RUMINAL MICROBIAL ALTERATIONS ASSOCIATED WITH SULFIDE GENERATION IN STEERS WITH DIETARY SULFATE-INDUCED POLIOENCEPHALOMALACIA

Holstein steers were fed carbohydrate-rich, short-fiber basal diets wi th and without added sodium sulfate. Steers fed the high-sulfate diet developed the CNS disorder polioencephalomalacia (PEM). The onset of s igns of PEM was associated with increased sulfide concentration in the rumen fluid. Over the course of the disease, anaerobic rumen bacteria were enumerated in roll tubes by use of the Hungate method to determi ne the effect of dietary sulfate on sulfate-reducing bacterial numbers . Media used included a general type for total counts and sulfate-cont aining media with and without cysteine to assess sulfate-reducing bact eria. Changes in total and sulfate-reducing bacterial numbers attribut able to dietary sulfate content were not observed. The capacity to gen erate hydrogen sulfide from sulfate in fresh rumen fluid in vitro was substantially increased only after steers had been fed the high-sulfat e diet for 10 to 12 days, which coincided with the onset of signs of P EM. The low capacity for hydrogen sulfide production of rumen fluid ta ken at earlier times in the feeding period suggests that numen microor ganisms must adapt to higher dietary sulfate content before they are c apable of generating potentially toxic concentrations of sulfide.