Evaluation of ruminal sulfide concentrations and seasonal outbreaks of polioencephalomalacia in beef cattle in a feedlot.

摘要

Concentrations of thiamine in blood, and sulfide in ruminal fluid, were measured in 14 steers with acute signs of polioencephalomalacia (PEM) and 26 healthy steers. Records of all cattle in a feedlot for the past 6 years were reviewed. 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. 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 starting use of a water well containing a high content of sulfate. It is concluded that 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. It is suggested that when water is an important source of dietary sulfur, riskof PEM may increase during hot weather.