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Heat Detection, Ovulation Prediction, and Timing Insemination
Breeding Horses: Heat (Estrus) Detection, Ovulation Prediction, Insemination Timing, and Pregnancy Diagnosis
Introduction
To get the most out of this article you should first understand the reproductive pattern of mares, more.
The determination of heat (estrus), ovulation, and pregnancy in a broodmare is an important aspect of any breeding program. With natural service and a available stallion these can be determined, on most mares, with a well run teasing program. With the increased use of artificial insemination (AI) many breeding mares today are on farms where there is no stallion on site to constantly tease mares. Even when there is a stallion and good teasing practices are used, a percentage (appx. 10%) of normal mares may be difficult to tell when in heat. The accurate timing of insemination and the early detection of non-pregnant mares helps prevent a late season foal or a missed season all together. Even when a stallion is present, accurate ovulation prediction can help reduce breeding pressure on a stallion and increase the number of mares a stallion can cover in a season.
This article discusses the various techniques available to the horseman and veterinarian for heat (estrus) detection, ovulation prediction, and insemination timing in equines and their relative advantages and disadvantages. Links to related articles and scientific reports are also present.
Heat (Estrus) Detection
Experience Counts! No matter what technique is used in reproductive work, experience is an important factor in the accuracy of the assessment. For most people it still requires years of experience to become proficient at rectal palpation. Cornell University believes it takes 100 mentor-guided rectal palpations to become minimally proficient. You would be surprised at the variations you run into commonly with mares whether you are discussing heat, ovulation, or pregnancy.
Teasing Mares With a Stallion
In the middle of the breeding season heat is usually between three and eight days long with five being a good average with 14 days out of heat between each heat. On each end of the season heat can be irregular or longer.
Still one of the best ways to decide if a mare needs breeding is the appearance of estrus (heat). Most mares do not show obvious signs or heat without the presence of a stallion to tease them but there are exceptions at both ends of the scale. Some mares will show obvious signs even if other horses are not about and then there are some mares that are difficult to tell even if aggressively teased. By teasing every other day and careful observation it should be fairly easy to tell when most mares are in heat. The most obvious signs in usual order of appearance:
- An interest in the stallion that is neither aggressive or fearful: she no longer pins her ears, squeals, and tries to kick him.
- The tail lifts a little and the vulva winks.
- She break downs and begins to urinate.
Cervical Observation and Palpation
The cervix goes through dramatic changes when the mare goes into heat. By failing to detect these changes from days 16 to 21 post breeding you can get a pretty accurate idea if a mare is pregnant. During the early and late parts of the breeding season this test is a little tricky as heat cycles lengthen and become erratic.
The changes in the cervix are quite palpable with the cervix going from high, dry and tight of diestrus, to a soft flaccid structure during heat. If you are visualizing the cervix the color must be judged fairly quickly as the mucosa will redden when it contacts the air. A couple of precautions:
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| Starting from the left: The cervix represents diestrus when a mare is not in heat, she is not receptive to the stallion and not ovulating. The cervix is pale with the opening high off the floor of the uterus and tight. The mucosa appears fairly dry. | In the middle is a cervix either early in estrus or as a mare is going out of heat. The cervix is softer than during diestrus and becoming pinker. See how the upper folds hang down but are not yet in contact with the floor of the vagina. | On the right is a cervix that represents the middle to late phases of estrus around the time of ovulation. The mare should be very receptive to stallions and pretty close or just have ovulated. |
- Be very careful, over stimulation of the cervix causes: prostaglandin release, CL resolution and would abort the fetus. You will want to detect the change in tone of the cervix but NOT try and poke a finger into it. Perhaps better would be to visualize the cervix in a dark stall with a disposable equine vaginal speculum and a small bright flashlight. You can easily see the changes in the cervix.
- You should probably check several times for the irregular cycling mare: Say, day 16, day 18 and day 21.
- Of course this should be done under very clean conditions and I would recommend you use gloves and nontoxic sterile lube.
- Practicing for a season and checking yourself against the vets would help build your skills and let you know if you are causing problems like infections or increased early embryonic loss.
Heat Detection by Palpation and Ultrasound of the Uterus and Ovaries
The ovaries and uterus change remarkably during the heat cycle of a mare. While a mare is out of heat the uterus is firm feeling and the ovaries approximately 2" in diameter with a bean shape. On ultrasound the uterus has a homogenous appearance and the ovary will have many tiny follicles and a hyperechoic round structure on one of the ovaries that is the corpus luteum, it represents the location of the past ovulation.
As she comes into heat, follicles begin to grow and the uterus begins to soften due to increasing fluid in the tissues. On ultrasound the follicles are little black circles five to 50 mm in size. Generally a mare will start displaying heat when the follicle hits about 20 to 25 mm in size. It will on average grow at the rate of three to 4mm a day and ovulate when they reach 40-43 mm but the range for ovulation is 31 to over 50mm. The uterine body develops an irregular wavy pattern that radiates from the center outward. On cross section it resembles a star burst. At first the pattern is only lightly seen and not uniform throughout the uterus. But as the heat progresses, the follicle grows and the pattern becomes more evident and throughout the whole uterus.
Controlling and Timing the Onset of Heat (Estrus)
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