title: A retrospective study of artificial insemination of 251 mares using chilled and fixed time frozen-thawed semen.
abstract: BACKGROUND
  Historically, artificial insemination (AI) using frozen semen has been perceived to have poorer success rates and be more labour intensive than using chilled semen. A retrospective study was therefore conducted to compare the conception rate achieved by AI between chilled and frozen semen, using fixed time insemination protocols over 2 breeding seasons.
  
  
  OBJECTIVE
  Artificial insemination using chilled semen produces a higher conception rate than that achieved with frozen semen.
  
  
  METHODS
  Mares (n = 251) were inseminated with either chilled (n = 112) or frozen (n = 139) semen in the 2006 and 2007 northern hemisphere breeding season. Per rectum ultrasonography of the mare's reproductive tract determined the timing of insemination, and deslorelin acetate was used to induce ovulation. Chilled semen insemination was performed using a single preovulatory dose delivered into the uterine body. Frozen semen was administered as 2 doses (pre- and post ovulation) using a deep uterine insemination technique. Pregnancy was detected ultrasonographically at 15 days post insemination. Conception rates were compared using a Chi-squared test.
  
  
  RESULTS
  Insemination with frozen semen produced a significantly (P = 0.022) higher seasonal conception rate (82.0%) than that achieved with chilled semen (69.6%).
  
  
  CONCLUSIONS
  Insemination with frozen semen can achieve conception rates equal to those with chilled semen, enabling the mare owner a greater selection of stallions.
authors.affiliation: Willesley Equine Clinic Limited, Byams Farm, Willesley, Gloucestershire GL8 8QU, UK.
authors.forename: C A M
authors.initials: CA
authors.lastname: Crowe
authors.forename: P J
authors.initials: PJ
authors.lastname: Ravenhill
authors.forename: R J
authors.initials: RJ
authors.lastname: Hepburn
authors.forename: C H
authors.initials: CH
authors.lastname: Shepherd
mesh_terms: D000818:Animals; D016009:Chi-Square Distribution; D015925:Cryopreservation / Q000662:veterinary; D005260:Female; D006736:Horses / Q000502:physiology*; D007315:Insemination, Artificial / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D008297:Male; D010062:Ovulation Induction / Q000379:methods / Q000662:veterinary; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies; D012662:Semen Preservation / Q000379:methods / Q000662:veterinary*; D017329:Triptorelin Pamoate / Q000008:administration & dosage / Q000031:analogs & derivatives
chemical_list: D017329:Triptorelin Pamoate; C066438:deslorelin