Oral Dimensions Related to Bit Size in Adult Horses and Ponies.
Authors: Anttila Mirjami, Raekallio Marja, Valros Anna
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Oral Dimensions Related to Bit Size in Adult Horses and Ponies Fitting a bit correctly requires understanding the significant variation in oral anatomy across different horses and ponies, yet little data has been available to guide selection beyond owner preference. Researchers measured four key oral dimensions—mouth width, jaw separation, tongue thickness, and lower jaw width—in 554 adult horses and ponies (aged 5–29 years) under sedation during routine dental examinations, then compared these measurements against the bit sizes owners were actually using. Considerable anatomical variation emerged by breed and sex: coldblood Finnhorses had substantially larger oral dimensions than other breeds, ponies were considerably smaller, mares had significantly smaller dimensions than geldings, and mouth width and jaw separation increased with age. Concerningly, poorly fitted bits were remarkably common, with over 10 mm length discrepancies, tongue compression between the jaws, and centre-link dimensions causing potential nutcracker effects on the bars occurring frequently in the study population. These findings have direct practical implications: horses tolerate approximately 14 mm tongue thickness without compression, individual measurement-based bit selection is more reliable than breed or age assumptions alone, and since oral dimensions change throughout a horse's life, bit fit should be reassessed regularly rather than assumed constant.
Read the full abstract on PubMed
Practical Takeaways
- •Measure your horse's mouth width directly rather than relying on breed assumptions—significant individual variation exists even within breeds, and mares require smaller bits than geldings on average
- •Re-evaluate bit fit annually as horses age, since jaw dimensions increase over time; check that your bit doesn't compress the tongue between upper and lower jaw or create a nutcracker effect on the bars
- •Use 14mm as a safe maximum bit thickness to avoid tongue compression in most adult horses, and ensure bit length matches mouth width within ±5mm rather than the commonly oversized selections seen in this study
Key Findings
- •Oral dimensions vary significantly by breed and sex, with coldblood Finnhorses having larger dimensions and ponies smaller dimensions than other breeds
- •Over 10mm discrepancy between selected bit size and mouth width was common, with majority of horses using ill-fitting bits
- •Mouth width and jaw distance correlated positively with age, indicating bit fit requirements change throughout the horse's life
- •Horses averaged 14mm tongue thickness capacity without compression, providing a practical reference for bit thickness selection