Problems in Equine Reproduction

Mare and foal gazing at the horizon and looking to the future.
Mare and foal gazing at the horizon and looking to the future.

Reproduction problems can affect the mare and the stallion, as well as the foal. Awareness of possible problems that can occur is the best insurance against a reproduction disaster that may affect both the health and life of the equines involved.

Mare reproductive problems

Reproduction problems for mares usually fall into three categories:

  1. Breeding soundness problems
  2. Complications that affect the foal or carrying a foal to term
  3. Complications during and after delivery of the foal

Problems related to breeding soundness

Before breeding any mare, it is important to have a veterinarian perform a breeding soundness examination. This examination is an overall physical examination with special emphasis on the reproductive organs.

In most cases, procedures will include the standard rectal palpation and speculum vaginal examination, an endometrial culture and cytology exam, an endometrial biopsy, transrectal ultra sound and endocrine assays.

In cases of an infertile maiden mare, chromosome analysis or cytogenic studies may be indicated. Some veterinarians, but not all, will have the facilities for a fiberoptic examination of the mare's uterus.

Fortunately, once the proper conditions are met for breeding, most equines will perform as nature intended.

The general health and age of the mare are important considerations. Mares that are more than 15 years old may have infertility problems. Nutritional deficiencies, bad teeth, and chronic laminitis can interfere with the mare's ability to carry a foal.

Some mares have a condition known as "windsucking" or pneumovagina which is a conformation defect that permits air and fecal material to enter and pool in the vagina leading to bacterial infections. These infections are the primary cause of infertility in mares. Surgical repair using a procedure known as a Caslick's operation is often successful in treating this problem.

A history of scarring or fibrosis in the wall of the uterus often correlates with infertility and early embryonic death. Your veterinarian may recommend surgery or other treatment when these conditions exist.

Complications that affect the foal or carrying the foal to term

A candidate brood mare

A candidate brood mare

Physical and environmental conditions may reduce the ability of a mare to conceive and deliver a healthy foal.

Mares are affected by a number of conditions during their pregnancies. Although nutritional deficiencies have not been associated with abortion, mares that are too thin often have difficulty in conceiving and producing a healthy foal.

It is a well-known fact that mares seldom deliver healthy twin foals. Most mares don't have the necessary ability to develop sufficient fetal membranes to accommodate and provide nutrition to two developing foals. With the use of ultrasound, twin pregnancies can be detected early, and your veterinarian can make recommendations as to the best course of action.

Congenital chromosomal or genetic defects that lead to improper development of the embryo may lead to spontaneous abortion. Through the use of ultrasound, these situations can be discovered early and steps taken to abort the pregnancy when recommended by a veterinarian.

Abortions at the fourth or fifth month are thought to be the results of a progesterone deficiency. In some cases, a veterinarian will recommend that a mare be treated with synthetic progesterone (Regu-Mate) to help maintain the pregnancy. Foals born without normal increases in maternal progestogens are small, weak, and often stillborn.

Certain plants or fungi, if ingested by a pregnant mare can have an effect on both the mare and on the foal. Ergo alkaloid toxicity caused by saprophytic and endophyte fungi can produce mycotoxins in the class of chemicals known as ergot or ergopeptine alkaloids.

In the U. S. fescue toxicity is the most commonly seen form of ergot alkaloid toxicity. Care should be taken to make sure that pregnant mares do not ingest fescues which are often used for erosion control and on golf greens. Endophyte-free varieties of fescue have been developed to prevent fescue toxicity in horses.

These alkaloids found in fescues and other sources have toxic effects on the reproductive tract and mammary gland of the mare and can cause a prolonged gestation and a thickened edematous placenta by decreasing the normal rise of progestogens and prolactin during the last 40 days of gestation.

Ergotism is a clinical syndrome caused the Clavicepts, a saprophytic fungus that lies on a variety of hays and pasture grasses including bluegrass and cereal rye. These fungi has an effect similar to that of the alkaloids found in fescues.

A syndrome known as Mare Reproductive Loss Syndrome can cause spontaneous abortion in mares. Evidence points to Eastern tent caterpillars as the primary cause of this problem. They become embedded in the lining of the gastrointestinal tract and cause areas of inflammation and an entrance for bacteria. These bacteria can then enter the blood stream and localize in the placenta and fetus, resulting in abortion.

Certain drugs such as corticosteroids have been reported to cause abortion in mares, although few cases have been substantiated. Always examine drug labels to see if administration to pregnant animals is contraindicated.

Bacterial abortions and sterility are sometimes caused by organisms in the Streptococci group. Other bacteria that have been found in aborted fetuses include Leptospira, Nocardia, Klebsiella and Staphylococcal species.

When these bacterial agents gain entrance to the reproductive tract and travel to the uterus, they can cause infection of the fetal membranes, resulting in abortion.

During the late stages of pregnancy, the umbilical cord, which normally has three clockwise turns, may become excessively twisted or wrapped around the limb of the fetus resulting in shutting off the blood flow in the cord. If complete, this lack of blood flow will result in the death of the fetus.

Complications during and after delivery of the foal

Sometimes during the latter days of pregnancy, the fetus does not drop normally, making the presentation during birth complicated. The foal is normally delivered in an anterior presentation and dorsosacral position with the head, neck and forelimbs extended.

One front hoof of the foal precedes the other and facilitates passage of the elbows and shoulders through the birth canal. If the foal is not positioned correctly as it attempts to pass through the pelvic canal, the mare may be subjected to tearing or rupturing injuries, and the foal may suffer from premature rupture of the umbilical cord resulting in asphyxia and leading to neurologic abnormalities.

In some cases, the placenta fails to rupture making it impossible for the foal to pass out of the membranes. In such cases, it is necessary to rupture the placenta and deliver the foal manually before it becomes asphyxiated. The foal's nostrils should be wiped clean of fluids and the breathing rate of the foal should be evaluated.

As noted previously, the umbilical cord should be allowed to break naturally and the stump treated with iodine or Chlorhexidine. If the umbilical cord does not break within 30 minutes, break it by hand by grasping it firmly two to three inches from the navel and pulling the cord in the direction of the placenta until it breaks. Do not cut it, since this may produce bleeding.

The mare should be allowed to rest to prevent the still-relaxed vulva from possibly sucking in air and risking post-partum endometritis or metritis. Some veterinarians recommend using Michel clips to hold the upper vulva shut and reduce air contamination.

With some births, the placenta is expelled along with the foal. In others it may take several hours before it is completely expelled. It the complete placenta has not been expelled after three hours, consult with your veterinarian.

The placenta should be examined to make sure that no missing pieces have been left behind in the uterus. Small tears can be detected by filling the placental sac with water and ballooning it out. A complete placenta will be in an F shape with no holes or tears.

Problems that can affect the mare after delivery of the foal include the following:

  1. Hemorrhage: internal bleeding caused by rupture of a large blood vessel will be evidenced by signs of severe pain in the abdomen followed by weakness, staggering, pale mucous membranes, shock and collapse. Usually there are no external signs of the bleeding. It is imperative that a veterinarian be called if any evidence of hemorrhage occurs.
  2. Perineal and Vulvar Lacerations: The feet of the foal often tear through the mare's organs and membranes causing injuries to the vagina, vulva, and rectum. These injuries should be treated as soon as swelling and hemorrhage stop. Initially,careful cleansing of the wounds should be done.
  3. Delayed Uterine Involution: Immediately following foaling, the uterus should begin to shrink and return to its normal size and shape. If your veterinarian finds that involution is not proceeding properly, oxytocin may be administered to stimulate uterine contractions.
  4. Postpartum Metritis: This serious infection of the uterine wall, characterized by onset of toxemia, blood poisoning and laminitis is uncommon, but tends to occur after prolonged or complicated deliveries. A veterinarian will evacuate the uterus of infected blood and pus and administer intravenous oxytocin and antibiotics. Quick action is required to prevent a severe case of laminitis which can be severe enough to cause sloughing of the hooves.
  5. Prolapsed Uterus: Prolonged straining during and after a difficult labor can cause the uterus to turn inside out and protrude from the vulva. The procedure to replace the uterus within the mare's body properly calls for an experienced veterinarian. Care must be taken to keep the prolapsed uterus from becoming contaminated or injured. Usually the mare is sedated for the procedure. Intravenous oxytocin and antibiotics are administered to prevent infection and shrink the uterus once it is back in place.
  6. Nursing Problems: Some mares will have an insufficient milk supply and the foal will need to have supplemental feedings. If the foal nurses frequently and for long periods of time, it is likely it isn't getting enough milk. Mastitis is an inflammation of the mammary gland, and, although rare, it can occur a few weeks after foaling. The udder becomes warm, swollen and painful. The milk will appear curdled and usually contain blood. The foal will need to be hand fed and the mare's udder will need to be emptied by hand. Mastitis responds rapidly to treatment and the foal is usually able to begin nursing again within one week.

Reproductive problems in stallions

As with mares, any stallion to be used in breeding should undergo a breeding soundness examination. This is a general physical examination with special emphasis on the reproductive tract.

The medical history of the stallion is important and should include past breeding performance, recent illnesses, information about injuries to the testicles or penis, and musculoskeletal injuries that might prevent the stallion from mounting the mare.

A history of drugs given to the stallion is important since anabolic steroids and testosterone are known to cause testicular degeneration.

The history of the stallion should include any stereotypies or negative or undesirable habits such as biting, kicking, or being overly aggressive.

Veterinary examination of the stallion's reproductive tract using ultrasound and urethral endoscopy should be used when indicated. Both testicles should be present in the scrotum and of normal size, texture and consistency. Testicular size is closely related to sperm production and fertility, and a stallion with very small testicles is less likely to be potent.

The penis and prepuce should be examined for scars, pustules and growths. The condition of the prostate, seminal vesicles and secondary sex glands is determined by rectal palpation and the inguinal canals are examined for hernias.

The collection and analysis of semen is the most important part of the exam and should be done by an equine practitioner. The number of sperm per milliliter and the quality of the semen sample help the veterinarian to predict the number of mares a stallion can cover efficiently.

Blood in the sample may be an indication of infection and infertility. When semen contains less than 60 percent live sperm cells, there may be a problem with the epididymis or testicles. Tests can also indicate infections within the urethra or secondary sex glands.

Loss of sexual interest and arousal is the most common behavior problem in stallions. Rough handling, a painful or traumatic breeding experience, excessive punishment or severe discipline can discourage a stallion from expressing natural sexual urges. Also, breeding fatigue may occur if the schedule is to strenuous for a prolonged time period.

Lack of libido may be caused by testosterone deficiency that results from a protracted illness or the administration of male hormones to enhance racing performance. Unfortunately, the dose of testosterone that stimulates the stallion's libido also depresses sperm formation.

Some stallions are not able to erect the penis or perform the act of coitus for various reasons, some of which are medical/psychological or the result of management problems.

Penile injuries can produce temporary or permanent loss of the ability to perform. Ejaculatory failure causes some stallions to be poor choices for breeding purposes.

Sexually transmitted diseases including bacterial infections can cause sterility in stallions. Urethritis, orchitis, epididymitis and infections of the accessory sex glands can be painful and cause a stallion to lose interest in breeding.

Testicular hypoplasia and testicular degeneration are usually congenital conditions and may be unilateral or bilateral. When a young stallion is bred to several mares with poor conception rates resulting, the stallion should be checked for these conditions.

Making sure that the stallion is a good breeding match for the mare is important. The size of the animals should be taken into consideration and thorough reproduction soundness examinations should be done before breeding takes place.

Consider this

Fortunately, once the proper conditions are met for breeding, most equines will perform as nature intended and before you know it, you will be taking care of a new foal and looking forward to many rewarding experiences with your horses.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.