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Influence
of a Tall Fescue Ergot Alkaloid on Plasma Concentrations of Metabolic
Regulators and Intermediates in Cattle
Richard
Browning, Jr.
Cooperative
Agricultural Research Program
Seminar Series
Tennessee State University, Nashville, TN
March 31,
1999
Introduction. Most tall fescue (Festuca
arundinacea Schreb.) pastures grazed by cattle are infected with the
fungal endophyte Neotyphodium coenophialum. The endophyte
produces alkaloids beneficial to the grass but detrimental to cattle
performance. Reduced growth and reproductive rates are common
occurrences in cattle consuming endophyte-infected (EI) tall fescue. A
consequence of cattle consuming EI tall fescue is "fescue
toxicosis." Fescue toxicosis causes a significant loss of income to
the largest segment of the agricultural economy in Tennessee and the
United States. Fescue toxicosis results in annual losses of at least $85
million to Tennessee beef producers, and $600 million to $1 billion
nationally. Basic mechanisms by which ergot alkaloids reduce cattle
productivity are not known, but previous research in this laboratory of
treating cattle with ergotamine, an ergopeptine alkaloid, suggests that
disrupted endocrine function may be involved.
Objectives. The objective of this research
effort was to determine if an ergopeptine alkaloid isolated from EI tall
fescue altered plasma concentrations of hormones important to regulating
metabolic function. Metabolism plays a central role in bovine
reproduction and growth. Shifts in metabolic processes could lead to
poor nutrient utilization, reduced nutritional status, and a subsequent
lowering of performance for traits of economic importance to cattle
producers.
Methodology. Crossbred cows were serially
bled for eight hours to determine plasma concentrations of metabolic
hormones (cortisol, triiodothyronine, insulin, glucagon), metabolites
(glucose, urea nitrogen, triglyceride), and leptin. Cows were treated
intravenously with saline vehicle or ergotamine tartrate after one hour
of blood sampling in a simple crossover design. Four cows were used in
the summer of 1997; six cows were used in the summer of 1998.
Results. Ergotamine significantly increased
plasma concentrations of each blood constituent measured, with the
exceptions of a significant decrease in plasma insulin and a biphasic
rise, then fall, in triglyceride concentrations. These responses
correspond with noted poor growth and reproduction.
Impact. Findings of this study are unique to
the current literature and suggest that altered metabolic function and
nutrient utilization may be a means by which EI tall fescue hinders
cattle performance. As past work at this location has done, this
research should help to stimulate research on mechanisms of fescue
toxicosis at other locations. Knowledge gained from this study will
provide the basis for future research aimed at elucidating the
fundamental pathways through which ergot alkaloids cause fescue
toxicosis. This information will also be helpful in efforts to devise
products or practices that would minimize production and economic losses
for cattle producers feeding EI tall fescue.
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