When the silage changes, watch the cows

The corn silage harvest may be finished, but the crop is still changing. October can become crunch time when it comes to counting available feed, deciding when to open the new crop and identifying the silage lots that warrant closer testing.

Give fermentation time

Most initial fermentation occurs in the first two to four weeks after corn silage is packed and sealed. Starch availability continues to improve for months as the protein structure surrounding corn starch breaks down. If old-crop inventory allows, waiting about four months before feeding new silage can provide more digestible starch. If it does not, test the new feed and adjust the ration rather than making an unplanned switch.

Total starch alone does not tell the whole story. Newly ensiled silage may supply less usable energy than the same crop will later in storage; poor kernel processing can also leave starch passing through the cow. Ask the nutritionist whether to measure starch digestibility and kernel processing; then, retest as the silage ages. More available starch may support milk and protein yield, but a ration with too much rapidly fermentable starch and too little effective fiber can disrupt rumen function and depress butterfat. Track pounds of fat and protein, not just percentages.

Test the crop that grew in your fields

Field conditions help identify which lots need mycotoxin testing. Cool, wet weather around silking and grain fill favors Gibberella ear rot, associated with deoxynivalenol, or DON, and zearalenone. Hot, dry conditions favor Aspergillus ear rot and possible aflatoxin. Hail and insect damage can open paths for infection, and prolonged wet weather before harvest can increase ear rot problems. After chopping, silage that is too dry to pack tightly, damaged plastic and a slowly advancing face increase mold and spoilage risk.

Label higher-risk lots in the inventory and work with your veterinarian and nutritionist on representative samples and toxin-specific tests before feeding. A general mold count is not a substitute for a mycotoxin test. DON can be present even when ears show little visible mold, and its concentration can change during ensiling. If a harvest sample raised concern, test again at feed out.

What quality, waste cost

A University of Wisconsin research summary found that cows fed a more digestible type of corn silage averaged 3.3 pounds more milk per cow per day than cows fed comparison silages, but also ate 2 pounds more dry matter. Milk fat percentage was slightly lower, while fat yield was similar. The useful measure is added milk and component income minus added feed cost. These results compare silage types; they do not promise a specific return from longer storage.

Waste also has a price. Using a Penn State Extension example production cost of $43.30 per ton, losing 5% of a 1,000-ton crop means 50 tons or $2,165 worth of silage grown but never fed. Replacement feed may cost more. Use your own crop costs to calculate the loss.

Health costs matter as well, especially when a forage switch reduces fresh-cow intake. University of Minnesota Extension estimates $289 per case of subclinical ketosis. That is a reason to monitor fresh cows closely, not an estimate of disease prevented by longer fermentation.

Count feeding days, then protect the face

Record every bunker, pile, bag and hay lot separately. Use harvested load weights where available; otherwise, measure storage dimensions and estimate density with a feed inventory worksheet. Calculate daily use across milking cows, dry cows, heifers and calves, allowing for storage and feed-out loss. Keep amounts on the same as-fed or dry-matter basis. Usable inventory divided by daily use estimates the feeding days remaining. Update the number as feed and herd size change.

At feed out, pull back only enough plastic to expose about one day’s worth when practical and weight the remaining cover tightly. University of Wisconsin Extension advises leaving no more than three days’ worth unprotected. Uncover only a day or two at a time on a bag. Maintain a smooth face, remove loosened feed promptly and keep workers clear of the face because silage can collapse without warning.

Mark the date new silage enters the ration. Then watch intake, refusals, sorting, manure, rumination, milk yield and components. Good inventory gives fermentation time, careful feed out protects the crop and cow records tell you how the ration is working.

Portia Seckerson is the owner of Nortnern Valley Livestock Services in Plainview, MN. Their office of six veterinarians cover Minnesota and Wisconsin. She can be reached at pseckerson@nvls.vet