There are two or more theories on the use of the frozen semen in the mare, all based on the fact that frozen-thawed spermatozoa have a shorter life, and need to approach and fertilize the ovocite within few hours from thawing.

According to the first theory, usually easily managed in a well organized Fertility Unit, mares are examined every 6-8 hours in order to detect as close as possible the ovulation time, and they are inseminated within 6 hours from ovulation.

According to the second theory, more easily performed at the farm, when a 35 mm follicle is detected in a oestrus mare, ovulation is induced with hcg or gnrh analogue, and the mare is inseminated blindly at 24 and 40 hrs. It has been published that about 80% ovulations are likely to occur within this window, so this technique should minimize the number of ultrasounds on the mares.

Unfortunately the “blindness” can promote inseminations on anovulatory follicles with semen wasting, moreover multiple inseminations are shown to promote inflammation in a susceptible uterus. The first technique allows the use of one inseminating dose only for each cycle. When the mare is considered ready to inseminate, she has to be aseptically prepared for the procedure by cleaning the perineal area.

Eight 0,5ml straws are usually thawed by quickly putting them from the nitrogen tank into a 37c° waterbath for 30 seconds. After carefully drying the straws they need to be rechecked for the stallion i.d. and then alternatively: 1-straws are cut into a sterile 5-10 ml tube (4ml total volume) and aspirated through the inseminating pipette into a silycon free syringe, then inseminated into the uterus. 2-a multiple straw inseminating system with pistolet (imv–minitube) can be used, allowing the insemination of the straws one-by-one while leaving the inseminating pipette still in the mare.

The mare is usually checked by the veterinarian the day after ovulation to detect possible signs of inflammation (edema-fluid) and eventually treat it.

In our experience best results in terms of good pregnancy rate (over 90%) in the shortest time, are achieved with good mare preparation and close monitoring of the ovulation time.

Overall, when the mare is taken to a Fertility Unit, the vet can daily evaluate her reproductive status and provide fine variations in therapies that allows to achieve more rapidly the pregnancy, avoiding missed ovulations or time loss in case of anovulatory heats, all factors that we know are too frequent under the breeding season pressure.

For a best start we suggest to provide exposure to photoperiod lightening of the mares from December 1st, so that 14 hrs of continuous light (combining natural and artificial light) is assured in the stall for about 60 days.

It has been published and shown that 100% of the mares who undergo this protocol are fully cycling be the February the 1st,while mares left to natural lightening might start cycling in late March or later with some single mare even showing the first heat in May. Early starting combined with proper management are the keys for good fertility rate.