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Mycotoxins in Silage Cause Multiple Effects in Dairy Cattle Including Oxidative Stress
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Lon Whitlow, Ph.D.
Professor and Departmental Extension Leader
Department of Animal Science, NCSU |
| In most regions of the country, silage makes up a sizable portion of the TMR for dairy cattle. Preservation of feeds by ensiling is a cost saving and labor efficient method, but silage management is essential to ensure a high quality product. Ensiling preserves feed through a microbial process that depletes the oxygen supply and lowers pH due to production of lactic acid and other organic acids. Silage management recommendations are designed to achieve an anaerobic and acidic environment to prevent further microbial growth. Under these perfect conditions, undesirable spoilage microorganisms will not grow. However, because the ensiling process is never perfect, silage commonly contains unwanted bacteria, yeasts and molds, along with mycotoxins, which are toxins produced by molds. |
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Air is the primary factor that can destroy silage. Without excellent silage management, air can infiltrate the silage mass and support the growth of acid tolerant yeast and molds (Penicillium). As yeasts grow, they utilize and deplete lactic acid, allowing pH to rise. At this higher pH (less acid), silage becomes a suitable environment for growth of other molds and spoilage bacteria. Penicillium molds are the most common molds found in corn silage because Penicillium are acid tolerant and have a low oxygen requirement. Other molds commonly found in silage include Aspergillus, Fusarium, Alternaria, Mucor, Rhizopus and Cladosporum. The presence of mold indicates deterioration, dry matter loss, lower nutritional value and the possible presence of mycotoxins. Moldy feed and mycotoxins have been associated with lower feed intake, reduced digestibility and health disorders. An array of mycotoxins can be present in moldy silage, some of which are not normally found in concentrates. The mycotoxins of greatest concern are those produced by Penicillium (PR toxin, mycophenolic acid, roquefortine C, patulin), Fusarium (deoxynivalenol, zearalenone, T-2 toxin), and Aspergillus (aflatoxin, gliotoxin, fumitremorgens, fumigaclavines), but others may also be present.
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Herd health problems associated with moldy silage have been most highly correlated with presence of PR toxin and secondly with deoxynivalenol. Therefore, these two mycotoxins should be included in a diagnostic analysis of silage. Additional analyses may include other common mycotoxins such as T-2 toxin and zearalenone, a test for the amount of yeast and mold, and an identification of the mold. Obtaining representative silage samples for mold and mycotoxin analyses is difficult because molds grow in spots. For accuracy, several samples should be taken from a load of silage, but only after thorough mixing. Samples should be sent to the laboratory without delay by express delivery. If not put into the mail immediately, the sample should be frozen.
Chronic toxicity resulting from long term low level consumption of mycotoxins is more likely than acute toxicity. Ruminants are somewhat protected from acute toxicity because the rumen destroys a large portion of many mycotoxins. Rumen degradation of mycotoxins may, however, hide the acute symptoms resulting in undetected chronic problems. Mycotoxins can produce a variety of symptoms in dairy cattle including low feed consumption, altered rumen fermentation, digestive upsets, diarrhea, intestinal irritation, reduced production, lower fertility, lethargy and increased morbidity. An increase in disease and death rates can occur also. One of the more important effects of mycotoxins is suppression of immunity and mycotoxins are considered one of the most important dietary factors that suppress immunity. The main mechanisms of mycotoxin toxicity are lipid peroxidation, inhibition of protein synthesis and apoptosis (programmed cell death).
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Lipid peroxidation resulting from mycotoxicoses can modulate the immune response. Therefore, antioxidants can have a protective effect against several mycotoxins. In numerous experiments, vitamin E has helped protect against the toxicity of aflatoxin, deoxynivalenol, T-2 toxin, fumonisin, zearalenone, and ochratoxin, in some species. Selenium appears to have a protective effect against the toxicity of aflatoxin and T-2 toxin, in some species. Antioxidant compounds including vitamins A and E, co-enzyme Q10, selenium and others including synthetic antioxidants are thought to protect against lipid peroxidation caused by mycotoxins./span>
There are several processes that have been studied in an attempt to find ways to reduce the toxicity of mycotoxins. These methods include improved field and storage management, feed treatments to reduce mycotoxin content, adsorbents to prevent animal absorption and supporting the animal through better management or nutrition such as the use of antioxidants to reduce oxidative stress.
Silage management for the prevention of silage molds and mycotoxins begins with selection of varieties that have resistance to fungal diseases. Planting and harvest dates must be timely to avoid plant stress. Other agronomic practices like proper fertilization and insect control can help reduce fungal disease. Harvest timing to get the proper moisture is necessary for dense packing and exclusion of air. Sealing the silo is essential to maintain an anaerobic environment. Inoculants enhance fermentation for rapid production of organic acids. After opening, daily removal of 6 to 12 inches from the silo feeding face is recommended to prevent continuous deterioration of the feeding face. The feeding face should be cut cleanly to avoid deterioration. Today, more face cutters are being used in bunker silos to prevent face spoilage. Silage should be fed soon after removal from the silo. If silage heats in the feed bunk or if there is obvious deterioration on the feeding face, organic acids can be used on a daily basis as a preventative. Any spoiled or obviously moldy silage should be discarded.
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Animals exposed to mycotoxins are better able to remain healthy and productive with an array of supportive therapies. A therapy that has been effective in research is the use of a mycotoxin adsorbent that binds with mycotoxins in the feed and reduces their absorption by the animal. This effectively reduces the mycotoxin exposure to the animal, but does not totally eliminate exposure. A robust rumen fermentation is important in mycotoxin prevention by maximizing mycotoxin degradation in the rumen. Therefore, the use of buffers, sufficient effective fiber and microbials to stimulate rumen function can be helpful. Because many nutrients interact with mycotoxins to modify their toxicity, optimal levels of nutrients can be helpful to reduce mycotoxin effects. To help protect the animal against increased oxidative stress caused by mycotoxin exposure, the TMR should contain additional antioxidants.
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