RESUMEN
The effect of sulphur on thiamine-destroying activity was studied in native or thiamine-spiked rumen content cultures. The treatments consisted of water [control (Ctrl)], sodium chloride (NaCl) and sodium sulphate (Na2SO4). A net gain (relative to 0 h) of thiamine in native cultures was observed for at least 48 h at levels of S ranging from 0.25 to 8 mg S added per ml of the culture and also in the Ctrl and respective NaCl cultures. However, after 48 h of incubation thiamine concentration was lower (p < 0.05) in native cultures treated with Na2SO4 relative to Ctrl and NaCl treatments. There was a linear (p < 0.03) time trend indicating an effect of Na2SO4 over time on changes in thiamine concentration in native rumen cultures. In thiamine-spiked rumen content cultures, the cultures treated with Na2SO4 produced higher (p < 0.05) thiamine-destroying activity. There was no effect of cation (Na) on thiamine-destroying activity. Initial heat treatment of thiamine-spiked cultures inactivated part of the thiamine-destroying activity. There were no differences among treatments in heat treated cultures. It is concluded that sulphate increases thiamine-destroying activity in the rumen content and the destructive mechanism involves thermolabile factor(s), however, the ruminal synthesis of thiamine is not affected by sulphate.