RATES OF OXALIC-ACID DEGRADATION IN THE RUMEN OF SHEEP AND GOATS IN RESPONSE TO DIFFERENT LEVELS OF OXALIC-ACID ADMINISTRATION

Oxalic acid is found in high concentrations in some plants consumed by ruminants and may cause renal toxicity. To determine whether exposure to oxalic acid affects the capacity of the rumen of sheep and gents t o degrade the compound, 20 animals (10 sheep and 10 goats) were dosed with free oxalic acid by gelatin capsule twice daily for 3 weeks at on e of five levels (0.0, 0.3, 0.6, 0.9 and 1.2 mmol/kg live weight (M) p er day). Rumen samples were collected by stomach tube in the week prio r to the start of dosing and in each week of the 3-week experiment. Ox alic acid degradation capacity was measured by adding C-14-labelled ox alic acid to rumen fluid in vitro and capturing evolved (CO2)-C-14. Ra tes of degradation increased with increasing level of administration ( 2.30, 4.71, 6.74, 9.83 and 13.90 mmol of oxalic acid degraded per 1 ru men fluid per day for doses 0.0, 0.3, 0.6, 0.9 and 1.2 mmol/kg M per d ay, respectively; P < 0.001). Rates of degradation increased during th e dosing period (P < 0.001) with the largest increases occurring in th e Ist week of dosing. Goats showed a greater response than sheep, with a higher mean oxalic acid degradation capacity (9.04 v. 5.95 mmol of oxalic acid degraded per l rumen fluid, P < 0.05). Oxalic acid adminis tration did not influence plasma calcium concentration or cause renal function impairment as measured by plasma creatinine concentrations. T he experiment demonstrated adaptation in the rumen to potential toxins in the host diet and suggests that the rumen micro-organisms of goats may have been move adapted to degrading oxalic acid than sheep.