Caution: Don’t kill your bugs! (Dr. Michelle Windle)

That was the question Dr. Owen Mickley, Vita Plus dairy specialist, posed during the heat of last year’s corn silage harvest in central Ohio.

Just a couple weeks earlier, Mickley hosted a custom harvester meeting for about a dozen chopper operators. The subject of inoculant tank mix temperatures was covered and it seemed the information presented was rather eye-opening for the group.  When the harvest season commenced a couple weeks later, Mickley discovered that high tank mix temperatures are all too common.

He reported extremely high tank mix temperatures, especially in the black plastic, frame-mounted tanks on large choppers.

In a text message he sent to the Vita Plus Forage Team, Mickley reported, “I’ve got 130 degrees.”  A day or two later he texted again, “How about 140 degrees?”

Obviously, those numbers are much too high for inoculant viability in a tank mix.  Here’s what Dr. Michelle Windle, who recently finished her Ph.D. work and supports Vita Plus dairy and forage efforts throughout our market area, has to say about high temps in inoculant tank mixes.

Caution:  Don’t kill your bugs!

Dr. Michelle Windle, Vita Plus forage products & dairy technical service specialist
Bacterial inoculants are commonly added to forage at ensiling because they result in more desirable fermentations that improve the recovery of dry matter (DM) and energy.  Certain strains of lactic acid bacteria can improve aerobic stability.  Many factors have the potential to affect how well an inoculant works, such as storage conditions prior to application, moisture level of the crop at ensiling, water conditions in the inoculant tank, application rate of the inoculant, and distribution of the inoculant on the forage.

Recent research has focused on the conditions in the inoculant tank and how they may impact how well an inoculant works.

Although it has been well documented that heat can kill bacteria (especially within the realm of food safety), limited research has explored the impacts of heat in the inoculant tank on bacterial inoculants.  In fact, some inoculant companies assert that warm temperatures in the inoculant tank do not adversely affect bacterial numbers.  Peer-reviewed, published scientific research indicates otherwise.

In a laboratory experiment, Mulrooney and Kung (2008) mixed various different commercially available inoculants with water that was either 86, 95, 104 or 113 degrees F for six hours. Next, all inoculants were transferred to conditions that were 86 degrees F for the next 18 hours.  This was done to simulate a situation where an inoculant tank heated up and then was cooled (such as in the evening, when weather cools down, or due to the addition of ice packs).

Results indicated that incubation at 86 degrees did not adversely affect bacterial viability, but incubation at all other temperatures did.  Higher temperatures resulted in decreased bacterial viability.

Although bacterial numbers decreased in all strains, there were strain variations in thermotolerance:  Researchers reported that Lactobacillus plantarum MTD/1 (the bacteria in Crop-N-Rich) was unaffected by all temperatures after three hours of incubation.  Numbers of L. plantarum MTD/1 and of L. buchneri 40788 (the bacteria in Crop-N-Rich Buchneri and Crop-N-Rich Stage 2) both increased in the 18 hours following a heat challenge, also indicating better thermotolerance than other inoculants tested.

More recently, the University of Delaware and Vita Plus collaborated on a field study to investigate the relationship between conditions in the tank and numbers of bacteria in the field.  These results were presented at the American Dairy Science Association Joint Annual Meeting in July 2013.

In this study, inoculant-water mixtures from more than 60 tanks were sampled and immediately plated on agar to enumerate bacteria.  Several different inoculants (more than 15) and tank types (more than 7) were sampled with the goal of reporting an average of different field conditions.  Due to the uneven number of each inoculant, it was not possible to report strain differences.

Results from this study indicated that ambient temperature did not affect bacterial numbers, but that the time the inoculants sat in the applicator tank prior to application and the temperature of the inoculant-water mixture in the tank did.  As time went on, bacterial numbers decreased, probably due to bacterial starvation.  On average, when water temperatures were greater than 92 degrees, half of the bacteria were dead, rendering the inoculant essentially useless.

This study was the first to present scientific data that linked high water temperatures with tank placement:  Higher temperatures in the tank coincided with tanks that were located closer to the chopper engine and lower bacterial numbers.

It is easy, during the hustle and bustle of the silage harvest season, to forget that bacterial inoculants are living, fragile organisms.  When they are starved or heat-stressed, they die.  Decreased bacterial numbers result in ineffective inoculants and a waste of an investment.  Bacterial inoculants can provide you with valuable tools during harvest, but those tools must be used correctly to prove valuable.  Paying attention to conditions in the tank can help you use these tools and get the best return on your investment.