Brown Midrib Corn Silage Feeding Considerations

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Shared from Inside the ZONE^® newsletter.

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:

When determining inventory needs, recognize that BMR yields may be 5-10% less than conventional hybrids and that cows will consume more BMR silage due to the intake response.
Ration intakes that are typically elevated with BMR silage also contribute to an increase in the intake of total daily starch. This will be magnified if corn silage inclusion rates are also increased.
Ration adjustments may be needed with BMR corn silage, as with conventional corn silage, to compensate for increased starch digestibility over time in fermented storage.
Field experience suggests the physically effective fiber (peNDF) is less than that of conventional corn silages due to the fragility of reduced lignin fiber and may result in the reduction of the rumen mat, compared to conventional corn silage.
Some nutritionists adjust BMR-based rations with slightly higher NDF (32-35%) and peNDF (23-25%) levels than in herds feeding conventional corn silage and sometimes request that BMR silage be chopped 2-4 mm longer (e.g., 19-21 mm) to help maintain a suitable rumen mat. When chopping longer, it is essential that kernels be monitored to assure adequate kernel damage, which is as important with BMR silage as conventional silage.
Growing environment impacts BMR similar to conventional hybrids. If the growing environment results in lower fiber digestibility among conventional hybrids (e.g., excessive moisture during vegetative growth), BMR hybrids will also be lower in NDFD than expected. It is important to analyze for the digestion rate of the B3 (NDF) pool (e.g., via Fermentrics™) so ration-balancing programs can properly estimate the energy and microbial protein production from the BMR silage.
When feeding significant amounts of highly digestible corn silage, it is advisable to frequently monitor milk components along with manure consistency, cud-chewing, TMR particle size consistency and any evidence of sorting.
Field experience with herds that are borderline for effective fiber and/or acidosis issues and experience fat-test depression problems when starting to feed BMR silage have been successful in resolving the problem by either reducing grain (especially high-moisture corn), or adding sources of peNDF, such as straw, to help build a rumen mat and encourage cud-chewing.

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).

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