Estimation of body weight and development of a body weight score for adult equids using morphometric measurements

Excessive BW has become a major health issue in the equine (Equus caballus) industry. The objectives were to determine if the addition of neck circumference and height improved existing BW estimation equations, to develop an equation for estimation of ideal BW, and to develop a method for assessing the likelihood of being overweight in adult equids. Six hundred and twenty-nine adult horses and ponies who met the following criteria were measured and weighed at 2 horse shows in September 2011 in Minnesota: age >= 3 yr, height >= 112 cm, and nonpregnant. Personnel assessed BCS on a scale of 1 to 9 and measured wither height at the third thoracic vertebra, body length from the point of shoulder to the point of the buttock, neck and girth circumference, and weight using a portable livestock scale. Individuals were grouped into breed types on the basis of existing knowledge and were confirmed with multivariate ANOVA analysis of morphometric measurements. Equations for estimated and ideal BW were developed using linear regression modeling. For estimated BW, the model was fit using all individuals and all morphometric measurements. For ideal BW, the model was fit using individuals with a BCS of 5; breed type, height, and body length were considered as these measurements are not affected by adiposity. A BW score to assess the likelihood of being overweight was developed by fitting a proportional odds logistic regression model on BCS using the difference between ideal and estimated BW, the neck to height ratio, and the girth to height ratio as predictors; this score was then standardized using the data from individuals with a BCS of 5. Breed types included Arabian, stock, and pony. Mean (+/- SD) BCS was 5.6 +/- 0.9. BW (kg) was estimated by taking [girth (cm)(1.48)6 x length (cm)(0.554) x height (cm)(0.599) x neck (cm)(0.173)]/3,596, 3,606, and 3,441 for Arabians, ponies, and stock horses, respectively (R-2 = 0.92; mean-squared error (MSE) = 22 kg). Ideal BW (kg) was estimated by taking [length (cm) x 2.8] + [height (cm) x 4.2] - 611, 606, and 577 for Arabians, ponies, and stock horses, respectively (R-2 = 0.86; MSE = 24). Equids with a BCS of >= 7 had a greater likelihood of being overweight, and the model suggested cutoffs at the 48th and 83rd percentiles for underweight and overweight individuals, respectively. Morphometric measurements were successfully used to develop equid BW-related equations.