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Silage smells

The best way to evaluate the quality of silage is by appropriately sampling it and requesting both fermentative and nutritive analyses from an accredited analytical laboratory.

However, there are some clues that can be drawn about what happened during the fermentation process from the appearance of the silage and its smell.

Sweet Acid• Probable strong fermentation
• pH could be too low
• Could have stability problems during feedouT• Check pH
• Check yeast and mold levels
• Elevated acetic acid level caused by either:
1. High lactate, acetate and propionate resulting in good stable silage, that feeds well
2. Lower acetate, some ethanol, maybe some butyric, iso-butyric (messy VFA profile), also some ammonia resulting in slow fermentation
• In the case of lower acetate levels, silage may not be stable • Check VFAs
• Focus on optimal feed management (remove loose silage, maintain tight face, etc.)
• Slow fermentation and/or contamination (ash > 8%) has resulted in clostridia dominating the fermentation and producing butyric acid, ammonia, amines (e.g. putrescine, cadaverine)
• Possible overcompaction of very low DM forage
• Possible ensiling at very high temperatures
• Silage will be wet, pH may be elevated or may be low
• Silage will be very stable but intakes will be low
• Forcing high intakes can cause health and fertility problems
• Spread out to aerate and reduce butyric acid levels
• Feed as low proportion of ration, mask with suitable flavor (e.g. butterscotch, caramel after checking for toxins)
• Do not feed to pregnant cows, transition cows or cows in first 100 days of lactation
Earthy• Bacillus growth • pH will be high
• Silage will heat and may also go moldy
• Must be fed quickly, removing moldy material
• Discard spoiled silage
• Consider treating TMR with preservative and/or flavoring
No smell to
alcoholic or fruity/
bread odor
•Yeast growth, consumption of VFAs• pH will be elevated, may be some alcohol on analysis
• Micro will probably show high yeast levels
• Silage to very likely be warm, hot or likely to heat
• May also be or go moldy
• pH will be elevated, may be some alcohol on analysis
• Micro will probably show high yeast levels
• Silage to very likely be warm, hot or likely to heat
• May also be or go moldy
burnt odor
• Silage has undergone excessive heating due to yeast and/or Bacillus growth
• May also be moldy
• Analysis shows little or no VFAs or other volatiles
• May have a high level of bound/heat damaged protein (ADIN) indicating temperatures have been in excess of 100˚F (38˚C)
• May have reasonable/high intake (cows like the taste) but will not perform well since most of the energy has already gone
• Adjust ration to provide adequate energy and nutrients
• Consider treating the TMR
• Consider inclusion of corn cob mix (ccm); crimped grain, molasses and soy
• Molds are growing in the silage, probably visibly
• Silage has already heated due to yeast growth with losses of dry matter and nutrients
• Possible presence of mycotoxins• Remove and discard moldy silage
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