Combo inoculants hold promise for best of both worlds

How can a homofermentative inoculant improve milk production by 2 to 3 pounds per cow per day? Can farmers expect that from all homofermentative inoculants? And what are expectations for L. buchneri and the combo inoculants? Those are some of the questions addressed by U.S. Dairy Forage Research Center research engineer Richard Muck during World Dairy Expo in Madison earlier this month.

Muck admits he thought inoculants were improving dry matter digestibility, but two trials with alfalfa silage – and homofermentative inoculants as well as the heterofermenter, L. buchneri – didn’t show that. Muck admits that was “disappointing to us.” However, gas production was lower with some inoculants than predicted.

Muck points out that the main products of rumen fermentation are: Rumen microbes, volatile fatty acids and gases. With inoculants they’ve measured more rumen microbes and less of the gases. Rumen microbes are one of the main sources of protein for the cow. It appears what may be causing the difference in animal performance with inoculated silage is that cow is getting more protein, which supports more milk production. He reports that “inoculated silages from 3 of the 4 inoculants (researched in the lab) produced 8 percent more rumen microbes than untreated silage. That could support up to four pounds more milk per cow per day, he adds.

Muck went on to share results of a lactating cow trial with alfalfa silage (treated with L. plantarum). There was a “nice response” in pH, he mentions of 4.93 untreated silage and 4.56 inoculant-treated. The alfalfa silage was fed at 50 percent of the ration, along with corn silage, high moisture corn and soy hulls. The additional two pounds more milk with the inoculant wasn’t statistically significant. The MUN (milk urea nitrogen) level is noteworthy. Muck says the 10 percent reduction in milk urea N indicates better N utilization by the cows on the inoculated silage, suggesting more rumen microbe production. (That’s also a potentially positive environmental impact with less ammonia loss.)

What more does Muck need to know? He says they have to confirm that more rumen microbes were actually produced in the trial, but he’s fairly confident that’ll show up. He also needs to figure out “why” certain inoculants are causing silages to produce more rumen microbes, and confirm that the in vitro test really does screen for inoculants that can produce a significant animal response.

The bottom line? Muck says there’s “sound evidence that some inoculants can increase rumen microbe production in vitro,” and that “these increases can explain the milk production increases observed with some inoculants.” He adds that the inoculant they tested in their production trial increased milk and reduced MUN like they’d expected. MUN is a good indicator of better nitrogen utilization by the cow.

There’s “good strong evidence” that makes these products look even more attractive now, notes Muck.

“We now have increased confidence that some inoculants can truly increase milk production 2 to 4 pounds per cow per day,” he states, admitting more research is needed to understand why this is happening. He says they also may have a “tool for looking for better inoculants in the future.”

Muck characterizes the homofermenters as the best choice to improve DM recovery and animal performance. They’re a good fit for hay-crop silage, but less likely to be successful on corn silage. However, in vitro tests with corn silage (BMR and regular) indicate production of more rumen microbes (i.e. an effect on the cow). He admits he’s starting to change his tune a tad.

Aside from their preferred use on alfalfa silage, positive outcomes with homofermenters are more likely to occur with corn silage when it’s harvested on the dry side or immediately after a killing frost.

The heterofermentative inoculants like L. buchneri, he says, consistently increase bunk life/aerobic stability (an issue in warm weather with corn and small grain silages). Studies show L. buchneri raises acetic acid and results in higher-pH silage. Because acetic acid inhibits yeasts and molds, L. buchneri-treated silage is more aerobically stable. Heterofermentative inoculants work more consistently across a wide range of conditions, while success with homofermenters are best in hay crop silage with a wilt time of a day.

In terms of DM loss, L. buchneri is intermediate between untreated silage and homofermentative inoculants. That’s not surprising because carbon dioxide gas is made and lost while producing acetic acid. Typically there’s a 1 to 2 percent improvement in DM recovery over untreated silage. In lactation trials with L. buchneri, acetic acid also increased. However, there’s been no effect on DM intake by cows and generally little or no effect on milk production (except in keeping silage cool).

But when combining the two types of inoculants – homofermenters and L. buchneri – it seems there is indeed potential to “get the best of both worlds,” notes Muck of the DM recovery and animal performance of a standard inoculant and the bunk life/aerobic stability of L. buchneri. The potential for more milk appears to be happening on more than one crop, he notes, admitting that more animal trials are needed though.

This ag engineer reminds producers that the bacteria in the inoculant has to be alive when it goes on the crop to work. Keep the inoculant tank cool the best you can in the heat of summer. He also prefers to add the inoculant on the forage harvester as there are multiple opportunities for the inoculant to be mixed with the crop; good distribution is important.