Bovine Teat Injury Study Guide

Overview and Clinical Importance

Teat injuries are among the most economically significant conditions affecting dairy cattle. These injuries frequently lead to premature culling, reduced milk production, increased mastitis risk, and substantial treatment costs. Understanding teat anatomy, injury classification, diagnostic approaches, and treatment options is essential for the NAVLE examination and clinical practice.

The bovine teat is a delicate anatomical structure prone to various traumatic and congenital conditions requiring surgical intervention. The papillary duct (streak canal) and sphincter muscle represent critical components of the udder defense mechanism against mastitis and are the most frequently injured portions of the teat.

Functional Anatomy of the Bovine Teat

The bovine udder consists of four separate glands (quarters) suspended by medial and lateral collagenous laminae. Each quarter functions independently with its own milk-producing parenchyma and drainage system.

Key Anatomical Structures

Classification of Teat Injuries

Teat injuries can be broadly classified into external injuries (lacerations) and internal injuries (obstructions). The Ontario Veterinary College classification system organizes lesions into five types based on location and extent.

Five-Type Classification System

Laceration Classification

Teat lacerations are classified by four parameters:

Common Types of Teat Injuries

Teat Lacerations

Etiology: Stepping injuries (ipsilateral limb or neighboring cow), barbed wire, machinery, horns, sharp housing edges. More common in cows with pendulous udders, poor hoof care, and inadequate housing.

Clinical Signs: Visible wound, bleeding, milk leakage (if full thickness), swelling, pain on palpation, reluctance to allow milking, milk contamination.

Key Point: All teat lacerations are considered severely contaminated wounds. Cold hydrotherapy should be applied while awaiting veterinary attention.

Teat Stenosis and Obstructions

Etiology: Contusion or wound causing swelling, blood clot or scab formation, mastitis infection (especially in prelactating heifers), repeated cannulation injury, granulation tissue proliferation.

Clinical Signs: Difficulty milking, prolonged milkout time, blind quarter, palpable hardness or mass in teat, reduced milk yield from affected quarter.

Key Point: Obstructive fibrosis of the Furstenberg's rosette accounts for 80% of all teat stenosis in dairy cattle. Most stenoses result from blunt trauma causing mucosal swelling and granulation tissue formation.

Teat Hematomas

Etiology: Trauma, often related to inadequate housing. Internal hematomas can form within the teat wall (mural hematoma).

Clinical Signs: Soft tissue swelling (cranial to fore udder or caudodorsal to hind udder), may be difficult to differentiate from abscess, internal hematoma may cause ball-valve obstruction ('teat spider').

Treatment: Conservative management with pressure wraps and rest. Do NOT incise or drain unless infected. Monitor for continued enlargement (emergency due to blood loss risk).

Complication - Teat Spider: Mural hematoma that coalesces into a fibrous ball with a stalk. Acts as ball-valve blocking the sphincter during machine milking (but cow can be hand milked). Remove with Hug's tumor extractor once pedunculated.

Teat Fistulas

Types: Congenital (often associated with accessory gland) or Acquired (following full-thickness injury or surgical complication).

Clinical Signs: Milk leakage from teat wall, raised skin area around opening (more prominent in webbed teats), scar tissue visible in acquired cases.

Clinical Significance: Major mastitis risk due to continuous bacterial exposure. Small fistulas may be closed with silver nitrate scarification. Large fistulas require elliptical excision and layered closure.

Webbed (Siamese) Teats

Description: Two teats share a common wall but cisterns do not communicate. Represents congenital variant of teat fistula with associated accessory gland.

Treatment: Surgical repair similar to fistula closure. When repaired in calves, complete closure ensures pressure atrophy of accessory gland. Best performed during dry period in lactating cows.

Diagnostic Approaches

Physical Examination

Careful visual inspection and palpation are essential. Assess wound characteristics (depth, location, orientation), evaluate sphincter integrity by gentle milking, palpate for masses or fibrosis within the teat wall, and evaluate milk quality (mastitis test). Note: Best examination occurs BEFORE milking when udder is full, as empty teats may appear stenotic due to mucosal apposition.

Ultrasonography

Ultrasonography is the method of choice for evaluating obstructive teat lesions, particularly at the base of the teat (annular fold region).

Theloscopy (Teat Endoscopy)

Theloscopy provides direct visualization of the teat cistern mucosa, Furstenberg's rosette, and streak canal. It is excellent for diagnosing covered (internal) teat injuries and allows minimally invasive surgical therapy. The procedure requires minimal time and gives precise diagnosis of internal teat injuries. A prostatic Doyen clamp at teat base and air insufflation via papillary orifice facilitate visualization.

Contrast Radiography

Useful for complex obstructions, determining fistula direction and extent, and identifying accessory gland cisterns. Less commonly used than ultrasonography due to equipment requirements and radiation exposure.

Surgical Treatment of Teat Injuries

Preoperative Considerations

Patient Preparation: Perform milk culture before surgery for antibiotic selection. Apply cold hydrotherapy to injured teat while awaiting surgery.

Preoperative Medications: Procaine penicillin 22,000 IU/kg IM twice daily; Flunixin meglumine 1 mg/kg IV for analgesia and anti-inflammatory effect.

Positioning: Lateral or dorsal recumbency with sedation; limbs restrained. Tilt table is ideal but parlor repair is possible.

Anesthesia: Ring block at teat base (8-10 mL 2% lidocaine using 25-gauge needle) plus 3-5 mL lidocaine infused into teat cistern for mucosal anesthesia.

Surgical Principles for Laceration Repair

• Debridement: Gentle cleaning, sharp debridement preferred; minimize tissue removal to avoid constricting milk flow
• Layered Closure: Full-thickness wounds require 3-layer closure (mucosa, submucosa/stroma, skin) to minimize fistula formation
• Suture Selection: Use small diameter (USP 3-0 to 4-0) absorbable monofilament; Polydioxanone (PDS) is BEST choice for teat surgery
• Mucosal Closure: Simple continuous pattern with 4-0 monofilament absorbable suture; CRITICAL for preventing granulation tissue and fistula
• Atraumatic Technique: Use Adson or Brown-Adson thumb forceps; teeth cause less trauma than atraumatic forceps which crush tissue

Suture Material Selection

Postoperative Care

Milking Protocol: Wait 6 hours for fibrin seal to form before machine milking. Avoid hand stripping and hand milking for at least 24 hours (more traumatic than machine). Use teat cannula if milkout is difficult.

Indwelling Cannulas: Self-retaining cannulas (SIMPL silicone or NIT wax implants) can facilitate milkout and act as dilators to prevent streak canal adhesions. Keep open to drain for several days postoperatively.

Antibiotics: Systemic antibiotics for 3-5 days; intramammary infusion after repair. Teat dipping continues as normal after suture line has sealed.

Oxytocin: May be needed at milking (5 IU) to facilitate letdown if cow is painful or anxious.

Suture Removal: External skin sutures removed in 10-14 days.

Specific Procedures

Complications and Prognosis

Surgical Complications

• Wound Dehiscence: Allow to heal by second intention before re-attempting repair
• Fistula Formation: Most common complication; close after complete healing of primary laceration
• Mural Abscess: Can be diagnosed with ultrasonography; may require drainage
• Teat Cistern Fibrosis: Results from incomplete mucosal closure or excessive granulation tissue
• Mastitis: Most frequent complication (occurred in 17 of 67 cases in one study); has statistically significant negative impact on long-term prognosis

Risk Factors for Poor Outcome

• Cows with teat injury in 1st or 2nd parity: 4.1 times odds of fistula formation versus parity 3 or greater
• Teats sutured at 48-72 hours: 8.3 times odds of fistula versus within 24 hours
• Horizontal lacerations (disrupt blood supply)
• Sphincter involvement (cannot be reconstructed)
• Early lactation (first 60 days): more susceptible to teat injuries

When to Consider Culling

• Complete sphincter damage (cannot be repaired)
• Type IV lesions with complete teat cistern obstruction
• Persistent milk leakage despite treatment (free milker)
• Recurrent mastitis in affected quarter
• Low production cow where treatment cost exceeds economic value