BMR Corn Silage

Brown mid-rib (BMR) corn silage has unique genetics providing lower lignin content and higher fibre digestibility (NDFD). This enables higher forage intakes and increased milk production in dairy cows. However, this improved livestock performance comes at the cost of lower silage yields per acre. So, where does BMR fit to its best advantage? 

BMR gets its name from the “brown mid-rib” characteristic that makes it visually distinct. Four naturally occurring BMR genetic mutations have been discovered since the 1930’s. The characteristic is not GMO. The mutation causes incomplete lignin formation. Plant breeders have taken this gene and incorporated it into modern corn genetics to commercialize silage-only hybrids. BMR corn silage is marketed in Ontario by Mycogen Seeds. The BMR characteristic is also found in sorghums. 

Higher Intakes & Milk Production

Fibre levels (NDF) of BMR corn silage are similar to normal levels, but lignin is typically 25 - 35% lower. The lower lignin results in much higher fibre digestibility (NDFD). NDFD levels are typically 8-10 percentage units higher than normal corn silage.

Research has shown that a 1% unit increase in forage NDFD results in 0.37 lbs more dry matter intake, resulting in 0.55 lb/cow/day more milk. University studies have consistently shown increased intake levels with BMR corn silage of 3 - 5 lbs dm/day. Reviewed research results vary, but milk production is typically improved by 3.5 - 6 lbs/day. The increased milk/day appears to be a result of increased dry matter intake, rather than higher energy content (NE_L). Higher intakes should enable fresh cows to maintain weight better and get back in calf sooner. Higher fibre digestibility enables increasing the amount of corn silage in the ration and reducing the amount of grain corn without adverse effects.

Because of the higher fibre digestibility of BMR, it is more advantageous to target it to classes of livestock where intakes are limited by physical fill. In large herds feeding TMR to groups these priorities would be close-up dry cows, fresh cows and first-calvers, and high producing dairy cows.

Lab Analysis

When sending BMR silage samples to a laboratory for analysis, use starch, NDF, and an in vitro NDFD to estimate energy, not the old method of estimating energy from ADF and NDF levels. The cheaper NIR analysis may require more calibration before we can accurately predict NDFD in BMR hybrids. BMR corn silage may have lower starch levels, offsetting the higher NDFD contributions to NE_L (mcal/kg).

Ration Balancing

Work closely with your nutritionist in ration formulation when feeding BMR corn silage. Because of its dramatically higher fibre digestibility, BMR silage behaves very differently in a ration. If you feed BMR silage the same way you would normal silage in a high grain ration, problems will result. Mycogen recommends feeding a minimum of 40 - 45 lbs/cow/day BMR silage (as fed). Higher fibre levels are required to maintain optimal rumen function and pH. Increase NDF and decrease grain levels in the ration to avoid acidosis. Provide adequate physically effective NDF. Do not include BMR in high grain diets. Mycogen also recommends a minimum forage to concentrate ratio of 55:45, and a minimum dietary NDF of 30%, or 32% where BMR is more than 50% of the forage dry matter.

Agronomics

In the past, we have typically seen a 10% yield drag with BMR corn. Lower yields (up to 20%) have been observed during seasons with more stress under marginal environmental conditions. However, there have been continued improvements in breeding. The fourth-generation hybrids now available are much improved over the original BMR hybrids commercialized over a dozen years ago, with better drought tolerance, disease resistance, and standability. Bt and RR traits are being incorporated. Mycogen claims they have narrowed the gap to a 5% yield drag. Ontario needs more independent silage yield data to evaluate these hybrids.

Harvesting

BMR cell walls are more fragile, so it is more prone to seepage and packs tighter. Harvest BMR silage slightly drier (2%) than normal silage. A longer theoretical length of cut (TLC) is necessary to maintain physically effective fibre, especially if using a kernel processor. Without a processor, a TLC of ¾ - 1 inch is recommended in a horizontal silo, and 5/8 - ¾ inch in a tower silo. With a processor, the TLC should be 1 - 1.5 inch in a horizontal silo, and ¾ to 1 inch in a tower silo. Avoid storage of BMR silage in bottom unloading silos. Using the milk-line to estimate moisture at harvest is not accurate. Moistures are best estimated by chopping a sample and using a Koster Tester, microwave or laboratory analysis.

Economics

There are some increased costs associated with BMR in addition to substantially higher seed costs. BMR corn silage produces more milk/ton, but not more milk/acre. Because of the lower yields and higher intakes, more corn silage acres will be required. This will partially be offset by fewer grain corn acres. What is the cost and availability of land rental in your area? BMR is most profitable when fed to close-up, fresh and high yield groups, and much less profitable if fed to the whole herd. What is the size of your dairy herd and can BMR be practically fed to specific groups?

Dairy producers should weigh the nutritional benefits against the agronomic costs associated with BMR hybrids to determine whether BMR has a place on their operations. Perhaps the most obvious situation where BMR may have an advantage would be in high corn silage diets. BMR is of interest to some milk producers in the Ottawa Valley, where there is a higher risk of alfalfa winterkill and more desire to increase the percentage of corn silage in the ration.

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