Water and electrolytes are excreted from the body primarily through sweat, urine and fecal output.  The body attempts to maintain a balance between dietary intake of electrolytes and excretion rates.  Kidneys adjust the volume and concentration of urine based on the water and electrolyte balance in the body through an intricate hormone signaling system.  Electrolytes are not stored in the body, so the amount needed daily must be provided in the diet.  If dietary electrolyte level is lower than needed, the kidneys will conserve and reabsorb electrolytes.  If dietary electrolyte supply is more than needed, the kidneys will flush any excess.  This very complex mechanism keeps water and electrolyte balance tightly regulated under normal circumstances.  However, when the relationship between intake and output is challenged, normal mechanisms may not maintain the balance. Hard work, especially in hot and humid conditions will challenge normal water and electrolyte balance mechanisms.  Under these conditions, horses can lose as much as four gallons of sweat per hour, which carries with it approximately 10 tablespoons of electrolytes – primarily sodium, chloride and potassium.  Human sweat is hypotonic, meaning the concentration of electrolytes in the sweat is lower than the concentration in the blood.  As people sweat, sodium concentration in the blood rises.  This triggers the thirst response causing the person to want something to drink.  Horse sweat is hypertonic, the concentration of electrolytes in the sweat is higher than the concentration in the blood.  As the horse sweats, sodium concentration in the blood remains unchanged even though large amounts of sodium are being lost in the sweat.  Without the rise in blood concentration of sodium, the thirst response doesn’t kick in.  This is why dehydrated horses often show no interest in drinking, which simply makes the situation worse.

Hay and pasture contain high levels of potassium and a normal diet will provide adequate potassium to meet requirements of most horses.  Usually, only hard working horses that sweat for prolonged periods need additional potassium supplementation.  Most commercial horse feeds contain 0.5 – 1.0% added salt (sodium chloride) which, along with free-choice access to a salt block, will supply adequate sodium and chloride to meet requirements of horses in light activity.  Horses being ridden regularly and sweating moderately on a daily basis cannot eat enough salt from a salt block to meet their needs.  Providing 2 – 4 tablespoons of loose salt daily in the feed will meet the increased requirements.  For horses that are sweating profusely, a mixture of 2/3 sodium chloride and 1/3
potassium chloride (Lite salt), would provide adequate sodium, chloride and potassium to replenish the higher losses.  Commercial electrolyte supplements are also available, but should contain sodium chloride as the primary ingredient.

Providing daily electrolyte supplementation beyond what a horse needs to maintain balance can be very counterproductive.  The kidneys will become very efficient at flushing the excess electrolytes out of the system and then on a day the horse really needs a higher level, they won’t be available.  The current recommendation for electrolyte supplementation is to provide additional electrolytes the day before, the day of and the day after a horse is going to work very hard and sweat a great deal.  It is also very important that electrolytes are only given to well hydrated horses.  Since you can lead a horse to water but you can’t make him drink, dehydrated horses should receive fluids intravenously to be sure water balance is adequately restored.

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

Vitamin E is the most abundant fat-soluble antioxidant in the body. The concentration of naturally occurring vitamin E activity varies considerably in typical feeds used for horses. Fresh forages and immature harvested forages
contain the highest concentrations of vitamin E activity, ranging from 15 – 50 IU/lb. Grains, such as oats and corn tend to have lower concentrations, from 10 – 15 IU/lb. Vitamin E content declines over time in stored grains and
hay. For example, vitamin E in alfalfa stored for 12 weeks has been reported to decline 54 – 73 percent. Vitamin E intake will be extremely variable in typical, unfortified diets for horses. Therefore, choosing a formulated feed that is fortified with vitamin E will ensure adequate vitamin E intake. Fortification may be accomplished with synthetic or natural vitamin E sources. The natural source, alpha-tocopherol, is more readily absorbed and is more effective at improving vitamin E status in the body, but is usually more unstable than synthetic sources.

According to the National Research Council (NRC) Nutrient Requirement of Horses, the vitamin E requirements for horses have not changed since the NRC was last published in 1989. For a mature horse at maintenance the
requirement is reported to be 0.45 IU vitamin E/lb of body weight, which is 500 IU/day for an 1100 lb horse. The vitamin E requirement for pregnant and lactating mares is 0.9 IU/lb of body weight, or 990 IU/day for an 1100 lb
mare. Growing horses should also consume 0.9 IU of vitamin E per pound of body weight, or 540 IU/day for a 600 lb weanling.

Mature exercising horses need between 0.72 and 0.9 IU/lb of body weight per day, depending on the workload. This calculates to 792 IU/day for an 1100 lb horse doing light work, to 990 IU/day for the same horse doing very
intense exercise. Some research suggests that very hard working horses, such as those running endurance races, might benefit from dietary vitamin E levels as high as 5000 IU/day. This has not been well duplicated in other
studies, but there are no reported adverse effects to intakes in that range. Most research supports the recommendation of 0.9 – 1.0 IU of vitamin E per pound of body weight for hard working horses. But, for horses
exhibiting some muscle stiffness or elevated muscle enzymes in blood work, the higher level may be of some benefit.

A diet of fresh pasture containing 50 IU/lb of vitamin E activity would well meet the vitamin E requirements of all horses mentioned, except possibly for those doing very intense exercise that may benefit from higher than normal recommended levels. However, when you harvest that pasture for hay or buy hay that has been stored for awhile, the vitamin E activity is greatly reduced. A horse eating fresh alfalfa hay will usually consume adequate vitamin E, but if hay is very mature when it is cut, or is stored for an extended period, another source for vitamin E may be necessary. Well-fortified commercial feeds should contain adequate amounts of tocopherols to meet the vitamin E requirements, even when the forage is not contributing a significant amount. Caution should be taken when adding a vitamin E supplement to a well fortified concentrate because most vitamin E supplements also contain selenium.  It is possible to over-supplement selenium to the point of causing harm, so contact your veterinarian or an equine nutritionist for help in determining if you need additional vitamin E supplementation and if the supplement you are using is safe to use with your current ration.

by Karen E. Davison, Ph.D., Manager-Equine Technical Services, Purina Mills, LLC

Land O’Lakes, Inc.

The term exertional rhabdomyolysis is the scientific description for tying-up, and simple means muscle cell death from exertion.  First identified int he late 18o0’s as Monday Morning Sickness or azoturia, it

was observed in working horses given the weekend off, confined in stalls and fed their full grain ration.  When brought out to work on Monday morning, affected horses would suffer severe muscle cramping, profuse sweating, rapid breathing, and possibly pass dark reddish-brown urine.

We now know that horses tie-up for a number of different reasons, including dietary electrolyte imbalance, high body temperature, unusually intense exercise or stress.  These situations occur in otherwise normal horses and are remedied by correcting the electrolyte balance in the diet or maintaining a more consistent exercise program and avoiding highly stressful situations.  Other horses have a muscle disorder, Polysaccharide Storage Myopathy (EPSM or PSSM), which makes them more prone to tie-up.  EPSM is found in all breeds, but appears more prevalent in Quarter Horses, Arabians, draft breeds and Warmbloods.  It has been documented in horses from 3 months to 29 years of age.

Tying-up is the most obvious symptom of EPSM but there may be many more subtle symptoms.  Horses with EPSM may show a lack of energy, decreased performance, back soreness, abnormal hind leg movement, stiff gait, loss of muscle over the topline and hindquarters, muscle tremors following exercise, episodic colic and/or general irritability and bad attitudes while being groomed, saddled and ridden. Symptoms can suddenly appear in a horse that has never tied-up before.

The underlying cause for EPSM is a defect in muscle metabolism and how these horses store an utilize energy in the muscles.  They often respond well to therapy, including diet changes and regular exercise.  Response to therapy is a good indication of the disorder, but a muscle biopsy provides the more definitive diagnosis.  A complete veterinary exam is recommended to differentiate between EPSM and  other conditions with similar symptoms.

Diet changes for EPSM horses involve adjusting the caloric sources in the diet.  Typical diets of oats and other grain mixes provide calories primarily from starch and sugar, but EPSM horses may benefit from diets that provide more calories from fats and fewer calories from starch and sugar.  There does not appear to be a one-size-fits-all diet, since horses with EPSM can have variations in starch/sugar sensitivity and the level of fat needed to help alleviate symptoms.  Finding the diet that best manages an individual horse may take some trial and error.

For horses suspected of having EPSM, changing from a grain or grain mix to a pelleted feed with lower starch and added fat is the initial step.  Horses seem to have an individual tolerance level for fat in the diet and, as fat is increased, some horses may back off feed.  Therefore, small, gradual adjustments may be necessary.  Higher fat, lower starch feeds such as Purina Ultium make these diet changes easier because the fat is already included in a palatable, nutritionally balanced pellet.  When you add oil to existing feeds, additional supplements may be needed because increasing fat typically reduces total intake and increases the requirements for nutrients.

Some researchers recommend total fat intake up to 1 lb. of fat for 1000 lb horse, and reducing starch and sugar as much as possible.  To calculate total fat intake, multiply the percent fat in the product times the amount fed.  For example: 8 lbs of Ultium with 12.4% fat provides 8X0.123=1 lb of fat.  There are also good fat supplements such as Purina Amplify which has 30% fat, so 3.3 lbs provides a pound of fat.  One pound of fat could be provided by 2 cups of vegetable oil or 5 pounds of rice bran, but these fat sources do not provide balanced nutrients, so the total balance of the ration might be compromised and require adjustment.

After changing to a higher fat, lower starch diet, it may take four months to see significant changes in a horse with EPSM. However, if there is any improvement in symptoms during this period it is likely the horse will continue to respond well if maintained on the new diet. Some horses show an increase in energy level, sometimes to the point of “bouncing off the walls” during the first few months of diet change.  This may be due to changing the metabolism of muscles to burn fat, and finally delivering energy to previously energy-starved tissues. These horse generally settle down after they  adapt, and show improvement of EPSM symptoms on the new diet.

In addition to diet therapy, horses with EPSM are best managed by providing regular exercise and plenty of turnout time.  It is important that they not be stalled for days without exercise.  If they must be stalled without exercise, reduce their grain intake or eliminate grain altogether and instead feed a low starch concentrated protein, vitamin and mineral supplement, such as Nature’s Essentials Enrich 12 or Enrich 32.  Horses with EPSM will always have the disorder, but adjustments in diet and management may help them continue to perform at very high levels.

The goal in all of these is to reduce starch and sugar and increase fat, which can be tough due to some of them not working hard enough to eat many calories.

Some of the programs we have that will work include:

1) Ultium
2) Enrich 32 + Amplify (horses with lower calorie needs)
3) Enrich 32 + Horse Chow + oil (for horses with higher fat needs, Horse Chow soaks up oil well, but not real high calorie requirements, Horse Chow can replace part of the hay)
4) Equine Senior + 1-2 pounds of Amplify or 1-3 cups of oil.
5) Strategy + 1-2 pounds of Amplify or 1-3 cups of oil.
6) WellSolve L/S + 1-2 pounds of Amplify or 1-3 cups of oil.

It will take a trial and error to find the program that works to manage each horse, as there is no “one size fits all” diet.  Keep in mind, we can only offer to help better manage these horses, which means we can help reduce the incidence and the severity of the symptoms (tying-up episodes) but the horse has a condition that they will always have; it cannot be cured with feed alone.

Courtesy of Purina Horse Feed

However, during the last 3 – 4 months of pregnancy, the foal begins grow and develop more rapidly. In fact, during the last 90 days of pregnancy, developing foals gain approximately 1 lb per day. Considering the average foal weighs 100 – 110 lbs at birth, 90 of those pounds happened in the last 4 months of gestation. This rapid development requires significant nutritional support to lay down the foundation of bones, muscles and tendons. The only way to provide this nutrition to the fetus is through the mare so it is critical to provide her with the proper balance and quality of protein, vitamins and minerals during this time. The increased size of the growing foal also takes up room in the mare’s body cavity such that she may actually eat less hay or forage. This reduction in forage intake, coupled with the increased nutritional needs, means mares in late gestation should be supplemented with a nutritionally-balanced concentrated grain ration. Even in situations where forage alone is maintaining mares in acceptable body condition, it is important that they receive quality concentrate supplementation. While good quality forage may be able to provide sufficient calories to maintain body condition of the mare, other nutrients such as protein, vitamins and especially trace minerals, will be deficient.

While body condition certainly affects reproduction efficiency and health of the mare, having mares in good condition doesn’t guarantee proper foal development. Body condition is directly correlated with calorie intake but doesn’t necessarily reflect intake of protein, vitamins and minerals. Research has shown that foal birth weight can be negatively affected when mares fed inadequate protein during late gestation, even when mares were maintained in a fleshy condition. It is not uncommon to see fat mares have small, weak foals when the mare’s diet was adequate in calories but low in quality protein. Even when mares are fed high protein forage, like alfalfa, the diet can be deficient in important amino acids and other nutrients. Late gestation mares should be fed a grain mix or supplement containing quality protein sources that will meet amino acid requirements fo r optimal foal development.

During the tenth month of gestation the greatest amount of mineral retention occurs in the unborn foal. Mare’s milk is practically devoid of trace minerals that are essential for proper bone development, such as copper. Forages, including pasture and hay are also low in trace minerals. Therefore, adequate trace mineral supplementation of the mare is critical for normal fetal development. Feeding a ration with the proper trace mineral balance during late gestation will meet the mare’s requirements and provide sufficient minerals for the developing foal. In the first weeks of life, foals will not eat sufficient amounts of fortified feeds and may not have adequate absorption of dietary trace mineral sources at this early stage of development. Proper mineral nutrition of the mare in late gestation helps insure that the developing foal will actually store a supply of these important nutrients for use after he is born. This will bridge the time from birth until foals are old enough to consume and assimilate these important nutrients from a well-balanced foal feed.

If a mare is thin during late gestation, meaning her ribs can be seen, this is the best time to provide enough calories in her diet to facilitate weight gain. It is nearly impossible to put weight on a lactating mare, and thinner mares, especially those nursing a foal, are less likely to become pregnant when rebred. This means that late gestation is the last chance to get a thin mare in good shape. In these situations, select a feed that is very calorie and nutrient dense, in order to supply the needed energy and nutrients to support weight gain without having to feed excessive amounts of grain.

While research has shown that fat mares don’t have a higher incidence of foaling difficulties, they may have a reduction in milk production which can negatively impact foal growth. If a mare is significantly overweight during late gestation, where ribs cannot be seen and are difficult to feel, you must provide adequate protein, vitamins and minerals to support optimal fetal development without adding unnecessary calories. In these cases, choose a concentrated protein, vitamin, mineral supplement that is designed to be fed at 1 – 2 lbs per day. This type of supplement will meet the nutrient needs of the foal without causing weight gain in the mare. It may be necessary to restrict hay intake to 1.5 lbs of hay per 100 lbs of body weight in significantly overweight mares in order to facilitate weight loss.

Proper nutritional management of the broodmare during late gestation will give her foal the best start in life. With all the time and money invested in getting a mare in foal and all the promise and potential that comes with a newborn foal, you don’t want to skimp on mare nutrition during this critical time.

Karen E. Davison, Ph.D. – Manager-Equine Technical Services Land O’Lakes Purina Feed

Title: HOW Meeting – Horse Owner’s Workshop
Location: Ark Country Store, Waxahachie, TX
Description: Mark you calendars now! Our Purina Horse Owner’s Workshop (HOW Meeting) is scheduled for April 8!

Learn about new discoveries being made at the one-of-a-kind Purina equine Research Farm in Gray Summit, MO, that will change the way you feed growing horses.

Get back-to-basics training on how to use various tools to keep your horse on the right nutritional path.   Discover how fat, fiber, sugar and starch are different and what combination works best for your horse.

Register for our HOW sweepstakes, win door prizes from our industry partners, and save on Purina Horse Feed and other great products!

“Trade in your empty for a full!”  Attendees who register and attend our HOW meeting and bring an empty bag of their current horse feed (non-Purina) will receive a free, like bag of like Purina Horse Feed. Limit one bag per household.

REGISTER ONLINE for this FREE workshop!  Bring a friend and you’ll both receive a coupon for $10 off!   [contact-form]
Date: 2010-04-08
Start Time: 6:30 pm
End Time: 8:30 pm

Critical temperature is the temperature below which the animal must produce additional heat to maintain normal body temperature. Mature horses in good condition have a critical temperature around 30 degrees Fahrenheit during early winter. Horses will require an estimated 15 – 20% more calories for each 10 degrees Fahrenheit 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.