Scientists Move Closer to Solving Pasture Bloat Problem

Livestock love alfalfa. Alfalfa doesn't always love them back.

As a crop, alfalfa is worth about $8 billion each year to the United States economy because of its role in the domestic beef cattle and dairy industries, as well as exports. Agricultural producers value the legume because it can grow without nitrogen fertilizer by virtue of a symbiosis it forms with bacteria called rhizobia. The bacteria convert atmospheric nitrogen (N2) to ammonia (NH3) that is used for plant growth.

There's just one problem: Livestock that graze extensively on alfalfa often develop pasture bloat, a form of severe indigestion where gas collects in the rumen and cannot be expelled. Extreme bloat can kill an animal. Less severe bloat can still reduce weight gains, lower milk production, reduce feed efficiency and increase labor costs.

Noble Foundation researchers have been studying condensed tannins as a bloat remedy. This naturally occurring class of chemical compounds possesses the ability to reduce bloat in livestock. Humans may be more familiar with the role of condensed tannins in red wine, where they provide the drink's bitter taste.

Tannins are naturally found in small amounts in the seed coat of alfalfa. Unfortunately, seeds include only trace amounts of tannins, and livestock consume too little of the compound to be effective. Researchers have been looking at ways to engineer plants with tannins in the leaves and stems so animals could ingest much more of these compounds.

Recently, Noble Foundation scientists became the first group to generate tannins in a part of the alfalfa plant beyond the seed coat.

"This work is a significant step towards reduced-bloat alfalfa," said Michael Udvardi, principal investigator for the laboratory that made the breakthrough. "Pasture bloat impacts the productivity of animals in agricultural systems. Reducing the impact of bloat would have an industry-wide impact."

The discovery occurred in part because of a scientist with a keen eye. Noble Foundation Research Scientist Jerome Verdier was examining genetic variations of Medicago truncatula (a model plant used for the study of legumes) when he spotted one with lighter-colored seed coats, a telltale sign of a plant that had trouble making tannins.

Working with Jian Zhao, a postdoctoral fellow in the laboratory of Richard Dixon, Verdier found that plants with the light seed coats were defective in a gene encoding a transcription factor — which regulates multiple genes, like a fusebox controls a home's electrical system. This particular transcription factor controlled a portion — but not all — of the tannin production process.

This knowledge allowed the scientists to develop plants that had tannins in the roots, and a small amount in the leaves and stems.

"Up until now this has never been achieved," said Dixon, director of the Noble Foundation's Plant Biology Division. "This kind of understanding could eventually lead to bloat control and improved forage quality for agriculture. Furthermore, this type of discovery is a credit to the research environment at the Noble Foundation, where scientists across the institution come together to share ideas and collaborate for the advancement of the science."

The ground-breaking research was recently published in the Proceedings of the National Academy of Sciences, one of the world's most cited multidisciplinary scientific journals.

— News release provided by the Noble Foundation

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