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Nature seems to have done a pretty good job of developing the anatomy of the horse: not only to survive, but reproduce efficiently.
In an attempt to get more foals from an individual mare to satisfy our insatiable desire to produce great athletes, we put enormous pressure on the mares’ reproductive tract to perform well beyond her natural breeding years and capabilities.

For the sake of all articles in this group, I am referring to the region from vulvae lips to the cervix as the sexual tract.

Definitions of the sexual tract used in this and related articles

Labia –
The outside lips of the vulva
Clitoris located at the bottom of the vulva, it is the sensitive erectile organ (and for males of all species, usually harder to find than Lasseter’s Reef!)
Perineum or Perineal region – (that useless bit of skin) generally refers to the area between the anus and the top of the vulva having ‘binding’ effect between the two tracts. (Technically the perineum extends to the udder in the mare or scrotum in a stallion), but in this article the ‘Perineal region’ will be used to describe the whole region around the external genitalia of the vulva and the anus on the mare and the adjoining skin.
Vulva – The vulva is the region acting as the ‘entrance’ to the inner sanctum: the vagina and uterus. This includes the clitoris, labia, the vagina and cervix.
Vestibule – the chamber from just inside the vulva and leading to the vagina. The vestibular constrictor muscle is integral with the main vulvae constrictor muscle to keep the seal of the vulva tight. The urethral opening is located in the vestibule.
Vagina – the void passage between the vulva and cervix, and is sometimes referred to as the vaginal vestibule
Cervix – a neck shaped muscle projecting into the vagina separating and protecting the uterus. Visually it resembles an anus when the mare is not in season or pregnant as it is a tight circular muscle closing off the tract. It becomes very soft, flaccid and open when a mare is in season, accommodating penetration of the stallion, sperm to flow through and debris evacuation.
Uterus – includes uterine body, horns and ovaries.

What the sexual tract should look like

There are a number of factors that contribute to sub fertility or infertility in the mare. Perhaps the most common of these is the integrity of key components of the reproductive tract which are challenged and compromised. In particular, the perineum, vulva, vagina and the cervix have active roles to the physical defence mechanisms against bacterial invasion of the uterus. Naturally bacterial/infectious assault will have a profound effect on conception and the ensuing pregnancy.

Vulva - ideal comformationQuick visual examination of the perineal region (area under the tail) should reveal the labia displaying a tight seal no more than 10 degrees slant from vertical, lining up with the anus. Approximately two-thirds of the vulva should be below the ventral (lower) floor (the pelvic brim, or top of pelvic bone). If the lips of the vagina are gently separated they should ‘pop’ back into place upon release. Should the visual examination look as described right, then it is probable that the two-third ratio will also be correct. This can be confirmed by inserting a clean finger inside the top of the lips (only about 50mm) and slide down gently until the pelvic brim is felt. The mare must be ‘crushed’ for this examination, and is only to be performed by experienced persons with adequate assistance, or by professional veterinarians. Internally the vestibule will be sloped downward over the urethra (urinary tract outlet) to the vagina and exterior. During the periods of diestrus or anestrus (when the mare not in season) the vagina has a healthy light pink color and shiny surface. The cervix will protrude into the vagina, appearing pale, tight and sitting well up from the vaginal floor. The vulva pictured has excellent perineal conformation: vertical, tight and dry.

Should there be variation from the ideal conformation, then the mare’s main defence to protect the uterus is under threat. A tilted, or worse, a very sunken vulva, will compromise the ‘seal or door’ into the vaginal region allowing air – and therefore airborne bacteria – to enter the sexual tract (pneumovagina) and/or the splash back of urine into the anterior of the vagina in front of the cervix, causing urovagina, i.e. urine pooling. Plus there may be the risk of direct faecal contamination. If the vulva has external scarring, or internal lacerations, again there is an increased risk of exposure to infection

This mare depicted is only 13 years old with good body condition, whose vulva has already become sunken to the point where there is a vertical shelf of 5cm. She has a limited and/or expensive reproductive future

Reasons for the perineum, vulva, vagina and the cervix to lose efficiency and integrity


  • The increased number of foalings equates to increased general wear and tear of the uterus, cervix and perineal region as a result repeated stretching.
  • Repeated infectious attack over the years may collectively cause inflammation and maybe scaring to the cervix, thus reducing efficiency as a barrier even when the mare is not in season
  • Repeated caslick surgery being performed and cut creating increased scar tissue
  • The ‘dragging down’ of the reproductive tract causing a sunken vulva of varying degrees and, in extreme cases, a horizontal shelf over the pelvic brim, is mostly attributed to age
  • Sway back through natural aging process (or mares predisposed with a sway back) alters top line of spine, affecting the angle in which the uterus lay (downward), hence a sloped or sunken vulva
  • The broad ligaments (ligaments that suspend the reproductive tract from the roof of the abdominal cavity) losing elasticity.
  • The perineal muscles lose elasticity allowing vulva and anus to sink.


Most of the problems associated with foaling can cause damage to the perineal region and to a lesser extent the cervix, affecting elasticity and therefore the ability to form efficient barriers.

  • Post foaling – for a period the whole reproductive tract will be stretched and loose. This is when the mare is the most exposed to contamination. She has foetal fluids inside her, she has lost all vulvae tone and her cervix will be wide open. It is at this point that mare will need careful management: especially the mare that already has a sloped vulva, lower immunity levels, or other contributing damage from foaling.
  • Stabled mares post foaling – it is not unusual for the mare to remain stabled for a few days, or even longer post foaling. This is not going to help at all, particularly to enhance the normal physical status, post foaling, mentioned earlier. Ideally we would leave the mare in the paddock to help them push out foetal fluids and tone up her muscles. Due to other commercial concerns such as weak legged foals etc. this is not how it happens in most cases. Therefore, the mare will need artificial help to clean up and tighten up: oxytocin and short bursts of exercise and other managerial tools.
  • Vestibular and/or vulva lacerations – cuts usually accompanied by bruising as a result of a difficult foaling prolonging the return of tone to the vaginal area and cervix. The sloughing from these wounds can be the source of infection and irritation and will require care to aid recovery. Pictured right is an example of bruising and lacerations in the vulva that can occur during foaling.
  • Rectrovestibular fistula – a perforation between the top of the vestibular and rectal tract. The tear is caused by a foal’s hoof, and possibly nose, perforating the tissue between the vagina and rectal tract just prior to the first glimpse of the foal. Surgical correction will be required. This will likely delay the breeding of the mare for a cycle or so.
  • Rectovaginal tear – Progressive injury feom the fitula, starting as a fistula but continued tearing when the whole perineal region will become one opening: i.e. there will be a tear causing the rectal tract and vaginal tract becoming one from the point of perforation. Surgical correction will be required, delaying the breeding of the mare for an extended period. Depending on the time of foaling in the breeding season and severity of the injury, she may have some chance of being bred in the same season.
  • Damaged cervix – a tear or bruising of the cervix during a difficult or abnormal presentation of the foal.


  • Not cutting caslick pre foaling – this can cause internal vaginal/vulvae lacerations and likely tearing of vulva off line – perhaps to the ring of the anus – as a result of the foal forcing its way through at birth. Vulval lacerations and resultant scaring may be quite extensive under this circumstance.
  • Serving the mare not fully in season. If the mares sexual tract is not naturally lubricated, the vulva and cervix not fully relaxed, stretching, lacerations and bruising may occur
  • Not reinstating caslick soon after foaling.


This 7 year old maiden mare arrived in this condition after being left in the paddock for 2 years. Her vulva is very sunken with 2 contributing reasons. Firstly due to poor body condition, and secondly her mother has poor perineal conformation, so this mare has inherited the trait also. She has probably been sucking in air for an extended period so is likely to have endometritis. She received a caslick upon arrival. Her perineal shape will improve as she gains weight but she has a fair bit going against her from the onset.) Footnote: this mare gained weight well and went in foal on her first service. She did receive some treatment during her transitional heat, and a small post service treatment.

  • A very common factor: poor body weight or weight loss – the perineal region will sink.
  • Predisposed to poor perineal conformation – we see it all the time: mares that had a naturally sloped vagina at a young age are passing this trait on to their daughters. In most cases this will prematurely affect the extent of the mare’s normal effective reproductive life
  • The mare in season: During estrus the mare’s reproductive tract is relaxed. This is a period when the mare is most likely to be challenged by bacterial contamination.
  • Stallions with rough behaviour or a disproportionally large penis for the mare during serving can damage and bruise the mare internally. A serving roll will be placed between the mare and stallion to suppress the stallion from full penetration during the mating on these occasions.
  • Elevated tail set of the mare – again will cause the perineal region to sink prematurely and for the long term.
  • Inherent lower natural immunity or perhaps low endocrine secretion levels.
  • Young mares recently out of racing may appear to have a sloped vulva due to their racing condition. With maturity and weight gain, the integrity of the perineal conformation may well self correct. Some race fillies may already have a “racing caslick” due to sucking in air during fast work, which may lead to pneumovagina and inflammation which may lead to poor performance. Generally these fillies will require a caslick thereafter as the natural vulval seal is damaged by suturing and cutting.

Tip: When purchasing a mare, make sure an experienced person has a peek at her fanny. Ensure the integrity of the perineal region and slope of the vulva is age relevant. Provided the degree of slope is ok, the fact she may have a caslick should not be an issue.

Related Story that should be read next is: The Caslick; A Stitch In Time

Other Related Stories:

No One Home: Causes of Infertility and Sub Fertility in Mares

Putting Together the Reproductive Cycle

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