Effect of tricarballylic acid, a nonmetabolizable rumen fermentation product of trans-aconitic acid, on Mg, Ca and Zn utilization of rats.

trans-Aconitic acid has been implicated in magnesium deficiency of ruminants since the 1960s, but recent experiments indicated that much of it can be converted by rumen bacteria to tricarballylic acid (TCBA). Rats were used as experimental models in the studies described here because analogous experiments in ruminants would have been very expensive. When TCBA was fed to young male Sprague-Dawley rats as 2% of an AIN-76A diet with marginal (200 mg/kg) or adequate (500 mg/kg) Mg, virtually all of the dietary acid was recovered in the urine. Mg and Ca absorptions were unaffected by TCBA but urinary losses of Mg, Ca and Zn were higher than in pair-fed controls. TCBA was highly correlated (r = 0.93) with titratable acid excretion, and Mg, Ca and Zn retentions were reduced by 90, 35 and 56%, respectively. Rats fed 2% citric acid, a structurally similar but metabolizable acid, excreted more Zn than controls but did not excrete excess Mg or Ca. Since TCBA led to a depletion of Mg and other cations, it could be a contributing factor in the etiology of the Mg deficiency known as grass tetany in ruminants. Additional work in ruminants now seems warranted.