Reference Values and Association of Body Weight, Age, and Sex With Echocardiographic Measurements in Non-Athletic Quarter Horses.

This study established echocardiographic reference ranges for non-athletic Quarter Horses and examined how body weight, age, and sex relate to cardiac measurements. Body weight showed significant positive associations with several dimensions, including a thicker systolic left‑ventricular free wall and a larger left atrial diameter, supporting weight-adjusted interpretation.

What the researchers wanted to find out

• Whether breed- and activity-specific echocardiographic reference intervals could be defined for sedentary (non-athletic) Quarter Horses.
• How physical characteristics—body weight, age, and sex—are associated with standard echocardiographic measurements.

Why this matters

• Cardiac size and function vary by breed, body size, and training status; using generic reference values can lead to misclassification of normal adaptations as disease (or vice versa).
• Quarter Horses are common in North America, yet published echocardiographic reference intervals for non-athletic individuals are limited.
• Clarifying how body weight, age, and sex influence dimensions helps clinicians interpret studies more accurately and decide when weight-corrected values are preferable.

Who was studied

• Forty-one sedentary Quarter Horses from a university research herd.
• All horses were free of cardiac disease based on clinical evaluation and echocardiography.
• Population reflects non-athletic (sedentary) animals, not performance-trained horses.

Study design and methods

• Cross-sectional study conducted between 2020 and 2022.
• Standardized transthoracic echocardiograms were performed using a consistent protocol.
• Reference intervals (RIs) were calculated for:
  • Raw echocardiographic measurements.
  • Weight-corrected (normalized) values to account for body size differences.
• Multiple linear regression was used to assess associations between physical characteristics (predictors: body weight, age, sex) and echocardiographic variables (outcomes).

Main findings

• Body weight was a key determinant of cardiac dimensions:
  • For every 100 kg increase in body weight, the left ventricular free wall thickness in systole was 3 mm greater (95% CI 1–6 mm; p = 0.02).
  • For every 100 kg increase in body weight, the left atrial diameter was 8 mm larger (95% CI 2–13 mm; p value reported as significant; the abstract text provided is truncated and does not show the exact value).
• Reference intervals were established for the cohort for both raw and weight-corrected measurements, enabling breed- and activity-appropriate interpretation in clinical practice.
• Associations for age and sex were evaluated; the abstract emphasizes body weight as the primary driver, and detailed age/sex effects are not provided in the excerpt.

How to interpret these results

• Larger horses naturally have larger cardiac structures; without adjusting for weight, clinicians risk labeling physiologic size as pathologic.
• Weight-corrected reference intervals are particularly useful for parameters sensitive to body size, such as left atrial diameter and ventricular wall thickness.
• Because the study population was sedentary, these reference intervals are most applicable to non-athletic Quarter Horses; athletic training can further remodel the heart and would require separate reference values.

Clinical applications

• Select reference intervals matched to:
  • Breed: Quarter Horse.
  • Activity status: sedentary/non-athletic.
  • Body size: use weight-corrected ranges when available, especially for atrial and ventricular dimensions.
• When evaluating left atrial size or left ventricular wall thickness, consider that heavier Quarter Horses may fall near the upper end of raw reference ranges but still be normal when weight-adjusted.
• Use serial measurements in the same horse, ideally with consistent technique, to detect true change over time rather than normal between-horse variability.

Strengths of the study

• Provides breed- and activity-specific reference intervals for a commonly encountered equine population.
• Uses standardized echocardiographic methods and multivariable modeling to disentangle the effects of body weight, age, and sex.
• Reports both raw and weight-corrected values, improving clinical utility across a range of body sizes.

Limitations and cautions

• Sample size is modest (n = 41), which may limit precision for some reference limits and for detecting smaller age/sex effects.
• Single-herd, sedentary population may not capture the full variability present in broader Quarter Horse populations or athletic horses.
• Cross-sectional design cannot address longitudinal changes with aging or training.
• The abstract excerpt is truncated, so some numerical results (for example, exact p-value for the left atrial association) are not visible here.

What would strengthen future research

• Larger, multi-center cohorts to refine reference intervals and improve generalizability.
• Separate reference intervals for athletic Quarter Horses at different training levels.
• Longitudinal studies to quantify how aging and conditioning alter cardiac dimensions within individuals.
• Evaluation of additional normalization strategies (for example, allometric scaling) to optimize weight correction across very small and very large horses.