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Vasomodulatory Effects of Endophyte Infected Tall Fescue in Horses
K.J. McDowell, L. Lawrence, L. Bush
Department of Veterinary Sciences
Need: Pregnant mares grazing endophyte infected (E+) tall fescue frequently incur problems in late pregnancy such as extended gestation, thickened placenta, difficult births, lack of milk production, and potentially death of the foal and/or mare at parturition.
Rationale: Responses of individual mares grazing the same pastures are variable, and currently there are no convenient premonitory physiological measurements to determine which mares may experience problems of fescue toxicosis.
Methods: This project will determine if changes in vasoconstriction and blood flow parameters, as measured with Doppler ultrasonography, are satisfactory response variables to indicate which animals are consuming potentially detrimental levels of E+ fescue.
A change in fundamental and applied knowledge, in addition to learning new methods and techniques, by the PI and trainees in adapting the new and powerful tool of Doppler ultrasonography to equine basic research and field studies.
A change in action by field veterinarians as they improve their skills and learn to apply the technique to monitor mares for signs of fescue toxicosis.
Better and less expensive animal health care by providing field veterinarians with tools to monitor mares for signs of fescue toxicosis, and hopefully to be able to avert expensive and sometimes life threatening pre-parturient effects of fescue toxicosis in pregnant mares.
2009 Project Description
Pregnant mares grazing endophyte infected (E+) fescue frequently incur problems in late pregnancy such as extended gestation, thickened placenta, dystocia, agalactia, and potentially death of the foal and/or mare at parturition. Responses of individual mares grazing the same pastures are variable, and currently there are no convenient premonitory physiological measurements to determine which mares may experience problems of fescue toxicosis. This project is based on the hypothesis that E+ fescue consumption by mares will cause vasoconstriction that can be measured with Doppler ultrasonography.
Preliminary experiments were conducted 1) to determine a good candidate vessel for study, 2) to compare automated measurements calculated by the ultrasound machine vs manual trace measurements on those given parameters, and 3) to confirm the ability to detect vasoconstriction in the candidate vessel with Doppler ultrasonography. These experiments were successful, and the palmar artery of the left foreleg was chosen as the test focal vessel.
Then an experiment was conducted to test the central hypothesis stated above. Horses were fed E+ whole fescue seed (E+W), E+ ground fescue seed (E+G), or E- ground fescue seed (E-G). The experiment was divided into two periods (P), where P1 was an adjustment period in which animals received their normal daily ration of sweet feed and alfalfa cubes. P1 varied from 7 to 14 days as horses adapted to the diets. P2 was a 15-day treatment period during which the fescue seed was mixed into the ration. Consumption of E+G fescue seed caused vasoconstriction which could be readily measured by Doppler ultrasonography. The ground seed was more effective in causing vasoconstriction than was the whole seed, presumably because grinding the seed allows for better uptake of the E+ alkaloids by the digestive tract.
Future studies include experiments to determine 1) the minimum amount of E+ alkaloid necessary to cause vasoconstriction, 2) how quickly after the animal's first consumption of E+ fescue seed does vasoconstriction occur, and 3) how long after last consumption of E+ seed does vasoconstriction return to pretreatment levels.
Events and Dissemination:
Abstracts of the above experiments were presented in 2009 at the national Equine Science Society Meeting in Keystone CO, the 28th Annual University of Kentucky Symposium in Reproductive Sciences and Women's Health, and the University of Kentucky Forum for Reproductive Sciences.
These projects have resulted in new research collaborations with faculty and personnel of the University of Kentucky Departments of Veterinary Science, Animal and Food Sciences, Plant and Soil Sciences, the equine units of the University of Kentucky Agricultural Experiment Station, and the USDA-Agricultural Research Service-Forage Animal Production Research Unit in Lexington, KY.
The per annum impact of the horse industry to the gross domestic product of the United States is approximately $112.1 billion, with $7.4 billion of that attributed to the horse breeding industry. There are approximately 30 million acres of fescue in the United States and approximately 80% of that estimated is to be E+ tall fescue. Although currently there is no estimate of the economic impact of grazing E+ fescue in horses, in cattle the economic impact is reported to be approximately $600 million annually.
This work provides new information: to our knowledge these are the first experiments demonstrating that E+ fescue causes vasoconstriction in horses. Further research is needed to refine the techniques and determine applicability to pregnant mares. In the future transfer of this new knowledge and technology, may, for the first time, provide veterinarians, farm manages, and research scientists with a convenient and satisfactory response variable to determine premonitory signs of fescue toxicosis in broodmares. With such a biomarker, decisions can be made to treat affected pregnant mares and/or remove them from undesirable pastures before problems associated with fescue toxicosis at parturition occur, thus providing better and less expensive animal health care.
McDowell, K.J., Moore, E.S., Parks, A.G. Parks, and Lawrence, L.M. (2009) Use of Doppler ultrasonography on horses to detect vasoconstriction caused by endophyte infected fescue. Equine Science Society Proceedings, J. Eq. Vet. Sci. 29:338.