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BRILLION – As winter turns to spring, an emerging concern on farms is how the hygiene of ensiled feeds can be at risk from bad micro-organisms and compounds that can be activated once that silage is again exposed to air and its pH rises.

How to cope with that threat was topic for VitaPlus forage specialist Michelle Chang-Der Bedrosian (subsequently referred to as Chang) in a presentation for the Extension Service's “Meeting Tomorrow's Feeding Challenges Today” program. 

Chang explained how ensiled feeds have an aerobic phase, in which they use up sugars and proteins, as they are harvested and go into storage, then enter an anaerobic stage with a lower pH as they ferment and are held in storage, and finally re-enter an aerobic stage (exposure to oxygen and the risks that entails) during feedout.

Describing the undesirables

The unacceptable micro-organisms are some bacteria strains, molds, and the yeasts that can generate the development of e.coli and salmonella while the compounds, of which there are thousands in silage, include mycotoxins and biogenic amines, Chang indicated.

As they stand in fields, plants are covered with micro-organisms and they thrive there because of the full exposure to oxygen, Chang pointed out. In what she described as “silage microbiology 101,” each gram of silage (about the size of a quarter) can contain more than 10 million aerobic bacteria, 1 million lactic acid bacteria (good ones), 1 million enterobacteria (bad ones), 100,000 yeasts, and 10,000 each of molds and clostridia.

Diagnosing the problems

In trouble-shooting visits to VitaPlus clients who are having problems with dairy cattle health or production, one or more of the bad micro-organisms or compounds can often be identified as the culprit, Chang reported. She suggests a fermentation analysis and a test for yeasts and molds and urges farmers to resist a quick diagnosis of clostridia which is sometimes used as a fear tactic to sell one or more products.

Regarding unfermented haylage and corn silage that was harvested at or below freezing temperatures in late 2019, Chang doesn't see any risk in feeding them while they are still frozen, noting they would be similar to green chopped forages. Because they are likely to ferment once they thaw, those unfermented silages should be treated with an inoculant and checked for the presence of butyric acid, she advised.

Dealing with the nasties

Because they degrade the beneficial proteins in silage, clostridia and enterobacteria are “the nasties” among the list of “bad guys” in silages, Chang remarked. She noted that clostridia, which causes hemorrhagic bowel syndrome in cattle, can originate in the soil or on plants and can be spread by equipment.

Clostridia and enterobacteria can overlap as they compete with the valuable lactic acid bacteria, thrive in a high pH and relatively high moisture, and produce ammonia, biogenic amines, and certain acids (all of which smell bad), Chang observed. The enterobacteria, which nurture salmonella and E. coli, result from poor fermentation and cause pneumonia, fever, diarrhea, and septicemia in cattle, she indicated.

Corn and alfalfa silage samples collected by a student intern on 40 Wisconsin farms immediately after defacing at the storage unit consistently showed that they were “actively spoiling once removed” in the followup laboratory analysis, Chang reported. The unsurprising findings were that the undesirable components were lower with the drier silages and with those having the lower pHs, she stated.

No clear-cut correlations

But those findings aren't necessarily a tell-all, Chang emphasized. That's because there's no consistent correlation between dry matter and pH, clostridia, and enterobacteria, between pH and the biogenic amines, between ammonia and biogenics and the clostridia and enterobacteria counts, or between yeast and mold, she indicated.

As Chang sees it, the inconsistency among those factors and the finding that laboratory tests are not conclusive about the overall hygiene status of silages nonetheless leads to several conclusions. They are the importance of dry matter at harvest (geared to the particular storage unit), of the lowering of pH immediately in storage, of realizing that simple plate counts do not necessarily reflect actual biological activity, of knowing that clostridial counts of up to 100 cfu per gram “are normal,” and of believing that advanced tests can identify the specific problems in spoiled silage, she advised.

For dairy herd nutritionists, dry matter content tends to be the top criterion for silages, Chang pointed out. Obtaining a low pH rapidly in storage serves to improve dry matter recovery at feedout, reduces protein degradation, and limits the growth of bad micro-organisms, she stated. To support the low pH goal, she strongly recommends use of an inoculant, especially with alfalfa haylage.

If a storage unit is likely to be susceptible to clostridia for reasons such as a slow filling, wet or rained-on alfalfa, or improper sealing, feed that silage soon, Chang stressed. If unacceptably high counts of clostridia are known, “air it out, don't feed to transition cows, and don't feed more than 50 grams per day to cows. I'll calculate that for you.”

Even without laboratory tests, the signs that feed is spoiling are the smell, black molds, off color variations, and warming of the silage, she pointed out. “Mold and heat are the last signs.”

Mycotoxin management

Regarding the concern for mycotoxins, Chang said there is not always a link between mold and the harmful mycotoxins such as penicillium, fusarium, and aspergillus (the product of a stress such as a flood or drought). “Corn with no visible mold may still have mycotoxins,” she advised.

Don't rush to blame a mycotoxin for dairy cow health or production problems when the culprit could be disease, trauma, weather or rapid feed changes, nutritional errors, or stray voltage, Chang remarked. To test for mycotoxins, combine 8 to 12 subsamples from a mixed ration and ask for DON (a marker) and T-2 and ZEA counts, she advised.

To deal with mycotoxins, realize that “a healthy rumen is your first and best defense because it destroys 25 percent of the mycotoxins,” Chang stated. “It's amazing.”

Beyond that, the solutions include dilution, diverting that feed to less susceptible animals, cleaning and screening such as removing the broken corn kernels that are top candidates for mycotoxin development, placing a binder in the ration, or using heat or an acid inhibitor to curb more mycotoxin growth, Chang concluded. In addition to VitaPlus, she mentioned All-Tech as a commercial testing firm for silage feeds.

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