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 feedlot, 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.