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.