Shipping semen: chilled or frozen?

What exactly is chilled semen?

With chilled semen, the sperm is diluted with an extender shortly after collection and cooled to approximately 5 °C. At that temperature, quality remains viable for 24 to 48 hours — sometimes slightly longer, depending on the stallion and the extender. The material is shipped in a specialised transport container (such as an Equitainer) by courier. Arrival within 24 hours is the standard; after 36 hours, motility often drops off sharply. Chilled semen is therefore time-sensitive: insemination must take place within 6 to 12 hours of arrival, just before or shortly after ovulation.

How does frozen material work?

Frozen semen is stored in nitrogen at -196 °C and can in principle be preserved for decades. The straws are held at an accredited semen bank or by the stallion owner themselves. Once a suitable follicle is identified, you request the straws and schedule the insemination. That sounds ideal, but there is a downside: the freezing and thawing process damages a proportion of the sperm cells. On average, 30–50 % survive the thaw in good condition, compared to 70–80 % with freshly chilled semen. Timing is also more critical: insemination preferably takes place within 6 hours before to 6 hours after ovulation.

Conception rates by method

First-cycle pregnancy rates vary. With chilled semen from a good stallion, you can expect an average of 55–65 % per cycle. With frozen semen, this is around 40–55 %, depending on the thawing protocol and the individual quality of the frozen material. Some stallions freeze poorly, bringing the frozen result closer to 30 %. Always ask your AI technician for the post-thaw analysis report before making a decision. You can save this report in the horse profile in EquiSight, so you can quickly refer back to it during the next cycle.

Costs and logistics compared

• Chilled semen: shipping costs per dose usually € 50–120 including container hire; material is single-use.
• Frozen: purchase price per straw € 15–50, but you also pay storage fees (approx. € 50–100 per year at a semen bank).
• Express transport of chilled semen on Sundays or public holidays can cost an additional € 150–200.
• Frozen semen can be requested when the mare is ready — no dependency on the stallion owner at the time itself.
• For international transport, frozen semen is almost always the only viable option due to transit times and customs requirements.
• When using chilled semen, always factor in a backup dose; if ovulation fails you will otherwise lose an entire cycle.

When should you choose which method?

Chilled semen makes sense when the stallion is based in the Netherlands or Belgium, makes semen regularly available, and you or your vet can monitor the cycle closely with ultrasound. Frozen semen is the better choice if the stallion is abroad, has limited availability (popular stallions during the breeding season), or if your mare is difficult to time and you want to plan multiple insemination moments without sending for semen each time. Some breeders combine both: one chilled dose for the first cycle, frozen as a backup for a possible second attempt.

Timing and preparation are crucial

Regardless of the method, success starts with thorough cycle monitoring. Begin with ultrasound around day 14 of the cycle to track follicle development. A follicle of 35 mm or larger is the moment to take action. With chilled semen, order the dose immediately; with frozen semen, instruct the semen bank to prepare the straws for dispatch. Record all results — follicle diameter, date of ovulation induction, time of insemination, and post-thaw semen quality — in EquiSight. EquiCoach can use this data to remind you of the timing that worked previously when the next cycle comes around.

Questions for your vet and AI technician

• What is the post-thaw progressive motility percentage for this stallion?
• Has the mare previously undergone ovulation induction, and with which product?
• Is a covering certificate or health certificate required for this semen?
• How many straws per insemination are recommended for this stallion?
• What is the policy if the mare is not pregnant after two cycles?