Observations of ryegrass staggers in weaned lambs grazing different ryegrass pastures

Abstract

Weaned lambs grazing on ryegrass pastures in summer 1980/81 at Lincoln, Canterbury, were affected by ryegrass staggers, the outbreak being severe on an old-pasture ecotype, moderately severe on ‘Grasslands Nui’ (Lolium perenne L.) ryegrass, but absent on ‘Grasslands Ruanui’ (Lolium perenne L.) ryegrass. The attack occurred during a drought with high soil and daily minimum grass temperatures. Herbage mass was less than 2000 kg DM/ha and was predominantly dead leaf and flowering stalk. Old-pasture ecotype had a higher percentage of green leaf tissues (between 18–33%) than for Nui and Ruanui pastures (between 7–25%). Because of the severity of the attack, lambs on the old-pasture ecotype were removed and replaced during this period, whereas lambs less severely affected on Nui pasture remained there throughout. Although most of the lambs on Nui showed the severe symptoms of staggers during the outbreak, their liveweight at the end was similar to those lambs on Ruanui pasture. The subsequent linking of this variable incidence of ryegrass staggers to occurrence of Lolium endophyte, the duplication of the attack in mouse assay, and the occurrence of neurotoxins in the affected pastures are discussed.