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 mm 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 mm (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
