Why is my horse losing weight?

What it looks like

• •Ribs, spine, or hip bones becoming easier to see or feel over weeks
• •Loss of muscle over the topline, rump, or neck rather than just fat cover
• •A body condition score of 3 or below on the 9-point Henneke scale, where most horses should sit between 4 and 6
• •Quidding: dropping half-chewed balls of feed, or long stems and large feed particles appearing in the manure
• •Eating slowly, tipping the head to one side when chewing, or leaving hay it used to finish
• •Dull coat, poor appetite, mild recurrent colic, or a girthy reaction when tacking up
• •Loose manure or diarrhea alongside the weight loss
• •In an older horse: a coat that sheds late, more drinking and urinating, or repeated infections

Likely causes, ranked

A tag marks the causes that are pain wearing a behavior label. Those are the ones to rule out first.

1. 01Dental diseasecommonpossible painThe University of Florida IFAS Extension lists weight loss among the signs a horse needs dental attention and describes how poor oral health leads to inefficient digestion and weight loss despite adequate nutrition, plus decreased feed consumption. Quidding, difficulty chewing, and long stems in the manure are the visible version. It recommends a yearly oral examination for mature horses over five.
2. 02Gastric ulcerscommonpossible painMerck gives poor performance, colic, poor appetite, mild weight loss, poor body condition and attitude changes as the adult signs of gastric ulcers, and puts prevalence at at least 90 percent in racehorses in active training and 40 to 60 percent in nonracing performance disciplines. Risk rises with intense exercise, grain-heavy diets with limited hay, long gaps between meals, travel and stall confinement. Gastroscopy of an empty stomach is the only definitive diagnosis.
3. 03Not enough foragecommonThe simplest cause is the one people check last. Iowa State University Extension puts the requirement for aged healthy horses at 1.5 to 2.0 percent of body weight in dry matter per day of good quality grass or legume mixed hay. A horse low in the pecking order, on a bare paddock, or on a hay net that empties by midnight is eating less than the yard thinks it is.
4. 04Parasitespossiblepossible painThe AAEP's internal parasite control guidelines list weight loss among the hallmark findings of larval cyathostominosis, alongside diarrhea, low blood albumin and ventral edema. They also warn that detecting parasite eggs in a fecal sample does not indicate a parasitic contribution to a clinical presentation, because egg shedding is normal in healthy animals, so parasitic disease is diagnosed by pattern recognition across clinical findings, not by a fecal egg count alone.
5. 05PPID (equine Cushing's disease) or another endocrine problempossiblepossible painThe University of Illinois lists weight loss and muscle atrophy among the signs of PPID and says it commonly affects horses and ponies aged 15 and older. Colorado State lists weight loss and muscle wasting among the clinical signs of equine Cushing's disease. In an older horse losing topline, an ACTH test belongs in the same visit as the dental exam.
6. 06Age-related change in how the horse uses feedpossibleIowa State University Extension notes that aged horses lose body condition and muscle along the topline because they process certain nutrients less efficiently, most notably protein, and points to reduced hindgut fermentation and decreased small intestine function. It suggests alternative forages such as hay cubes and pellets for horses with poor teeth, and beet pulp or soybean hulls to raise fiber intake.
7. 07Another chronic diseaseless commonpossible painWeight loss with a good appetite and clean teeth points at absorption or a chronic internal problem: liver, kidney, chronic infection, inflammatory bowel disease, or a tumor. None of these can be told apart in the field, and none of them respond to more feed. This is the group a vet finds with blood work and imaging, which is why weight loss that survives a dental exam and a forage audit becomes a diagnostic work-up rather than a feeding experiment.

What to try

1. 1Weigh the problem instead of eyeballing itRutgers Equine Science Center describes the Henneke body condition score, developed at Texas A&M, as a 1 to 9 scale assessed on fat cover over the ribs, neck, withers, loin, tailhead, and shoulder and elbow, with most horses sitting between 4 and 6 and horses scoring 3 or below needing to gain weight. Score the horse and use a weight tape on the same day each week, because a falling trend is a different conversation with the vet than an impression that the horse looks poor.
2. 2Book a dental examThe University of Florida recommends a yearly oral examination for mature horses over five, and lists weight loss and quidding among the signs a horse needs one. This is the cheapest, fastest thing on the list to rule in or out, and it is the cause that most often turns weight loss around on its own.
3. 3Count the forage the horse actually eatsWeigh the hay rather than counting flakes, and watch a full feed. Iowa State puts the requirement at 1.5 to 2.0 percent of body weight in dry matter per day of good quality hay for aged healthy horses. Then watch the herd: a horse that gets moved off the pile eats a fraction of what it is offered.
4. 4Ask the vet about ulcers, parasites and endocrine testing togetherMerck notes gastroscopy of an empty stomach is the only definitive diagnosis for gastric ulcers. The AAEP warns that fecal egg counts should not be used to diagnose disease because there is no correlation between the count and the disease-causing life stages, so parasites are assessed by pattern, and a fecal egg count reduction test tells you whether the dewormers used on the yard still work. In a horse over 15, add an ACTH test.
5. 5Add calories with fiber and fat, not more grainIowa State points at highly digestible fiber sources such as beet pulp, soy hulls and dehydrated alfalfa meal, notes that fat carries twice the calories of a carbohydrate without triggering an insulin response, and suggests a slurry of a complete or extruded feed for a horse that cannot chew well. Do this after the vet has found the cause, not instead of finding it.

Questions people ask

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Sources

Every figure on this page traces to one of these. We cite registries, associations, government and veterinary bodies, and published cost surveys - not other blogs.

1. [1]Equine Dental Care- University of Florida IFAS ExtensiongovThat weight loss, quidding, difficulty chewing, dropping partially chewed food, excess salivation, head tossing, reluctance to accept the bit, bad breath and facial swelling are signs a horse needs dental attention, that poor oral health leads to inefficient digestion and weight loss despite adequate nutrition and decreased feed consumption, that long stems and large feed particles appear in the manure when chewing is compromised, and that mature horses over five should be examined yearly.
2. [2]Gastric Ulcers in Horses- Merck Veterinary ManualeditorialThat prevalence of EGUS in racehorses in active training and racing is at least 90 percent and 40 to 60 percent in nonracing performance disciplines, that adult signs include poor performance, colic, poor appetite, mild weight loss, poor body condition and attitude changes, the risk factors of intense exercise, grain-heavy diets with limited hay, long gaps between meals, travel and stall confinement, and that gastroscopic visualisation in an empty stomach is the only definitive method of diagnosis.
3. [3]AAEP Internal Parasite Control Guidelines- American Association of Equine PractitionersassociationThat weight loss is a hallmark finding of larval cyathostominosis alongside diarrhea, hypoalbuminemia, neutrophilia, dehydration and ventral edema, that detecting parasite eggs in feces does not indicate a parasitic contribution to a clinical presentation because egg shedding is normal in clinically healthy animals, that fecal egg counts should not be used to diagnose disease as there is no correlation with disease-causing life stages, and that an annual fecal egg count reduction test is used to check anthelmintic efficacy.
4. [4]Feeding the Senior Horse- Iowa State University Extension and OutreachgovThat aged horses lose body condition and muscle along the topline because they process certain nutrients less efficiently, most notably protein, that aged healthy horses with a body condition score of 5 to 7 require 1.5 to 2.0 percent of body weight in dry matter per day of good quality grass or legume mixed hay, and that hay cubes and pellets, beet pulp, soybean hulls, added fat and a slurry of complete or extruded feed are options for horses with poor teeth.
5. [5]Pituitary Pars Intermedia Dysfunction (PPID) in Horses- University of Illinois College of Veterinary MedicinegovThat weight loss and muscle atrophy are among the signs of PPID, that PPID commonly affects horses and ponies aged 15 and older, and that diagnosis is by an ACTH blood test.
6. [6]Equine Cushing's Disease- Colorado State University Veterinary Health SystemgovThat weight loss and muscle wasting are among the clinical signs of equine Cushing's disease, and that most cases occur in horses over 15 years of age.
7. [7]Your Horse's Body Condition: Too Much, Too Little, or Just Right?- Rutgers Equine Science CentergovThat the body condition score developed by Dr. Henneke at Texas A&M University is a 1 to 9 scale, that most horses should fall between 4 and 6 depending on their job and level of fitness, that horses scoring 3 or below need to gain weight, and that scoring assesses fat cover on the ribs, neck, withers, loin, tailhead, and shoulder and elbow area.