The effect of long-term onion consumption on red blood cell antioxidant enzymes [glucose-6-phosphate dehydrogenase (G6PD), superoxide dismutase (SOD) and glutathione peroxidase (GPx)], were measured. The relationship of these enzymes with PCV and hemoglobin (Hb) concentrations was also determined. Twelve adult female goats were used for the experiment and randomly assigned to three groups. Animals of group 1 and 2 received diets containing 30% and 60% spring onions (DM basis) for 60 days, respectively. Goats of group 3 served as control and were fed whole alfalfa hay. Blood samples were obtained before feeding onion and every 10 days up to 80 days. In the onion groups, PCV amounts decreased from day 10 and reached the lowest value at day 40. Although onion consumption reduced PCV, the measures were within the normal range for goats. G6PD activity decreased from day 10 and the lowest value was detected at day 40. After day 40, a slow and gradual return toward the baseline values was seen. In the onion groups, SOD showed a negative correlation with PCV and Hb (P<0.01). On the other hand, there was a positive correlation between G6PD and Hb (P<0.01). It seems that up to 60% of onions in diet can be consumed by goats without noticeable clinical anaemia. Moreover, it seems that SOD has a compensatory role in protection of erythrocytes against oxidative stress induced by onion consumption in goats.

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