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BMR: How a Gene Mutation Became a Breakthrough in Digestibility

By   /  November 14, 2016  /  No Comments

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bmr-ssx-248x300Over the course of the past decade, Brown Midrib, or BMR forages have become widely familiar as the elite of summer annual forages. The “cream of the crop,” these corn hybrids, sorghums, and pearl millets are distinguished by a genetic makeup that reduces their lignin content and can be visually evident as a light to dark brown tint in the stalk and leaf midrib. The BMR characteristic is actually caused by a natural genetic mutation that was discovered in the 1920s, which has the effect of increasing whole-plant fiber digestibility (usually expressed as NDFd and TTNDFD).

BMRs do have some drawbacks, but these have been managed with better genetics and handling in the field. For one, the lower lignin content can mean reduced standability, since lignin is what gives structure to the plant to support its weight, and becomes more critical once the plant gets tall and top-heavy with heading. This has been addressed by breeding for a dwarf structure, resulting in a shorter plant with greater amounts of leaf material in proportion to stalk tissue. Shorter, leafier plants can rival traditional sorghums in yield and get the bonus of greater fiber digestibility from a higher leaf-to-stem ratio. A dwarf BMR combines the advantages of lower lignin with a greater leaf to stem ratio.

Lowering nitrogen applications and seeding rates can also help alleviate standability issues.

Yield drag is another concern that sometimes afflicts BMR products. Our trials generally show slightly higher yields for non-BMR forage sorghums and sorghum-sudans, as well as superior and rapid regrowth. But looking closer at the nutritional data makes us question the edge these standard products truly provide. NDFd and TTNDFD are often several points higher for the BMR products, and each percentage point increase in NDFd is linked to an average 0.55 lb increase in milk production per cow/day. It’s also linked to a 0.37 lb increase in feed intake/cow/day, which is critical. What’s the point of a higher yield if it’s less digestible and leads to less feed intake? As Progressive Dairyman puts it, “the true measure of your hybrid is not apparent in the field, but rather when the work is done in the milking parlor.”

The following King’s AgriSeeds data taken from Mt. Joy, PA shows AF 8301, a non-BMR forage sorghum, coming in first for yield against a BMR lineup cut at soft dough stage, but at least 3 percentage points behind all the others for NDFd 30 hr. The differences do not appear stark, but each point lower in digestibility makes a difference in milk production. (Click to see it full size)

bmr-data

 

Corn silage has been the traditional standard for combining yield and quality in a forage, but BMR sorghums are now a contender – especially in droughty soils or dry conditions – as these products are more efficient than corn in both water and N use. In ideal soil and weather conditions, corn still wins for energy content (mostly from grain) and yield, and is still considered preferable for lactating dairy cows.

BMR sorghum products and millets can also fit nicely into a rotation where corn would struggle. Since they need to be planted later, in warmer soil temperature, the timeline for harvesting a double crop small grain is more generous. The bonus is that the sorghums handle hotter, drier conditions that might knock corn yield back.

With their lower lignin content, BMR products also generally have improved palatability, so cows eat more of the stem and leave less leaf litter on the ground. It is important to keep in mind, though, that a BMR product is not a guarantee of better quality. The nutritional advantage still varies by variety, and is of course heavily dependent on proper management.

BMR products have seen many breeding and management advances that make improve standability and harvest to allow this high quality product to work hard as a feed.

BMR sorghums are now part of the King’s AgriSeeds Feeding Pack Program, which rewards you with per-bag discounts when you diversify your order. The Feeding Pack Program promotes on-farm diversity to improve risk management for both the field and the feed inventory.

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About the author

Genevieve provides forage and cover crop research and marketing support for King's AgriSeeds Inc. in Lancaster County, PA. She has also worked on organic vegetable farms and as an intern in agricultural field trials at the Rodale Institute.

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