Weather and Plant Age Affect the Levels of Steroidal Saponin and Pithomyces chartarum Spores in Brachiaria Grass

Brachiaria species are cultivated worldwide in tropical and subtropical climates as the main forage source for ruminants. Numerous tropical and warm-season grasses cause hepatogenous photosensitization, among them several species of Brachiaria. Steroidal saponins present in these plants may be responsible for liver damage. However, sporidesmin and other hepatotoxic mycotoxins are likely to produce synergistic effects, which could explain the sporadic incidence of poisoning. The objective of this study was to evaluate the relation between steroidal saponin (measured by HPLC/ELSD), Pithomyces chartarum spores present in plots of Brachiaria, and the possible influence of meteorological factors on saponin and spores levels. The saponin detected in B. brizantha and B. decumbens was protodioscin. The saponin concentration was higher in immature plants during early growth; further, B. decumbens had a higher amount of saponin than found in B. brizantha. The level of saponin concentration was moderately influenced by weather variables; the two main variables were the maximum sunshine duration and total cumulative precipitation. P. chartarum spore count was higher in older plants and did not differ between B. brizantha and B. decumbens. Spore counting was influenced by maximum precipitation and average evaporation (Class A pan).