Weigh tape more accurately estimates equine body weight than morphometric formula: a controlled technical assessment.

Objective Overview

• This study evaluates and compares the accuracy of a commercial equine weigh tape versus a morphometric formula for estimating horse body weight, using precise digital scale measurements as the reference standard.
• The goal was to determine which method provides more reliable and consistent body weight estimates over time under controlled conditions.

Introduction and Importance

• Body weight (BW) estimation in horses is crucial for appropriate clinical care and nutrition management.
• While calibrated digital scales provide the gold standard for body weight measurement, they are often not available in field or practical situations.
• Therefore, indirect methods such as commercial weigh tapes and morphometric formulas are commonly used for estimating horse BW.
• It is important to understand how accurate and consistent these indirect methods are, especially when monitoring weight changes longitudinally.

Study Design and Methods

• A prospective longitudinal experimental design was used, meaning six horses were followed and measured repeatedly over time.
• The sample included six clinically healthy adult crossbred horses, averaging about 355.5 kg in body weight, monitored weekly for 63 days.
• Body weight measurements at each time point included:
  • Real body weight (Rbw) using a calibrated digital scale (gold standard)
  • Weight estimated via a commercial weigh tape (Tape)
  • Weight estimated using the Carroll and Huntington morphometric formula (Formula)
• The study environment and management conditions were controlled to minimize external factors influencing body weight changes.
• Data analysis used mixed-effects regression models to evaluate:
  • Agreement or bias between methods
  • Estimation error magnitude and variability
  • Correlation between indirect methods and scale measurements
  • Consistency of estimates over time

Key Results

• Actual body weight (Rbw) increased moderately from 355.5 ± 21.2 kg at baseline to 372.7 ± 27.0 kg at day 63, representing about a 4.83% increase (+17.2 kg).
• Both indirect methods overestimated body weight throughout the trial period.
• The commercial weigh tape produced a smaller mean overestimation (+2.48%) compared to the morphometric Formula (+9.89%).
• The minimum estimation error (absolute difference from scale) for the Tape decreased during the study from 8.33 kg at baseline to 5.66 kg on day 63, showing improved precision over time.
• The Formula produced consistently larger and less variable errors ranging from approximately 37.2 to 45.6 kg, indicating less accuracy.
• Correlation with the gold standard scale weight was higher for the Tape (correlation coefficient r = 0.916) than for the Formula (r = 0.821), indicating stronger agreement.
• Mixed-effects regression analysis revealed that the Tape had lower variability in estimates and better temporal consistency compared to the Formula.

Conclusions and Implications

• While both indirect methods stayed within clinically acceptable limits for estimating body weight, differences were notable.
• The commercial weigh tape was significantly more accurate, less variable, and provided more consistent estimations over time compared to the Carroll and Huntington morphometric formula in healthy adult horses.
• These findings support preferential use of commercially available weigh tapes for regular body weight monitoring in field conditions when scales are not available.
• Improved accuracy and consistency can better inform clinical decisions, dosing of medications, and nutritional management.
• Further research might assess these methods in different horse populations, health conditions, or under less controlled environments.