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Nutrition Focus
Mycotoxin Effects in Dairy Cattle
CHRISTMAS 2021 ❆ BC HOLSTEIN NEWS 41
  Glenn Smith, Senior Nutritionist, Trouw Nutrition
Mycotoxins are toxic substances produced by fungi (molds) growing on crops in the field, during handling or in storage. While over 400 mycotoxins have been chemically identified, the impact of only a few mycotoxins are known. Common types of mycotoxins include aflatoxin, deoxynivalenol (also referred to as DON or vomitoxin), zearalenone, T-2 toxin and fumonisin. Of the thousands of mold species that can grow on feedstuffs, only a small proportion produce mycotoxins.
Mold Growth and Mycotoxin Formation
Some molds proliferate while the crop is growing, while others propagate during handling and storage. Field mold spores propagate in both the grain and forage parts of plants. Weather-related growing conditions contribute to the onset of molds that may produce mycotoxins. Storage fungi are soilborne mold spores brought into the silo with forages. Most molds identified in silage do not produce mycotoxins.
Corn silage harvesting may pick up mycotoxin contamination from soil in lodged corn plants. The limiting factor for mold growth in stored silage is pH. If silage is stored too dry, or is insufficiently packed/ covered, then air allows for microbial activity which depletes silage acids allowing pH to rise with subsequent mold growth and possible mycotoxin contamination. With hay, the limiting factor for mold growth is moisture where contamination is more likely in higher moisture hay.
Mycotoxin Effects
Ruminants have some capability to tolerate the adverse effects of mycotoxins at lower
thresholds – perhaps due to the ability of certain rumen microorganisms to detoxify mycotoxins. However, with high producing dairy cattle, increased rumen passage rates overwhelm the ability of the rumen microorganisms to completely denature the toxins.
An excess of mycotoxins causes undesirable effects resulting in major losses in health and performance of animals including:
1. Reduction in amount of nutrients available for use by animal
2. Effects on hormonal systems and subsequent reproductive performance
3. Suppression of immune system
4. Negative mammary related effects, e.g., reduced milk production (due to reduced intake or feed refusal), potential for toxic contaminants in milk (i.e., aflatoxin), mastitis risk and altered milk composition.
Mycotoxicosis Symptoms and Diagnosis
The diversity of symptoms makes mycotoxicosis diagnosis confusing and difficult. Symptoms of mycotoxicosis may be vague or nonspecific but may include: reduced feed intake, feed refusal, unthriftiness, rough hair coat, poor body condition and reproductive problems. Mycotoxins have also been associated with increased transition cow problems including more substantive symptoms such as displaced abomasums, ketosis, retained placenta, metritis, mastitis, and other infectious diseases because of immune suppression.
A definitive diagnosis of mycotoxicosis cannot usually be made from symptoms,
Mycotoxins from molds can come from grains and forages and originate in the field or while storing/handling. It’s important to understand the variables that influence mycotoxins so that you can take measures to protect your herd from a variety of ill effects.
 tissue damage or feed analyses independent of each other. Molds can grow in hot spots and associated mycotoxins may not be uniformly distributed within a silo, making it difficult to obtain a representative sample. Regardless of the difficulty of diagnosis, mycotoxins should be considered as a possible cause of production and health problems when symptoms exist and problems are not attributable to other typical causes. These same factors make it difficult to establish levels of safety for mycotoxin ingestion. Interactions with other stress factors make recommendations difficult, as animals under environmental or production stress may show more pronounced symptoms. Also, partial degradation in the rumen complicates recommendations.
Adsorbents
When animals are exposed to mycotoxins, favourable results have been seen if adsorbent materials and complex indigestible carbohydrates are added to the ration. There are several natural based mycotoxin binding adsorbents on the market and responses to some of these products in dairy cattle have been encouraging.
The intent of dietary mycotoxin adsorbents is to bind mycotoxins within the gastro- intestinal tract and prevent toxins from absorption across the gut wall. For best results, an adsorbent should: effectively bind mycotoxins, reduce mycotoxin availability and activity, reduce animal toxicity and tissue residues, not be detrimental to the animal or food product, be resistant to the physical effects of feed manufacturing and be cost effective.
Take Home Message
Mycotoxins and molds occur in many feed types including hay and silage and can be the root cause of animal disorders. Chronic symptoms such as low performance and reduced immune status can be the result of mycotoxin ingestion. Most molds do not produce known mycotoxins. Proper crop management from field to feed out will reduce opportunities for mold growth and subsequent toxin production. Even after implementing good agronomic and feeding management practices, it may not be possible to completely eliminate mycotoxins from the diet. Many adsorbent type products are used in the feed industry to help minimize the effects of mycotoxins.
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