Bridle Up – Mare Anatomy

I love horses! Any breed, age, gender, color or discipline. I drove my parents crazy from the time I could talk. Foolishly, they thought I would outgrow my fantasy. Instead it directed my life and became my adult reality. I embraced my obsession with such tenacity that soon, riding, showing, teaching and even judging were not enough. If I had been blessed with artistic talent, I would have painted, drawn, or sculpted endlessly in an effort to recreate the essence of perfect beauty and harmony which is the perfect horse. But no such talent did I possess. Then, one day, by pure accident, I stumbled on a stallion who took my breath away.

I had never considered owning a stallion, nor did I have the facility to keep one. An hour later, that stallion was on his way home with me, and together we began a journey. It is now seventeen years later, and my quest to create the perfect horse has taken me to two Universities and three continents. I have sought out great breeders, and studied legendary stallions to add to my pallet. I have also encountered many like minds with the same goals and frustrations. Creating true genetic quality, both genotype and phenotype, is not a toss of the dice. History has shown us great and thoughtful horse breeders since the earliest written records.

Today we have understanding and technology available to the public never before imagined. Stallion Collection, Shipped Chilled Semen, Artificial Insemination, Cryopreservation, Embryo Transfer, Diagnostics, and on and on. We have more colors on our pallet to create then ever. But with new techniques come fear and misuse. Proper handling, collection, and evaluation, greatly increase conception rates. Yet this has not been the case across the board, due to shortcuts and greed.

How many of you on ordering shipped semen have asked, how many progressively motile cells are being shipped per dose, that ejaculates concentration, motility and how they arrived at that dose? The correct dosage to ship is ONE BILLION PROGRESSIVELY MOTILE CELLS, in a volume of under fifty mls. if possible. Many breeding centers will get call for threeshipments, and regardless of correct dosage, extend the sample and just divide it three ways and ship. If there were only two billion cells, no one gets a correct dosage and conception chances are severely reduced. If only two had been sent, the odds would have favored two satisfied customers and two foals next season.

How about on the mare owner’s end. Does you vet or tech use a non spermicidal syringe, and evaluate the sample for viability after insemination? As the recipient, consumer, of the semen, you have the right to ask questions and receive a written evaluation of what you ordered. This should be included in the packaging. If not, this constitutes mail fraud. There are stallions so potent that error seems not to effect their success. But, this is the exception not the rule. When your dollars and cents are on the line, you must remove the blindfold. I do not believe, or even wish, we will ever breed the perfect horse. He or she must remain in the fertile fields of our own imaginations. It is there that we seek perfection that is individual ourselves, and allows new ideas to benefit all. AN EDUCATED BREEDER WITH A GREAT MARE HAS THE WORLD AT HIS/HER FINGERTIPS. Remember a foal takes on sixty to seventy per cent of it’s dam’s physical, genetic and athletic traits.

The mare is by far the most important contributor to the quality of the foal. A stallion that can override the majority of a mare’s genetic traits and replace them with his own is called “prepotent,” and is an exception rather than a rule. When this happens, these great ones become the icons of their breed, and by all means should be revered. By finding a stallion that “nicks” with a mare, a good breeder can produce a superior foal of championship potential year after year. A stallion is always dependent on the quality of the mares booked to him. Regardless of your affection for your mare, or perhaps she was a great buy, you should take a hard look before you decide to breed.

First, pedigree; if all her well known ancestors or champions are stallions, take another look. The most important line in a pedigree is the “TAIL FEMALE LINE.” This is the bottom most line on the dam’s side of the pedigree. These are the strongest inheritable genes.

Second, Age; Mares of more than fourteen years of age have significantly more inflammatory and degenerative changes of the uterus and less contractile activity than younger mares. Physical conformation of the vulva may make a “Caslick” procedure imperative. On the other side of the coin, clients have brought me two and three year olds who were not reproductively mature, regardless of cycling.

Third, General Health; A good nutritional diet, suited to your mare’s age and level of activity has been proven to be an important contributor to conception and development of the fetus. Inoculation, and worming history, with continuation throughout pregnancy should be routine. Before breeding, a vet should perform a “Breeding soundness” exam. Also an excellent idea before purchase.

Lastly, know or try to find out your mare’s past breeding history. Subfertility in mares is multifaceted. If I were to attempt to group reasons, they would fall into three categories:

  • Age
  • Contamination and infection of the reproductive tract
  • Malfunctioning of the hormonal system.


I would like to give you a quick review of what happens when your mare’s body prepares her for pregnancy:

  • First the mares eyes bring in added light which is recorded by the Pineal Gland, with either the advent of spring or artificial lights. This stimulates the Hypothalamus Gland which is located in the tissues of the mid brain. It starts the reproductive cycle by producing Gonadatrophic Releasing Hormone of GnRH.
  • When GnRH is secreted in the proper amount, the Pituitary Gland located at the base of the brain is stimulated.
  • The Pituitary Gland then secretes 2 hormones that effect the ovaries. The first is called Follicle Stimulating Hormone (FSH.) It travels in the bloodstream to the ovaries where it stimulates the development of one or more follicles. When the follicles reach 20 to 25 millimeters in diameter, they secrete Estrogen.
  • This hormone stimulates estrus (heat) activity, causes relaxation of the cervix, stimulates contractions along the mares reproductive tract, and signals the Pituitary Gland to stop producing FSH and at the same time stimulates the second gonadatrophic hormone, Luteinizing Hormone or LH.
  • LH facilitates maturation of the growing, egg bearing follicle. Ovulation occurs when the mature egg eaves the follicle and begins it’s trip through the oviduct. Following ovulation, the Estrogen level begins to fall, and the remains of the ovulated follicle are converted to a form of Corpus Luteum, or yellow body.
  • These Luteal cells secrete the hormone Progesterone. It is it’s job to stop heat stimulating hormones, and to set the stage for maintaining pregnancy. It subdues the contracting reproductive tract, and tightens and closes the cervix. It also prohibits the secretion of FSH and LH from the Pituitary, thereby putting the mare out of heat.

Obviously, progesterone is a highly important hormone in maintaining pregnancy. In some sub-fertile mares the correct amount of progesterone is not secreted. When this happens the other hormones swing into action and terminate the pregnancy, bringing the mare back into heat. Fortunately, progesterone levels can be checked and monitored. Supplemental progesterone can be administered to the mare throughout her pregnancy. Proper timing and appropriate levels of al hormones are required to maintain a balance during breeding and pregnancy. Wherever there is an imbalance, breeding problems will follow.

If your vet has found no physical, internal, or conformational reason for a mare’s sub-fertility, ask him/her to do a hormonal assay. Perhaps your mare is a nervous type, or age, or physical disability or makes travel undesirable, or simply the stallion of you choice is beyond your geographic reach. Transported semen may be perfect for you. As we discussed earlier, properly timed and executed, it has a very high percentage of conception on first cycle, with less risk and expense.

At the risk of repeating myself, the first step should be to call your vet for a breeding soundness exam. In the case of a mare that has just foaled, you should be certain there were no tears or complications post partem. Mares that have been open should have a culture AND cytology. A large percentage of problem mares have clean cultures but will show up “dirty” on a cytology. A cytology is an added test, inexpensive, taking twenty-four hours to ascertain a wide range of infection and contamination. Most mare owners ask for a culture not realizing this is not an accurate picture, and many vets do not recommend further tests if not asked.

Another suggestion, particularly on aged mares is a uterine biopsy. A small sample is excised, cultured, and gives a very good picture of the uterus. This, coupled with a sonogram, will arm you with enough information to make an educated decision as to go on with the further expense of contracting a stallion and transporting semen.

Next step, your mare comes into heat. Once again contact your vet. He/she will want to palpate your mare on about day threeto assess her follicle and coordinate with the stallion manager. You do not want to order semen too early. Semen should arrive no earlier then twenty-four hours prior to ovulation, and not more then six hours after. Keeping in mind mares ovulate between four in the morning and ten a.m. If your shipment arrives and your vet says she has just ovulated, do not panic. This is still good timing. The egg will rest in the Ova Fossa for a few days. This is the site of conception. If you inseminate too early, the sperm arrive but are weakened by the time the egg does.

Your Vet or A.I. technician should work closely with the stallion manager to coordinate timing of shipment and ovulation. When the shipment arrives do not open the container. I strongly suggest your vet or tech have a microscope to check the semen AFTER insemination. Do not warm the packet or let it come to room temperature. The mare’s body is the perfect incubator. Do not use more then one dose id you think she is going out of heat, and you don’t want to waste any. The calculated dose is sufficient, and according to the studies at Colorado State University, inseminating with more then fifty mls., is actually detrimental to conception.

Do ask your Vet or tech to use a non-spermicidal syringe. These are all plastic. The black tips on regular syringes are spermicidal to many stallions semen. Do be sure to wash and dry your mare’s parinatal area thoroughly with warm water and mild soap, making sure there is no residue remaining. Towel dry with clean, white paper toweling. The dose will be drawn into a syringe, (or in the case of an Equine Express container being used, it is already in the proper syringe) a pipette attached. It is then inserted vaginally, passing through the soft and open cervix. The procedure is quick. Since the semen is placed in the uterus, you don’t have to worry about “dumping” the inseminate, as you do with natural cover.

If you have covered your basics and followed a sound reproductive program, the result will be a win / win situation for all the players, and you will have the quality of foal to be a contender. Whether your goal is the show ring, trail, or adding another beloved family member, breeding success = good horse cent$.

Next month is the stallion issue and so we will address the subject of the breeding stallion, anatomy, semen evaluation and the effect of adding artificial light on a stallion’s libido and potency.


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