Equis ISSN 2398-2977

Female: anestrus during ovulatory season

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

Introduction

  • A period of true anestrus with complete absence of luteal function is occasionally seen during the physiologic breeding season.
  • Cause: obscure; nutritional factors may be involved. Rarely (3-4% of foaling mares), may be a true lactational anestrus. Sometimes associated with having foaled very early in the breeding season (when days are still short) - mares enter a period of anestrus following foaling and then start to cycle normally once day length increases.
  • Signs: ovarian inactivity and loss of uterine tone.
  • Diagnosis: serial plasma progesterone assays.
  • Treatment: wait for return to cyclicity or GnRH by minipump or implant.
  • Prognosis: reasonable unless nearing the end of the ovulatory season, in which case return to cyclicity may be delayed until the next year.

Pathogenesis

Etiology

  • Difficult to elucidate where only one horse affected.
  • Nutritional factors may be responsible where a number of horses in a group affected, especially mares in poor body condition or older mares.
  • Individual mares may be in true lactational anestrus.
  • Common cause of anestrus in mares with foal at foot (lactational anestrus).
  • In individual mares may be associated with foaling early in season.

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.
  • Meyers P J et al (1997) Use of GnRH analog, deslorelin acetate, in a slow-release implant to accelerate ovulation in oestrous mares. Vet Rec 140 (10), 249-252 PubMed.
  • Koskinen E, Huhtinen M & Katila T (1996) Serum progesterone levels in mares in winter and during transitional periods. Acta Vet Scand 37 (94), 409-414 PubMed.
  • Meinert C et al (1993) Advancing the time of ovulation in the mare with short-term implant releasing the GnRH analog deslorelin. Equine Vet J 25 (1), 65-68 PubMed.
  • Alexander S L & Irvine C H (1991) Control of onset of breeding season in the mare and its artificial regulation by progesterone treatment. J Reprod Fertil Suppl 44, 307-318 PubMed.
  • Davis S D & Sharp D C (1991) Intra-follicular and peripheral steroid characteristics during vernal transition in the pony mare. J Reprod Fertil Suppl 44, 333-340 PubMed.
  • Nequin L G, King S S, Matt K S & Jurak R C (1989) The influence of photoperiod on gonadotropin-releasing hormone stimulated lutenizing hormone release in the anestrus mare. Equine Vet J 22 (5), 56-358 PubMed.
  • Kelly C M, Hoyer P B & Wise M E (1988) In-vitro and in-vivo responsiveness of the corpus luteum of the mare to gonadotropin stimulation. J Reprod Fertil 84 (10), 593-600 PubMed.
  • Lofstedt R M (1988) Control of the estrous cycle in the mare. Vet Clin North Am Equine Pract 4 (2), 177-196 PubMed.
  • Hyland J H et al (1987) Infusion of gonadotropin-releasing hormone (GnRH) induces ovulation and fertile estrus in mares during seasonal anestrus. J Reprod Fertil Suppl 35, 211-220 PubMed.
  • Allen W E et al (1987) Extraspecific donkey-in-horse pregnancy as a model of early fetal death. J Repro Fert Suppl 35, 197-209 PubMed.

Other sources of information

  • Thompson D L (2001) Anestrus. In: Equine Reproduction. Eds: McKinnon A O, Squires E L, Vaala W E & Varner D D. Wiley Blackwell, Oxford, UK. pp 1696-1701.


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