Management of Mares with Frozen-Thawed Semen

Introduction

Only recently have nearly all equine breed registries allowed the use of shipped cooled or frozen equine semen, so economic interest and therefore funds for research in this field have been restricted and scientific progress has been slow.
Breeders have embraced the use of transported cooled semen for all the benefits associated with shipping semen to mares as apposed to shipping valuable mares and foals to stallions for live cover or on-farm artificial insemination (AI). As the fertility of cryopreserved stallion semen has improved and simple AI protocol have evolved, breeders are more often opting to use transported frozen semen for the additional benefits realised. Access to semen from stallions standing abroad, competition stallions, stallions that become ill, injured or overbook during the breeding season and the ability to have semen on hand and available for use when the mare is at the optimum time for breeding are among the added benefits of frozen semen. Success with cooled and frozen semen however requires that the practitioner be familiar with the techniques for properly handling of it as well as the breeding strategies that are being employed to maximise fertility. Additionally, practitioners need to be informed of the limitations of any technology so as to better assist their clients in making decisions about what is appropriate for their particular situation.

What is the Expected Fertility When Using Frozen Semen?

Although cooled semen is a well-established method for insemination of mares, the fertility of mares inseminated with cooled semen is difficult to determine.
Few studies have provided a comparison of fertility from cooled and frozen semen. Jasko et al. (1992) reported a one-cycle pregnancy rate of 65% and 56% for cooled and frozen semen, respectively. These mares were all inseminated with semen from the same stallions and processed by skilled technicians. Loomis (2001) reported similar one-cycle pregnancy rates for mares inseminated with cooled (59%) and frozen (51%) semen in a commercial setting. A retrospective study (Squires et al., submitted for publication) conducted during the 2002 and 2003 breeding seasons in six different AI centres throughout the United States and Europe showed a per-cycle pregnancy rate of 44% and 46% for cooled and frozen semen, respectively. Several recent studies have reported the fertility of frozen-thawed equine spermatozoa (Barbacini et al. 1999; Barbacini 2000; Vidament et al. 2000; Samper 2001; Sieme et al. 2003). The per-cycle pregnancy rate in a survey conducted by Samper (2001) was 56.7% for 578 mares inseminated in a clinical setting with frozen semen from a variety of sources and 53.6% and 52.3% for mares inseminated in Italy during the 1999 and 2000 seasons respectively (Barbacini 2000). [...]