More than a few dairy producers have experimented with cutting corn silage hybrids higher than normal in an effort to improve digestibility. The logic: most of the highly indigestible lignin is in the lower part of the stalks. By cutting them 18" or more off the ground, a more digestible feed with less lignin is put into the silo.
University of Delaware dairy nutrition specialist Limin Kung believes planting and harvesting brown midrib (BMR) corn silage hybrids may be a more worthwhile strategy for many of those producers.
In a 2006 study, Kung compared digestibility of BMR corn silage cut at a normal height to a conventional silage hybrid cut at normal and higher-than-normal heights. He found that NDF digestibility (NDFd) was about 12% higher in the BMR silage than in other hybrids in the study.
“A limited number of studies have shown that high-cut, conventional corn silage will increase NDFd compared to conventional corn silage cut at a traditional height,” notes Kung. “But the increase is just one or two percentage points. That's basically insignificant, nothing to write home about. With BMR, though, the increase in NDFd can be very significant.”
When Kung fed the silages to lactating cows, he found milk production, milk protein and lactose were all greater for cows fed BMR than for cows fed the high-cut silage or the silage cut at a conventional height. Dry matter intakes were relatively constant among all three groups.
Even so, producers need to consider some possible negative factors as they mull over options for utilizing BMR corn silage as part of an overall strategy to improve forage quality. Yield drag is one concern. Typically, you'll need to plant more acres to BMR to get the same amount of feed in the silo that you'd get from traditional corn silage or dual-purpose hybrids.
The good news is that the yield drag has been decreasing in recent years.
“Not that long ago, the yield drag for BMR on average was somewhere around 10-12%,” notes Karl Nestor, senior nutritionist with Mycogen Seeds, which collaborated with Kung in the 2006 study. “Now, with genetic improvements, the average yield drag is probably closer to 5%.”
Reduced drought tolerance of BMR compared to non-BMR corn is another possible negative.
“It's a matter of risk management,” says Kung. “If you're in a dryland situation and find yourself in a drought year, you'll likely take more of a hit on yield with BMR than you would with conventional corn silage varieties.”
One strategy worth considering: Target BMR plantings to soils that hold water well.
Dairy producers will also want to make sure they're working with a nutritionist willing to accommodate BMR in the ration.
“It feeds completely different,” says Nestor. “If you're working with a nutritionist who isn't willing to make the changes in the ration that go along with BMR corn silage, you'll likely have some problems.”
A key factor is that BMR is relatively high in energy. That means you won't feed as much grain. Also, because BMR is so digestible, you'll need to feed more of it. Mycogen recommends a minimum feeding level of 45 lbs/cow/day to gain a milk production increase of 4-5 lbs/day. In turn, that will mean more fiber in the ration.
“Going with a higher fiber level than what they're used to could be a problem for some nutritionists,” says Nestor. “Traditionally, increased fiber is negatively correlated with feed intake. What people need to understand is that, since the fiber in BMR is more digestible, intake is nota problem.”
Dairy producers can help their nutritionists manage BMR feeding programs by segregating BMR and conventional silage hybrids at harvest.
“If you blend them in the silo, you'll set up a nightmare for the nutritionist,” says Nestor.