How accurate are weight calculation formulae for horses? Researchers test them

Seven mathematical formulae for estimating the body weight of horses from simple measurements have been put to the test by researchers in Poland.

Accuracy varied among the formulae tested, and different breeds had a major influence on the results, the study team found.

Researchers with the Wroclaw University of Environmental and Life Sciences have described the outcome of their work, involving 299 adult horses of five breeds, in the open-access journal Animals.

Wanda Górniak and her colleagues said body weight estimation and monitoring of weight variations are necessary to determine the amount of feed and additives to give to horses.

Due to the cost and practical challenge of weighing horses on a large scale, several methods for estimating the body weight of horses have been developed.

One option is to determine a horse's body weight using a formula.

The seven formulae, described in the table below, were put to the test using a group of ponies, the Polish Noble Half Breed, the Silesian breed, the Wielkopolski breed, and the Thoroughbred.

The horses lived at five stud farms across Poland. All were at least three years old and had been assessed with a body condition score of 5.0 to 5.5 on the nine-point scale.

The formulae were applied to all breeds of horses, and not only to those groups for which some were originally developed.

For each of the 299 horses, their actual weights were obtained using electronic scales. The required body measurements, using a measuring stick and tape, were obtained for the use with the various formulas.

Using the measurements, the weight of each animal was then calculated and the results compared against the actual weight to determine accuracy.

The average value of mass calculated using all of the formulae, as well as the measured value of mass, along with the standard deviation, is shown in the table below.

In the group of ponies, the most accurate formula was the one developed by Martinson and others for Arabian-type horses, and the least precise were Ensminger and the formula developed by Martinson and others for ponies.

In the case of the Silesian horses, the results of the Martinson formula for Arabian-type horses and stock horses were closest to the true body weight. The least accurate was the Ensminger formula that was developed by Jones and others.

For the Polish Noble Half Breed, the most accurate was again the Martinson formula for Arabian-type horses, whereas the furthest from the true body weight were the results from Ensminger.

For the Wielkopolski horses, the Marcenac and Aublet formula proved most accurate, while the least accurate were the Ensminger and Jones formulae.

The most accurate formula in the group of Thoroughbreds was the Carroll and Huntington formula, whereas the least accurate was the formula from Ensminger.

The authors, noting that the Martinson formula for Arabian-type horses was the most accurate for the group of ponies, the Silesians, and the Polish Noble Half Breed, said it was linked to a similar fat distribution pattern among these breeds.

Overall, for a more accurate estimate, the body fat and muscularity of the horse should be considered, the authors said. "Horse weight can vary greatly depending on the quality of work performed; horses in sport training should, in principle, be heavier due to greater muscle development."

They found that the use of formulae for body weight estimation can be useful in determining quantities of feed and additives, medicines, or deworming agents.

The full study team comprised Górniak, Martyna Wieliczko, Maria Soroko and Mariusz Korczyński.

Górniak, W.; Wieliczko, M.; Soroko, M.; Korczyński, M. Evaluation of the Accuracy of Horse Body Weight Estimation Methods. Animals 2020, 10, 1750.

The study, published under a Creative Commons License, can be read here.