By Bill Powel-Smith, DuPont Pioneer dairy account manager
Brown midrib (BMR) corn silage hybrids have been on the market for nearly two decades. This article provides examples of the growing and feeding experiences of dairy producers who have successfully incorporated BMR into their forage program.
BMR mutants were first discovered at the University of Minnesota in 1924, and BMR genes have been introduced into sorghum, sudangrass, millet and corn. BMR derives its name from plants displaying reddish-orange coloration on the underside of the leaf mid-vein (midrib), starting at the 4-6 leaf stage. BMR corn has 20-30% less lignin and reduced cross-linkages with other cell-wall carbohydrates. This results in improved neutral detergent fiber digestibility (NDFD). The reduced lignin content makes standability an issue for BMR hybrids, which relegates them to use for silage only. Early BMR hybrids were plagued with agronomic and drought-tolerance issues and had reduced silage yield (10-30%) compared with conventional silage hybrids. Modern BMR hybrids have much improved agronomics and disease resistance and often produce yields of total dry matter (DM) and starch that are very comparable to conventional silage hybrids.
BMR silage has been a success with crop and dairy managers who: 1) understand how to minimize agronomic risks by planting BMR on high-fertility soils, 2) desire high-forage (corn silage) diets, 3) are able to segregate the storage of BMR silage, and 4) allocate BMR silage to transition cows and cows producing more than 75-80 lbs. milk/cow/day.
The majority of BMR is grown in separate, high-fertility fields to minimize agronomic risks. BMR needs to be managed and harvested similar to conventional hybrids — ideally when the kernels are at a half to three-quarter milkline maturity. BMR hybrids are subject to the same effects of growing environment as conventional hybrids and can vary significantly in NDFD from year to year (or field to field), depending upon the unique growing environment. As with conventional hybrids, attention to kernel damage during harvest is critical to assure maximum ruminal starch availability. BMR silage also tends to be more prone to aerobic stability problems (i.e., heating) due to extremely high levels of sucrose in the stalk. This tendency for heating at feedout can be significantly reduced with the use of inoculants containing Lactobacillus buchneri strains like those found in Pioneer® inoculant 11C33.
The reduced lignin in BMR silage results in a 4- to 10-point higher NDFD value when analyzed in the lab. In the lab, the BMR sample cannot escape the analysis vessel. But in the cow, the net effect is a faster rate of NDF digestion and the more fragile fiber exiting the rumen much quicker than conventional corn silage. The bottom-line result is typically higher intakes of the entire ration (important in transition and early-lactation cows), which usually drives higher milk yields. The improved rate of digestion and feed passage allows for higher-forage diets, improved rumen health and the potential to remove some supplemental energy or protein (due to higher microbial production) from the diet.
Here are general considerations that dairy producers and nutritionists have developed over the past two decades of feeding BMR corn silages:
Remember that high-quality forage does not necessarily assure high milk production (e.g., cow comfort is equally important) but low-quality forage almost certainly guarantees low milk production (or very expensive rations).