Keeping Weight on Horses Through Winter: An Evidence-Based Guide

Winter brings predictable challenges for horse owners trying to maintain their horses' body condition. Cold temperatures, limited pasture, and increased energy demands can lead to unwanted weight loss. Understanding the science behind winter weight management can help you keep your horse in good weight through the coldest months.

Before making any changes to your horse's diet or feeding program, consult with your veterinarian or equine nutritionist to ensure the modifications are appropriate for your horse's individual needs. If your horse experiences weight loss—particularly sudden or dramatic loss, or loss accompanied by lethargy, changes in manure, decreased appetite, or other symptoms—contact your veterinarian immediately to rule out underlying health issues such as dental problems, parasites, metabolic disorders, or other medical conditions. Professional guidance is essential for maintaining your horse's health and addressing nutritional challenges effectively.

Why Horses Lose Weight in Winter

The Thermoneutral Zone and Critical Temperature

A thermoneutral zone is the range of environmental temperatures in which organisms, in this case horses, can maintain core body temperature without expending additional energy for heating or cooling beyond their baseline metabolic rate. Healthy adult horses can balance the accumulation and dissipation of body heat to maintain their body temperature between 99.5 and 101.3°F when they are in their thermoneutral zone (41 to 77°F). This thermoneutral zone represents the temperature range where horses maintain body temperature with minimal additional energy expenditure.

The lower critical temperature (LCT) varies widely among horses; those in mild climates have an LCT of 40°F, while horses accustomed to extreme cold have an LCT of 5°F. For most horses in good body condition, the critical temperature is around 40°F with a summer coat and 18°F with a winter coat. Individual variation exists based on breed, with research showing that Standardbred trotters acclimatized to 59-68°F had an LCT of 41°F. In contrast, some American Quarter Horses had an LCT as low as 12°F when acclimatized to temperatures between 5 and 50°F.

Environmental Factors and Energy Demands

Chilly rain, combined with wind and severe cold, can be the most demanding conditions for horses. Wind and precipitation dramatically increase heat loss and energy requirements. According to research, for each 10-degree change below 30 degrees Fahrenheit, horses require an additional intake of approximately 2 pounds of feed per day, while a 10- to 15-mph wind will need horses to consume an additional 4 to 8 pounds of hay, and when a horse becomes wet and encounters wind, it must consume an additional 10 to 14 pounds of hay.

The reduced quality and availability of pasture also means horses can no longer meet their nutritional needs through grazing alone. Due to the combined decrease in protein and higher fiber content, hay usually has lower digestible energy compared to pasture, and horses relying primarily on hay need to consume more forage dry matter to get the same number of calories.

The Foundation: Quality Forage

Forage as a Heat Source

Forage should form the cornerstone of any winter feeding program. Feed digestion produces heat, with the digestion of high-fiber feeds, such as hay, releasing the greatest amount of heat, resulting in more heat being generated during digestion than with low-fiber feeds. This process of heat generation through fiber fermentation in the hindgut is particularly important for maintaining body temperature in cold weather.

Forage digestion occurs in the horse's hindgut, where the cecum contains bacteria, fungi, and protozoa that work together to break down fibrous material. This process helps maintain the gut by keeping the bacteria healthy and active. This microbial fermentation process is significantly more thermogenic, creating more heat, than grain digestion.

Quantity and Quality Requirements

Assuming 20 percent of the hay will be wasted, an average 1,000-pound horse would require 24 pounds of hay per day (20 pounds to meet the recommendations plus an additional 4 pounds to account for waste). Many horses will benefit from free-choice hay during the winter months.

Quality matters as much as quantity. Leafy, fine-textured hay is more digestible for horses and delivers more calories than coarse, stem-heavy hay. The maturity at harvest significantly affects nutritional value, with early-cut hay providing higher digestible energy and protein content than late-cut hay.

Most mature horses are idle or see occasional use during the winter and can be fed good- or average-quality hay (moderately green with a moderate amount of leaves, slightly stemmy), while above-average hay (mostly green, good amount of leaves, few large stems) should be fed to young, growing horses; pregnant mares in the last two months of gestation; and lactating mares. 

Forage Types and Digestibility

There are two major kinds of forages used for feeding horses: grasses (orchard, timothy, brome types) tend to be lower in protein and energy, while legumes (alfalfa, clover) are usually higher in protein and energy. Research on forage digestibility indicates that the fiber composition and maturity of forage-based diets significantly impact the water-holding capacity in equine cecum and colon digesta, which in turn affects overall digestive efficiency.

Both grass and legume forages support thermoregulation through heat production during hindgut fermentation, though legumes' higher energy density may provide an advantage for horses struggling to maintain weight in cold weather.

Strategic Concentrate Feeding

While forage should always come first, some horses need additional calories from concentrates. Hard-keepers, senior horses with dental issues, and those in work may require grain or commercially prepared feeds to maintain condition.

In extreme conditions, hay alone is usually insufficient to supply the energy demands for a horse to maintain its body weight, and some type of additional grain source is recommended. However, increasing forage is better for the horse's digestive tract than increasing grains, as feeding too much concentrate can overload the small intestine and lead to digestive issues.

Fat Supplementation: The Most Concentrated Energy Source

Digestibility and Energy Density

Fat supplements offer the most concentrated energy source, providing 2.25 times more calories per pound than carbohydrates or protein. Research has demonstrated that various fat sources are highly digestible for horses. Apparent fat digestibility was similar between dry fat, rice bran, and corn oil, with estimated fat digestibility of each source being very high (88-94%) and not significantly different.

Rice Bran as a Fat Supplement

Rice bran has become a popular fat supplement for performance and hard-keeping horses. Research has confirmed that the fat in stabilized rice bran is highly digestible and is equally as digestible as corn oil. Rice bran contains gamma oryzanol, which has been suggested to have muscle-building properties in horses.

Recent research on senior horses has shown promising results for maintaining weight. When horses over 20 years of age were supplemented with rice bran at 1 pound per day for four months, their body condition score improved.

Considerations for Fat Supplementation

Fat can be safely increased in the diet up to 10-15% of the total ration volume. When adding concentrates or fat supplements, increase amounts gradually over 7-10 days to allow the digestive system to adapt.

Addressing Individual Needs

Senior Horses

Senior horses often need special attention due to dental wear, reduced digestive efficiency, and difficulty chewing long-stem hay. Rice bran contains highly digestible fiber as well as 20% fat and 17% protein, and feeding rice bran to senior horses can improve body score and coat condition by meeting their higher protein requirements. Soaked hay cubes, senior feeds, or complete pelleted rations can help these horses maintain weight.

Breed Differences

Various studies have found differences across breeds in thermoregulatory processes. Specifically, Spanish breed horses appear to tolerate heat stress better than Friesian horses when exposed to winter tropical conditions, and different breeds exhibit distinct lower critical temperatures. These differences mean that management strategies may need to be tailored to breed characteristics.

Body Condition Monitoring

Body condition scoring should be performed regularly throughout the winter using the Henneke Body Condition Scoring system, which rates horses on a scale of 1 to 9. Most horses should maintain a score of 5-6 through winter. If you notice your horse dropping condition, don't wait to make feeding adjustments.

Beyond Nutrition: Environmental Management

Shelter and Weather Protection

A shelter offers the horse protection from wind, precipitation and radiation, which it can use when weather conditions change rapidly. Research has shown that shelter can reduce heat loss by 20%, not only because it allows their hair to stay dry, but also because it reduces heat loss from wind chill.

Blanketing Considerations

Blanketing decisions should be based on individual circumstances. Many healthy horses with full winter coats won't need blankets if they have adequate shelter and nutrition, as their natural coat provides excellent insulation. However, horses in regular work are often clipped to prevent excessive sweating during exercise, and these horses require appropriate blanketing to compensate for the loss of their natural insulation.

For clipped horses, blanket weight should correspond to the degree of clipping and weather conditions. A trace or hunter clip may require a medium-weight blanket in moderate cold, while a full body clip necessitates heavier blanketing or layering in severe weather. Working horses benefit from having multiple blanket weights available to adjust for changing temperatures and activity levels.

Unclipped horses should be evaluated individually. Horses can easily be over-blanketed, leading to overheating, which can cause heat stress. Since it takes more energy for a horse to cool down than to heat up, an over-blanketed horse is likely to lose weight due to increased energy requirements. When possible, horses should have access to shelter so they can seek protection from wind and precipitation while allowing their natural coat to function properly.

Water Availability

Fresh, unfrozen water is essential. An average adult horse will drink 5 to 10 gallons of water per day, and during the winter months, horses consume large amounts of dry forage; reduced water intake can increase the chances of horses suffering from impaction and colic, and feed intake is closely related to water intake. Heated water buckets or tank heaters encourage adequate water consumption. According to researchers at the University of Pennsylvania School of Veterinary Medicine, horses consumed up to 40% more water per day if they were given water between the temperatures of 45-65 degrees Fahrenheit.

Monitoring and Adjustments

Winter weight management isn't a "set it and forget it" proposition. Weather conditions change, and so do your horse's needs. Check your horse's body condition weekly by running your hands over the ribs, spine, and hindquarters. You should be able to feel the ribs with light pressure but not see them prominently. Adjust feeding before significant weight loss occurs, as it's much easier to maintain weight than to restore it.

The Bottom Line

Keeping weight on horses through the winter requires attention to forage quality and quantity, strategic use of concentrates when needed, and management practices that minimize energy loss. Research has clearly demonstrated that:

1. Forage should form the foundation of winter nutrition due to its thermogenic properties.

2. Environmental factors like wind, precipitation, and cold dramatically increase energy requirements.

3. Fat supplementation provides concentrated calories with high digestibility.

4. Shelter significantly reduces heat loss and energy expenditure.

5. Individual factors, including age, breed, and body condition, influence nutritional needs.

By understanding your horse's individual needs and monitoring condition regularly, informed by current research, you can help your horse thrive through even the coldest winters.

References

This article incorporates findings from peer-reviewed research, including studies published in:

• Journal of Equine Veterinary Science

• Equine Veterinary Journal

• Livestock Production Science

• Animals (MDPI)

• Research from North Dakota State University Extension, Utah State University Extension, and other academic institutions