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Estimating Weight and Condition

Last revised April 26, 2017.

A heavy horse.1

Estimating Weight

When a horse weighs less than his optimum weight, it may be due to health problems, old age, parasites, dental issues, overwork, an unbalanced diet, insufficient feed (sometimes a result of having low rank and reduced access to food sources, or genetics. Excess weight has varied causes too, including health problems, insufficient exercise, an unbalanced diet, over-feeding, or genetics. Health problems, an unbalanced diet, and genetics can result in either underweight or overweight conditions.2

There are claims that too much body fat is likely connected to “obesity disorders” in the horse, including insulin dysregulation and laminitis. There is research connecting both generalized and localized obesity to laminitis in ponies3. And there is some evidence that when horses and ponies have access to excessive amounts of certain kinds of carbohydrates, there may be changes in the hindgut which precipitate laminitis.4 Perhaps intake of large amounts of lush grass at certain times of the year produce carbohydrate fermentation which is enough to change the hindgut pH in some horses.5 Researchers at Michigan State suggest that laminitis may be induced by “the grazing of pasture with high nonstructural carbohydrate content (e.g., during spring or when pastures are stressed by drought or frost), consumption of other feeds rich in starch and sugars (grains, sweet feeds), overfeeding that induces or worsens obesity, and the administration of corticosteroids.6” I think it likely that diet is the source of trouble in the hindgut, which then may contribute to the chances of laminitis. Feral horses don’t get laminitis, it seems, perhaps because they do not have access to the same rich pastures as our horses have. My sense is that cutting back on grain and sweet feeds in the spring would be a good idea if your horse’s pasture grass is rich and sweet. If your horse is a bit overweight, a grazing muzzle at this time of year will do no harm. But I do not recommend grazing muzzles simply because you think he is overweight.

Knowing your horse’s weight is handy in diet analysis, determining dosages of wormers and supplements, and possibly for estimating fluid loss after an extended strenuous workout. Being able to accurately assess your horse’s weight is important in determining dosages: if you underestimate his weight, you’ll underdose; if you overestimate his weight, you’ll overdose (or he will).

If you determine that your horse is carrying too much body fat, you can cut back on his grazing with a grazing muzzle, which has been shown to reduce intake by up to 83%.7 And you can add to his weight with improved diet, such as adding beet pulp to your feeding schedule. But whatever you do, monitor him closely, look for likely causes, and check with your vet.

If you record his weight, measuring it at the same time of day or the same conditions (e.g., just before morning feeding), you’ll have a record you can use to monitor his health and see trends in his weight.

The best way to estimate your horse’s weight is to not estimate at all, but put him on a scale. But if he won’t fit on the bathroom scale, you’ll need to estimate.

Basic Measurements

Use a plastic or cloth measuring tape that is at least 75 inches long. Make your tape taught before taking a reading. You will benefit by having an assistant to help in positioning your tape and holding your horse. Horses will change in size from before breakfast to after, so if you are tracking his weight, always measure at the same time of day. Before you begin, get your horse standing somewhat square. If your arm span is less than the length of your horse, you’ll either need an assistant to help in this measurement or you’ll need to use the method of Huggin’ and Chalkin’8 — measure what you can, then place a chalk mark, move the tape, and measure the rest.

Measure heart girth: run your tape around the horse, crossing the highest part of his withers. Use a tape measure and run it over his withers, and around his chest where you place your girth. If you use a weight tape, you are finished.

Measure body length (Point method): Measure body length from the point of the shoulder around the corner of the hip and the actual point of the buttock, which is half the distance from the corner to tail.

Measure body length (Stifle method): Measure body length from the point of the shoulder to the midpoint of the distance between the widest part of the stifle and the tail when viewed from the rear. Your tape should be horizontal along his side.

Measuring for Weight: Placement of measuring tape in determining body length when viewed from the side (A) and rear (B). Point method: The upper, diagonal line corresponds to the body length measurement from the point of the shoulder to the ischial tuberosity — the sit bones. Stifle method: The lower, horizontal line measures to the midpoint of the distance between the widest part of the stifle and the tail when viewed from the rear.9

Methods for Estimating Weight

None of the methods described below will be accurate for very tall horses, very short horses, miniature horses, very young growing horses, pregnant mares, or horses with extreme body types — very heavy or thin barreled.

Guess. The guessing method of estimating is worthless. Some studies10 have found that human estimates are typically low, while other studies11 find them typically high.

Girth to Weight via Lookup. Use a standard tape measure, and just measure girth as described above. You can now look up his weight in the table below. Example: your horse has a girth of 78 in. You’d find the row closest to this value (the last one in the table below) and read across to find a weight estimate of 1,300 lbs.

Estimating a Horse’s Weight without a Weight Tape12

You may also guess the weight of a foal that is 2 months or less using girth alone.13 Your formula for this is (girth-25)/.07

Girth to Weight via Weight tape. Use a weight tape, and just measure girth as described above. There are many weight tapes, they differ from one manufacturer to the next, and so will not all agree for your horse. They will differ in accuracy for a given horse, but we can be sure that there is some horse out there for which a given tape will be remarkably accurate. And they are very affordable.

One of many weight tapes on the market.14

Girth and Length to Weight via Math Use your measurements of girth and one of the two methods of measuring length. Now you will do a little math. Plug your numbers into a formula below. Use 330 for the adjustment factor for a mature horse, 301 for a yearling, and 280 for a weanling, and 299 for a pony. If you are estimating a pregnant mare, all bets are off.

In inches and pounds: ((Girth x Girth x Length) / 330) +5015 = Approximate weight in lbs.

In centimeters and kilograms: (Girth x Girth x Length) / 11,927 = Approximate weight in kg.

Example: your horse has a heart girth of 78” and a length of 65”. Your calculation would be

(78 x 78 x 65 / 330)+50 = 1,248 lbs

If you are defeated by math, then you can use an online weight calculator.16 Note your mileage may vary from mine (1,198 lbs from a girth of 78” and length of 65”) because they may not use my 50 lb fudge factor.

Accuracy

Which method is most accurate? Research by scientists at Auburn University17 compared three tape methods (weight tape, point method, stifle method) with actual weight measurements on a livestock scale. They found that the point measurement was best, averaging 17.25 kg (38 lbs) less than the actual weight. Next best was the stifle method, averaging 45.26 kg (100 lbs)less than actual. The weight tape was the least accurate, averaging 65.81 kg (145 lbs) less than actual.

Girth and Length to Weight via Nomogram

A nomogram is a diagram that shows the relation between 3 or more variables by providing scales for each. A straight line connecting the best value on the left side with the best value on the right side will intersect the scale in the middle at a value estimated for this variable. In the example below, Mr. Horse had a girth of 180 cm, and a length of 175 cm. We connect the two scales, and find that his weight is likely about 475 kg. If you live in pounds and inches, first convert your inches to centimeters (lots of sites to do this for you). After drawing your line on the nomogram, convert kg to pounds. The horse below is 475 kg, or 1,047 lbs.

Estimating Condition18

In the world of horses, “condition” doesn’t mean being fit. It means being neither too fat nor too lean. If a horse has a “nice weight” as my mother used to say, it doesn’t mean that he is strong or has great stamina — only that the ratio of body fat weight to total weight is in a normal range.

Weight and Height to BMI

In humans, body fat percentage is often estimated via the Body Mass Index — BMI — which is found by:

  • For metric measures, divide weight (in kg) by height (in squared meters.)
  • For pounds and inches, divide weight (in lb) by height squared (in inches) then multiply by 703.

BMI ranges considerably. The BMI is normally higher in women than men, and higher in older folks than younger ones. There are many online calculators if you wish to find your own BMI. But if you want to calculate your horse’s BMI, you’ll need to wait until someone develops a useful scale and theory on how to use it.

Percentage Body Fat

The BMI is not the only way to determine how fat or thin we are. And that is good, because body builders and the linemen on a football team have more muscle weight, not much fat, and may have poor BMI scores. We should aspire to have a low percentage of body fat, as in the athletes in the table below.

Percentage body fat in humans, according to the American Council on Exercise.19

Body fat has a lower density than bone and muscle, so estimating body fat can be done by filling a bath tub, climbing in and asking a friend to hold you completely under, then climbing out and measuring how much water is left. Your volume, plus your weight, will provide a good estimate of your body fat. If that leaves too much water on the bathroom floor, you might consider a fat caliper.20 But if we are to use such a caliper on your horse, we’ll need to have a chart or something to get from caliper inches to something more useful.

If you are going to do your horse a big favor, don’t bother losing weight. Stay strong, and lose fat. There are a number of scales out now that use impedance analysis to measure weight, body fat percentage, muscle mass, bone density, and water weight. Amazon has one for under $35 which you can have tomorrow, if you need it. You’ll need to stand on such scales with bare feet, something you won’t be able to ask your horse to do.

Scoring Fat in your Horse

I’ve never been too sure about how humans have decided when a horse is too fat or too thin. But the extremes are surely to be avoided. Some crude scoring of your horse’s condition is possible without knowledge of height or weight, as I explain below.

One horse may carry more fat in the neck and shoulders than another, but less in the middle or hind quarters. So reviewing each of these areas, then taking an average will produce better estimates of condition. Fat will feel spongy under your fingers; muscle will feel firm. Crest fat will harden when it has been there for a while and might rock from side to side when he walks.

Searching for Fat

Check for fat in these six areas:

  1. Fat forming a crest and thickening the neck; you should be able to see muscles and feel where the bones are.
  2. Fat covering the withers and backbone (the spinous processes of the spine). There should be barely any fat here — you should be able to feel the bones underneath a supple covering of skin. Fat will build up either side of the spine until it is higher than the spine itself creating a ‘gutter’.
  3. Fat behind the shoulder and where the shoulder blends into the neck. There should be clear definition around the shoulder blade; fat will fill in the hollow in front of the shoulder and build up a pad behind the shoulder.
  4. Fat over the ribs — there should be a little fat between the ribs but not over them. This way you can feel but not see them.
  5. The definition of the bony points of the pelvis (croup and point of hip) — a healthy layer of fat under the skin will not cover up the bones; you should be able to see where they are and certainly feel them.
  6. From behind – the quarters should slope down away from the croup. An ‘M’ shape with a gutter along the backbone will be due to a large layer of fat. Fat builds up on the inner thighs too – lift up the tail to look.

Body Scoring

Body score your horse.21

There is more information on condition assessment on the Internet if you want more details.22

Condition and Height to Weight via Nomogram

Now that you know your horse’s condition, you may use it and height to guess your horse’s weight.

A nomogram allowing you to estimate weight from condition score and height.23

Personally, I would prefer to use two nomograms: girth and length to weight, and then condition and height to weight. Once I have these two results, if they are similar I can average them. If they are far different, I might want to repeat my measurements.

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1 Image source: https://c1.staticflickr.com/1/578/21414517135_c6f98fae44_b.jpg

2 Wright, Bob and Tania Sendel. “Estimating Body Weight for Horses” Ontario Ministry of Agriculture, Food and Rural Affairs. http://www.omafra.gov.on.ca/english/livestock/horses/facts/10-085.htm#health

3 Carter, Rebecca A., K. H. Treiber, R. J. Geor, L. Douglass, and Pat A. Harris. “Prediction of incipient pasture‐associated laminitis from hyperinsulinaemia, hyperleptinaemia and generalised and localised obesity in a cohort of ponies.” Equine veterinary journal 41, no. 2 (2009): 171-178.

4 Bailey, Simon R., Celia M. Marr, and Jonathan Elliott. “Current research and theories on the pathogenesis of acute laminitis in the horse.” The Veterinary Journal 167, no. 2 (2004): 129-142.; Hinckley, K.A., Henderson, I.W., 1996. The epidemiology of equine laminitis in the UK. In: Proceedings of the 35th Congress of the British Equine Veterinary Congress, Warwick, p. 62.

5 Bailey, Simon R., Celia M. Marr, and Jonathan Elliott. “Current research and theories on the pathogenesis of acute laminitis in the horse.” The Veterinary Journal 167, no. 2 (2004): 129-142

6 Geor, Raymond J. “Metabolic predispositions to laminitis in horses and ponies: obesity, insulin resistance and metabolic syndromes.” Journal of Equine Veterinary Science 28, no. 12 (2008): 753-759.

7 Longland, Annette C., Clare Barfoot, and Patricia A. Harris. “Effects of grazing muzzles on intakes of dry matter and water-soluble carbohydrates by ponies grazing spring, summer, and autumn swards, as well as autumn swards of different heights.” Journal of Equine Veterinary Science 40 (2016): 26-33.

8 Huggin’ and Chalkin’: Hear this Hoagie Carmichael song at https://www.youtube.com/watch?v=h_QfAzJP2Zo See the lyrics at https://play.google.com/music/preview/Tofdqiezq4sipuim7x6dj55jkvm?lyrics=1&utm_source=google&utm_medium=search&utm_campaign=lyrics&pcampaignid=kp-songlyrics

9 Image source: Wagner, Elizabeth L., and Patricia J. Tyler. “A comparison of weight estimation methods in adult horses.” Journal of equine veterinary science 31, no. 12 (2011): 706-710.

10 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.; Potter, G.D. and P.G. Gibbs. 1993. Body condition scoring and weight estimation of horses. Pres at Texas Agricultural Science Teachers’ Workshop. TAMU.; 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.; 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.

11 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, Oklahoma. P.240.

12 Table from Sendel, Tania. Estimating body weight for horses. Ontario, Ministry of Agriculture, Food and Rural Affairs, 2010. Originally from Lewis, Lon D. Feeding and care of the horse. John Wiley & Sons, 2013.

13 Sendel, Tania. Estimating body weight for horses. Ontario, Ministry of Agriculture, Food and Rural Affairs, 2010. Originally from Lewis, Lon D. Feeding and care of the horse. John Wiley & Sons, 2013.

14 Image source: http://www.harnessstuff.co.uk/easy-measure-weigh-band-1469-p.asp

15 Most recommended formulas underestimate a horse’s weight by about 50 pounds using the formula (Girth x Girth x Length) / 330 so I’ve added this “fudge factor.”

16 “Adult Horse Weight Calculator”. Oct 12, 2010. The Horse. http://www.thehorse.com/articles/31852/adult-horse-weight-calculator

17 Image source: Wagner, Elizabeth L., and Patricia J. Tyler. “A comparison of weight estimation methods in adult horses.” Journal of equine veterinary science 31, no. 12 (2011): 706-710.

18 Material for this section is only lightly digested from Blue Cross for Pets. “How to body score your horse.” https://www.bluecross.org.uk/pet-advice/how-body-score-your-horse

19 Image source: American Council on Exercise (ACE). Ask the Expert Blog. December 2, 2009. “What are the guidelines for percentage of body fat loss?”

20 Example: Accu-Measure Fitness 3000 Personal Body Fat Caliper Measurement Tool, available from Amazon.

21 Image source (previous 6 images): Blue Cross for Pets. “How to body score your horse.” https://www.bluecross.org.uk/pet-advice/how-body-score-your-horse

22 Carroll, C.L., and P.J. Huntington (1988). Body Condition Scoring and Weight Estimation of Horses. Equine Veterinary Journal 20 (1), 41-45.; Henneke, D.R., G.D. Potter, J.L. Kreider, and B.F. Yeates (1983). Relationship Between Condition Score, Physical Measurement and Body Fat Percentage in Mares. Equine Veterinary Journal 15, 371-372.

23 Nomogram from Ellis, Patricia, and Andrew Cameron. Condition scoring and weight estimation of horses. Department of Natural Resources and Environment, Victoria, Australia. 2002.

 

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