Lolitrem B concentrations, counts of Acremonium lolii hyphae, and the incidence of ryegrass staggers in lambs on plots of A. lolii-infected perennial ryegrass

Abstract Lolitrem B concentrations in Acremonium lolii-infected perennial ryegrass plants were highest in the basal halves of leaf sheaths, lower in the upper halves and in flowering stems and seeds, and lowest in leaf blades. Lolitrem B concentrations in bulk herbage samples from plots of ryegrass with high A. lolii infection rates were below 1 μ/g in winter, rose in spring, and fell in late autumn. Lambs grazing the plots in summer and autumn developed symptoms of ryegrass staggers when concentrations were greater than 2–2.5 μ/g dry grass. In a trial in which half of each of four plots had been topped to remove flowering stems, the incidence of ryegrass staggers was significantly higher on the untopped than on the topped plants. In another trial lolitrem B concentrations increased and grazing lambs developed ryegrass staggers symptoms as dry matter in the plots decreased. The amount of A. Lolii mycelium in infected plants, measured by visual counts of hyphae in leaf sheaths, rose in spring and fell in l...