EVALUATION OF RUMINAL SULFIDE CONCENTRATIONS AND SEASONAL OUTBREAKS OF POLIOENCEPHALOMALACIA IN BEEF-CATTLE IN A FEEDLOT

Objectives-To measure concentrations of thiamine in blood and sulfide in ruminal fluid in cat-tie with polioencephalomalacia (PEM) and to ev aluate temporal associations between PEM and risk factors. Design-Epid emiologic analysis. Sample Population-14 steers with acute signs of PE M, 26 clinically normal steers, and records of ail cattle in a feedlot for the past 6 years. Procedures-Concentrations of thiamine in blood and sulfide in ruminal fluid were measured. Values were compared betwe en healthy steers that had been in the feedlot for 3 weeks or 2 months . Records were used to estimate the incidence of PEM and the time when cattle were at greatest risk of developing PEM. Results Thiamine conc entrations in steers with PEM were within reference ranges. Healthy st eers had significantly greater sulfide concentrations 3 weeks after en tering the feedlot, when the incidence of PEM was greatest, than 2 mon ths alter entering the feedlot, when risk of developing PEM was low. T hiamine concentrations were within reference ranges at these times. An nually recurrent outbreaks of PEM during the summer began after initia ting use of a water well containing a high content of sulfate. Clinica l Implications-Excessive ruminal sulfide production is an important fa ctor in the pathogenesis of PEM, without concurrent thiamine deficienc y. Most cases of PEM developed between 15 and 30 days after introducti on to a high-sulfur diet. When water is an important source of dietary sulfur, risk of PEM may increase during hot weather.