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A Search for Condensed Tannins in Annual and Perennial Species of Medicago, Trigonella, and Onobrychis¹

Bloat of ruminant animals feeding on fresh, green alfalfa (Medicago sativa L.) is caused by high levels of soluble plant proteins which act as foaming agents. It is postulated that bloat-safe cultivars may be bred by introducing condensed tannins (flavolans) which would act as protein precipitants to preclude foam formation and consequent bloat. Using the vanillin-HCl spot test, large populations of alfalfa were screened for tannins. These included several accessions, cultivars, and breeding populations. Extensive screening of 2n M. falcata L. and 4n M. sativa treated with the chemical mutagens ethyl methanesulfonate or ethyleneimine failed to reveal any mutations for tannins. Screening of 33 species (a total of 86 accessions) of annual Medicago was negative. Similarly, screening of 28 species (a total of 92 accessions) of perennial Medicago was also negative. Examination of 30 species (46 accessions) of the closely related Trigonella genus did not reveal any tannin-containing plants. On the other hand, testing of 123 accessions of 10 species of Sainfoin (Onobrychis) showed that all plants examined within this bloat-safe genus contained high levels of tannins.

Several of the common pasture legumes, including both bloat-causing and bloat-safe types, were examined for tannins in leaf tissue, flower (petal) tissue and seeds. All of these legumes except alfalfa and cicer milkvetch (Astragalus cicer I.,) contained tannins in petal tissue. All of the legumes, including alfalfa, contained tannins in seedcoat tissue except that of a homozygous recessive, white-seeded strain of alfalfa.

The implications of breeding for tannins to provide a bloat-safe alfalfa are discussed.

Key Words: Flavolans • Pasture bloat • Protein precipitants • Alfalfa

² Section head and senior research scientist, Agric. Canada, Saskatoon; assistant professor, Food Sci. Dep. and professor emeritus, Dep. of Genetics, Univ. of Alberta, Edmonton, respectively.

Received for publication February 27, 1980.

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