Submitted to: New Zealand Veterinary Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2006
Publication Date: 7/28/2006
Citation: Schultz, C.L., Lodge-Ivey, S.L., Bush, L.P., Craig, A.M., Strickland, J.R. 2006. Effects of Initial and Extended Exposure to an Endophyte-Infected Tall Fescue Seed Diet on Faecal and Urinary Excertion of Ergovaline and Lysergic Acid in Mature Geldings. New Zealand Veterinary Journal. 54(4):178-184.
Interpretive Summary: Tall fescue (Festuca arundinacea Schreb.) is a perennial, cool-season grass commonly used for forage and turf purposes. Despite its good nutritive value, consumption of tall fescue by livestock results in a decrease in both reproductive and growth performance due to the presence of an endophytic fungus (Neotyphodium coenophialum). Three primary classes of alkaloids produced by the fungus play a potential role in affecting animal performance. These classes of alkaloids include: ergot (e.g., ergovaline and lysergic acid), unsaturated pyrrolizidine (e.g., lolines), and pyrrolopyrazine (e.g., peramine) alkaloids. Limited data concerning the fate of ergot alkaloids in grazing animals and the effects of exposure time to ergot alkaloids has limited progress in improving animal tolerance to toxic tall fescue. Therefore, the objective of this experiment was to determine the amount of ergovaline and lysergic acid retained or excreted by geldings fed endophyte-infected seed containing known concentrations of these alkaloids. Further, the effects of exposure time to ergovaline and lysergic acid on rectal temperature, serum prolactin and selected serum enzyme profiles were determined. Concentrations of ergot alkaloids detected in the urine and faeces did not change with increasing exposure time, thus the route for elimination of ergovaline and lysergic acid was similar between the Initial and Subacute Exposure Phases, which suggests the animal eliminates these compounds similarly regardless of exposure time. Faecal and urinary concentrations of ergovaline suggest that metabolism of or storage of ergovaline occurs. The negative balance of lysergic acid suggests that ergovaline and other alkaloids are eliminated via biotransformation to lysergic acid. Along with the need to establish a more satisfactory laboratory technique to measure individual alkaloids and metabolites, further research is needed to understand degradation of these compounds in both fore- and hind-gut fermentors. Delineation of the fate of ergovaline and lysergic acid will aid in the development of management protocols to enhance tolerance to toxic endophyte infected tall fescue in horses and other herbivores.
Technical Abstract: AIM: To determine the amount of ergovaline and lysergic acid retained or excreted by geldings fed endophyte-infected seed containing known concentrations of these alkaloids and the effects of exposure time to ergovaline and lysergic acid on rectal temperature, serum prolactin and selected serum enzyme profiles. METHODS: Mature geldings (n = 10) received diets containing either endophyte-free (E-) or endophyte–infected (E+) tall fescue seed during three experimental phases. The first phase (d -14 to -1) was an Adaptation Phase to allow horses to adapt to a diet containing E- tall fescue seed. The second (d 0 to 3) was the Initial Exposure Phase to E+ tall fescue seed used for the delivery of ergovaline and lysergic acid at 0.5 and 0.3 mg/kg of diet/d, respectively, to test the initial exposure effects on alkaloid routes and amounts of elimination. During this phase, half the geldings (n = 5) were exposed to an E+ diet while the remaining geldings (n = 5) served as controls by remaining on the E- diet. The third phase (d 4-20) served as the Subacute Exposure Phase to an E+ seed diet. Treatments in this phase were the same as the Initial Exposure Phase. Total faecal and urine collections were conducted within each phase to determine ergovaline and lysergic acid retention, and faecal and urinary output of each alkaloid. Nutrient digestibility was determined within each phase. Blood collected weekly, was analyzed for serum enzymes and prolactin. Body weights and rectal temperatures were recorded weekly. RESULTS: Body weight, rectal temperature, serum enzymes and prolactin, and nutrient digestibility were not affected by treatment. Total intake of ergovaline by E+ geldings was 3.5 and 3.6 mg/d (SE = 0.20) with 2.1 and 2.3 mg/d (SE = 0.11) retained by the animal, respectively for initial and subacute phases. In contrast, the amount of lysergic acid excreted in the urine (4.0 and 4.9 mg/d; SE = 0.97) and faeces (2.5 and 2.7 mg/d; SE = 0.35) was greater than that consumed (2.0 mg/d; SE = 0.09). Neither initial nor subacute exposure to E+ seed had any effect on the amount of ergovaline (p=0.09) or lysergic acid (p=0.38) retained by the geldings. However, animals exposed to E+ seed for a period of 20 d appeared to excrete more (1.5 vs 1.2 mg/d; SE = 0.08; p=0.03) faecal ergovaline than those exposed for only 4 d. CONCLUSIONS: Exposure time to the ergot alkaloids had limited effects on the route of elimination or the ergovaline or lysergic acid concentrations excreted by the animal. The primary alkaloid excreted was lysergic acid with urine as the major route of elimination. In addition, geldings consuming 0.5 and 0.3 mg ergovaline and lysergic acid/kg diet/day, respectively, for 21 d are minimally intoxicated as shown by the limited expression of signs associated with fescue toxicosis. Metabolism of the ergot alkaloids is an area of interest and warrants further research. However, increased knowledge and understanding of the fate of these compounds will hopefully aid in future research.