The horse body mass is highly variable, depending on breed, model, physiological state, condition, owner's purpose and usage of the animal. Always 65% to 75% water, it is divided on average between 50% muscle, 11% bone and 10% fat. Depending on whether it's a pony or a draft horse, it can range from less than 200 kg to over a ton, with an average of 500 kg for saddle horses. It also differs with the season, as horses are almost always fatter in summer than in winter. Various tools are used to estimate their weight and body condition, and veterinary scales have been created to determine whether a horse has an ideal body mass according to precise criteria. Thinness is associated with mistreatment, but owner-independent factors such as age and illness can cause dramatic weight loss in horses. In Western countries, equine obesity is one of the major veterinary health problems of the 21st century. It is directly linked to numerous pathologies, such as laminitis, osteoarthritis, insulin resistance and colic. It also favors the development of equine Cushing's disease, and causes a drop in stallion fertility.
General information
The horse body mass is always 65-75 % water. The horse is considered a "thin animal" (with little fat), whose weight is divided into approximately 11% bone, 50% muscle and 9% fat; but a large number of factors influence its weight. Some breeds (draft horses) are naturally heavier than others (ponies), and differ in size and bone structure, so the weight range of horses is highly variable. Ponies can weigh less than 200 kg and heavy horses more than a ton, while the average weight of a saddle horse is estimated at around 500 kg. Champion show-jumper Jappeloup de Luze, for example, weighed around 470 kg. Heavy horses bred for slaughter reach particularly high weights, as it's in the breeder's interest to get maximum meat weight out of them.
Weight is also affected by physiological conditions: the horse may be growing, pregnant or breeding. The purpose of breeding and the animal usage also call for different body conditions: for example, a horse destined for sport should always be as close as possible to its ideal weight, to remain a top performer. On the other hand, a pregnant or nursing mare will be in better shape if she has a higher than average body mass, with some fat reserves.
Estimating a horse's weight is important in a number of ways for the owner of a domestic horse: dosing its feed ration, administering anthelmintics or other medication, or monitoring its growth and state of health. In these cases, we're talking about the horse's weight, not its health.
Growth Foal growth leads to particularly rapid weight gain in the first few months. At birth, foals weigh 8 to 12% of their mother's live weight. They double their birth weight during their first month of life. By the time they reach weaning age, at around 6 or 7 months, their weight has quintupled. By the age of one, they have reached around 65% of their adult weight and 90% of their adult height, which explains the often gangly appearance of foals at this age. Draft foals fattened for slaughter weigh on average 59.3% of the adult horse's live weight at 8 months, then 70.1% at 12 months, and 90.1% at 30 months.
Seasonal variations
Horses are almost always fatter in summer than in winter, especially if they live outdoors all year round, or in the wild. In summer, changes in light levels lead to an increase in appetite and changes in metabolism, which generally result in weight gain. In winter, on the other hand, appetite is reduced and the efficiency of energy conservation is increased, as the food available is generally scarcer. This particularity seems to stem from the horse's long evolutionary history in an environment that does not always offer the same quantity of food from one season to the next, nor from one year to the next. The obesity rate can differ by around 8% depending on whether measurements are taken in summer or winter. The horse body condition is at its lowest at the end of winter.
Estimating weight and body condition Weight and body condition are two notions that are assessed independently. Along with body dimensions, weight is a component of size.
Estimating weight Weight can be estimated visually, by weighing or by tape weighing.
Visual estimation Visual estimation is the simplest, but it is empirical and often wrong, depending on the experience of the assessor. Consequently, this is the method used by professionals in everyday conditions, without excluding the use of weighing in special situations, notably to monitor animal growth.
Weighing Weighing is the process of estimating weight using specialized weighing equipment. A priori, this is the most accurate method of determining an animal weight, but in the case of a horse, it is necessary to use equipment such as a weighing cage (preferably removable) or a weighing platform. These tools are relatively expensive, and the vast majority of horse owners don't own them.
On the other hand, breeders and professionals in the horse market often acquire them, not only for the precision of the measurement, but also to perfect their judgment, through visual appreciation. In breeding areas, some communes are equipped with a weighbridge, which can accommodate a van or cattle truck. Weighing results must also be interpreted according to the assumed state of replenishment of the digestive tract.
Tape weighing Tape weighing is the method of estimating an animal weight using mathematical formulas based on body dimensions. These formulas were devised to compensate for the disadvantages of visual estimation and the constraints of mechanical weighing. They were initially used for educational purposes, in training centers, and as a complement to previous methods. These formulas have generally been developed for adult, mesomorphic animals in a normal state of maintenance and with an average level of digestive tract replenishment. The values collected must therefore be interpreted according to age, body proportions (brachymorphic, mesomorphic or dolichomorphic), state of maintenance and estimated replenishment of the digestive tract.
As a result, various scales and mathematical formulas have been created to estimate a horse weight using simple tools, or without tools at all. The tape weighing, placed around the body between the withers and the girth area (corresponding to the thoracic perimeter, TP on the diagram), gives an estimate of weight.
Crevat formula In 1890, Jules Crevat created a formula and a tape weighing bearing his name, still used today for educational purposes in zootechnics. Crevat's original idea was to quickly estimate the weight of cattle that had to pay a octroi tax. It is a simplification of a formula developed for humans by Adolphe Quetelet, which was based on two measurements (chest and waist perimeter). It is not very precise, but has the advantage of being easy to calculate, requiring only a measurement of the thoracic perimeter (TP). This is one of the most widely used formulas in France, especially for weighing saddle horses, but, as with all formulas, the estimate must be interpreted according to the state of maintenance of the animals and their proportions.
It is calculated as follows: Weight = 80 × (TP)3, with Weight in kilograms and TP in meters. The margin of error is 25 kg. For example, for a horse with a thoracic perimeter of 1.82 m, Weight = 80 × (1.82)3, giving 482 ± 25 kg.
Hapgood's formula Alyssa Hapgood's formula was conceived in 1999, designed in 2002 and approved in 2004, when she was just 17 years old. It's one of the most accurate, but also requires more measurements, since it takes into account not only thoracic perimeter (TP), but also withers height (WH) and body length (BL), measured from the point of the shoulder to the point of the buttock: Weight = TP1,64 × WH0,95 × BL0,40 / 278. The formula works with weight expressed in pounds (0,453 592 37 kg) instead of kilos, and withers height in inches rather than centimeters.
To convert inches into centimeters, perform the following operation: po= cm x 0,393700787.
INRA formula for draft horses A formula specific to draft horses was developed in 1990 by William Martin-Rosset, researcher in charge of equine nutrition at INRA: Weight = 7.3 × (TP) - 800. The margin of error is also 25 kg.
INRA formula for growing foals Growing foals require special parameters, as withers height (WH) cannot be taken into account. INRA has devised a formula for this purpose: Weight = 4.5 × (TP) - 370.
Body condition assessment This last measurement is designed to assess the relative development of muscle and fat mass. It is performed by palpating certain areas of the body.
Henneke scale The Henneke horse body condition scoring system is used to assess the amount of fat on a horse's body. It was developed by Don R. Henneke at Texas A&M University in 1983, initially for pregnant Quarter Horse mares. This standardized system can be used for all horse breeds and without specialized equipment, but it may be more effective for saddle horses than ponies. Another limitation is that horse owners are not always the most objective when estimating their animal's body condition.
Body condition is assessed visually and by palpation. Scores range from 1 to 9, with 1 being a horse in poor condition and 9 being an obese horse. The ideal condition for most animals is between 4 and 6. Scores of 7 to 9 are considered obese, although a certain lack of precision in assessments sometimes leads to a horse with a score of less than 7 being classified as obese.
The table below describes the different scores used to assess a horse's body condition. The system is based on both visual and tactile assessment of the fat present on six points of the body, as shown in the illustration below.
This system is used by Anglo-Saxon organizations for legal purposes, as an objective method of determining a horse's physical condition during investigations into cruelty. +Henneke horse body condition scoring systemScoreDescriptionImage1.PoorExtremely emaciated, no visible fat deposits. Vertebrae, ribs, tail head, withers, shoulder and neck bones are very visible.2.Very thinEmaciated, slight muscular coverage of bones, vertebrae and ribs clearly visible. Tail set, withers and shoulder bones, neck visible.3.ThinVery light fat deposits all over the body, with vertebrae and ribs visible but not individually discernible. Withers, shoulders and neck do not appear thin.4.Moderately thinThe line of the spine and the long rib lines are visible; the tail set may be visible depending on the breed. Withers, shoulders and neck do not appear too thin.5.ModerateThe spine and ribs may not be visible but are easy to feel; the base of the tail is spongy. Withers, shoulders and neck are rounded and smooth.6.Moderately fleshySlight swellings along the spine; ribs and tail head are covered with a light deposit of fat; detectable fat deposits along the withers and neck, and behind the shoulders.7.FleshyBulging along the spine, ribs show fat filling between them; base of tail is spongy; fat deposits along withers and neck, and behind shoulders.8.FatApparent bulge along spine; ribs difficult to feel; soft fat surrounding base of tail; fat deposits along withers, behind shoulders and inside thighs.9.ObesityObvious fat deposits all along the spine, fat deposits on ribs, at base of tail, withers, behind shoulders, and on neck. Fat covers flanks and inner thighs.
Problems associated with under- and overweight Horse fat is neither inert matter nor the result of simple "storage". Studies have shown that it is active tissue, particularly in the secretion of hormones and inflammatory proteins (cytokines), the presence or absence of which can severely affect the animal's health. More surprisingly, body condition is related to dominance, with horses in better condition tending to dominate others.