Why Is My Horse Losing Weight? Causes & Feeding Solutions

By Sarah Bennett, Certified Animal Nutritionist

Warning: Unexplained weight loss in horses always warrants a prompt veterinary assessment. Do not attempt to diagnose or treat the underlying cause on your own. Contact a qualified equine veterinarian — not a small animal or general practice vet — as horses have unique physiology that demands specialist knowledge.

Few things are more concerning for a horse owner than watching their animal gradually lose condition despite apparently eating well. Weight loss in horses is never "just one of those things." It is always a symptom — of something physical, environmental, social, or metabolic. The good news is that once you identify the root cause, targeted feeding and management changes can make a dramatic difference. Here is a practical guide to the most common reasons horses lose weight and what you can do about each of them.

Understanding Body Condition Scoring

Before diving into causes, it is worth understanding how to measure the problem. The Henneke Body Condition Score (BCS) is the industry-standard tool for assessing fat cover in horses. It runs from 1 (extremely emaciated) to 9 (obese), with 4–6 considered ideal for most horses. You assess fat deposits over six areas: the neck, withers, behind the shoulder, ribs, loin, and tailhead.

A horse scoring 3 or below has visible bone structure, prominent withers and ribs, and little detectable fat. If your horse has dropped even one point on the BCS scale over a few weeks without explanation, that warrants concern. Weigh your horse regularly using a weigh tape or, ideally, a livestock scale, and keep records. A loss of more than 1–2% of body weight per week is clinically significant.

Dental Problems: The Most Overlooked Cause

Horses have hypsodont (continuously erupting) teeth that wear unevenly over time. Sharp enamel points, hooks, waves, and infected or missing teeth can make chewing painful and inefficient. A horse with dental disease may drop food (known as "quidding"), produce partially chewed boluses in the water bucket, or simply eat less because it hurts.

Annual dental examinations by an equine vet or a qualified equine dental technician are essential. In horses over 15 years old, twice-yearly checks are advisable. If dental disease is found, a professional float (rasping down sharp points) can produce rapid improvements in condition within four to six weeks. In the meantime, soaked hay nuts, chaff, or complete feeds can help horses with severe dental problems maintain caloric intake while healing.

Parasite Burden

Internal parasites — particularly cyathostomins (small redworms), large strongyles, and tapeworms — compete directly with your horse for nutrients and can cause significant gut damage. A horse with a heavy worm burden may eat normally yet still lose weight because the parasites are interfering with nutrient absorption.

The responsible approach is targeted selective treatment based on fecal egg counts (FECs) rather than blanket worming on a calendar schedule. Work with your equine vet to establish a monitoring programme. A FEC of over 200–500 eggs per gram (depending on the threshold your vet recommends) generally warrants treatment. Tapeworm burdens require either a saliva-based ELISA test or a double dose of pyrantel/single dose of praziquantel, as standard FECs do not detect tapeworm eggs reliably.

Inadequate Forage Quantity or Quality

Horses are hindgut fermenters designed to graze for 16–18 hours a day. The foundation of any equine diet must be forage — hay, haylage, or pasture — at a minimum of 1.5–2% of body weight per day in dry matter. Many horses that appear to be "hard keepers" are simply not receiving enough forage.

Hay quality varies enormously. Mature, stalky hay cut late in the season may be low in digestible energy and protein. Have your hay analysed by a laboratory: look for digestible energy (DE) values and crude protein percentage. For a 500 kg horse in moderate work, aim for hay delivering at least 8.5 Mcal DE per day from forage alone, topping up with hard feed as needed. Switching to earlier-cut hay or adding haylage can substantially increase caloric density without dramatically changing feeding volume.

Social Competition at Feeding Time

Horses are hierarchical animals, and subordinate individuals are frequently pushed away from hay piles or feed stations by dominant herd mates. A horse that appears to eat well in your presence may actually be consuming far less than you think when you are not watching.

Solutions include feeding in individual stables or pens, using multiple hay stations (always one more than the number of horses), and placing feed points far enough apart that dominant horses cannot guard more than one simultaneously. Installing cameras in the field or yard for a few days can be revelatory.

Metabolic Disease: Cushing's and EMS

Pituitary Pars Intermedia Dysfunction (PPID), commonly called Cushing's disease, is extremely common in horses over 15 years of age. While it is frequently associated with abnormal fat deposits (particularly a cresty neck and a "pot belly"), Cushing's horses can also lose topline muscle and body fat, especially in the early stages or if the disease is poorly controlled. Other signs include a long, curly coat that fails to shed, increased drinking and urination, and a dull, lethargic demeanour.

Equine Metabolic Syndrome (EMS) is a separate but related condition involving insulin dysregulation and is most common in native breeds and "easy keeper" types, though it can occur in any horse. Paradoxically, EMS horses often carry abnormal fat patterning while losing structural muscle mass.

Both conditions require blood testing — ACTH measurement for PPID, and an insulin/glucose profile for EMS — and should be managed in close collaboration with your equine vet. Medical treatment with pergolide is available for PPID and is highly effective when started early.

Old Age and the Senior Horse

Older horses (typically 20+) face a "perfect storm" of weight-loss risk: deteriorating dentition, reduced gut motility, decreased digestive efficiency, and often concurrent PPID. A senior horse may need 20–30% more calories than a middle-aged horse performing equivalent work simply to maintain the same condition.

Senior-formulated complete feeds that are designed to be soaked into a mash are invaluable for older horses with dental compromise. These feeds are high in digestible fibre, readily fermented in the hindgut, and nutritionally balanced. Many also contain elevated levels of lysine and threonine, the amino acids most critical for maintaining topline muscle.

A Systematic Diagnostic Approach

When you notice unexplained weight loss, work through the following sequence with your equine vet:

Physical examination — body condition scoring, muscle mass assessment, palpation for pain responses
Dental check — by an equine vet or qualified dental technician
Fecal egg count — to assess parasite burden
Blood work — full biochemistry panel, ACTH for horses over 15, insulin/glucose profile if EMS is suspected
Forage analysis — send a hay sample to a lab
Diet audit — calculate actual daily DE intake vs. estimated requirements
Management review — observe feeding behaviour, assess social dynamics

Feeding Solutions for Hard Keepers

Once underlying causes have been addressed, the following nutritional strategies can help horses regain condition:

Increase digestible energy from fibre first. Add sugar beet pulp (soaked), alfalfa chaff, or haylage before reaching for cereal-based feeds. High-starch diets can cause hindgut acidosis in horses prone to it.

Add a conditioning supplement or high-fat feed. Oil (up to 200 ml per day, introduced gradually) or a high-fat conditioning mix provides dense, slow-release energy. Fat does not cause the "hot" behaviour associated with cereal-based feeds.

Consider a balancer. If forage quality is good but your horse is lean, a protein and vitamin/mineral balancer (fed in small amounts) ensures amino acid requirements are met without excessive starch.

Feed little and often. Horses have small stomachs relative to body size. Multiple small meals are safer and more digestible than one or two large feeds.

Looking for high-quality conditioning feeds and calorie-dense supplements for your hard keeper? Browse equine conditioning feeds and supplements at Zooplus — a wide selection of trusted brands delivered to your door.

Key Takeaways

Always consult a qualified equine vet first — unexplained weight loss requires professional diagnosis before treatment.
Dental disease, parasite burden, and inadequate forage are the three most common — and most correctable — causes of weight loss in horses.
Use the Henneke Body Condition Score (1–9) to monitor your horse's condition objectively and regularly.
Horses over 15 should be tested for PPID (Cushing's disease) if they are losing weight, especially alongside other clinical signs such as a long curly coat or increased thirst.
For hard keepers, increase digestible fibre (sugar beet, alfalfa, haylage) and consider adding dietary fat before switching to high-starch cereal feeds.

References

Donaldson MT, McFarlane D, Jorgensen AJ, Beech J. "Correlation between plasma alpha-melanocyte-stimulating hormone concentration and body weight, age, and season in healthy horses and ponies." American Journal of Veterinary Research. 2004;65(7):1013–1019. PMID: 15280380
Henneke DR, Potter GD, Kreider JL, Yeates BF. "Relationship between condition score, physical measurements and body fat percentage in mares." Equine Veterinary Journal. 1983;15(4):371–372. PMID: 6641685

Written by Sarah Bennett, Certified Animal Nutritionist. The information in this article is intended for educational purposes only and does not constitute veterinary advice. Always consult a qualified equine veterinarian for the diagnosis and treatment of health conditions in your horse.