Horse Diet: Hay, Pasture, Concentrates & Supplements Guide

Feeding a horse correctly is one of the most important responsibilities you take on as an owner or caretaker. Horses are non-ruminant herbivores with a digestive system designed for near-constant, slow intake of fibrous plant matter. When we disrupt that natural pattern — overloading concentrates, skimping on forage, or mismanaging pasture — the consequences can be serious: colic, laminitis, metabolic disorders, and poor performance. This guide walks through everything you need to know to build a sound, evidence-based feeding program.

The Forage-First Principle

The single most important rule in equine nutrition is this: forage comes first. Horses evolved grazing for 16 to 20 hours a day, and their hindgut microbiome depends on a steady flow of fermentable fibre to function properly. The National Research Council recommends a minimum of 1.5% of body weight in forage dry matter daily, with 2% being the ideal target for most horses.

For a 500 kg horse, that translates to roughly 10 kg of hay or equivalent pasture per day. Restricting forage below this threshold increases the risk of gastric ulcers (the stomach produces acid continuously and needs fibre to buffer it), stereotypies like crib-biting, and dangerous slowdowns in hindgut motility. Before you reach for a bag of grain, always ask: is this horse getting enough forage?

Types of Hay: Grass vs. Legume

Not all hay is created equal, and the right choice depends on your horse's workload, age, and metabolic status.

Grass hays — timothy, orchard grass, meadow hay, bermuda — are the workhorses of equine diets. They are moderate in energy and protein, high in fibre, and appropriate for the majority of adult horses at light to moderate work. Timothy in particular is widely researched and considered a gold standard for quality forage.

Legume hays — alfalfa (lucerne) and clover — are significantly higher in calories, protein, and calcium. They are valuable for horses with elevated needs: growing youngsters, heavily lactating mares, or horses in intense performance work. However, feeding alfalfa to easy keepers or metabolically sensitive horses can contribute to unwanted weight gain and, in some cases, exacerbate conditions like equine metabolic syndrome.

Always have your hay tested by a forage laboratory at least once per year. Nutrient content varies enormously by cutting, geography, and weather. A hay analysis is the only reliable way to know what your horse is actually eating and what gaps remain to be filled.

Pasture Management

Fresh pasture can be an excellent, economical forage source — but it demands careful management. Lush spring grass is high in non-structural carbohydrates (NSC), particularly fructans, which can trigger hindgut dysbiosis and precipitate laminitis in susceptible animals. Ponies, easy keepers, horses with insulin dysregulation, and those with a history of laminitis should have their pasture access strictly limited or eliminated during rapid grass growth periods.

Rotational grazing keeps pastures healthy and prevents overgrazing, which paradoxically leads horses to consume more of the short, stressed grass that is highest in sugars. Strip grazing and dry-lot turnout with hay are tools worth having in your management toolkit. Track the body condition score (BCS) of pastured horses at least monthly using the Henneke scale; a score above 6 out of 9 suggests the horse is receiving more energy than it needs.

When Are Concentrates Needed?

Many horses — particularly easy keepers, mature horses in light work, and those with access to quality pasture — do not need any grain or concentrate at all. A well-formulated ration balancer (a low-intake, nutrient-dense pellet) paired with good-quality hay will meet nearly all their requirements without excess calories.

Concentrates become genuinely necessary in several situations:

• Hard keepers: horses that cannot maintain body condition on forage alone, often Thoroughbreds, senior horses with dental issues, or horses recovering from illness.
• Performance horses: those in moderate to heavy work have energy demands that forage alone cannot meet practically. Concentrates provide a calorie-dense way to bridge the gap.
• Breeding stock: late-gestation and early-lactation mares, as well as breeding stallions in active season, have elevated protein, energy, and micronutrient requirements.
• Growing horses: foals, weanlings, and yearlings need carefully calibrated protein and mineral ratios to support correct skeletal development without overfeeding energy.

When concentrates are fed, divide them into at least two, ideally three, small meals per day. Never feed more than 2 kg of grain-based concentrate per meal — large starch loads overwhelm small intestinal digestion capacity and allow starch to reach the hindgut, disrupting the microbial population and increasing colic risk.

Ration Balancers vs. Complete Feeds

A ration balancer is fed at 0.5–1 kg per day and supplies vitamins, minerals, and amino acids without significant calories. It is the correct choice for horses that hold weight easily and need nutritional insurance on top of forage. Complete feeds, by contrast, are formulated to be the horse's entire diet (or the majority of it) and are fed at much higher rates. They are useful for senior horses who can no longer chew long-stem forage effectively.

Avoid the common mistake of feeding a complete feed at a low rate. A 500 kg horse fed 1 kg per day of a product designed to be fed at 5 kg per day receives only 20% of the intended micronutrient levels — far less than what the label suggests. Read the feeding directions carefully and match the product to the horse's actual situation.

Water: The Most Critical Nutrient

Water is often overlooked, but dehydration is a leading contributor to impaction colic. An adult horse at rest in temperate weather drinks 25–50 litres per day; a horse in heavy work on a hot day may need 70 litres or more. Ensure water sources are clean, fresh, and always available. Automatic waterers should be checked daily for flow and cleanliness — horses will voluntarily reduce intake if the water smells or tastes foul, even if they are thirsty.

In cold climates, heated water troughs are not a luxury; they are a colic prevention tool. Horses prefer water between 7°C and 18°C and will drink significantly less if offered near-frozen water, increasing their impaction risk during winter months.

Common Feeding Mistakes to Avoid

Even experienced horse owners fall into these traps. The most frequent errors include: feeding hay on the ground in round bales without monitoring consumption (leading to obesity or, conversely, inadequate intake in submissive herd members); switching feeds or hay types abruptly without a 10–14 day transition period; relying on visual appraisal rather than a weight tape and body condition score to assess nutritional status; and ignoring the mineral content of the local water supply, which can sometimes significantly alter calcium-to-phosphorus ratios.

Always consult an equine veterinarian — not a small animal vet — or a qualified equine nutritionist when designing or overhauling a feeding program. Equine digestive physiology is complex and species-specific, and the expertise needed to navigate it correctly differs substantially from that required for dogs or cats.

References

1. National Research Council. Nutrient Requirements of Horses, 6th Revised Edition. Washington, DC: National Academies Press; 2007. Available at: https://pubmed.ncbi.nlm.nih.gov/21598413/
2. Luthersson N, Hou Nielsen K, Harris P, Parkin TDH. Risk factors associated with equine gastric ulcer syndrome (EGUS) in 201 horses in Denmark. Equine Veterinary Journal. 2009;41(7):625-630. PMID: 19927590. https://pubmed.ncbi.nlm.nih.gov/19927590/

Written by Sarah Bennett, Certified Animal Nutritionist