With winter approaching quickly, it’s time to prepare “hard keepers” for colder temperatures to prevent unwanted weight loss. Providing additional energy is the best way to help get these horses through the colder season.

Why do Horses Lose Weight Seasonally?

“It is common for many horses to experience seasonal weight loss during the colder winter months for various reasons,” says Carey Williams, PhD, a professor and equine extension specialist specializing in equine nutrition for over 20 years based at Rutgers University, in New Jersey. “This can be particularly challenging when managing hard keepers.”

The two main culprits responsible for cold weather-induced weight loss are the dietary change from grass pasture to hay and horses’ increased energy expenditure to stay warm in cold climates.

Like humans, horses are warm-blooded animals, and their internal body temperature stays within narrow limits, or the thermoneutral zone. When their core temperature drops below the lower critical temperature (LCT), horses must produce more heat, such as through shivering, to keep their core temperature stable. They do this by increasing their metabolic heat production.

“If it is colder, then horses need more calories/energy to maintain body temperature and might need to eat more,” says Shannon Pratt-Phillips, PhD, professor of equine nutrition and physiology in the Department of Animal Science at North Carolina State University, in Raleigh. “Of course, if they aren’t eating enough, they would start to lose weight.” Therefore, horse owners should remain vigilant and closely monitor hard keepers’ body condition and weight, which can be challenging when horses have winter coats.

Feed High-Quality Forage to the Hard Keeper

“For the increase in energy usage in cold weather, the rule of thumb is a 2% increase in energy requirement for every one degree below 18 degrees Fahrenheit (note: horses can sustain their  thermoneutral zone temperature when the ambient temperature is 18-59 degrees F),” Williams says. “Typically, that equates to about 2-4 pounds of extra hay for an average horse.”

Horses with higher energy demands, such as growing or working individuals, pregnant or lactating mares, and older horses, need even more calories during the colder months.

Generally, forage (grass or hay, but for this discussion, hay) is the ideal fuel to help horses keep their core temperature within the thermoneutral zone. “Hay is high in fiber, so it has to be fermented in the horse’s large intestine by microbes to produce volatile fatty acids that the horse can use for energy,” says Pratt-Phillips. “Fermentation also produces heat, which the horse can utilize to stay warm.”

Therefore, providing good-quality forage with higher fiber content can help hard keepers produce more heat.

Consider Preserved Forages for Hard Keepers

“In the winter, horses might get a different or shorter turnout time, and pasture quality may be lower in most areas of the U.S.,” says Pratt-Phillips. “Therefore, the importance of hay/preserved forages usually becomes more significant.”

Both Williams and Pratt-Phillips recommend adding bagged forage, such as chopped hay (aka chaff), hay cubes, or hay pellets (i.e., alfalfa, timothy) to your horse’s diet during cold weather. Other alternative fiber sources, including soaked beet pulp shreds, can be fed as a supplement to your horse’s regular hay and can enhance the overall feed quality, particularly in areas where good-quality forage is limited. At all times, but especially when feeding dried forage, it is important to ensure that fresh, clean water is always available to your horse to help them maintain an appropriate hydration status.

The manufacturer’s label on cubed or pelleted forage also includes a guaranteed nutrient analysis, which allows you to know exactly what you’re feeding your hard keeper.

Add Fat Supplements, Such as Rice Bran, to Hard Keepers’ Diets

“For some hard keepers, feeding about 2-4 lbs more of a good-quality hay/forage during colder temperatures might be all they need,” Williams says. If horses cannot maintain their weight with the additional forage, she suggests adding 1-2 pounds of rice bran to their daily diet.

Rice bran is an excellent supplement to hay, she adds, particularly for horses who do not eat enough hay and need an additional energy source (i.e., senior horses).

“Rice bran is not only high in fat and has rapidly fermentable fiber, which will both help the hard keeper’s energy requirement, but it also is very palatable and can be found in pretty much any feed store,” Williams says. Rice bran will help the horse maintain body condition and weight, and, contrary to corn, does not make the horse hyperactive or overly energetic because of its lower sugar and starch content. However, because rice bran is rapidly digested in the small intestine, she explains, it does not provide the same heating qualities as forage does with its large-intestine fermentation process.

Balancing Vitamin and Mineral Intake in the Hard Keeper in Winter

Keep in mind that lower-quality hay during the winter might be lacking in some nutrients, particularly vitamins and minerals. “While pasture is rich in vitamin E and beta carotene (the precursor to vitamin A), hay vitamin levels will start to decrease over time, potentially becoming deficient after a few months of storage,” says Pratt-Phillips. “Therefore, horses would need to be supplemented with some of these vitamins.”

She and Williams recommend adding a ration balancer or a vitamin and mineral supplement to your horse’s daily ration to counteract this. “Balancer pellets are nice because horses can still be on an all-forage diet but have balancers added at about 1 pound per day (depending on their weight and manufacturer recommendations),” Williams explains. “These pellets are very low in calories but high in concentrated protein, vitamins, and minerals that balance out poor-quality forage nicely.”

Other Essential Considerations for Feeding Hard Keepers

“It is important to look at other factors, such as age and management practices, before changing any hard keeper’s diet,” Williams says.

Older horses typically struggle to maintain weight more than their younger counterparts because thermoregulatory capacity decreases with age. Also with progressing age, an older horse’s ability to chew and digest long-stem forage could also be compromised. These horses might benefit from adding fat sources such as rice bran to their diet.

Blanketing hard keepers in very cold weather or when it’s both humid and cold, and providing water and windproof shelter can reduce the amount of energy horses need to maintain their core body temperature, Williams says. “Especially if a horse is clipped in the colder months, it will take a lot more care on your part to help them thermoregulate with blankets and/or shelter.” Therefore, owners should weigh the pros and cons before clipping a hard keeper in cold weather.

Take-Home Message

Offering hard keepers extra sources of good-quality forage, either as high-quality hay, hay cubes, or pellets, can help horses maintain their core temperature through hindgut fermentation. Owners might consider adding fat to hard keepers’ diet, for instance, in the form of rice bran. Blankets and access to shelters can help horses stay warm and burn fewer calories in frigid environments but, no matter the season, all horses should always have access to clean water.