The genus Astragalus is the most numerous of the legumes, globally there are more than 2,000 species. In North America, there have been identified 368 species and 184 varieties, the seeds can remain alive in the soil for up to 50 years. Many of these species are toxic to cattle, sheep, horses, and wildlife. Currently, there are three toxic syndromes associated with the consumption of Astragalus in livestock: a. acute and chronic poisoning by nitro-compounds; b. acute and chronic poisoning by selenium; c. poisoning by alkaloids. Poisonings cause serious economic losses in livestock, not just by deaths, but for problems associated with nutrition, production, and reproduction. Our objectives were to identify the species of Astragalus in the Sonoran rangelands, and to recommend management practices that reduce damages in these areas. The study included 15 major vegetation types in the state: 4 were selected on forests, 4 on grasslands, 6 on scrublands and 1 in deciduous forest. In each vegetation type, five sampling sites of 1 ha (20 x 500 m) were randomly selected, and were monitored to identify the presence of Astragalus in the summer of 2009 and spring of 2010. Our results indicate that in these vegetation types there are 12 species of Astragalus toxic to livestock. In 75% of the total sites we found species growing in both spring and summer. We conclude that the diversity and dispersion of toxic species of Astragalus are affecting production in rangelands and present a serious threat to livestock in the state of Sonora.
Rangeland Ecology & Management
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