interact with T-2 toxin and diacetoxyscirpenol (Devegowda and Murthy, 2005).

Mycotoxin tactics

Some strategies for preventing mycotoxicoses in our herds include:

• Dilution with non-contaminated feed
• Diversion to less susceptible species
• Processing methods such as cleaning and sorting
• Use of mold inhibitors, such as proprionic acid, and silage inoculants while storing grains and TMR
• Use of mycotoxin adsorbents in TMR

Adsorbents

When all possible preventative measures have been taken, the use of adsorbents is the final chance of preventing the mycotoxin negatively impacting animal health and productivity. Much work has been done in this area with both inorganic and organic adsorbents. Inorganic adsorbents such as clays and zeolites have been shown to bind aflatoxin efficiently; however they have shown to have little effect on other types of mycotoxins and are also required to be fed at relatively high feeding rates.

Organic binders have been shown to be more efficient against a wider range of mycotoxins than inorganic binders, which has been seen to be positive given the wide range of toxins that can contaminate a single feed. Recent work by Alexandros Yiannikouris has demonstrated that the glucan fraction of yeast cell wall is directly involved with the adsorption of mycotoxins and that this adsorption is stable throughout the pH range of the digestive tract. Yeast cell wall material also has the benefit of being fed at rates which are more conducive to feed formulation.

The only complete solution to the problems arising from mycotoxins in dairy feeds is to avoid the feeding of mycotoxin-contaminated feedstuffs, which may not be practical at all times. This is particularly true for 2010 as we will face the dilemma of using feed ingredients with higher mycotoxin contamination due to delayed harvesting. PD

References omitted due to space but are available upon request by e-mailing editor@progressivedairy.com.

Trevor Smith is a professor with theDepartment of Animal and Poultry Science at the University of Guelph. Email Trevor Smith.