Physio-pathological aspects of thiamin (vitamin B1) in ruminants

Abstract

This review aims first to provide specific information on microbial synthesis, the absorption and the metabolism of vitamin B1 in healthy ruminants, and on the influence of low thiamin production on rumen microbial activity. In the second part the authors discuss the etiology and the pathogenesis of cerebrocortical necrosis in the light of the most recent data. The factors involved in the microbial synthesis and catabolism of thiamin under usual feeding conditions are well known ; however factors liable to disturb the net production or absorption of thiamin in the digestive tract under low- or overfeeding conditions, or in the case of inbalanced diets, are not well understood. Classical pathogenesis of cerebrocortical necrosis involves the ruminal overproduction of thiaminases I.This theory is not entirely satisfactory, since the normal rumen microflora has a low thiaminase I activity and since factors which allow the establishment of thiaminase producing bacteria are not known. Excess of sulphur in the diet also induces typical signs of cerebrocortical necrosis but its relation to a thiamin deficiency is not clear. It isore likely that we are dealing with two independant etiologies which are expressed by the same clinical syndrome.