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 cattle with polioencephalomalacia (PEM) and to evaluate temporal associations between PEM and risk factors. Design - Epidemiologic analysis. Sample Population - 14 steers with acute signs of PEM, 26 clinically normal steers, and records of all 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 between 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 concentrations in steers with PEM were within reference ranges. Healthy steers had significantly greater sulfide concentrations 3 weeks after entering the feedlot, when the incidence of PEM was greatest, than 2 months after entering the feed-lot, when risk of developing PEM was low. Thiamine concentrations were within reference ranges at these times. Annually recurrent outbreaks of PEM during the summer began after initiating use of a water well containing a high content of sulfate. Clinical Implications - Excessive ruminal sulfide production is an important factor in the pathogenesis of PEM, without concurrent thiamine deficiency. Most cases of PEM developed between 15 and 30 days after introduction to a high-sulfur diet. When water is an important source of dietary sulfur, risk of PEM may increase during hot weather.