What type of sample bag should be used for silage to be analyzed for yeasts and molds — paper or plastic?

Some forage testing laboratories recommend submitting these samples in paper bags. However, no research supports this recommendation. It may be labs might be recommending paper bags because that’s what they read somewhere or “because we’ve always done it that way.”

Almost all samples submitted to forage testing labs are in plastic bags: That’s what the labs supply in their forage sample kits, so that’s what the farmers use. To shed some light on the matter, and with financial support from Lallemand Nutrition, Miner Institute ran a simple trial to answer the “paper vs. plastic” question.

We used plastic forage sample bags and small paper bags at four simulated shipping conditions: 48 hours at temperatures of -4°, +39°, +70° and +95°F. Here’s what we found:

1. Percent dry matter increased much more in samples stored in paper bags, particularly at 95°F. The increase was only about 1% when stored in plastic bags.

2. Silage pH changed little except at 95°F, but at that temperature it changed a lot, an increase of 0.25 pH units. At the other temperatures the changes were less than 0.1 pH unit, but in all cases the changes were positive, suggesting “forage lab pH” is probably slightly higher than the forage pH in the silo. The increase in pH was greater when the samples were stored in paper bags.

3. Mold score was greatly reduced when the samples were frozen, with the biggest reduction when the samples were frozen in paper bags. There was a large increase in mold score when samples were stored in paper bags at 95°F. Don’t freeze samples submitted for yeast and mold counts, The change in mold score was very small when samples were stored in plastic bags at 70°F.

Recommendations: Send unfrozen mold and yeast samples in plastic bags, in an insulated container with a coolant pack to prevent heating. Although there weren’t any time variables in the study, the sooner the sample gets from silo to testing lab the more accurate the results. Sample and ship the same day if possible. “Next day delivery” samples for mold and yeast analysis should be shipped Monday through Wednesday so they won’t arrive at the lab on a Friday afternoon or weekend.

 -- Ev Thomas

Find the Miner Institute January Farm Report online here: http://whminer.org/farmreport.html