Yearling laryngeal function grades II.2 and below are not associated with reduced performance

Area of Science:

• Equine science
• Veterinary diagnostics
• Animal performance studies

Background:

• The correlation between Thoroughbred yearling laryngeal function (YLF) grading and subsequent race performance remains incompletely understood.
• Laryngeal function is a critical factor influencing respiratory efficiency and athletic potential in racehorses.

Purpose of the Study:

• To investigate the impact of yearling laryngeal function grading on the future race performance of Thoroughbreds.
• To establish whether specific YLF grades are predictive of long-term racing success.

Main Methods:

• A retrospective cohort study analyzed endoscopic recordings from 5175 Thoroughbred yearlings sold in Australia between 2018-2019.
• Race performance metrics, including career earnings and age-specific performance, were evaluated.
• Multivariable generalized linear modeling was employed to assess the association between YLF grade and race outcomes.

Main Results:

• The majority of yearlings (95%) presented with YLF grades I, II.1, or II.2, exhibiting negligible differences in race performance.
• Horses with grade III.1 YLF demonstrated comparable early career performance to lower grades but showed significantly reduced performance from age four onwards.
• Grade III.2 YLF was associated with lower overall career earnings compared to referent grades I/II.1.

Conclusions:

• Yearling laryngeal function grading, particularly grades I, II.1, and II.2, shows minimal predictive value for early race performance.
• While grade III.1 YLF does not impact early career earnings, it is linked to diminished race performance in older horses (≥4 years).
• Further research is needed to address limitations such as lack of follow-up data and exclusion of unraced horses.