Equis ISSN 2398-2977

Behavior: aggression - hormone related

Synonym(s): aggression

Contributor(s): Bonnie Beaver

Introduction

  • Aggressive behavior may be directed towards other horses or towards people.
  • Aggression may be normal, eg maternal aggression   Behavior: maternal  , or abnormal.
  • Aggression in mares should be investigated to rule out an organic cause, eg ovarian neoplasia   Ovary: neoplasia - overview  .
  • If there is no obvious cause, aggression should be controlled by proper handling and training, surgery, eg castration, or drug therapy.
  • Extremely aggressive horses may need to be euthanazed.

Pathogenesis

Etiology

Predisposing factors

General
  • Inappropriate training or handling.
  • Mating.
  • Presence of foal.

Specific

  • Hormonal abnormalities.

Pathophysiology

  • Cause of aggression may be hormonal in many cases.
  • In other cases may be due to inappropriate handling.
Normal maternal aggression
  • Mare protecting foal from intruders.
  • Normal response, but can be modified by learning.
  • Great individual variation.
    Normal sex-related aggression
  • Anestrous mare may be aggressive towards stallions.
  • Only a mare in full behavioral estrus will not show aggression.
  • Individual variation.
  • Sex-related aggression is also shown between stallions.
  • Stallions may normally bite the withers area of a mare before mounting.
    Abnormal aggression due to hormonal abnormalities
  • Hypertestosteronism may cause aggressive behavior in mares or stallions.
  • Hypertestosteronism in mares may result from:
    • Secretion by granulosa cell tumor   Ovary: neoplasia - granulosa / theca cell  .
    • Impairment of enzyme pathways in estradiol synthesis; testosterone is the precursor of estradiol.
    • Secretion of adrenocorticotrophic hormone and gonadotropin by hypothalamus/pituitary may stimulate sex steroid secretion by the adrenals.
  • Hypertestosteronism in stallions may be associated with retained testicles   Testis: cryptorchidism  .

Timecourse

  • Usually chronic or recurrent.

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.
  • Crabbe B G, Freeman D A, Grant B D et al (1992) Testicular feminization syndrome in a mare. JAVMA 200 (11), 1689-1691 PubMed.
  • Beaver B V & Amoss M S (1982) Aggressive behavior associated with normally elevated serum testosterone in mares. Applied Animal Ethology 8, 425-428 VetMedResource.


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