Calculating Body Weight in Foals

Knowing a foal’s body weight is important in tracking growth and determining the correct doses of dewormers and medications.

Weight tapes designed for mature horses are not always accurate when used on young foals, and making estimates based on visual examinations is rarely helpful.  Researchers in Chile have developed a formula that gives a better idea of a foal’s weight. The formula is based on one measurement, making it easy to use on foals that won’t stand still long enough for multiple measurements to be taken.

The measurement is of the foal’s girth (G), with a tape placed just behind the elbow and one inch (2.54 cm) behind the highest point of the withers. The measurement is taken when the foal has exhaled and is expressed in meters. The formula is:

G³ x 90 = foal’s weight in kg.

The formula was derived after measurements were made on 80 Thoroughbred foals with various body weights. Results are slightly less accurate than those that use several body measurements, but it is accurate enough to gauge weight gain or loss and to determine correct dosages.