Assessment of intra-horse variability in Thoroughbred yearling laryngeal function

Summary

Upper respiratory tract endoscopy of Thoroughbred yearlings is a critical component of the pre-sale evaluation process, with laryngeal function grades significantly influencing sales prices and clearance rates. Industry stakeholders have raised concerns that laryngeal function grades may vary within the same yearling when assessed at different timepoints and under different endoscopic conditions. Given the substantial weight placed on a single endoscopic evaluation at the time of sale, this gap in knowledge continues to raise questions about the reliability of endoscopic assessments, underscoring the need for further investigation to enhance confidence in yearling sales evaluations.

Stakeholder concerns regarding intra-horse variability in laryngeal function have been documented in a previous AgriFutures-funded project and are supported by published evidence documenting variability in resting laryngeal function grading. Yearlings commonly undergo multiple endoscopic assessments over a short period, both on-farm during sales preparation and again at the sales complex. These examinations may differ in timing, environment, and endoscopic technique, all of which may contribute to the industry perception of variability in an individual yearling’s laryngeal function. However, the true extent of this intra-horse variability remains unclear.

Currently, pre-sale radiographs submitted to the xray repository may be acquired on farm up to 42 days prior to the sale. In contrast, pre-sale endoscopic examinations must be performed on the sales complex to be eligible for repository submission. Many vendors would prefer to avoid endoscopy at the sales due to welfare concerns, logistical burden, and disruption during an already high-stress period. However, at present there is no objective evidence demonstrating equivalence between on-farm and on-complex endoscopic assessments, and therefore no data to support modification of existing guidelines.

Variation also exists in the nasal passage used for pre-sale endoscopy, with current guidelines permitting either side. This study aims to address a key industry concern by quantifying the extent of intra-horse variability in yearling laryngeal function across different timepoints using a standardised endoscopic technique. Laryngeal function will be graded by two experts using an objective grading method to minimise observer variability. By controlling external variables whilst closely replicating standard Australian pre-sale endoscopic procedures, the findings remain directly relevant to industry practice. The study will also evaluate the impact of nasal passage selection on laryngeal function grading. Together these outcomes have the potential to inform evidence-based refinements to industry guidelines and enhance consistency and reliability of the yearling sales endoscopy.

Program

Thoroughbred Horses

Research Organisation

Murdoch University