Aerobic stability in silages is crucial to maintaining quality, said Limin Kung, University of Delaware dairy nutritionist, who spoke at last month’s California Alfalfa and Forage Symposium in Visalia.

“Silages that have short stability spoil rapidly when exposed to air, and that leads to a reduction in nutritive value, a reduction in intake and problems with animal production,” he said.

To keep silage as stable as possible when moved between storage structures and exposed to air, move the product quickly and in cool weather. Good packing density and plastic-covering management are also critical, he said.

“On many large dairies, it is now quite common to find several days worth of silage to be fed in temporary piles brought in from other farms or silos and dumped at a staging area. During hot weather, this can be a worse-case scenario because the moved silage is usually not repacked to exclude air,” Kung warns.

In a small survey of TMRs sampled in Delaware, Pennsylvania and Maryland over two years, more than half of 30 TMRs sampled within an hour of being made had spoiled in less than 12 hours when incubated at a controlled lab temperature of about 72°F. On these farms, TMRs had the potential to spoil in the feed bunk even if farms fed twice a day.

“The numbers of yeasts were generally greater, and the aerobic stabilities of the TMR were generally shorter than that usually observed in laboratory silages alone,” Kung said. “The reason for this was probably because silages used to make the TMR had more than likely already gone through some degree of aerobic exposure and spoilage before being mixed into the TMR.” Byproducts such as wet distillers grains may be a source of spoilage yeasts and molds and reduce aerobic stability when incorporated into a TMR.

Kung suggests adding chemical preservatives that contain antifungal compounds, such as buffered propionic acid, sorbates, benzoates, acetic acid, etc., at about 2-6 lbs/ton when moving silage.

The amount of preservative needed depends on the condition of the silage and ambient temperatures. If poor bunker management causes silage to spoil “considerably” in the silo before it’s mixed into the TMR, 4-8 lbs of additive per ton of TMR may be needed to prevent further spoilage at feeding. Start with a high dose in the bunker for several days.

“This should temporarily fix the problem right away and also ‘clean out’ the equipment and feed bunks. Then slowly reduce the dosage to a level that keeps the TMR from heating in the bunker.” Preservatives can help, but aren’t economical for long-term use, he added.

They also don’t stop the initial heating and nutrient losses that can occur in the silo, Kung stressed. Use caution when adding any feed to a TMR that has begun to spoil.

“A better idea would be to consider treating these silages at the time of ensiling with an additive to enhance aerobic stability (chemical additives or L. buchneri).” Microbial-based additives and ammonia are ineffective on forages that have already fermented, he added.

Signs of spoiling include temperatures of more than 115-120°F found 4-8” in back of the silo face at feed out, reheating in the bunk, visible mold, lack of a sharp or sweet smell to the silage and/or a flat or moldy-musty smell. If a pH meter is available, use it. A moldy smell coupled with a high pH may also indicate that a feed has undergone aerobic deterioration.

To check the stability of your silage, Kung suggests using a 2-3’ temperature probe. Silages can also be sent for lab analyses, but be sure that samples are representative of what is being fed. Keep samples for microbial analyses refrigerated and not frozen, then send them to a lab as quickly as possible – preferably stored with ice packs.