Endophytic fungi (A. coenophialum and A. lolii) which infect grasses produce ergot alkaloids that serve as the grasses' chemical defenses and enhance the vigor of the grass. Turf-type tall fescue with high endophyte levels has been deliberately developed to produce a greener, more vigorous, pest-resistant turf. Consumption of endophyte-infected grass causes various toxicity symptoms in livestock. Cattle in the southeastern and midwestern United States, where tall fescue is grown on 14 million hectares, often develop signs of toxicosis during summer months from grazing plants in fected by A. coenophialum. A more severe form of the disease, fescue foot, has been associated with cold environment and reported in late fall and winter months not only in the southeastern United States but also in the northwest United States. In New Zealand, where perennial ryegrass is grown on 7 million hectares of pasture, sheep often develop a condition called ryegrass staggers from grazing plants infected by A. lolii. New Zealand reports economic losses grazing plants infected by A. lolii. New Zealand reports economic losses associated with the sheep industry of $205 million per year. In the United States, economic losses associated with the beef cattle industry alone is estimated at $600 million per year. Range finding experiments and case studies of fescue foot and perennial ryegrass staggers (PRGS) were conducted on cattle and sheep under grazing and barn conditions. The main objective was to determine threshold levels of the endophyte toxins, ergovaline (EV) (appendix 1) and lolitrem B (appendix 2), associated with the diseases of fescue foot and PRGS respectively. Fescue foot was experimentally induced in cattle under barn studies in the spring with 825 ppb ergovaline. The ergovaline contaminated feed was given for a period of 42 days. Similar barn studies in sheep in spring to early summer did not produce clinical fescue foot with up to 1215 ppb. Field studies of natural fescue foot in a herd of sheep were conducted, (ie 540 ppb) values of ergovaline in the feed, but clinical disease was not produced in late fall through winter. A case study from a herd of sheep revealed 813 ppb dietary ergovaline had produced fescue foot in the months of fall (November). Fields of perennial ryegrass (PRG) where sheep received 2,135 ppb lolitrem B toxin were associated with clinical cases of PRGS in 42 sheep of 237 sheep (18 percent incidence rate) in the Willamette Valley of Oregon. Three months later, sheep on this same field which then had 1,465 ppb lolitrem B, did not have PRGS. These were the first range finding experiments undertaken in this locale to document threshold levels of endophyte toxins associated with fescue foot and PRGS. / Graduation date: 1994

Les associations symbiotiques entre différentes espèces de champignon du genre Epichloë et des plantes fourragères sont à l’origine de la production de mycotoxines responsables, dans certains pays, de toxicoses du bétail et de pertes économiques. Le développement de d’E. coenophiala dans la fétuque, qui est associé à la production d’ergovaline, est responsable de « fescue foot disease » alors que la présence d’E. festucae var. lolii dans le ray-grass anglais, qui est accompagnée d’une production de lolitrem B, est responsable du « ryegrass staggers » et de la production d’ergovaline, dont les effets toxiques associés à la présence de lolitrème B sont mal documentés. Mon travail de thèse a consisté à explorer les effets de la distribution de différents fourrages de fétuque et ray-grass endophytés toxinogènes produits dans des conditions agricoles françaises, sur la santé et la production animale et les mécanismes d’action de l’ergovaline et du lolitrème B. / The symbiotic associations between different varieties of fungi of the Epichloë kind and forages are responsible for the production of mycotoxins which are responsible of toxicoses in livestock and economic losses in some countries. The development of E. coenophiala in tall fescue, which is associated with the production of ergovaline, is responsible for « fescue foot disease » while the presence of E. festucae var. lolii in ryegrass, which is accompanied by the production of lolitrem B, is responsible for the « ryegrass staggers ». and the production of ergovaline, whose the toxic effects associated in the presence of lolitrem B are poorly documented. My thesis was to explore the effects of the distribution of different toxic forages of endophyte-infected tall fescue or ryegrass produced in French agricultural conditions on health and animal production and the mechanisms of action of ergovaline and lolitrem B.