Prolonged gestation, decreased triiodothyronine concentration, and thyroid gland histomorphologic features in newborn foals of mares grazing Acremonion coenophialum-infected fescue

Timothy R. Boosinger From the Departments of Pathobiology (Boosmger, Wright), Large Animal Surgery and Medicine (Brendemuehl), and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine; Agronomy and Soils (Bransby, Kee), College of Agriculture, Auburn University, AL 36849-5519.

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James P. Brendemuehl From the Departments of Pathobiology (Boosmger, Wright), Large Animal Surgery and Medicine (Brendemuehl), and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine; Agronomy and Soils (Bransby, Kee), College of Agriculture, Auburn University, AL 36849-5519.

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David L. Bransby From the Departments of Pathobiology (Boosmger, Wright), Large Animal Surgery and Medicine (Brendemuehl), and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine; Agronomy and Soils (Bransby, Kee), College of Agriculture, Auburn University, AL 36849-5519.

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James C. Wright From the Departments of Pathobiology (Boosmger, Wright), Large Animal Surgery and Medicine (Brendemuehl), and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine; Agronomy and Soils (Bransby, Kee), College of Agriculture, Auburn University, AL 36849-5519.

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Robert J. Kemppainen From the Departments of Pathobiology (Boosmger, Wright), Large Animal Surgery and Medicine (Brendemuehl), and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine; Agronomy and Soils (Bransby, Kee), College of Agriculture, Auburn University, AL 36849-5519.

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David D. Kee From the Departments of Pathobiology (Boosmger, Wright), Large Animal Surgery and Medicine (Brendemuehl), and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine; Agronomy and Soils (Bransby, Kee), College of Agriculture, Auburn University, AL 36849-5519.

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SUMMARY

Newborn foals of mares grazing on Acremonium coenophialum-infected fescue pasture throughout gestation or from gestation day 300 to parturition had increased gestation duration and decreased serum triiodothyronine concentration. Pregnant mares were allotted to 4 treatments: grazing continuously on endophyte-free (E) fescue, grazing continuously on endophyte-infected (E+) fescue, grazing on E+ fescue from gestation day 300 to parturition, and grazing on E+ fescue from conception to gestation day 300. Morphometric studies indicated that foals born to mares exposed to endophyte late in gestation had large, distended thyroid follicles lined by flat cuboidal epithelial cells. Mean triiodothyronine concentration in foals exposed to endophyte (395.2 ng/dl) was decreased (P < 0.01), compared with mean values in control foals (778.0 ng/dl). Thyroxine and reverse triiodothyronine concentrations were not significantly different among groups. Foal organ weight as a percentage of foal body weight was not significantly different among experimental groups.

SUMMARY

Newborn foals of mares grazing on Acremonium coenophialum-infected fescue pasture throughout gestation or from gestation day 300 to parturition had increased gestation duration and decreased serum triiodothyronine concentration. Pregnant mares were allotted to 4 treatments: grazing continuously on endophyte-free (E) fescue, grazing continuously on endophyte-infected (E+) fescue, grazing on E+ fescue from gestation day 300 to parturition, and grazing on E+ fescue from conception to gestation day 300. Morphometric studies indicated that foals born to mares exposed to endophyte late in gestation had large, distended thyroid follicles lined by flat cuboidal epithelial cells. Mean triiodothyronine concentration in foals exposed to endophyte (395.2 ng/dl) was decreased (P < 0.01), compared with mean values in control foals (778.0 ng/dl). Thyroxine and reverse triiodothyronine concentrations were not significantly different among groups. Foal organ weight as a percentage of foal body weight was not significantly different among experimental groups.

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