Rates of oxalic acid degradation in the rumen of sheep and goats in response to different levels of oxalic acid administration

5 pages, 1 table, 1 figure.

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 goats to 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 one of five levels (0.0, 0.3, 0•6, 0.9 and 1.2 mmol/kg live weight (M) per day). Rumen samples were collected by stomach tube in the week prior to the start of dosing and in each week of the 3-week experiment. Oxalic acid degradation capacity was measured by adding 14C-labelled oxalic acid to rumen fluid in vitro and capturing evolved 14C02. Rates 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 rumen fluid per day for doses 0.0, 0.3, 0.6, 0.9 and 1.2 mmol/kg M per day, respectively; P < 0.001). Rates of degradation increased during the dosing period (P <0.001) with the largest increases occurring in the 1st week of dosing. Goats showed a greater response than sheep, with a higher mean oxalic acid degradation capacity (9.04 y. 5.95 mmol of oxalic acid degraded per 1 rumen fluid, P < 0.05). Oxalic acid administration did not influence plasma calcium concentration or cause renal function impairment as measured by plasma creatinine concentrations. The experiment dermonstrated adaptation in the rumen to potential toxins in the host diet and suggests that the rumen micro-organisms of goats may have been more adapted to degrading oxalic acid than sheep.

P. Frutos is grateful to the Spanish Council for Scientific Research (Consejo Superior de Investigaciones Científicas, CSIC, Spain) for the provision of a postdoctoral grant.

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