Larry Catt, D.V.M.
Larry G. Martin, D.V.M.

24 Hour Emergency
El Cajon (619) 590-1991
Ramona (760) 789-6845

It’s Time to Get My Mare Ready to Breed

<< Back to Reproduction and Foaling

It’s the time of year to begin thinking about breeding your mare. Assuming that you have already chosen a stallion and the time of year that you want your foal to be born, we will now set up a “game plan” to get your mare ready.

First, we need to get the mare into heat. Horses are seasonally polyestrous, which means that they stop cycling, usually in the late fall, and do not begin again until the early spring. However, we can alter this process by putting them under lights to artificially create springtime. We want the mare under lights 16 hours per day. This can be done with a timer and a 100 watt light bulb. Usually, having the light on from 4pm to midnight is adequate. This process should begin 4-6 weeks prior to breeding.

As veterinarians, we want to check the mare with ultrasound prior to breeding, particularly in the months of February and March to be sure that your mare is cycling and is not transitional. Mares that are not yet cycling will have small inactive ovaries and a “quiet” uterus (a uterus unresponsive to estrogen and progesterone).

Mares go through a “transition” period as they begin to cycle at normal intervals. During this transitional period, the mare may have inconsistent “heat” cycles and inconsistent “heat” behavior. Mares are not generally fertile during the transition period, but can successfully respond to hormone therapy while in transition and then be bred.

Hormone therapy for mares has become a mainstay in the industry to make breeding more efficient, reducing costs and increasing fertility rates. The hormones most routinely used are Lutalyse (prostaglandin), Regu-Mate (progesterone), HCG (human chorionic gonadotrophin), and Deslorelin (Ovuplant).

OK, your mare is ready so let’s get started. You have selected a stallion. You want to ship semen to AI (artificially inseminate) your mare. We need to synchronize your mare for breeding during the mid-week to facilitate shipping and avoid weekend inconveniences and costs.

This would be the reasonable protocol for most circumstances:

  • Have your mare ultrasounded to be sure she is cycling properly and to observe for intrauterine fluid or any other abnormalities in the uterus or of the ovaries. Mares with “fluid” will need culturing and uterine therapy. Maiden mares (mares not having been bred before) generally have a “clean” uterus.
  • Determine if your mare needs an intrauterine culture to rule out infection.
  • Begin giving Regu-Mate orally for 15 days to take “control” of your mare’s reproductive cycle. Begin Regu-Mate on a Monday.
  • Give a Lutalyse injection intramuscularly on day 16 (a Tuesday). The day of the Lutalyse shot can be adjusted based on semen shipment availability.
  • Ultrasound your mare 7 days later (a Monday) to determine follicle size and appropriate day for breeding, which would usually be Wednesday or Thursday.
  • Inseminate mare based on prior examination and give HCG or Deslorelin to stimulate more rapid ovulation and shorten the time interval between ovulation and insemination.
  • Have an Ultrasound pregnancy exam 15-18 days post-ovulation.
  • Other issues include what days the stallion owner provides semen and is the semen being transported via UPS or FedEx.
  • This protocol is also very efficient for mares that are being bred with live cover as well because it minimizes the handling and labor involved with teasing and multiple breedings, which can lead to injury and infection.
  • Most importantly, it is necessary to plan ahead to have the stallion owner, mare owner, and veterinarian all working together for optimal success.

Further questions can be personally addressed by calling the office at (619) 590-1991 or (760) 789-6845.