Conditions for harvest and storage of silage crops, especially corn, this fall have been less than ideal on many farms due to the poor condition of the crops.
Drought-stricken corn may have one or more of the following problems, compared to normal:
* higher in dry matter;
* higher in nitrates;
* lower in fiber;
* higher in non-fiber carbohydrates (NFC);
* higher in mycotoxin-producing fungi; and
* extreme variability in protein and energy content.
In the silo now. Now that the silage is in the silo, the real work begins to assure the cows receive a safe, properly balanced ration that is palatable and capable of supporting optimum production.
Close communication and cooperation with your nutritionist will be critical to achieving satisfactory results.
Although the fermentation process eliminates as much as 80 percent of the nitrates in drought stricken corn and mycotoxin-producing fungi do not compete well with silage fermentation fungi, I predict there will be some problems with excessive nitrates and mycotoxins in fermented feeds over the next year.
According to Gretchen A. Kuldau, plant pathologist at Penn State and Charles P. Woloshuk, plant pathologist at Purdue University, if proper moisture content is not maintained or oxygen is allowed into the silage by poor management of the bunker silage face or inadequate feeding rate, several problems can occur.
The problems can make it difficult or impossible to deliver a consistent, properly balanced ration to each group.
Besides fluctuations in dry matter intake and variations in nutrient content, high levels of nitrates or mycotoxins can bring about disastrous results if undetected.
Mycotoxins. Mycotoxins are toxic chemicals produced by fungi. The most common mycotoxin found in silage is deoxynivalenol, also known as DON or vomitoxin.
DON is produced by several species of Fusarium. DON is not known to significantly affect milk production, milk quality, feed intake or animal health.
Nonetheless, the researchers said, many producers have noticed a correlation between DON in rations and problems with reduced milk production, feed intake and herd health.
Thus DON appears to be an indicator of the presence of other possible toxins in feeds.
Other Fusarium mycotoxins that have been found in silage include T-2 toxin, diacetoxyscirpenol (DAS) zearolenone and fumonisins. T-2 and DAS are not commonly found in silage produced in the Midwest.
Contaminated silage. Zearolenone is produced by Fusarium graminearum and is often present in DON-contaminated silage. It has estrogenic effects in animals potentially disrupting reproductive efficiency. Large doses may also cause reductions in milk production.
Zearolenone levels exceeding 500 micrograms per Kilogram (500 ppb) are dangerous.
Fumonisins are a group of mycotoxins produced by Fusarium verticillioides and Fusarium proliferatum.
The most common fumonisin, FB1, has a variety of effects in animals, many stemming from damage to the kidney and liver.
The Food and Drug Administration has suggested that dairy cattle should not be fed more than 30,000 micrograms total fumonisin per kilogram of feed (30 ppm).
Details can be found at the Web site http://vm.cfsan.fda.gov/~dms/fumongui.html.
Other mycotoxins. In addition to the Fusarium mycotoxins, aflatoxin, ochratoxin, and ergot also occur in silage.
Aflatoxins are potent liver toxins and carcinogens produced by Aspergillus flavus and Aspergillus parasiticus.
Aflatoxins are of concern to dairy producers in particular because FDA regulations require aflatoxin residues in milk to less than 0.5 ppb. To prevent the carryover of aflatoxins into milk, silage and other feed components should contain no greater than 20 micrograms aflatoxin per Kilogram (20 ppb).
Ochratoxin. Ochratoxin is a toxic compound produced by several species of Penicillium and Aspergillus fungi, but rumen microorganisms are capable of breaking it down.
Ochratoxin levels in dairy cattle rations should not exceed 250 ppb.
Ergot. Ergot alkaloids are produced by Claviceps purpurea and related fungi.
C. purpurea infects nearly all grasses, including barley, rye and wheat. This fungus infects through the flower structure of the plant.
Ergot contamination is more common in haylage, however, infected grassy weeds can be a source of contamination in corn silage.
Penicillium roqueforti. Penicillium roqueforti is a fungus commonly found in the acidic, low oxygen environment of silage.
This fungus produces at least four mycotoxins (PR toxin, roquefortine C, patulin and mycophenolic acid) all of which have been documented in silage.
The effects of these mycotoxins on dairy cattle are not well understood.
Screening for mycotoxins. When you observe spoilage in your silage or your cows show reduced feed intake, reduced milk production or the appearance of poor health, you should consider the possibility of mycotoxins in the ration.
The presence of mold in the silage does not mean mycotoxins are present. Other chemicals such as nitrate can cause similar animal symptoms to those caused by mycotoxins.
The only means of determining the presence of mycotoxins is to test for them. Analysis for mycotoxins in silage can be extremely complex and expensive. Although same tests can screen for more then one mycotoxin at once, they may have a fairly high rate of false positives.
It is best to have positive results verified by re-testing using more specific chemical analyses.
Several private laboratories and some university veterinary schools can analyze samples for mycotoxins. Sample collection and preparation are important sources of error when testing silage. You must collect and ship a representative sample.
Two samples. Because mycotoxins will be produced in the silage that is exposed to the air, samples from moldy silage should give a good indication of any mycotoxins present.
However, if you sample moldy silage, be sure to take a second sample from an area that is not moldy. Make sure you handle samples carefully so that additional mycotoxins do not accumulate in the samples during shipment or while being held for analysis.
Drying the sample at moderate temperature (60 degrees C or less) will ensure that fungus stops growing. Freezing the sample and shipping on ice by one-day delivery is another option.
More information. For more information on mycotoxins in silage, visit the Internet site for the NC129 North Central Regional Research project, mycotoxins in cereal grains at: www.btny.purdue.edu/nc129.
Links are provided to many sources of information related to mycotoxins and silage. Please call us if you need information on testing laboratories that do mycotoxins analysis, or you need help in interpreting test results.
(The author is an agricultural extension agent in Columbiana County. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)