Harrisburg, South Dakota
Excellence in Large Animal Medicine and Surgery since 1981!
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Harrisburg, South Dakota Excellence in Large Animal Medicine and Surgery since 1981! |
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Barren Mares What if your mare is not pregnant? There are steps you can take to identify your mare’s problems. This article will explain the mare’s estrous cycle, help you identify problem areas in your breeding problem, and give you some ideas of what your veterinarian can do to help make the foaling season a productive one. The Natural Breeding Season A year can be broken down into four seasons. 1. Winter – as the days shorten, most mares go into “anestrus”, a period when reproductive functions are depressed or absent. 2. Early Spring – transitional phase. The ovaries begin developing follicles which secrete estrogen, the hormone which makes mares act receptive to a stallion or show heat. During transitional phase, no follicle actually matures enough to ovulate, or release an egg. Thus, your mare will show erratic heat cycles and breeding will be nonproductive. 3. Late Spring – normal estrous cycles. Each cycle lasts an average of 21 days and is composed of two phases: a. Estrus – lasts approximately 5 days. Ovarian follicle develops and secretes estrogen so the mare is receptive to the stallion. The follicle gradually enlarges and then ovulates, releasing the egg. b. Luteal Phase – lasts approximately 15 days. A corpus luteum (CL) forms where the follicle has been. The CL secretes progesterone, a hormone necessary to maintain pregnancy. The mare is nonreceptive to a stallion. 4. Fall – transitional phase, as a mare stops cycling. WHY IS YOUR MARE NOT PREGNANT? Answering this question requires a team approach. Evaluating different areas of your breeding program will help you determine where your problem lies.
The Owner 1. Is the mare receiving adequate nutrition? 2. How old is the mare? 3. What is the mare’s past pregnancy history? a. Has she been pregnant before? If so, does she foal every year, or less frequently? b. Did she have any difficulties during the last foaling? 4. Has she had any problems getting pregnant in past years? 5. What have her estrous cycles been like this year?
Breeding Manager 1. What is the farm’s overall conception rate? 2. What percentage of mares bred has the stallion settled this year? Has he had any recent changes in semen quality of conception rates? 3. What is their teasing program? Ideally every other day the mare will be individually exposed to the stallion and observed for signs of estrus. If one person does all the teasing, he will learn each mare’s idiosyncrasies. Some mares do not show heat well because they are timid, are protective of the foal at their side, or have silent heats. If teasing is performed by leading a stallion by a pasture, you frequently will miss a mare’s response – especially if she is pushed away from the fence by a more dominant mare. 4. How do they decide when to breed a mare, and do they breed daily or every other day? Are the mares ever palpated to determine the stage of the follicle?
The Veterinarian 1. The veterinarian will ask questions about the mare and the breeding program. They will try to determine if the mare cannot conceive, or cannot maintain pregnancy. If the mare was diagnosed pregnant, they will need to know how many days along she was, and how the diagnosis was made (palpation or ultrasound). 2. Was the mare pregnant and then suffered from early embryonic death? Did she lose the embryo because it was abnormal, or was the uterus abnormal and could not support the pregnancy? Did the mare have a progesterone deficiency so the pregnancy was not maintained? 3. Did the mare lose the fetus in the later stages of pregnancy? Did she have an abortion due to an infection such as rhinopneumonitis, Equine Viral Arteritis, etc. 4. Your vet will then do a breeding soundness exam of your non-pregnant mare. This is recommended for any barren mare, or a repeat breeder (a mare who does not become pregnant after being bred for two to three estrous cycles). a. General physical exam b. Vulva and vaginal conformation and appearance c. Rectal palpation of reproductive tract – evaluate the uterus and ovaries, establish the stage of the mare’s estrous cycle, notice any abnormalities d. Ultrasound – identify uterine cysts, fluid within the uterus, etc. e. Uterine cytology and culture – establish presence of uterine infection and identify the type of bacteria present and to which antibiotic it is most susceptible f. Uterine biopsy - remove a small piece of the uterus and examine it under the microscope. A biopsy will rate the uterus as to its ability to carry a foal to term. It identifies inflammation, scarring, or fibrosis, etc. g. After it is determined what problems the mare is facing, a course of treatment is determined.
Preparing for the Breeding Season 1. Evaluate the physical condition of your mare. Very thin or obese mares are less likely to become pregnant. 2. Have a veterinarian evaluate your barren mare and correct any problems before the breeding season begins. 3. Lights – Exposing a non-pregnant mare to 16 hours of daylight with 8 hours of darkness, beginning in early December will cause her to enter the transitional phase earlier. Place one 200 watt incandescent bulb, of two 40 watt florescent tubes 7-8 feet above a box stall. Your mare may require blanketing or extra feed, because she will being shedding her winter hair coat. 4. Synthetic Progestin (Regumate) – During the transitional phase, a mare that is cycling will constantly show heat due to numerous small follicles. Feeding Regumate for 15 days will suppress these follicles. After you discontinue the Regumate, the mare will return to estrus within 4-5 days, and will hopefully develop a more mature follicle. 5. Prostaglandin is an injectable hormone that will cause a mare to come into heat in 3-5 days. A mare must have a functional corpus luteum before a prostaglandin injection will work. 6. Estrous synchronization – Using a combination of Regumate and prostaglandin, you can cause multiple mares to come into heat at the same time. 7. Ultrasound for early pregnancy detection! A mare can be diagnosed as pregnant 14 days after the last day she was bred. The ultrasound also identifies twins, allowing termination of one of the two embryos, If there is anything we can do to help you with your breeding program, just give us a call.
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