CYANOGENESIS POTENTIAL AND IODINE CONCENTRATION IN WHITE CLOVER (TRIFOLIUM-REPENS L) CULTIVARS

Hydrogen cyanide (HCN) and iodine (I) concentrations in the herbage were determined for 51 white clover (Trifolium repens L.) cultivars that had been grown under uniform conditions in a glasshouse. HCN contents ranged from 120 to 1110 mu g HCN/g dry matter (DM). Cultivars that are agronomically successful in New Zealand, and cultivars of New Zealand origin, were mainly highly cyanogenic. There was evidence in 'Grasslands Kopu' and 'Aran' of a decline in cyanide content in plants raised from first generation seed, compared to plants from Breeders or Basic seed. This decline may result in part from contamination of seed crops by low HCN resident clovers. Iodine concentration in the white clovers ranged from 0.08 to 0.21 mu g I/g DM with 77% of values being below 0.12 mu g I/g DM. There was no correlation between I and HCN concentrations. It seems there is little potential to improve the I nutrition of stock by selecting for increased I content in white clover. The influence of cyanogenic clover on the metabolism of I, selenium (Se), and sulphur (S) in sheep is discussed. It is concluded that these factors, and safety margins against direct cyanide toxicity, warrant further study.