Influence of Fungal Endophyte Presence on the Attachment of Ruminal Microorganisms to Cellulosic Substrate
Locoweed poisoning (Astragalus spp. and Oxytropis spp.) results in multi-million dollar losses to producers in the western United States due to a decreased animal performance and death. Prolonged consumption of Astragalus and Oxytropis species by animals produces a multitude of syndromes, including neurological problems, depression, emaciation, reproductive disturbances, birth defects, and abortion. The principle toxicant responsible for inducing locoism has been identified as the indolizidine alkaloid swainsonine. Swainsonine is a potent inhibitor of lysosomal mannosidase (Tulsiani et al., 1984, 1988) and Golgi mannosidase II (Elbein, 1989). Swainsonine-producing fungal endophytes, Embellisia sp. isolated from locoweed have been correlated with the toxicity of locoweeds. Toxic Astragalus and Oxytropis plants lose toxicity when grown without the fungi (Romero et al., 2002). The microbial population present in the rumen serves as a first line of defense for the ruminant animal. Use of swainsonine by the microbial population would result in a detoxification of this plant. Locoweeds, if detoxified, could be used by livestock producers and wildlife managers as an alternative feed source for ruminants. Locoweeds are considered to be a good quality feed and they are one of the first plants to grow in the early spring when most other range grasses are still dormant. However, it has not been determined the effect of swainsonine in locoweed on certain microbial populations in the rumen of cattle or sheep or if specific members of the ruminal microbial population will preferentially utilize the swainsonine found in locoweed. Any shifts in the microbial population in the rumen could result in a change of digestibility of locoweed. Three experiments will be conducted to determine if swainsonine and endophyte infected locoweed will influence the attachment of ruminal cellulolytic microbes to locoweed and thereby reduce digestibility of the plant. Attachment of ruminal cellulolytic microbes to plant fiber is essential for the digestion of fiber in the rumen and will be evaluated using scanning electron microscopy.