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Weight, Condition, and Height Measurement of Horses
Weight, Condition, and Height Measurement and Prediction of Horses
Introduction
Accurate dosing of equine medications and supplements requires knowing the horse's accurate weight. Unfortunately, few of us have scales large enough for the job. By taking a few simple measurements, you can calculate a horse's weight within about 10% of his actual weight. Knowing a horse's weight, however, does not tell you anything about whether he is in his optimum condition. This article breaks weight down into nine stages ranging from emaciated to obese. Condition recommendations are then made based on the primary use of the horse. Also, provided is a set of tables based on breed and age for estimating the eventual height of a growing horse.
Weight Estimation
Many equestrians, trainers, and veterinarians feel they can estimate a horse's weight by looking at him. A study of 77 farm mangers and 62 veterinarians with an average of 17 and 21 years' experience with horses showed they were 20% off more than 80% of the time and more than 10% off over 95% of the time. The following calculations and tables should get you within 5 to 10% of the horses actual weight. I recommend you carefully take the measurements twice and then discuss with your veterinarian whether to add 10% to the weight determined. The efficacy of many treatments drops off rapidly with under dosing and there are very few drugs that are significantly more toxic when given at a 10% higher dose. For this reason adding 10% to your calculated weight for dosing dewormers and medications is a good practice with all but the most toxic drugs. Deworming products recommended on this site are not considered toxic at a 200% overdosage for instance. With prescription drugs proper dosage should be discussed with your veterinarian.
If you are using a commercial weight tape be sure to follow the instructions on the tape. For the calculations and table below two different ways of measing the girth are used. Girth measurements are best done with a cloth or very thin metal tape measure marked in inches or centimeters. The tape encircles the horse in the girth region.
Adults of non-pregnant light breed horses (QH, TB, Arabs, TWH, Pasos, etc)
Measuing Girth vs. Heart Girth
Note in the image above the withers are not readily observable on this Paso Fino. The determination of where the end of the withers can be aided by palpating the three highest vertebral spinous processes (T5-T6-T7) and placing the tape behind the last one.
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- Heart Girth: For heart girth the tape should start at a point just behind the withers and travel to the point just behind the elbows and back up the other side. There tape will end up at an angle with this measurement.
- Girth: The girth measurement also has the tape just behind the withers but is allowed to drop straight down then comes back up the other side.
Length
Length is measured from the anterior point of the shoulder to the posterior point of the buttocks. If you are looking at the horse from the side, these would be the most forward point of the shoulder and the most rearward point of the butt. The tape will need to bend a little to contact these two points.
Using Calculations
The most accurate estimation (within 5%) can be had by measuring the heart girth and length of the horse and putting them into one of these two equations:
- Lb body wt. = [heart girth (inches) squared x length (inches)] / 330
- Kg body wt. = [heart girth (cm) squared x length (cm)] / 11,880
A Simple Table
Though not quite as accurate as the calculations that incorporate length of the horse into the equation, this table is still accurate to within 10%.
| Girth Measurement in inches. Note this is not the same as heart girth, see above for description. | Weight (lbs) | Girth (cm) | Weight (kgs) |
| 32 | 100 | 80 | 45 |
| 40 | 200 | 90 | 70 |
| 45 | 275 | 100 | 90 |
| 50 | 375 | 110 | 120 |
| 55 | 500 | 120 | 150 |
| 60 | 650 | 130 | 185 |
| 62 | 720 | 140 | 230 |
| 64 | 790 | 150 | 285 |
| 66 | 860 | 160 | 345 |
| 68 | 930 | 170 | 410 |
| 70 | 1000 | 180 | 475 |
| 72 | 1070 | 190 | 545 |
| 74 | 1140 | 200 | 615 |
| 76 | 1210 | ||
| 78 | 1290 | ||
| 80 | 1370 |
Pregnant Light Breed Horses
For pregnant mares use the following multipliers to the results you obtained above:
- 8 months pregnant: 1.02
- 9 months: 1.06
- 10 months: 1.11
- 11 months: 1.17
Foals of Light Breeds 1 to 6 weeks of age
- Lb body wt. = [heart girth (inches) - 25.1] / 0.07
- Kg body wt. = [heart girth (cm) - 63.7] / 0.38
Other Breeds (heavy, pony, minatures) and Species (burros, mules, zebras) of Equines
Currently I have not found a equivalent nomogram describing how girth and length relate to weight. The best recommendation I have is to use the measured heart girth and length formula above but cannot attest to the accuracy of this method for these other types of equines.
Judging a Horse's Condition
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