Tannin-containing native legumes offer pasture potential, according to Canadian research. They’re bloat-free, produce nitrogen, increase protein absorption and potentially can reduce methane gas production.

The legume at the top of the list: purple prairieclover.

“Purple prairieclover was a big surprise to us,” says Kim Ominski, University of Manitoba animal scientist. Manitoba researchers found that the legume has a 7% condensed tannin content, much more than other forage species.

Alfalfa; sainfoin; kura, red and white clovers; cicer milkvetch; birdsfoot trefoil; and purple prairieclover were clipped and analyzed in two provinces in 2005 and 2006. Results, just published in 2011, showed alfalfa ranking close to zero for tannin content; cicer milkvetch and kura, red and white clover each had less than 1%. Sainfoin contained 4-5% tannin.

Condensed tannins bind to proteins in the rumen, keeping them from forming foam that can trap gases in the rumen and cause bloat, Ominski says. Tannins also act as antimicrobial agents, says Mike Schellenberg, range plant ecologist at the Canadian government’s Semiarid Prairie Agricultural Research Centre, Swift Current, Saskatchewan.

“There is evidence that you get better processing of plant protein in the small intestine and, potentially, a decrease in methane gas” with tannin-containing forages, he says.

Purple prairieclover functions similarly to a warm-season grass, growing actively in late spring and flowering in July-August.

“At that time in our area, grasses typically are dry and brittle. Cattle will go out and select for the purple prairieclover while still taking the grass. The legume is green and probably at its nutritional peak.”

He’s also interested in white prairieclover, less common than its purple cousin but with larger leaves providing more forage value and more tannin.

“We’re hoping that, in two to three more years, we will have populations of both (prairieclovers) ready for marketing,” says Schellenberg. Antelope, a white prairieclover variety, is available on a limited basis from the USDA-NRCS Bridger Plant Materials Center, Bridger, MT.

The agronomic properties of purple prairieclover, sainfoin and birdsfoot trefoil are being studied at the Lethbridge Research Centre in southern Alberta.

“It’s a big challenge to develop this wild plant (purple prairieclover) into being suitable for agronomic production,” says Tim McAllister, ruminant nutrition specialist. “We’re very much in the preliminary stages, starting the domestication with samples from different regions and checking the condensed tannin levels.”

Forage breeder Surya Acharya is also selecting sainfoin plants that persist better in mixed stands with alfalfa under grazing conditions. He hopes to release a variety in two to three years. If 15% or more sainfoin can be maintained in alfalfa pasture, its tannin content will reduce the probability of bloat, he says.

Sainfoin and alfalfa are planted in alternate rows, so animals can graze both at the same time. Alfalfa would be more likely to choke out sainfoin if planted in the same rows.

Interestingly, sainfoin leaves, with 4-5% tannin, taste more bitter or astringent than the higher-tannin-content purple prairieclover, the researchers say.