Alfalfa Reinvented Bioengineering could improve fiber, protein digestibility

January 13, 2010 09:12 AM

Alfalfa, once the queen of forages, has lost its crown. Dairy producers are growing and feeding more corn silage due to its higher yields, higher digestibility and consistent performance.

But researchers at the U.S. Dairy Forage Research Center (USDFRC) and the Consortium for Alfalfa Improvement hope to bring some of the sparkle back to alfalfa.

Specifically, alfalfa breeders are looking to improve fiber digestibility and slow down the rate of protein digestibility in the cow's rumen, says Neal Martin, USDFRC director. They hope that these improvements will renew interest in alfalfa and increase planted acres. That, in turn, will be better for erosion control, soil nutrient cycling and cow health.

"One goal is to decrease the amount of lignin by silencing genes in some cells of the plants but not others,” Martin says. Lignin is needed in stems to hold the plant upright, but not in leaves, where it inhibits digestibility.

Initial research with reduced-lignin alfalfa varieties shows neutral detergent fiber digestibility increasing 4 to 11 percentage points. Milk production, because cows digest more, jumps nearly 3 lb./cow/day. Longer cutting intervals might also be possible, which could improve yields and the consistency of the resulting feed.

Conversely, the protein in alfalfa is often too highly digestible, resulting in wasted protein and excessive nitrogen excretion. Here, researchers are looking at two avenues of attack:

  • Birdsfoot trefoil, another legume, produces tannins—phenolic compounds that bind with proteins—in its leaves and stems, with the result that more protein bypasses the rumen. Martin reports an increase of 11 lb./day of milk from cows fed birdsfoot trefoil over cows fed alfalfa silage. "It may be possible to engineer alfalfa to produce tannins that provide protein protection in the rumen and lead to less bloat,” he says.
  • Red clover has compounds that inhibit protein breakdown during fermentation. If these could be bio-engineered into alfalfa, ruminal protein digestion might be slowed and more protein made available to the small intestine, where it is directly absorbed and utilized.

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