Doctoral Dissertations

Date of Award

12-1990

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

Richard N. Heitmann

Committee Members

James K. Miller, Karl M. Barth, John C. Waller, Dileep S. Sachan

Abstract

Mature ewes were equipped with catheters in the portal, hepatic, mesenteric and femoral veins and femoral artery. Blood flows were measured by infusing a 1.5% solution of para-aminohippurate into the mesenteric vein at .764 ml/min. Net fluxes of metabolites were calculated by multiplying veno-arterial differences by tissue blood flows.

Study 1. Twenty experiments were conducted on five ewes to determine the effects of fungus-infested fescue hay on energy nutrients and regulatory hormone net fluxes. Ten experiments were conducted for each a fungus-free and fungus-infested fescue hay diet. Fungus-infested hay decreased arterial concentrations of acetoacetate and B­ hydroxybutyrate by 15 and 30% due to a 24% decrease in alimentary ketogenesis. However, this was less than 2% of the total digestible energy intake.

Alkaloids present in fungus-infested fescue may stimulate the energy wasteful hepatic mixed-function oxidase system and may explain the increased rectal temperatures and decreased weight gains in animals experiencing fescue toxicity because the entire energy change of the reaction must be dissipated as heat.

Study 2. Respiration rates, rectal temperatures and mixed­-function oxidase activity as measured by hepatic antipyrine uptake was measured in three ewes to determine the effects of fungus-infestation and i.v. cimetidine (800 mg/d/ewe). Antipyrine, (.218% w/v) was infused into a mesenteric vein. Respiration rates, rectal temperatures and hepatic antipyrine uptakes increased following 11 d consumption of fungus-infested fescue, whereas 4 d treatment with cimetidine lowered these parameters back to control values.

Study 3. The efficacy of oral cimetidine (1200 mg/d) to reverse the changes observed in ewes fed fungus-infested hay were investigated using five ewes. Oral cimetidine did not change rectal temperatures, however, it increased plasma prolactin and decreased hepatic antipyrine uptake in ewes fed fungus-infested fescue.

Study 4. The efficacy of ergotamine tartrate to mimic fescue toxicity and metoclopramide to ameliorate these effects were investigated using four ewes. Fungusinfestation and ergotamine tartrate decreased plasma prolactin 69 and 94% and increased hepatic antipyrine extraction. Metoclopramide increased plasma prolactin concentrations and decreased hepatic antipyrine extraction in ewes fed fungus-infested fescue and ergotamine tartrate.

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