Before the summer Olympic Games were held in Atlanta, Ga., considerable research effort went into studying how the horse is affected by heat and humidity. As a result of this research, veterinarians at the Olympics were well prepared to help the competing horses cope with heat stress. As I searched the research literature in preparation to write this column, I found that very little work has been done on the effects of cold weather on horses. If we are to help our horses withstand the stresses of cold weather, we must understand the metabolic demands brought on by exposure to low temperatures, dampness, and wind. We must know how to adjust the horse's diet and exercise to meet those demands. This column will present what science has to tell us about helping our horses warm up in winter.


LAURIE CERNY

Feed high-quality forages on a free-choice basis every day through the winter.

Diet And Cold Weather

Much has been learned in recent years about the nutritional requirements of horses. There is a consensus of opinion about the most appropriate diet for the horse when exposed to cold temperatures.

The horse's energy requirements increase as the temperature drops, and a higher caloric intake is needed to meet the increased metabolic needs. Because corn metabolism produces more calories than oat metabolism, it is often thought that one should increase the amount of corn fed during winter. This is something of a myth, according to Joe Pagan, PhD, of Kentucky Equine Research, a nutrition research center in Lexington, Ky. Pagan states that corn produces very little "waste heat," or heat that the body can use to maintain body temperature.

According to Pagan, if increased calories are needed, feeding corn is fine, but if you want to help your horse stay warm, feed him hay. Corn actually produces less body heat than does hay. A legume hay or a grass forage is fermented in the gut where bacteria are active. Bacteria produce considerable heat that the horse can use to warm himself from the inside out, rather than having to shiver or move to stay warm. Feed high-quality forages on a free-choice basis every day through the winter. Continuous feeding sustains a higher metabolic rate and distributes the heat produced by nutrient metabolism and the muscular activity of digestion more regularly over a 24-hour period.

Hay should be a good quality, fermentable fiber such as grass hay that is immature rather than overly mature. Immature hay has a water-holding capacity that more mature hay does not have. Impaction colic is more prevalent in winter when horses are prone to drink less because of frozen water in their buckets or water that is too cold to be palatable.

Pagan pointed out that straw is not fermentable in the horse's gut. Horses which are bedded on wheat straw should not be allowed to eat their bedding. You can avoid this tendency by providing plenty of good quality grass hay and clean water when your horse is in his stall. Water should be heated to about 2-10° C (36-50° F) to encourage drinking. If your horse continues to eat his straw bedding, change the bedding to paper, sawdust and sand, or wood shavings to break the habit. It is certainly easier to prevent impaction colic than it is to deal with it once it occurs.

Horses often lose weight in cold, wet weather. In a scientific study reported in 1987, mares fed at 150% of their normal caloric need still lost weight during cold, wet weather. Cold weather, associated with rain, causes significant evaporative heat loss. Metabolic heat production must increase to offset body heat lost to the environment. Horses living in a cold environment must be given extra feed, or feed energy will be diverted to heat production rather than tissue growth.

One cannot expect a horse to obtain complete energy needs from winter pastures. The amount of digestible energy is low in a winter pasture, and the energy cost of winter grazing might be 35% above that in summer as the horse must dig through snow or do more walking to find grass. Research has shown that energy needs for the horse can be as much as 40-50% higher in wet and windy winter weather.

Are there guidelines for feeding the horse during winter that will help us to meet his energy needs? I put this question to Amy Gill of Equine Marketing and Consulting in Versailles, Ky. She provided the following information, based on scientific data from nutritional studies:

  • The critical temperature below which horses must begin to use calories to maintain body core temperature, called thermoregulation, is -10° C (14 °F). When the temperature is above 14° F, there is no increase in energy requirement needed to maintain body temperature in a maintenance level horse which is not gestating, lactating, growing, or in work and is not subject to windy or wet weather. This information applies to the maintenance level horse turned out for the winter.
  • The 500 kg (1,100 lb) horse will experience a 35% increase in metabolic rate and heat production to stay warm once the temperature falls below -10° C (14° F). For every degree centigrade the temperature drops below this level, one must increase the digestive energy, or calories, by 2.5%. For that 500 kg horse, you would increase his caloric intake by .408 Mcal of digestible energy daily. This horse needs 16.4 Mcal daily for maintenance, and you are adding about one-half a Mcal per every one-half degree drop in temperature.
  • Now you need to know the digestible energy (DE) content of your feed. Every feed has a specific quantity of digestible energy per pound. The DE of oats is 1.3 Mcal per pound. Corn has a DE of 1.54 Mcal per pound. Although oats are less energy dense than corn, the hull of oats is all fiber. That fiber provides the same fermentation action in the gut as hay, providing more internal combustion and warmth, although lower nutrition.

To increase your horse's feed ration to compensate for the need to stay warm, you would increase your horse's daily ration by nearly one-half pound of oats or by one-third pound corn to get the necessary increase in mega calories. If your "maintenance level horse" already was getting plenty of feed daily and you are hesitant about increasing the quantity, you could substitute one-sixth pound corn oil (2 1/2 oz) and one-sixth pound corn to get safely the same caloric, or digestible energy, content when you are already feeding adequate grain.

Top dressing oil on the feed rather than increasing the feed quantity supplies two times the calories that grain supplies. It is a safe way to add calories when increased energy is needed.

"Simply throwing additional oats or corn on top of a balanced ration could result in imbalancing the ration," cautions Gill.

Ask your feed manufacturer about the digestible energy of the ration you feed your horses and have them supply you with the proper increases to avoid waste, overfeeding, or imbalancing your ration. The advice of your veterinarian or a local equine nutritionist can help you determine if vitamins or minerals need to be added as well, as these vary regionally.

As Gill points out, being a good manager of your horse's health means knowing about the feeds you are providing him. Feeding in winter can be a delicate balance to prevent your horse having a slow, downhill slide of body weight and health. It is much harder to bring him back up in winter.

Over-compensating by over-feeding in winter is not healthy either, as it leaves you with a fat horse when the lush spring grass appears. When planning your winter feeding routine, think of calories as a means of staying warm. Calories are not proteins, vitamins, or minerals. Calories come from grains, fats, and good-quality grass hay.

Newborn foals have high metabolic rates allowing them to tolerate low ambient temperatures. Foals rely on shivering, food intake, and activity to maintain body core temperature as they have little insulation in the form of body fat or hair coat. Wind and rain will raise the critical temperature at which thermoregulation will begin for the foal just as it does for the older horse.

Insulation Against The Cold

We know winter truly has arrived when we hear the term "wind chill" included in the weather report. Wind chill, the combined effect of the temperature and the wind, increases cold stress, especially in damp climates. It is interesting that wind and rain can be more thermally taxing than snow for cold- adapted horses. A horse with a dense winter hair coat and good body condition has insulation against body heat loss. Insulation derived from muscle and fat can provide vital protection when rain and wind reduce the thermal insulation of the hair coat.

Having a stored energy reserve is important to the horse's health in cold weather. Thin horses need to have a higher metabolic rate just to maintain core temperature. Palpate your horses regularly as their hair coats thicken for winter to assess the body condition. A thick hair coat can mask poor body condition, so regular palpation is important.

I read a very clever idea for assessing your horse's weight despite a thick hair coat written in the Whole Horse Journal. Mitch Benson, DVM, described using a string to measure the circumference of three areas of the body that can reflect as little as 20 pounds of weight change. Using the base of the neck, the circumference of the girth, and the belly at the end of the rib cage, one can keep track of weight loss or gain on a weekly basis. Simply tie a knot in the string to mark the measurements, measure the distance to the knot with a tape measure, and write down the results. It is important to measure in the same place each time and with the same tension on the string. It is also important to be consistent throughout the winter.

Horses which are turned out for the winter often spend the entire day and night outside and are fed outside. Because heat loss is greatly accelerated by wind, a horse which is turned out must be provided a south-facing, bedded shed or other wind shelter. If you feed outdoors, locate the feed in areas away from prevailing winds so your horse does not have to stand in the wind while eating.

As pointed out previously, there is an increase in the "resting energy requirement" for a horse which is turned out for the winter. At rest, skeletal muscle blood flow is low, compared to muscle blood flow during exercise. Consequently, muscle mass provides the body with passive insulation. It would be wise, therefore, to turn your horse out in good condition muscularly, rather than to take the attitude that conditioning can wait for the spring. Fat also acts as insulation for the body, but an over-fat horse might have poor muscle conditioning. Muscle mass accounts for a large portion of the maintenance of body temperature. Just as a small furnace cannot adequately warm a large house, low muscle mass cannot adequately prevent body temperature loss in cold weather.

Another issue to consider is the length of the hair coat. It has been found that the temperature at which cold stress causes an increase in metabolic demand in the horse is 0° F with a good winter coat, and 32° F when clipped. Having a good-quality hair coat will protect the horse to a lower temperature, allowing him to tolerate lower temperatures before thermoregulation begins.

Conversely, there can be an increased energy cost when performing work with a heavy hair coat. In humans there is about a 10% increase in oxygen demand when walking while wearing a winter coat. Most horses which exercise in cold weather are routinely clipped along their abdomen and chest to facilitate evaporative cooling. A horse which has been clipped should wear a blanket when at rest to help maintain body temperature.

Nutritionist Gill makes the point that a clipped horse should wear a quarter sheet when exercising in cold, wet weather. This is commonly seen in Ireland, and many Irish trainers have brought the custom to America. It is a beautiful sight to see a group of horses going out to train in the early morning, their breath floating around them in clouds of crystallized moisture, wearing neatly folded quarter sheets on their hind quarters. But it is for more than beauty that the trainers do this. The quarter sheets help maintain body heat so more energy can be used for performance rather than for staying warm. A clipped horse which is used to wearing a blanket will be cold when he is not wearing that blanket. Once you begin to blanket your horse, you must be consistent. Blanketing a horse is a responsibility not to be taken lightly. The blanket becomes his insulation, substituting for the thick hair coat he would otherwise grow. When you clip and blanket your horse, you are entering a contract with him to provide for his thermoregulation as the weather varies. Winter weather provides wide climactic variations between warm sunny days and days of cold, wind, and rain. You must be available to remove the blanket on warm, sunny days. He also must be checked daily, for even the best-fitting blanket will move out of place and could cause rubbing or get tangled around the horse's legs.

Never blanket a wet horse. The blanket will absorb the water, making the environment closest to the skin cold and wet. The horse might not be able to generate enough body heat to match the evaporative cooling, leaving him vulnerable to over-chilling. To dry a wet horse on a cold day, use a horse vacuum in the blower mode. Keep the horse covered with blankets and blow one area at a time until it is dry. Blowing the horse all over without the protection of blankets to hold in some body heat effectively increases the evaporative cooling and could cause a chill.

Muscle Exercise And Cold Weather

Exercising in cold weather presents a special challenge to muscle function, as well as to the cardiopulmonary system of the horse and human alike. Cooled muscle has a decreased capacity to generate force. As a consequence, it might be necessary to recruit more motor units, particularly fast twitch units. This could lead to higher lactate levels and greater rates of muscle glycogen depletion.

This means the muscles could reach fatigue sooner and have a greater amount of post-exercise muscle soreness. To avoid early fatigue and post-exercise muscle soreness, pay greater attention to your warm up and cool down routines during the winter.

The Warm Up

Whether exercise is taking place in the winter or in the summer, do not underestimate the value of walking. Include longer bouts of walking before exercise in cold weather to enhance blood flow through the muscles. Blood flow increases muscle temperature and oxygenation of the muscle cells, facilitating muscle function. A relatively small percentage of muscle fibers are recruited at the walk, and they are mostly slow twitch fibers. These fibers rely on oxygen from the blood for fuel so muscle capillaries dilate in response to their activity.

Brief, intense exercise will not raise cooled muscle temperature. Walking for extended periods before athletic exercise will improve oxygen delivery and waste product removal, benefiting the entire muscle. Ten minutes is the time allotment often recommended for the warm-up, but you must use your own horse as a guide. A larger, heavily muscled horse will require longer to become fully ready for an increase in muscle exercise, simply due to the greater amount of body mass.

Observe the increase in respiratory rate and heart rate as your horse begins to exercise. When it has come to a steady state, elevate the walking to a more brisk pace. Once the horse acclimates to this, increase the pace again. Reduced peripheral blood flow, brought on by cold weather, might leave the joints, tendons, and ligaments more stiff than in milder weather. Taking adequate time to warm these structures will aid in injury prevention by increasing flexibility and extensibility of these structures.

Walking as a warm-up can be done in hand, on a longe line, or by using a treadmill or horse walker. This should be followed by walking under saddle to ensure that your horse's muscles are fully ready for increased work.

The next step in a warm-up is to increase the speed of movement by trotting. Trotting increases the stretch of the connective tissues and recruits more muscle fibers into work. As the horse acclimates fully to slow trotting, proceed to a more brisk pace to increase the oxygen demands from the muscles. By gradually increasing the exercise stress, the additional stress brought on by cold weather can be tolerated. This first phase of the warm-up might take as long as 30 minutes in cold weather.

At this point one would consider the specific sport activity the horse will perform. Mild sport specific activities further prepare the horse for safe work in cold weather. Scientists looked at the effects of exercise at near-maximal tolerance levels in temperatures as low as -25° C (-13° F) and found no evidence of tissue damage in the horse's respiratory tract or musculature. This report would indicate that cold temperatures alone would not prohibit safe exercise if the horse is otherwise well cared for.

Cooldown

After the exercise bout is finished, the cooldown should be a mirror image of the warm-up. In winter, this could again take as much as 30 minutes. A gradual cooldown allows the body temperature to decline more slowly. To avoid excess lactate in the muscles, mild sport-specific activities, followed by trotting, then walking, and finally walking on a loose rein, will allow capillaries in the muscles to dilate and remove the waste products of exercise. As with the warm-up, the walking phase is vitally important in cold weather. Walking maintains capillary circulation in the muscles, so radiant cooling takes place, rather than evaporative cooling, reducing the need for sweating.

Once the tack is removed and the horse has acclimated to in-hand walking, manual stretches will complete the cooldown. Manual stretches have become a well-accepted means of maintaining or increasing joint range of motion in the horse and should be included in every cooldown. Stretching exercises are described in my book, Equine Sports Therapy, and will be discussed in future columns.


CORRECTIONS

(April, 1998) The information from Amy Gill, an equine nutritionist with Equine Marketing and Consulting, contained in the February Sports Medicine column should have included the following facts:

Horses fare extremely well in cold temperatures. The comfort zone of the horse in cold weather is very different from that of humans. The critical temperature below which horses must begin to use calories to maintain body core temperature, called thermoregulation, is -10° C (14° F), well below that of people! When the temperature is above 14° F, there is no increase in energy requirement needed to maintain body temperature in a maintenance level horse which is not gestating, lactating, growing, or working, and is not subject to windy or wet weather. This information applies to the maintenance level horse and should be considered as a basic guideline for the average horse. Every horse should be evaluated on an individual basis.

The 500 kg (1,100 lb) horse will experience a 35% increase in metabolic rate and heat production to stay warm once the temperature falls below -10° C (14° F). For every degree centigrade the temperature drops below this, one must increase the digestible energy (DE), or calories, by 2.5%. In other words, for the 500 kg horse, you will increase his caloric intake by 0.408 Mcal (one Mcal is equal to 1,000 calories) of digestible energy daily. The maintenance level horse needs 16.4 Mcal per day, so you would be adding about one-half a Mcal (500 calories) per every degree Celsius the temperature drops.

The very best way to accomplish this is by supplementing with good quality grass hay, such as timothy or orchardgrass, which generally provides around 0.8 Mcal per pound. With this information, determine how many pounds of hay you are feeding, how much DE the horse is deriving from that amount of hay, then increase accordingly to meet the increased requirements in cold weather.

Some horses still might need additional supplementation by increasing the concentrate (grain mix) portion of the ration (they can only eat so much hay!). At that point, you need to know the digestible energy content of the concentrate. Every feed ingredient has a specific quantity of DE per pound, and various mixtures of different ingredients produce concentrates with varying levels of DE. The DE of oats is 1.3 Mcal per pound, while that of corn is 1.54 Mcal. Although oats are less energy dense than corn, the oat hull provides some fermentable fiber. This fiber is fermented in the same fashion as hay--generating internal heat. This makes oats a good feed in the winter, but you must consider the horse will derive less actual calories than when consuming other feeds higher in DE. For example, to compensate of the increased energy requirements described previously, you would feed an extra half-pound oats or one-third pound corn to provide an extra 500 calories.

An alternative would be to add corn oil to the ration. If your maintenance level horse already is getting plenty of concentrate daily and you are concerned about increasing it any further, substituting one-sixth pound (2 1/2 oz) of corn oil also provides about 500 calories. Fats contain nearly twice the calories of grain, and adding them to the ration is a safe way to add calories without having to increase soluable carbohydrates to provide additional energy. This helps reduce the risk of metabolic disturbances, which can result in conditions such as tying-up, laminitis, or colic.

Gill also mentions that, "Simply throwing additional oats or corn on top of a balanced concentrate ration could result in an unbalanced diet, which is undesirable."

Small amounts of corn or oats by themselves won't make much difference, but if you are having to add a lot to the ration, it could become unbalanced. Because grains contain other feed nutrients besides energy, such as proteins, vitamins, and minerals, it is important to feed a concentrate that is already balanced. Ask your feed manufacturer about the nutrient levels of the product you are using. Generally, it is a pre-mixed concentrate, and you can increase as needed and still have all the nutrients being fed in the correct proportions. The advice of a local equine nutritionist can help you determine if vitamins or minerals need to be added as well, as these vary regionally.

As Gill pointed out, being a good manager of your horse's health means knowing about the feeds you are providing him. Feeding in winter can be a delicate balance in order to keep your horse from a slow, downhill slide of body weight and health. It is much harder to bring him back up in winter. Over-compensating by over-feeding in winter is not healthy, either, as it leaves you with a fat horse when the lush spring grass appears. When planning your winter feeding routine, think of calories as a means of staying warm. Calories are not proteins, vitamins, or minerals. Calories come from grains, fats, and good quality grass hay.

About the Author

Mimi Porter

Mimi Porter lives in Lexington, Ky., where she has practiced equine therapy since 1982. Prior to that, she spent 10 years as an athletic trainer at the University of Kentucky. Porter authored The New Equine Sports Therapy, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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