THE EFFECT OF A DIET CONTAINING CYANOGENETIC GLYCOSIDES ON THE SELENIUM STATUS AND THE THYROID-FUNCTION OF SHEEP

Six ewes were given a white clover/grass silage with a high content of cyanogenetic glycosides during the last 69 to 97 days of pregnancy (group CN+), while the five ewes of the control group (group CN-) received a white clover/grass silage with a low content of cyanogenetic glycosides during the last 67 to 92 days of pregnancy. Uniodized salt was the only mineral supplement offered. The daily intake of cyanide (in the form of cyanogenetic glycosides) and of selenium per animal was 1000 and 60 mg of cyanide and 30 and 23 mug of selenium in group CN+ and CN-respectively. Initial erythrocyte glutathione peroxidase activity (GPx) was identical in both groups. Two weeks before parturition GPx activity was significantly lower in the ewes of group CN+ than in the ewes of group CN-. The newborn lambs of the group CN+ had significantly lower erythrocyte GPx activities (P < 0.01) and tended to have higher plasma creatine kinase activities (P = 0.07) than the lambs of the group CN-. The results show that the intake of cyanogenetic glycosides affects the selenium status of sheep and increases the susceptibility of lambs to nutritional myopathy if the selenium content of the ration is marginal. Plasma thyroxine concentrations in the ewes in group CN+ were not reduced but their lambs tended to have slightly lower levels immediately after birth than the lambs of group CN- (P = 0.15). The intake of cyanogenetic glycosides presumably had no or at most only a slight effect on thyroid function, presumably because the body iodine reserves of the ewes were sufficient to offset the goitrogenic effect of thiocyanate.