Equis ISSN 2398-2977

Female: shortened diestrus

Synonym(s): Shortened interestrus interval

Contributor(s): David Dugdale, Graham Munroe, Sarah Stoneham, Madeleine L H Campbell

Introduction

  • Cause: shortened diestrus due to the failure of the corpus luteum can result from endometritis, endotoxemia, iatrogenic therapy, or cervical/uterine manipulations.
  • Signs: early return to estrus.
  • Diagnosis: palpation and ultrasonography of the reproductive tract; supportive laboratory testing where appropriate, eg cytology, bacteriology.
  • Treatment: treat cause.
  • Prognosis: depends upon cause.
  • See also Uterus: endometritis - bacterial.

Pathogenesis

Etiology

Pathophysiology

Normal reproductive physiology

  • Diestrus has an average duration of 16 days, and extends from ovulation to luteolysis.
  • Following ovulation, plasma progesterone concentration Endocrine: hormone assay - female increases from 0 ng/ml to 8 ng/ml by day 5. Peak concentration of 5-20 ng/ml is achieved between days 5 and 8 and maintained until days 14-15.
  • Progesterone exerts a negative feedback on gonadotropin releasing hormone (GnRH) which in turns decreases the concentration of luteinizing hormone (LH).
  • Follicle stimulating hormone (FSH) is unaffected and often peaks mid-diestrus.
  • Prostaglandin F2 alpha is released from the endometrium in the absence of pregnancy and → lysis of the corpus luteum.
  • A rapid decline in plasma progesterone concentration follows which initiates estrus by 'unmasking' estrogen.
  • Normal physiology is disrupted, resulting in shortened luteal phase/diestrus, for the following reasons: endometritis → inflammation of the endometrium → prostaglandin synthesis and release → luteolysis → premature return to estrus. Any mare that exhibits shortened diestrus should be assessed for endometritis:
    • Acute inflammation is more liable to cause early return to estrus than is chronic inflammation.
    • Contagious equine metritis Uterus: contagious equine metritis is a transient, but acute, infection which → decreased interestrous intervals in most cases.
Degenerative endometritis/endometriosis/uterine fibrosis however can → decreased release of prostaglandin, thus causing prolonged (rather than shortened) diestrus. In pregnant mares, endotoxemia can induce fetal death mediated via an PGF2α-induced reduction in luteal function.
  • Cervical/uterine manipulation:
    • For example uterine biopsy, non-surgical transfer of an embryo can result in leuteolysis by provoking a release of PGF2α.
    • Administration of a non-steroidal anti-inflammatory, eg flunixin Flunixin meglumine may reduce this prostaglandin release.
  • Iatrogenic therapy:
    • Treatment with exogenous prostaglandin F2α on day 5 or later after ovulation will cause luteolysis and thus shortened diestrus.
    • Treatment with exogenous prostaglandin F2α as early as day 1 or 2 post-ovulation can disrupt normal formation of the corpus luteum, and result in shortened diestrus.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Crowell-Davis S (2007) Sexual behavior of mares. Hormones and Behavior 52 (1), 12-17 ScienceDirect.
  • Daels P F, Stabenfeldt G H, Kindahl H & Hughes J P (1989) Prostaglandin release and luteolysis associated with physiological and pathological conditions of the reproductive cycle of the mare: a review. Equine Vet J 21 (S8), 29-34 VetMedResource.
  • Koskinen E, Kuntsi H, Lindeberg H & Katila T (1989) Predicting ovulation in the mare on the basis of the follicular growth and serum estrone sulfate and progesterone levels. Zentralbl Veterinarmed [A] 36 (4), 299-304 PubMed.
  • Lofstedt R M (1988) Control of the estrous cycle in the mare. Vet Clin North Am Equine Pract 4 (2), 177-196 PubMed.


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