Motor neurone disease in molybdenum-deficient sheep fed the endogenous purine xanthosine: possible mechanism for Tribulus staggers

Background The occurrence of Tribulus terrestris motor neurone disease (MND) in sheep is linked with grazing Tribulus growing on cultivation paddocks. A previous survey found that the molybdenum (Mo) content of Tribulus growing on uncultivated soils in the Coonabarabran district of New South Wales was 3.03 ppm, but on cultivated soils it was <0.04 ppm. Tribulus contains the purine, xanthosine, which functions as a neuromodulator, and the catabolism of xanthosine is Mo‐dependent. Design To investigate the relationship between xanthosine ingestion and low Mo concentration, eight sheep were fed Mo‐deficient lucerne chaff (<0.10 ppm), the Mo antagonist, sodium tungstate, and xanthosine (25 mg/kg/day) over 18 weeks and then returned to pasture. Results Signs of MND developed in two sheep 30 months later and astrocyte degeneration occurred in all sheep. Conclusion The findings were similar to those observed in sheep with T. terrestris MND, suggesting that the combination of xanthosine ingestion and Mo deficiency may be the cause of this disorder.