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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.
2011 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. In addition, reports on whether E+ fescue affects nonpregnant mares by altering the length of the estrous cycle and/or circulating hormone concentrations are sparse and inconclusive.
These experiments are based on the hypotheses that E+ fescue seed consumption by mares causes vasoconstriction that can be measured with Doppler ultrasonography, and that E+ fescue seed alters the estrous cycle and hormone concentrations in nonpregnant mares.
Experiments completed demonstrated that:
1) adding E+ fescue seed to horses' feeds caused significant constriction of the palmar artery, and measuring that vasoconstriction via Doppler ultrasonography provides an excellent bioassay for vasoconstriction due to ingestion of E+ fescue,
2) ground E+ fescue seed is more effective in causing vasoconstriction of the palmar artery than is whole E+ fescue seed, presumably because grinding the seed allows for better uptake of the E+ alkaloids by the digestive tract.
Studies are in progress to determine
1) if the palmar arteries of pregnant mares fed E+ fescue seed respond in the same manner as the palmar arteries of nonpregnant mares, and if the uterine arteries of those same pregnant mares respond in a similar manner to the palmar arteries,
2) if E+ fescue seed ingestion alters the length of the estrous cycle, hormone concentrations during the cycle, and blood flow to the corpus luteum in nonpregnant mares,
3) how quickly after the animal's first consumption of E+ fescue seed does vasoconstriction occur,
4) how long after last consumption of E+ seed does vasoconstriction return to pretreatment levels, and
5) which alkaloids are most effective in causing vasoconstriction of the palmar and uterine arteries in vitro.
Events and Dissemination: Abstracts of the above experiments were presented in at the American Society of Animal Science meeting and at the University of Kentucky Forum for Reproductive Sciences, Lexington, KY (2010 and 2011). These activities have also been presented and discussed at Field Days, as well as informally with various veterinary and student groups. Target audiences are animal scientists, veterinarians, extension agents, and reproductive scientists.
Products: These projects have resulted in new fundamental and applied knowledge: that endophyte infected fescue causes vasoconstriction in horses in vivo and that vasoconstriction can be readily assessed with Doppler ultrasonography. It has also fostered new research collaborations with faculty and personnel of the University of Kentucky Departments of Veterinary Science and the USDA-Agricultural Research Service-Forage Animal Production Research Unit in Lexington, KY.
There are approximately 9.2 million horses in the United States and the horse industry sustains approximately 1.4 million full-time jobs annually. The overall value of the horse industry, including goods and services is approximately $102 billion per annum. There are approximately 30 million acres of fescue in the United States and approximately 80% of that is estimated 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, so it is easy to understand that the economic impact of fescue toxicosis in horses could be of considerable significance.
This work provides new information: to our knowledge these are the first experiments demonstrating that E+ fescue causes vasoconstriction in horses in vivo. Current research is aimed at refining the techniques and determining the applicability to pregnant mares and effects of E+ fescue on cycle length and hormone concentrations in nonpregnant 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 mares and/or remove them from undesirable pastures before serious problems associated with fescue toxicosis occur, thus providing better and less expensive animal health care.