WHAT'S IN THE MYCOTOXIN MIX?
Mycotoxins are low-molecular weight secondary metabolites primarily synthesized by fungal genera Aspergillus, Fusarium, and Penicillium. They can contaminate feed and when consumed have toxic effects on animals and humans. Mycotoxins can originate from both the field and storage. Mycotoxins can negatively affect feed intake, rumen function, milk production, immune responses, reproduction, and susceptibility to disease. Furthermore, from a food system standpoint, mycotoxins can be transferred to milk.
For dairy cows, forage is the backbone of the ration and contributes to much of the intake each day. As a result, silage can be a major route for mycotoxin exposure. Silage is used to preserve feed quality throughout the year through anaerobic fermentation. Yet, some of the conditions in the silo, including microbial and biochemical processes, storage, and feedout may favor the proliferation of fungal species and the mycotoxins they can produce. Therefore, don’t think about silage as a “set it and forget it” feed but rather as a living ecosystem that is constantly evolving. Traditionally, we may discuss mycotoxins individually, but because of this dynamic evolution often there are multiple mycotoxins existing simultaneously within a silage. A recent review discusses the advances in silage science related to mycotoxins (JDS; http://doi.org/10.3168/jds.2026-28872).
The authors of this paper capture the dynamic nature of silage well by stating “The progression of fermentation, storage, and feed-out phases generates a highly dynamic and heterogeneous environment characterized by spatial and temporal gradients in oxygen availability, moisture, and microbial activity”. Some fungal species can survive the acidic and anaerobic environment of silage fermentation and become active upon oxygen exposure.
Most research has focused on a limited number of mycotoxins that are regulated. These include aflatoxins, fumonisins, zearalenone, ochratoxin A, and trichothecenes like deoxynivalenol and T-2 toxin. However, with new analytical approaches more diversity of fungal metabolites has been detected and therefore often more than one mycotoxin might be causing issues in the feed. Beyond the typical mycotoxins of concern, with advances in analytical techniques emerging mycotoxins are more commonly identified in animal feed and can often be identified at concentrations comparable to the regulated mycotoxins. The co-occurrence of multiple mycotoxins could result in interactions of the toxins that could be additive or synergistic. A challenge with that is much of the research is done on single mycotoxins alone.
A challenge with silage is the quantity fed and the number of samples needed to characterize the feed over time. Furthermore, this feed isn’t monitored or regulated to determine quality in terms of mycotoxin prevalence and abundance, unlike cereal grains and commodities. As a result, forages do not specifically have maximum limits or thresholds yet represent a large portion of the diet for dairy cows.
Factors that may influence mycotoxin production in ensiled feed could include stress to the crop (i.e. drought, disease, or insect damage), delayed harvesting, variable moisture, poor pack density and oxygen infiltration as well as overall poor management of the bunk and feedout. High temperatures, low rainfall, and drought often contribute to increased accumulation. Fungi that produce mycotoxins in the field include Fusarium and Alternaria spp. These will develop before harvest but can be maintained after ensiling.
Then there are mycotoxins that develop during storage or aerobic deterioration (ex. poor face management, slow feedout rate), generally Penicillium and Aspergillus species. Mycotoxin roduction after harvest could be related to aerobic respiration after harvest, ensiling, storage, feed handling, and feedout. Other management factors could include feeding refusals or poorly cleaning feeding equipment. Mycotoxins may not be uniformly distributed within the bunk.: Areas exposed to more oxygen such as the sides or top may have more mycotoxins, but there is some variability in the literature indicating there may not be any consistency of observed concentrations. However, once the bunk is open and oxygen penetrates the face, areas that are less dense may have more growth of fungi and production of mycotoxins.
How to reduce mycotoxin contamination?
Poor silo management can include delayed and/or inadequate sealing. Therefore, good bunk management is very important and should be an emphasis. Pay attention to packing on the sides, proper sizing of silos, proper sealing, additive treatment, and weighting plastic film (gravel, tires, tiles). Silage additives improve fermentation and enhance aerobic stability, potentially limiting fungal proliferation. Lactic acid bacteria produce antifungal and antibacterial compounds.
While the rumen has some capacity to detoxify mycotoxins, it is not exhaustive and can be influenced by diet, rumen function, passage rate, and overall toxin concentration. Mycotoxin sequestering agents (feed additives) reduce mycotoxin bioavailability. Inorganic adsorbents (bentonite, montmorillonite, zeolites, and hydrated sodium calcium aluminosilicates are highly effective against aflatoxin but can be less effective against DON and FUM. Organic adsorbents like yeast cell wall can have some broad-spectrum activity against mycotoxins while biological detoxification could be provided by some microorganisms or enzymes. These are often mycotoxin specific.
Overall, I think we will only learn more about mycotoxins in the future and how much the silage may be influencing dairy cow exposure. This is a major concern as we get more environmental challenges and scenarios that allow for mycotoxin production. Monitoring both field and bunk conditions will be important to limit how much your cows are exposed to mycotoxins. There are some tools we have that when included in the diet can help to limit the severity of exposure.
— Sarah Morrison
