Henderson County Horse Committee
Athens, Texas

ESTIMATING HORSE BODY WEIGHT
WITH A SIMPLE FORMULA

Knowledge of horse body weight is useful in determining how much daily feed is needed.' Also, paste wormers and other medications are designed to be dispensed at specific levels relative to a horse's weight. Unfortunately, most horse owners do not have easy access to a set of scales and must often resort to visual evaluation for estimating weight . However, one study conducted in Florida found that 88% of horse persons underestimated actual weight by an average of 186 pounds.: Similar trends have been observed at educational programs in Texas.'-` In one field study, 37% of horse owner estimates were at least 150 pounds below actual weights. Some horse owners tend to overestimate actual weights by visual observation. In the Florida study, 13% of participants overestimated by 90 pounds. 2

Fortunately, there is a simple formula that call be used to estimate body weights of individual horses fairly accurately ".6.7.8.9. This formula utilizes heartgirth circumference, body length measurements and an adjustment factor 710. This horse weight prediction equation is shown below:

Measurements should be taken and recorded in inches with a tape that is at least 75 inches long. Plastic measuring tapes are preferred over cloth tapes because they won't stretch. Metal tapes can be used but they sometimes scare horses, making them the least preferable."

As shown in tile figure, heartgirth is a measure of the circumference, taken by running the tape measure all tile way around the horse, using the highest part of tile withers. Body length is measured from the point of the shoulder, straight back along tile horse's side, and to the point of the buttock. The rear-view figure shows that the tape should go around the comer of the hip and to the actual point of the buttock, which is essentially half the distance from the comer to the tail. Two persons will be needed in taking body length measurements. For owners who are learning to take measurements for the first time, it 'is advisable to get an actual scale weight on one horse and compare it to the prediction equation. This will help determine whether or not measurements are being taken front the proper points. The horse should be standing somewhat square. Furthermore, measurements of a horse to compare changes in weight over time should always he taken at the same time of the day, preferably in the morning prior to feeding.

In two demonstrations conducted at Texas A&M` a total of 12 horses were taped. The horses were of Arabian, Quarter Horse or Thoroughbred breeding and had actual scale weights ranging from 725 to 1275 pounds. The tape measurements and equation underestimated actual weight of 5 horses by an average of 15 pounds and overestimated actual weight of 5 horses by 12 pounds. One mare, that was extremely heavy fronted, deephearted and light hipped, was overestimated by 150 pounds. The prediction equation estimated weight of I horse exactly. Overall, the procedure averaged being within - 24 pounds of actual weight.

In summary, the above mentioned prediction equation appears to be a more reliable method for estimating weight than visual observation. The procedure ran be used effectively on many horses, but may not be highly accurate for pregnant mares or for horses with extreme conformational irregularities, especially very unbalanced horses. All in all, horse owners should be able to utilize this simple tool in better managing horses.

REFERENCES

1) NRC. 1989. Nutrient Requirements of Horses. The National Research Council. Washington D.C.

2) Johnson, E.L., R.L. Asquith and J. Kivipelto. 1989. Accuracy of weight determination of equids by visual estimation. Proc. 11th Equine Nutrition and Physiology Symposium. Stillwater, Oklahma. P.240.

3) Householder, D.D. and P.G. Gibbs. 1990. A method demonstration comparing visual estimation and use of a prediction equation to actual scale

weights of horses. Pres. at Gulf Coast Women's Equine Association meeting. Houston.

4) Potter, G.D. and P.G. Gibbs. 1993. Body condition scoring arid weight estimation of horses. Pres at Texas Agricultural Science Teachers' Workshop. Texas A&M.

5) Gibbs, P.G. 1993. Weight estimation and determination of horses using scales, visual appraisal and a prediction formula. Pres. at Purina Mills Certified Dealer Workshop. Texas A&M.

6) Milner, J. and D. Hewitt. 1969. Weights of horses: Improved estimates based on girth and length. Canadian Veterinary Joumal.0 10(12) p. 314.

7) Hall, L.W. 1971. Wrights Veterinary Anesthesia and Analgesia. 7th Edition. London. p. 176.

8) Ensminger, M.E. 1977. Horses and Horsemanship. 5th edition. Interstate Printers and Publishers. p. 509.

9) Leighton - Hardman, A.C. 1980. Equine Nutrition. Pelham Books. London. P.9.

10) Carroll, C.L. and P.J. Huntington. 1988. Body Condition scoring and weight estimation of horses. Equine veterinary Journal. 20(l). p.41.

11) Householder, D.D. and P.G. Gibbs. 1992. Measuring and estimating weight of horses. A Method Demonstration Teaching Guide. Texas A&M.

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