Absorption of tricarballylic acid from the rumen of sheep and cattle fed forages containing trans ‐aconitic acid

Abstract Some forages accumulate high concentrations (< 5% of dry matter) of trans‐aconitate, and this acid has been implicated in Mg chelation and the occurrence of grass tetany in ruminants. In vitro experiments have indicated that rumen microorganisms convert trans‐aconitate to tricarballylate. The feeding studies described here were conducted to demonstrate absorption of tricarballylate by ruminant animals fed diets similar to those producing grass tetany. When sheep were switched from a diet containing alfalfa (lucerne) (Medicago sativa L.) hay (no detectable trans‐aconitate) to wheat (Triticum aestivum L.) and rye ( Secale cereale L.) forage containing 1.52 and 1.37% trans‐aconitate, respectively, there was a rapid increase in blood plasma tricarballylate. Trans‐aconitate was not detected in the plasma. At 16 h after feeding, plasma tricarballylate concentrations were 0.58.0.08 and 0.48.0.21 m M in sheep fed the wheat and rye forage, respectively. Tricarballylate concentrations remained relatively constant for the remaining 60 h of the experiment. Cattle were fed rye forage one week later, and the concentration of trans‐aconitate in the forage had dropped to 0.83% of the dry matter. Once again there was a rapid appearance of tricarballylate in plasma, but the maximum concentration was 0.31.0.05 m M (t = 27 h). When the cattle were removed from the rye forage, there was a linear decline in tricarballylate and none was detected 24 h later. The studies indicated that trans‐aconitate is converted to tricarballylate in the rumen and that tricarballylate rather than trans‐aconitate is absorbed.