Maternal dexamethasone treatment in late gestation induces precocious fetal maturation and delivery in healthy Thoroughbred mares

Authors

  • J. C. OUSEY,

    Corresponding author
    1. Department of Veterinary Medicine Equine Fertility Unit, University of Cambridge, Mertoun Paddocks, Newmarket, UK; and Department of Clinical Sciences, Faculty of Veterinary Medicine & Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.
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  • M. KÖLLING,

    1. Department of Veterinary Medicine Equine Fertility Unit, University of Cambridge, Mertoun Paddocks, Newmarket, UK; and Department of Clinical Sciences, Faculty of Veterinary Medicine & Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.
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  • H. KINDAHL,

    1. Department of Veterinary Medicine Equine Fertility Unit, University of Cambridge, Mertoun Paddocks, Newmarket, UK; and Department of Clinical Sciences, Faculty of Veterinary Medicine & Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.
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  • W. R. ALLEN

    1. Department of Veterinary Medicine Equine Fertility Unit, University of Cambridge, Mertoun Paddocks, Newmarket, UK; and Department of Clinical Sciences, Faculty of Veterinary Medicine & Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.
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email: jenny.ousey@rossdales.com

Summary

Reasons for performing study: The foal requires an active hypothalamo-pituitary-adrenal (HPA) axis for organ maturation and post natal survival. Prenatal administration of synthetic glucocorticoids may provide an effective method for inducing fetal maturation safely in the mare.

Objectives: To determine whether dexamethasone administered to late pregnant mares: 1) will induce fetal maturation and precocious delivery; 2) is safe to use and 3) to identify endocrine responses in the mare and foal.

Methods: Pregnant Thoroughbred mares received either 100 mg dexamethasone i.m. (treated n = 5) or 50 ml saline i.m. (control n = 5) at 315, 316 and 317 days of gestation. Plasma progestagens, cortisol and prostaglandin F metabolite (PGFM) concentrations were measured before and after treatment. The foals were weighed, the crown-rump length (CRL) measured and an adrenal stimulation test performed on Day 1.

Results: Dexamethasone significantly (P<0.01) reduced gestation length in treated mares without apparent adverse effects. Plasma progestagens increased (P<0.05), and cortisol and PGFM (P<0.05) decreased, following dexamethasone treatment compared with control mares. Foals were clinically mature but those from dexamethasone treated mares had reduced (P<0.05) CRL, but not bodyweights, compared with controls. Their cortisol concentrations increased following exogenous adrenocorticotrophic hormone stimulation but 2 foals from dexamethasone treated mares showed evidence of adrenal suppression.

Conclusions: Dexamethasone stimulates precocious fetal maturation and delivery in healthy late pregnant mares. However, fetal HPA activity may be suppressed.

Potential relevance: Dexamethasone treatment could be used to improve foal viability in mares at risk of preterm delivery. The endocrine effects of such a therapy must be evaluated before clinical intervention with glucocorticoids can be recommended.

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