Utilization of One-Dose Postovulation Breeding With Frozen-Thawed Semen at a Commercial Artificial Insemination Center: Pregnancy Rates and Postbreeding Uterine Fluid Accumulation in Comparison to Insemination With Chilled or Fresh Semen

Insemination with frozen-thawed (FZ) semen has been associated with an increased incidence of postbreeding intrauterine fluid (IUF) accumulation and decreased pregnancy rates (PRs) per cycle compared with fresh (F) and chilled (CH) semen. This retrospective study was undertaken to determine the PR and incidence of postbreeding IUF associated with insemination of FZ semen. Records for 1,023 insemination cycles (578 mares) using F, CH, or FZ semen from 240 stallions over a 3-year period from a single artificial insemination center were reviewed. Clinical data were collated for univariable and multivariable analyses. Over all semen types, PR was 52.2%. Frozen-thawed semen achieved a similar PR to CH semen (48.6% vs. 43%, respectively), and both were lower than F semen (63%). The use of FZ or CH semen also resulted in similar PR in mares of advanced age and old maiden mares (>11 years). The use of prophylactic uterine lavage (4-8 hours after insemination) in mares inseminated with FZ semen decreased over the study, being 40%, 22%, and 8% in years 1, 2, and 3, respectively. There was no difference in FZ semen PR over this time nor was there a difference in the incidence of >2 cm IUF 1-day after insemination in FZ cycles (5.5%, 8.3%, and 5.6%, respectively), and this incidence was less than that recorded for F (16.8%) and CH (17.8%) cycles over this time. These data indicate that FZ semen may be used in a commercial setting with no difference in PR or uterine sequelae to that for CH semen.