Sheep urinary lysergyls as a biomarker of exposure to ergovaline: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Science with Honours at Lincoln University

Abstract

Ergovaline is one of the ergot alkaloid toxins produced through association of the endophyte Neotyphodium lolii with perennial ryegrass. Ergovaline affects the health and productivity of sheep grazing ryegrass infected with Neotyphodium lolii. Ergovaline has been implicated in responses such as increased susceptibility to heat stress, lower plasma prolactin levels and reduced liveweight gains in ruminants. Little is known about the metabolism and excretion of ergovaline in ruminant animals and this hampers the development of strategies to limit or identify toxicosis. Therefore, there is a need to monitor lysergyl (ergovaline metabolites) excretion patterns and excretion rates in sheep after exposures to toxic feeds containing ergovaline. Peak excretion times after exposure may serve as the basis for development of a marker to diagnose whether sheep are grazing toxic alkaloid-containing pastures and also as a useful tool to further understand the metabolism of ergot alkaloids. Resistance of sheep to ryegrass staggers has been reported in sheep. The basis of resistance is not known. However, it could be due to reduced absorption, enhanced metabolism or increased excretion of the toxin.

Three experiments [I, 2 (2a, 2b), 3] were carried out with twenty-four sheep (resistant, outcross and susceptible sheep to ryegrass staggers) to monitor urinary lysergyl excretion pattern, plasma prolactin levels and thermoregulation following single/multiple exposure to endophyte-infected seed containing 30ppm ergovaline. The peak urinary lysergyl concentration occurred between 6 and 9 hours after exposure to ergovaline. Plasma prolactin levels were markedly reduced following exposure. Urinary lysergyls were less variable as a marker of exposure to ergovaline compared to plasma prolactin levels. The differences in peak excretion times and peak excretion rates of urinary lysergyls between the resistant, outcross and susceptible animals were not significant although the resistantanimals showed higher peak concentrations (experiments 2a and 2b) and the highest total lysergyl excretion (experiment 2b) compared with the susceptible and outcross sheep. Resistant animals given toxic feed containing ergovaline had a significantly lower rectal temperature (p<0.05) compared to the outcross and susceptible groups when exposed to a high ambient temperature and high humidity (experiment 3).

This study showed that urinary lysergyls may be used as a biomarker of exposure of sheep to ergovaline. It also showed that sheep resistant to ryegrass staggers are able to withstand heat stress more effectively than the susceptible and outcross animals. This is probably because the resistant sheep excrete more ergovaline metabolites as lysergyls in urine but this requires further validation