Alkaloids as a possible cause of ryegrass staggers in grazing livestock

Abstract

Ryegrass staggers has been observed in sheep and cattle grazing pastures consisting solely of ryegrass seedlings or new shoots. Ryegrass from these toxic pastures contained a much higher alkaloid content (0.15–0.25%) than more mature grass (0.02–0.06%). A high alkaloid content appears to occur consistently in seedlings and new shoots. The alkaloid content of seedlings rises to a maximum at the sixth to the eighth day after germination and then falls. In the decline period and probably in mature grass, the alkaloid content is subject to wide daily fluctuation thought to be due to meteorological factors. In mature grass the alkaloid is nearly all perloline, but in seedlings halostachine (Ph–CHOH–CH2–NHCH3) may also be present as a major constituent. Parenteral administration of perloline to guinea-pigs and sheep produces effects resembling the symptoms of ryegrass staggers and including tetanic spasm, at a dose level of 30 mg/kg which could be attained in sheep grazing toxic grass. On oral administration at 100–200 mg/kg, perloline produces the same effects in guinea-pigs out has no effect in sheep. Halostachine is known to have sympathomimetic properties but produced only mild effects in sheep and guinea-pigs at similar doses. The two alkaloids together, given either simultaneously by the oral route or in sequence (halostachine intravenously followed by perloline orally), did not lead to disturbances resembling staggers.