The effect of hydrogen cyanide potential (HCNp) and sward morphology on the relative acceptability to sheep of white clover and Caucasian clover herbage

The effect of cyanide concentration and plant morphology on the relative acceptability to sheep of fifteen cultivars of Trifolium repens and one cultivar one cultivar of Trifolium ambiguum were assessed in a field trial at Armidale, Australia (30°S). Preference was shown for the taller, larger leaved cultivars of white clover such as Lucky. Regal, Haifa, Aran, Olwen, and for Monaro Caucasian clover, when differences in leaf size and height were most accentuated. Dry matter consumption was a poor indicator of preference. Acceptability measures were not well‐correlated with HCNp. Cyanide contents increased from January to April, but were considerably lower in July and November. Aran and Olwen had consistently the highest HCNp while Lucky, Regal and Monaro had the lowest HCNp. Sulphur contents were always high (> 2%) and varied only slightly between cultivars. Sheep preferred clover cultivars that were easiest lo harvest; these were large leaved, tall types. However, once the obvious differences in ease of harvesting were removed, sheep grazed opportunistically. Since HCNp had no effect on acceptability, breeders should aim for cultivars with moderate to low HCNp to retain pest protection but minimize goitrogenic potential. Caucasian clover exhibited a different growth pattern to white clover but its acceptability was similar.