Lesson 61 Week 8 Systems 2 Dentition and Aging in Horses

Systems 2: Digestion, Metabolism, and Nutrition

Lesson # 62: Dentition and Aging in Horses

Dr. Mahesh Shriram Deokar

St. George's University, School of Veterinary Medicine, Grenada, West Indies

Learning Outcomes

By the end of this session, students will be able to:

• Describe the basic principles of aging in horses using their dental anatomy and teeth.

• Explain the process of aging in horses based on the eruption times and the wear patterns of their teeth.

• Outline key topics including:

  • Dental formulae of the horse

  • Eruption of deciduous and permanent incisors in horses

  • Aging horses using eruption times of the incisor teeth

  • Aging horses through wear and tear patterns of the incisor teeth

Dentition in Horses

Deciduous Teeth

• Total: 3 incisors, 0 canines, 3 premolars

• It is crucial to note the eruption times of incisors as they play a significant role in age estimation.

Eruption of Deciduous Teeth

• Di1 (Central): Erupts at 6 days (0-1 week)

• Di2 (Intermediate): Erupts at 6 weeks (4-6 weeks)

• Di3 (Corner): Erupts at 6 months (days 6-9 months)

Permanent Teeth

• Total: 3 incisors, 1 canine (present mainly in males), 3 premolars, 3 molars

• Notes on canines: Usually found only in males; they may be regressed or absent in females, with about 10% of mares displaying canines.

• Small premolars, known as wolf teeth, may occasionally be present, either unilaterally or bilaterally.

Comparison of Deciduous vs. Permanent Teeth

• Example: In an Arabian horse (2 years), the deciduous incisors show small ridges and grooves on the labial surface, indicative of their youthful texture.

• In contrast, permanent incisors of a Belgian draft horse (5 years 7 months) exhibit a yellowish appearance and are notably taller, reflecting the development stage of the horse.

Types of Teeth

• Brachydont Incisors

  • Components include:

    • Enamel

    • Dentine

    • Pulp cavity

    • Cementum

    • Apical foramen

• Hypsodont Incisors

  • Characteristics include:

    • Infundibulum (cup): critical for tooth durability and development

    • Peripheral enamel and infundibular enamel contribute to tooth longevity

    • Pulp cavity provides vital nourishment

    • Peripheral cement and infundibular cement

  • These are long teeth that wear down as the horse ages, which is an important factor in aging estimations.

Aging Horses by Teeth

Key Terminology

• Dental Cup (Infundibulum): Located closer to the lingual surface, remains present up to 10 years, providing valuable information for age estimation.

• Dental Star: When the pulp cavity is exposed, it emerges closer to the labial surface, marking an important aging indicator.

• Enamel Spot (mark): Indicates the base of the infundibulum and typically accompanies the dental star.

• Tooth in Wear: Exhibits signs of wear but may still remain uneven, important for assessment.

• Leveled/Level Tooth: Features a flat occlusive/table surface, characterizing mature horses.

• Galvayne’s Groove: A vertical groove on the upper corner incisor; its appearance assists in determining age.

• 7 Year Hook: Indicates the unworn part of the corner incisor, relevant for age assessments.

Aging Criteria

• Eruption of permanent teeth

• Disappearance of dental cups

• Appearance of dental stars

• Angle of incisors

• Shape of the occlusal surface of teeth

• Presence of dental hooks

• Development of Galvayne’s groove

Eruption of Permanent Teeth

• I1 at 2.5 years

• I2 at 3.5 years

• I3 at 4.5 years

• Full mouth eruption typically occurs between 4.5 to 5 years. Horses are considered "aged" when they exceed 15 years.

Observations on Tooth Wear

• 5 Years: All dental cups remain intact. I1 and I2 appear level, with stars only slightly visible. The occlusal surface presents a rectangular shape.

• 6 Years: Cup of I1 disappears, stars become clearer. I1, I2, and I3 are level.

• 7 Years: I1 and I2 cups are gone, creating a rounded/oval table shape; possibly a presence of the 7-year hook.

• Age Progression:

  • 8 Years: All cups are absent, dental stars clearer.

  • 9 Years: Stars are evident on I1 & I2, with a round/oval profile.

  • 10 Years: Stars fully clear, profile increasingly round/oval, Galvayne’s Groove becoming evident.

  • 15 Years: Galvayne’s Groove located in the middle of the incisor, with a triangular table surface.

  • 20 Years: Galvayne’s Groove reaches the bottom, confirming age, with a triangular table profile.

Other Considerations

• The height and angle of incisors can provide additional insight into a horse's age, enhancing the accuracy of assessments.

Summary

A horse has 24 deciduous teeth and 36-44 permanent teeth, with wolf teeth (first premolar) sometimes absent and removable when present.Canine teeth are absent in 90% of females. Equine incisors and canines are classified as hypsodont teeth, which continue to grow and erupt throughout the horse's life. Their unique structural changes due to wear and tear enable reliable aging, particularly in horses up to 10 years old. Key features for aging include dental cups, stars, enamel spots, Galvayne’s groove, and 7-year hooks, all of which are critical for veterinary assessments.