Equine Disorders of the Cervix Study Guide

Overview and Clinical Importance

The equine cervix is a critical sphincter-like structure that serves as the gateway between the vagina and uterus, playing essential roles in fertility, pregnancy maintenance, and protection against uterine contamination. The cervix is approximately 5-8 cm in length and 2-5 cm in diameter, composed of smooth muscle rich in elastic fibers. Disorders of the cervix represent significant causes of subfertility and infertility in mares, making this topic highly relevant for the NAVLE examination.

Understanding cervical pathology is essential because the cervix must perform seemingly contradictory functions: it must remain tightly closed during diestrus and pregnancy to protect the conceptus, yet relax adequately during estrus to allow semen deposition and uterine drainage. Any disruption to this dynamic function results in reproductive failure.

Normal Cervical Anatomy and Physiology

The equine cervix is a thick-walled muscular tube that protrudes 2-4 cm caudally into the vaginal fornix, creating a characteristic appearance often described as a "small volcano." The cervical mucosa is arranged in longitudinal folds that are continuous with the endometrial folds of the uterine body. This simple folding pattern (unlike the transverse rings seen in ruminants) allows for easy digital and instrumental passage during breeding management.

Histological Structure

The cervical epithelium consists of simple columnar cells of two types: non-ciliated goblet-like cells that produce mucin, and kinociliated cells. The mucosa branches into primary, secondary, and tertiary folds. The muscularis contains both longitudinal muscle along the cervical body and circular muscle at the internal and external os, which controls opening and closing.

Hormonal Control of Cervical Function

Cervical Lacerations

Etiology and Pathophysiology

Cervical lacerations are traumatic injuries to the cervical tissue that result in defects compromising normal cervical function. The most common cause is parturition trauma, particularly during dystocia. The foal's hooves can damage the cervix if improperly positioned during delivery, especially when there is insufficient cervical dilation or when excessive force is applied during assisted delivery or fetotomy.

Common Causes of Cervical Lacerations

Clinical Signs

Clinical presentation varies depending on the severity and timing of detection:

• Acute presentation: Hemorrhage may be visible post-partum; mare may show discomfort; large tears may be palpable immediately
• Chronic presentation: Infertility, early embryonic loss, abortion, placentitis, birth of septic foals
• Recurrent endometritis: Due to loss of cervical barrier function allowing ascending bacterial contamination
• Vaginal discharge: May be present intermittently, especially during estrus when cervix partially opens

Diagnosis

Digital palpation per vagina is the gold standard for diagnosing cervical lacerations. Examination is optimally performed during diestrus when the cervix is firm and contracted, making defects easier to appreciate. The examiner should systematically palpate the entire circumference of the cervix.

Clock-face localization: Cervical defects are described using a clock face analogy where 12 o'clock is the dorsal-most aspect and 6 o'clock is ventral. No specific site is predisposed to injury.

Vaginoscopy: Provides visualization but may miss defects during estrus due to tissue edema causing overlapping folds.

Post-partum timing: Examination at approximately 3 weeks post-foaling is recommended after uterine involution is largely complete and tissue edema has resolved.

Types of Cervical Defects

Treatment Options

Conservative Management

Small lacerations and mucosal defects may be managed conservatively with:

• Topical antibiotics and anti-inflammatory creams to prevent adhesion formation
• Exogenous progesterone (altrenogest) to maximize cervical closure during diestrus
• Monitoring for adhesion development and secondary endometritis

Criteria for conservative management: Defect involves less than 50% of cervical length AND cervix proves competent under progesterone influence during diestrus.

Surgical Repair

Larger defects require surgical correction. The procedure is typically performed under standing sedation with caudal epidural anesthesia. Key principles include:

• Timing: Surgery during diestrus when the cervix is firm; at least 60 days post-foaling
• Technique: Freshening of wound edges; two-layer closure reapproximating mucosa and muscularis
• Suture material: Absorbable sutures (Vicryl, PDS) in interrupted patterns
• Post-operative care: Sexual rest for 60-90 days; progesterone supplementation; monitor for dehiscence

Prognosis

Post-operative fertility in mares with cervical defects undergoing surgical repair is approximately 61.9%, compared to 48.4% in mares diagnosed but not surgically repaired. Importantly, mares with greater than 24 months of barrenness prior to diagnosis have significantly reduced post-operative fertility, emphasizing the importance of early detection and treatment.

Cervical Adhesions

Etiology

Cervical adhesions develop when areas of mucosal damage heal abnormally, creating fibrous connections ("spot welds") between opposing surfaces of the cervical canal. These adhesions may be partial or complete (transluminal), significantly affecting cervical function.

Common causes include: Post-dystocia trauma, fetotomy, cervical lacerations that heal by secondary intention, chronic irritation from repeated intrauterine procedures, and iatrogenic damage during AI or uterine therapy.

Clinical Consequences

Adhesions cause problems by either obstructing the cervical lumen (preventing drainage and causing fluid accumulation) or preventing normal closure (leading to cervical incompetence). The most severe consequence is pyometra secondary to transluminal cervical adhesions, where purulent material accumulates in a sealed uterus.

• Infertility: Inability to deposit semen; failure of uterine drainage
• Pyometra: Uterine distension with purulent material; may cause colic, fever, lethargy
• Mucometra: Accumulation of sterile mucoid secretions
• Early pregnancy loss: Ascending infection through incompetent areas

Diagnosis and Treatment

Diagnosis: Digital palpation reveals fibrous bands within the cervical canal. Transrectal ultrasonography shows uterine distension with echogenic fluid if pyometra is present. Mares with complete adhesions may lack vaginal discharge despite uterine infection.

Treatment approaches:

• Manual breakdown: Digital disruption of adhesions; often recur within weeks
• Cervical stent placement: Maintains patency for chronic drainage; mares have remained symptom-free up to 6 years
• Cervical wedge resection: Surgical removal of fibrotic tissue
• Ovariohysterectomy: Surgical procedure of choice for mares not intended for breeding

Cervical Fibrosis (Aged Maiden Mare Syndrome)

Pathophysiology

Cervical fibrosis is most commonly encountered in older maiden mares (12+ years) who have never been bred. These mares, often successful in sport or racing careers, are retired to breeding at an advanced age. The cervix develops pathological changes characterized by increased connective tissue deposition and failure of normal relaxation during estrus.

The exact etiology is not fully understood, but proposed mechanisms include:

• Breakdown of normal hormonal mechanisms driving cervical relaxation
• Failure at the level of estrogen receptors in cervical tissue
• Reduced collagen remodeling capacity with age
• Decreased metalloproteinase enzyme activity

Clinical Features

The hallmark feature is failure of the cervix to relax during estrus despite the mare showing behavioral signs of heat. The cervix remains closed and firm when it should be open and flaccid.

Consequences:

• Prevents intrauterine semen deposition during natural breeding
• Delays uterine clearance after insemination leading to fluid accumulation
• Pre-breeding endometritis (fluid present before breeding)
• Persistent post-breeding endometritis causing embryonic death

Treatment of Cervical Fibrosis

Congenital Cervical Abnormalities

Developmental abnormalities of the mare's cervix are rare but have been reported. These include:

• Cervical hypoplasia: Incomplete development; cervix may be shortened or abnormally narrow
• Cervical agenesis: Complete absence of cervix; extremely rare
• Congenital failure of cervical dilation: Cervix cannot relax despite normal hormonal environment
• Lateral deviation and stenosis: Reported in jennets; permanent anatomical displacement
• Double cervix (cervix duplex): Associated with uterine anomalies; may allow pregnancy in one horn

Congenital abnormalities are often associated with infertility despite normal ovarian activity and sexual behavior. Diagnosis requires thorough digital and visual examination; prognosis for fertility is generally poor.

Cervical Examination Techniques