Progesterone & Estradiole

Use and Scheduling

Use of P&E

When using artificial insemination, one of the most important components of breeding success is the detection of estrus or “heat” in the mare. This has historically been the most difficult and frustrating part of the procedure for mare owners, especially when there is no stallion available to help. To complicate matters, one must further determine when the third or fourth day of estrus occurs, as this is normally the optimum time for insemination. Often times, veterinarians need to perform multiple reproductive tract examinations using palpation and/or ultrasonograpy in order to pinpoint these important dates. This can be equally as frustrating and expensive for breeders.

Over the past few years, veterinarians have started using a safe new hormone combination in order to synchronize or regulate mares reproductive cycles so that more accurate prediction of ovulation can be achieved. The program includes a 10-day administration series of progesterone and estradiol, “P&E” injections. P&E safely “suppresses” a mares ovarian function so that she will begin a “new” cycle when the medication is withdrawn. Traditionally, progesterone (Regumate) alone has been used for this purpose, but again only with less predictable results. With this improved formulation, we can foretell that a mare will likely have a mature follicle suitable for breeding, 9 days after cessation of the P&E treatment. Some owners choose to administer HCG (which stimulates ovulation) on the eighth day after P&E treatment (day 18), then go ahead and breed on day 19 without involving a visit from the veterinarian. Because mares can potentially ovulate anywhere between day 18 to 21, this is not recommended. Instead, it is wise to have the mare checked using  reproductive ultrasound on day 17 to ensure that she is at the correct stage of her cycle (when the mare has a large preovulatory follicle) before giving any drugs to induce ovulation (ie. HCG or Deslorelin). Despite the day that HCG is administered (8th, 9th or 10th day after P&E), it should always be given first thing in the morning.  In “primed” ovaries, ovulation generally occurs 36-48 hours after the administration of HCG.  This will be the optimum time for conception to occur. If deslorelin is used instead, the optimum timing for administration will differ.

By using the P&E protocol, a breeder can significantly reduce veterinary costs when breeding mares with transported or frozen semen. Total cost for medication used on this program is approximately $60 - $70, per mare. Again, it is important to remember that a mare can be started on the program at any time during her normal cycle (she must be cycling), and odds are, that she will be bred 19 days following the first P&E injection. This technology allows you to preplan a breeding according to you and your veterinarians schedule, and/or semen availability. P&E is available through East Coast Equine Reproduction Center (in Nova Scotia) or Harbour Ridge Equine (in Florida).  

P & E Synchronization Schedule

This is an example of a schedule for a breeder who wanted to breed his mare to a stallion in another province / state. After checking with the stallion owner, this breeder found out that the stallion would be available for collection and transport on Mondays, Wednesday & Fridays.  The plan then was to work the P&E schedule so that the mare would 'best case scenerio' be ready for breeding on Day 18 (Tuesday with semen that was collected and shipped on Monday). Thus P&E injections were administered starting on a Saturday. (See schedule below). P&E would be given intramuscularly everyday for 10 days. On the 10th day of P&E, a subcutaneous injection of Lutalyse was also given. The mare would then be ultrasounded by a veterinarian on Day 17 (Monday), to assess for breeding within the next 1-3 days.

Despite our best efforts, mares do not always follow the rules. Be flexible and keep an open mind. In the event that the mare was not ready for breeding until Day 20 (Thursday), we could still obtain semen collected on Day 19 (Wednesday) either by overnight  courier or same day air.  If in the unlikely case that she was not ready to breed until Day 21 (Friday), the semen could be collected Friday and sent via same day air, or collected Wednesday and shipped via courier for arrival and insemination on Thursday (a day early). It is better to inseminate a mare too early than too late. Remember most stallion owners do not collect on weekends, all couriers do not deliver on weekends, and veterinary costs will be more expensive on weekends. Plan your P&E schedule carefully. Please go over your schedule with us before beginning treatment.