Faecal thiaminase in clinically normal sheep associated with outbreaks of polioencephalomalacia

Three flocks in which one or more sheep had succumbed to polioencephalomalacia (cerebrocortical necrosis) were used for faecal thiaminase studies. Up to one third of the clinically normal animals in these flocks were found to be excreting thiaminase on any one day and over half the flock could be thiaminase excretors at some time during an outbreak. The possible detrimental effects of subclinical thiamine antagonism in sheep are therefore worthy of consideration. Thiaminase excretion by individual animals was variable and sometimes intermittent. It was unaffected by changes in diet, pasture or environment. In two of the flocks multiple cases of polioencephalomalacia followed the administration of the anthelmintics, levamisole hydrochloride and thiabendazole. This aspect merits further investigation in view of the widespread use of anthelmintics of this type, especially as the profuse diarrhea which can be associated with outbreaks of polioencephalomalacia may be wrongly attributed to gastrointestinal parasitism.