Cover Journal of the American Veterinary Medical Association
Journal of the American Veterinary Medical Association
ISSN:
0003-1488
Publication Date:
15 Mar 2004

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Thyroid function and pregnancy status in broodmares

Travis B. MeredithSection of Reproduction, Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
Present address is Veterinary Reproduction Specialists, 2218 N Main St, Tarboro, NC 27886.

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 DVM, DACT
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Ina DobrinskiSection of Reproduction, Department of Clinical Studies- New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

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 Dr med vet, PhD, DACT
DOI:
https://doi.org/10.2460/javma.2004.224.892
Volume/Issue:
Volume 224: Issue 6
Online Publication Date:
15 Mar 2004
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Abstract

Objective—To determine whether thyroid function was associated with pregnancy status in broodmares. Design—Prospective study.

Design–Prospective study.

Animals—79 Thoroughbred and Standardbred broodmares between 2 and 22 years old.

Procedure—Serum triiodothyronine (T3) concentration was measured before and 2 hours after IV administration of thyrotropin releasing hormone (TRH), and serum thyroxine (T4) concentration was measured before and 4 hours after TRH administration. Pregnancy status was monitored by means of transrectal ultrasonography beginning 16 days after ovulation.

Results—Baseline T3 and T4 concentrations varied widely. In all mares, serum T3 concentration increased in response to TRH administration. Serum T4 concentration increased in response to TRH administration in all but 2 mares. Pregnancy rate was 76%. Baseline and stimulated serum T3 and T4 concentrations were not significantly different between mares that became pregnant and those that did not.

Conclusions and Clinical Relevance—Results suggest that decreased thyroid function is uncommon in mares and poor thyroid function is not a common cause of infertility. Thus, the practice of indiscriminately treating broodmares with thyroid hormone to enhance fertility appears questionable at this time. (J Am Vet Med Assoc 2004;224:892–894)

Abstract

Objective—To determine whether thyroid function was associated with pregnancy status in broodmares. Design—Prospective study.

Design–Prospective study.

Animals—79 Thoroughbred and Standardbred broodmares between 2 and 22 years old.

Procedure—Serum triiodothyronine (T3) concentration was measured before and 2 hours after IV administration of thyrotropin releasing hormone (TRH), and serum thyroxine (T4) concentration was measured before and 4 hours after TRH administration. Pregnancy status was monitored by means of transrectal ultrasonography beginning 16 days after ovulation.

Results—Baseline T3 and T4 concentrations varied widely. In all mares, serum T3 concentration increased in response to TRH administration. Serum T4 concentration increased in response to TRH administration in all but 2 mares. Pregnancy rate was 76%. Baseline and stimulated serum T3 and T4 concentrations were not significantly different between mares that became pregnant and those that did not.

Conclusions and Clinical Relevance—Results suggest that decreased thyroid function is uncommon in mares and poor thyroid function is not a common cause of infertility. Thus, the practice of indiscriminately treating broodmares with thyroid hormone to enhance fertility appears questionable at this time. (J Am Vet Med Assoc 2004;224:892–894)