Rates of Urinary Toxin Excretion in Unprotected Steers Fed \u3cem\u3eLeucaena leucocephala\u3c/em\u3e

Leucaena (Leucaena leucocephala) is a productive, nutritious, leguminous forage tree with high capacity for ruminant live weight gain. The plant does however contain the non-protein amino acid mimosine which is degraded within the rumen to 3-hydroxy-4(1H)-pyridone (3,4-DHP) with potential to cause adverse effects on animal health and production. Stock can be protected via rumen inoculation with the bacterium Synergistes jonesii, which is capable of degrading the toxin. However surveys have demonstrated sub-clinical toxicity is persisting in Queensland herds (Dalzell et al. 2012). Currently, testing for toxicity involves analysis of urine samples using high performance liquid chromatography (HPLC). A colorimetric urine test protocol has also been developed with the aim of providing a robust and reliable means for routinely testing herds (Graham et al. 2013). A significant problem affecting interpretation of the results from either method is the high variation in the concentrations of toxins excreted among animals on similar diets and by individual animals over time (Dalzell et al. 2012). Factors such as feed intake, water consumption, urine volume, as well as timing of sampling may be the cause of this variation. This research investigated the effect of sample timing by measuring the time taken for mimosine and its breakdown products, to present in the urine following the introduction of leucaena to the ration of cattle naïve to the plant