In the past several years, multiple sources have recommended yeast products for inclusion in equine diets for many purposes, including improving fiber and phosphorus digestibility, increase feed efficiency, support hindgut bacteria, and even prevention and cure of gastric ulcers. However, a close look at the published data available on the efficacy of supplementing yeast culture in the diets of horses does not support the claims of positive effects in horses fed quality diets that meet nutritional requirements.

AAFCO defines a number of yeast products as feed ingredients, including dried yeast, yeast culture and yeast extract. Dried yeast may be either active or nonfermentative. Yeast culture is a dried product composed of viable yeast cells and the media on which it was grown. Yeast extract is a dried or concentrated product of cell contents from ruptured yeast cells.

Studies in ruminants suggest that addition of yeast products to ruminant diets promote bacterial growth in the rumen. It is generally believed that yeast additives either directly facilitate fiber digestion and dry matter intake, or contain metabolites or compounds that stimulate bacterial growth to facilitate fermentation and animal performance in ruminants. Since horses have fermentative capability in the hindgut, it has long been proposed that yeast products may have beneficial effects on digestion/fermentation in the hindgut, resulting in enhanced fermentation and increased fiber and/or nutrient digestibility.

According to the 2007 National Research Council’s Nutrient Requirements of Horses, “Unlike observed effects in ruminant studies, supplementation of yeast in horse diets tended to show some beneficial effects on fermentation, but results were equivocalacross studies.” There is great variation in published results of feeding yeast products to horses – most studies report minimal to no increase in cecal or colonic bacterial cultures as a result of feeding yeast products, although a few studies have reported beneficial effects when yeast products were fed with very high starch diets, or with low quality forages. Some studies have reported no improvement in nutrient apparent digestibility when yeast products were fed to mature horses, but others have reported some improvements in fiber and nutrient digestibility. However, the reports of improved digestibility of nutrients with the addition of yeast products are most often seen when yeast products are added to nutritionally deficient diets. The Purina Equine Research team recently completed a thorough, long-term study that looked at the efficacy of yeast in enhancing fiber digestion in horses, as well as several other parameters, and the data indicated no effects of yeast on fiber digestion. This data is currently being prepared for submission for publication in a scientific journal. However, ongoing Purina research continues to investigate potential effects of yeast products on other parameters of equine digestion, health and performance.

Yeast products can be a source of quality nutrients, including essential amino acids and B-vitamins, so adding yeast products to a nutritionally deficient diet will result in improved performance in horses, just as addition of any ingredient that supplies deficient nutrients to a ration will result in improvement in performance. However, when yeast products are added to diets that are nutritionally balanced and fortified to meet a horse’s nutrient requirements, the additional nutrients provided by the yeast products have not shown measurable benefit. At this time, there is insufficient data to support the inclusion of yeast products in horse feeds for benefits other than those simply provided by the nutrient content of the yeast products, and there are many other feed ingredients that provide quality nutrients for optimal nutrient content in horse rations. Purina Premium Horse Feeds are nutritionally fortified and balanced with quality protein sources as well as specific essential amino acids, minerals and vitamins to meet horses’ nutritional requirements when fed as recommended. And, of course, if and when we elucidate beneficial effects of yeast products in horses, we will share those findings with our customers and add them to our feed formulations.

Katie Young, Ph.D. Land O’Lakes Purina Feed

Heat and humidity put an added burden on horses during training, showing and hauling. Horses are actually better equipped to work in cold weather than in the heat. They build up a tremendous amount of body heat due to the internal heat produced by fiber digestion and the large mass of working muscles, combined with insulation from their hair coat and body fat cover.

Normal body temperature for a mature horse at rest is 99 – 101° F. Under working conditions this can rise to 102 – 104° F, but with the same work under hot, humid conditions body temperature can elevate dangerously to 106 – 107° F. Body temperatures of 104° F or higher for any extended amount of time can be life threatening.

A horse’s main cooling mechanism is evaporation of sweat from the skin surface. Increased blood flow in the veins and capillaries close to the skin and elevated respiration rate help dissipate internal heat as well. Increasing humidity reduces the evaporation of sweat from the skin, thereby decreasing the cooling ability. Under extreme heat, especially when humidity is high, the body’s cooling mechanisms may not work well enough to dissipate the heat generated. This can lead to heat stress which is hard on the body and can impair performance.

A simple calculation of Ambient Temperature (° F) + Relative Humidity (%) – Wind Speed (mph) will indicate heat stress risk level. For example, ambient temperature of 98°F with a 55% relative humidity and wind at 5 mph; 98 + 55 – 5 = 148. If the calculation equals 130 or less, then the horse’s own cooling mechanisms will work effectively. Between 140 and 170, the horse has partial cooling capacity and may need some assistance cooling down. When the result is greater than 180, the horse has a significantly impaired ability to cool and is at high risk for heat stress or even heat stroke.

Horses unaccustomed to the heat or those not properly conditioned will sweat more for a given amount of work than fit or acclimatized horses. While it is necessary for horses to sweat to help cool the body, sweat generated during work robs the body of fluids and important nutrients that must be replenished. Horse sweat is more concentrated than human sweat, meaning it contains a higher concentration of electrolytes. Electrolytes are electrically charged mineral salts that play a large role in water balance and are integral to nerve and muscle function. An electrolyte imbalance can lead to heart problems, digestive dysfunction, muscle cramps and nervousness. The primary electrolytes lost in equine sweat are sodium, potassium, and chloride.

Horses working at light to moderate levels will receive adequate electrolytes from nutritionally balanced feed, good quality hay and a salt block or a couple ounces of loose salt per day. Even if these horses are sweating a bit, a good diet along with clean water will replenish everything lost in the sweat. However, horses working very hard in hot, humid climates and sweating a great deal may need additional electrolyte supplementation.

Electrolyte supplementation should be approached carefully. First, never give electrolyte supplementation to an already dehydrated horse. Second, the body has a set requirement for electrolytes but doesn’t store any extra. If supplemental electrolytes are provided in excess amounts, the body will become very efficient at eliminating them in the urine. This causes the horse to urinate more frequently, thus increasing water needs and making it more difficult to stay hydrated. Also, if the body is flushing excess electrolytes out of the system to keep the balance, on a day when additional electrolytes may be needed, they won’t be available. Therefore, the best recommendation is to p

rovide a well balanced feed, good quality hay and free choice salt and water on a daily basis. Provide additional electrolyte supplementation the day before, the day of, and the day after an event in which the horse works

extremely hard and sweats excessively. There are many commercial electrolyte supplements available, or a home-made mix of 3 parts salt (sodium chloride) and one part lite salt (potassium chloride) is an option. Remember though, for the vast majority of working horses, the sodium and chloride requirements can be met with a couple ounces of plain salt per day and the potassium, calcium and magnesium requirements will be met by a well balanced quality feed and hay. Therefore additional electrolyte supplementation is needed only at those times when a horse will be sweating large amounts for an extended time frame.

By Karen E. Davison, Ph.D., Manager – Technical Services, Purina Mills, LLC

Feeding horses correctly and safely often appears to be enormously complicated for the horse owner. Horses are unique in the livestock world, and cannot be fed the same way as cattle, hogs sheep, or any other livestock species. However, following a few guidelines will go a long way toward ensuring that your horse’s nutrient requirements are met without increasing the risk of the digestive disturbances that seem to plague many horses.

Feed horses according to lifestyle
Horses require different amounts of nutrients according to their lifestyle. The horse owner must be sure that each horse receives a total diet that meets the needs of that particular horse. Purina® Horse Feeds are designed to meet the nutritional needs of various classes of horses, such as Omolene #100® Horse Feed for pleasure horses, Omolene #200® Horse Feed for performance horses, Omolene #300® Horse Feed for growing horses, and Equine Senior® Horse Feed for older horses.

How much feed?
In order to feed the correct amount to a horse, the owner must know the horse’s body weight. To determine body weight, one can use a livestock scale, a weight tape (such as those available through Purina Dealers) or an equation, such as: BW(lbs) = Heartgirth (in) x Heartgirth (in) x Body length (in) divided by 330. (The heartgirth is measured as the circumference over the withers and around the barrel; the body length is measured from the point of the shoulder to the point of the buttocks.)

Once the horse’s body weight is determined, then the owner should use the guidelines on the bag of feed, or use the feeding calculator found on the Purina Website (http://horse.purinamills.com) to calculate how many pounds of feed and hay to feed each horse.

Measure feed by weight, not volume.
A 3-lb coffee can of oats is not the same amount of feed as a 3-lb coffee can of corn! The can may hold 2-3 lbs of oats, while the can of corn may be 4-5 lbs. Further, since corn is more calorie rich than oats, the can of corn may contain 2-3 times the energy as the can of oats. Any time a horse owner changes feed, he or she must weigh the can of feed to make sure the horse gets fed the same amount of feed every meal. Plus, every different batch of corn or oats may be a different weight. A can of Strategy® Professional Formula GX Horse Feed or Omolene #200® Horse Feed will weigh the same each time, however, sometimes the 3-lb coffee cans are different sizes! Another option is to use a pre-measured scoop.

Do not overfeed grain.
The horse has a very small stomach in relation to its total size, and feeding too much grain in one meal can overload the stomach and cause problems such as colic or laminitis (founder). A general rule of thumb is to feed no more than .5% of the horse’s body weight in grain per meal, or no more than 5 pounds of grain per meal for a 1000- pound horse.

Do not dilute balanced rations.
Purina’s equine nutritionists formulate Purina® Horse Feeds with precise, correct nutrient balances to meet the requirements of the various classes of horses. Many horse owners then dilute or “cut” these balanced feeds with a cereal grain (usually oats), thereby changing the nutrient balance and decreasing the feed’s nutritional value for horses. For those horse owners wishing to feed oats, corn or unfortified grain mixes, Nature’s Essentials® Enrich 32® Supplement is a concentrate pellet that can be used to supplement grains. Strategy® Professional Formula GX Horse Feed, Omolene #100®, #200®, #300® etc. are designed to be fed only with hay or grass.

Do not supplement balanced rations.
When a horse owner feeds a Purina® Horse Feed, it is already balanced to meet the horse’s nutritional needs and contains sufficient amount of all the necessary proteins and amino acids, vitamins and minerals. If an owner then top-dresses a protein, vitamin, or mineral supplement on the ration, it can cause serious nutrient imbalances, and possibly toxicities.

Feed adequate roughage.
Horses require at least 1-1.5% of their body weight per day of roughage in their diets. Feeding adequate amounts of high quality roughage can prevent many digestive disturbances as well as behavior problems. When providing a feed such as Equine Junior® Horse Feed, Senior® or Adult® Horse Feed, the roughage is included in the pellet, so all the horse’s nutritional requirements are met when these complete feeds are fed as recommended. However, it may be beneficial to supply some roughage to decrease the risk of horses developing boredom vices, especially when exercise is limited.

Use only top quality feeds.
Avoid dust and mold, and keep the feed manger clean. Proper feed storage reduces feed waste. Horses’ digestive systems are not equipped to deal with dust, mold, etc., so poor quality hay or grain will not be digested efficiently, and may cause health problems for the horse. The grains used in Purina® Horse Feeds must pass stringent quality tests before being utilized in the feeds, thereby ensuring only clean, high quality ingredients in each bag of Purina® Horse Feed.

Feed at the same time every day.
Horses that are fed on a consistent schedule are less likely to go off their feed or develop undesirable stall habits (vices). Horses that are fed on inconsistent schedules may get hungry and bolt their feed, possibly resulting in digestive disorders. Also, spacing meals evenly throughout the day is healthier for the equine digestive tract.

Properly manage group-fed horses.
If horses must be fed as a group, use individual feeders spread far apart, put out extra feeders, and make provisions for timid horses (low in the pecking order) to ensure that they have the opportunity to eat adequately. However, the only way to ensure that each individual meets its nutritional requirements is to feed separately.

Avoid sudden changes.
Consistency is one important factor in reducing the chance of digestive upsets in a horse. Changes in types of feed should be made gradually (4-7 days for small changes, up to three weeks for radical changes).

Provide clean, fresh water.
Horses should have access to clean, fresh water at all times, except when the horse is extremely hot. The hot horse should receive plenty of water, but only a few swallows at a time until the horse is cool.

Exercise horses regularly.
Daily exercise helps maintain regular eating habits, desirable stall behavior and general health.

Check teeth regularly.
Horses need routine dental care. Sharp points can develop on the teeth, which can cause problems with eating and also performance, as they may interfere with the action of the bit. The veterinarian can remove the sharp points by floating (rasping).

Practice parasite control measures.
Many digestive disturbances are caused by parasite infestation. Horse owners should practice parasite control measures such as a proper de-worming program, harrowing and/or rotating pastures, proper manure disposal, etc.

Keep an eye on horses’ droppings.
Changes in consistency, color, odor or composition of feces may indicate a digestive disorder.

Practice routine veterinary maintenance
In order for a horse to get the most out of its nutrition program, it must be in good health. Regular vaccinations, deworming, etc. are all essential elements of a good overall wellness program for the horse.

By Katie Young Ph.D., Consulting Equine Nutritionist, Purina Mills, LLC

Cold weather presents horses with some specific nutritional and management demands. As winter approaches it is a good idea to evaluate horses, housing and feeding programs to insure that horses get through the cold weather in good shape.

All warm-blooded animals have a critical temperature. This is the temperature below which the animal must produce additional heat to maintain normal body temperature. Mature horses in good flesh have a critical temperature around 30° F during early winter. After developing a winter coat and gaining 100 pounds, the critical temperature drops to 15° F. It is estimated that young horses, horses in thinner condition and those that have not developed a winter coat, may have a critical temperature around 40° F. When wet, windy conditions are present, the critical temperatures will be higher as well. In order to produce extra body heat, an increase in feed energy is required. Horses will require an estimated 15 – 20% more calories for each 10° F the ambient temperature falls below critical temperature. However, thin horses or horses with short hair may need even greater increases in dietary intake to maintain normal body temperature.

It is important that horses come into winter carrying enough body condition. The additional body fat serves as insulation and energy reserves in times when the thermometer dips below the critical temperature. Once cold weather sets in, it is difficult to put weight on horses. Thin horses get colder and use so much energy trying to stay warm, there often aren’t enough calories left for weight gain. Young horses and broodmares in late gestation, may not be able to consume enough of a high fiber diet, such as hay, due to restrictions in digestive system capacity. These horses must have access to good quality, highly digestible feeds in order to meet the additional energy requirements due to cold weather and higher production levels.

Historically, horsemen have often changed their rations from summer to winter to accommodate increased calorie needs. Typically, this is done by increasing the amount of hay and changing from oats to corn or a sweet feed. Feeding additional hay provides extra calories and also helps maintain body temperature due to the internal heat produced during digestion of fiber. The change from oats to corn or a sweet feed is based on the impression that corn or sweet feed is a “hotter” feed than oats. This concept of oats being a summer feed and corn a winter ration has some merit, but also has some flaws.

Nutritionally, oats and corn compare as follows:
Fiber,%    Protein,%
Oats    10.7    11.8    1200
Corn    2.2    9.0    1500

One pound of corn has more energy and is lower in protein and fiber than one pound of oats. Not only does corn have more energy per pound than oats, corn also weighs more per unit of volume. One scoop full of corn has about 45% more calories than the same scoop full of whole oats. This has led to the idea that corn is a “hotter” feed than oats. Actually, because of the higher fiber level in oats, oats produce more internal heat during digestion than corn, it just takes more oats to provide enough calories.

Corn or oats alone can provide adequate calories but not adequate protein, vitamin or minerals. The best option for the horse year-round is a nutritionally balanced diet of good quality hay and a high-quality, well fortified commercial feed. During the winter months, provide as much shelter as possible, especially from wind and wet weather, and Calories/lb increase feed intake to help maintain body condition. Then as warmer weather arrives, continue to feed the nutritionally balanced diet, simply reduce the amount fed. When a well balanced feed is used, the only adjustments necessary are to increase or decrease the amount fed, depending on body condition or energy demand.

Monitoring water intake is another very important consideration during winter weather. Mature horses in temperate climates will normally drink from 5 – 8 gallons of water per day. Increasing the amount of hay in the diet will increase the water consumption, up to 9 or 10 gallons of water with an all-hay diet. During cold weather, water intake can decline dramatically. Increased hay intake combined with decreased water intake contributes to the risk of impaction colic. This is especially a problem when horses are kept in stalls for several days due to inclement weather because confinement tends to slow intestinal motility. In cold weather, water should be kept fresh and free of ice to insure adequate intake and horses exercised whenever possible. Also, adding one or two ounces of salt to the feed may stimulate water consumption.

By Karen E. Davison, Ph.D., Managing Equine Nutritionist, Purina Mills, LLC