Estimation of neurotoxin levels in perennial ryegrass by mouse bioassay

Abstract The use of a mouse bioassay based on a visual rating scale for tremor assessment and estimation of neurotoxicity of ryegrass extracts is described. The neurotoxicity of 69 samples of 3 different lines of perennial ryegrass (Lolium perenne L.) — an old-pasture ecotype, ‘Grasslands Nui’, and ‘Grasslands Ruanui’ — was determined by the mouse bioassay. The ryegrasses were from a site at Lincoln, near Christchurch, and were sampled over a 6-month period from October 1981 to April 1982. The method of extraction of the ryegrass samples and purification of the ryegrass extracts is described. The mouse bioassay results indicated a high level of neurotoxicity of the old-pasture ecotype ryegrass extracts compared to the ‘Grasslands Ruanui’ extracts, with ‘Grasslands Nui’ showing intermediate neurotoxicity. These results paralleled the incidence of ryegrass staggers in sheep that occurred on these plots over the sampling period.