© Stephen G. Jackson, PhD, Kentucky Equine Research
presented at the 1996 Bluegrass Laminitis Symposium
published in ANVIL Magazine, June 1996
There is a great deal of speculation in the lay literature, as well as among horsemen, farriers, veterinarians and nutritionists, concerning the impact of nutrition on the health and functional integrity of the foot. I would have to say that if I had a sure-fire formula for curing the ills of the foot with nutrition, I would probably be enjoying the winter in a warmer climate.
I hope that the take-home message from this talk is that there is no easy fix. Being realistic about the state of the science of nutrition, I must say, there are still a great many unanswered questions with respect to the true dietary influence on many of the physiological functions and tissues of the horse, as well as many other animals.
The simplistic approach to nutritional problem solving, whether we are concerned with reproductive function, developmental orthopedic disease, laminitis or any other equine health problem is to identify a certain nutrient that may have bearing on the situation and throw heaps of that nutrient at the problem. We have seen this approach fail time after time. The main thing that we must remember is that nutrition is a complex series of interactions and that it is indeed rare that curing a deficiency of a single nutrient is going to solve the problem at hand. As such, even though some space will be allocated to specific nutrients and the structure and function of the foot, the overriding theme of this paper will be the positive impact that an accurate and well-conceived nutritional program can have on the foot.
In more cases than not, the greatest response one can achieve in terms of promoting hoof wall growth, integrity of the hoof tissues and maintaining structural integrity of the foot come from a well-balanced diet that meets the horse's requirements for all nutrients. There is no evidence to suggest that the response to hyperalimentation (ingestion of a greater-than-normal amount of nutrients) with specific nutrients is greater than if the requirement for that nutrient is met. I would like to take a minute to reflect on the major classes of nutrients and the possible impact that they would have on the integrity of the foot and then to consider the diet in total and how manipulation of plane of nutrition and nutrient intake may affect the health of the horse (hoof).
Energy & Energy Balance
In evaluating a feeding program when faced with a complaint of bad feet, the first thing I would consider is total feed (energy) intake. Put simply, energy intake is the number of calories that a horse consumes in a day. Energy intake is expressed as Mcal of digestible energy. Energy in the equine diet is provided by fiber, starch, fat and in some cases by protein. The horse is designed to be able to meet a significant percentage of daily energy needs from fibrous feed. This makes sense, as the horse evolved as a wandering herbivore; as such, he is equipped with a normally very efficient fermentation vat which not only enables the horse to digest cellulose and other fibrous components of the diet, but also may significantly contribute to the synthesis of microbial protein and B vitamins. Fiber and that dietary starch that escapes digestion in the small intestine are fermented to form volatile fatty acids that are then converted to either glucose (propionic acid) or fat (acetic and butyric acids). Thus, a significant amount of the horse's energy needs may be met with fibrous feeds.
Quite simply put, if energy requirements are not met, then the entire metabolism of the horse is going to be negatively affected. (Remember this as we discuss feeding of the laminitic horse later.) Assessing the adequacy of dietary energy is a simple thing. Just as we all know and are more painfully aware as we age, if caloric intake equals caloric expenditure, body weight change is zero - or we say that the horse is in "energy balance." A horse is in a negative energy balance if caloric intake is less than caloric expenditure, and in positive energy balance if caloric intake is greater than caloric expenditure. Remember that caloric intake has a direct effect upon just about every metabolic pathway and physiological function in the body.
One of the greatest disservices man can visit on a sick (i.e., foundered) horse is to starve it to death, believing that feed exacerbates the situation! Certainly there is no real productive function that is served by feeding a horse too much and getting him too fat, but conversely, I see no reason to maintain a horse in a negative energy balance for an extended period of time. Butler and Hintz (1977) reported that hoof wall growth was 50% greater in ad libitum-fed ponies (positive energy balance) than in restricted-fed ponies. Since these diets were not isonitrogenuous, one can't totally partition out the effects of energy. Still, the overwhelming evidence suggests that meeting energy requirements may be the first and most important step in insuring growth and functional integrity of the hoof horn.
Protein is the least understood, most talked-about, and most wrongly indicted nutrient in the equine diet. If a horseman, veterinarian, farrier, acupuncturist, trainer or hot walker knows nothing else about what they are feeding a horse, chances are they know the protein concentration in the grain mix. To the question: "What do you feed your horse?" the response is, "I feed him a 12% sweet feed." Because of this protein consciousness, protein is indicted as the culprit in everything from physitis to laminitis to infertility. It is especially appropriate in this venue to give some information on the protein concentration of hoof wall tissue. Both my own data and that of Doug Butler (Butler and Hintz, 1977) suggest that hoof wall is in the neighborhood of 93% protein on a dry matter basis (Table 1).
|Butler's findings, 1977|
|72.20%||27.80%||no data||17.80%||14 ppm||136 ppm|
|Jackson's findings, 1988|
|75.17%||24.83%||94.21%||no data||no data||no data|
The composition of the hoof wall is predominantly an insoluble protein called keratin. There is every reason to believe that the amino acid composition of the hoof wall features the sulfur- bearing amino acids. Characteristically, the sulfur-bearing amino acids (methionine, cystine and cysteine) are responsible for cross-linking in proteins such as wool and keratin. The characteristic crimp in wool is due to cross-linking, which is due to these sulfur-bearing amino acids. One can now see why so many of the commercially available hoof supplements contain methionine. However, many fail to realize that methionine is but one of the amino acids in the protein called keratin, and deficiencies of any of the dietary essential amino acids can be as detrimental as a deficiency of methionine. What all of this boils down to is that if you don't meet the protein requirements of the horse, hoof growth and the integrity of the hoof wall will be compromised.
One of the most remarkable things that I see annually is a growth response in hoof walls in response to spring grass. The protein concentration in cool season grasses in the fall and spring can be from 20-30% on a dry-matter basis. Additionally, I routinely recommend 25-30% protein supplement pellets for broodmares with bad feet and for horses in training that are on the historically significant timothy hay and oats diet. The response has been pretty staggering. It has always amazed me that everyone knows that rings in the feet can signify a change in nutrition, but rarely is a positive change credited to an increase in protein quality and quantity in the diet. If you are restricting protein intake in a horse with bad feet (foundered horses included), you are barking up the wrong tree!
In considering minerals in the diet, one should seek to design diets that are adequate in all minerals. The current thinking on the relationship between diet and hoof growth and function puts far too much emphasis on zinc and far too little emphasis on the other minerals necessary for metabolism. When evaluating the diet and making recommendations relative to nutrition, assessment of the adequacy of the diet in all macro and micro minerals should be considered. Remember that the health of the foot is an extension of health of the horse and that if mineral deficiencies compromise horse health in general, then the health of the foot is going to be negatively impacted, as well.
There is justification for looking specifically at zinc when trying to put together a hoof-healthy diet. Zinc is involved in the health and integrity of hair, skin and hoof. However, adding more zinc to an already zinc-adequate diet is not going to be very fulfilling. If a horse is consuming 400-500 mg of zinc per day from the basal diet, adding another 300-400 mg of zinc in a supplement is not going to result in any dramatic increases in soundness or growth of hoof wall. There is indication that horses may respond better to supplemental zinc in the form of amino acid chelates or zinc methionine than to zinc sulfate or other forms. Whether this is because of the increased bio- availability of zinc in this form or because methionine is being added as well, remains to be seen. After scouring the literature, I find no other mention of specific minerals in regard to hoof wall growth. However, mineral metabolism is currently a fertile area of research, and other minerals may be found to impact the foot.
Most of the emphasis on vitamins and the integrity of hoof wall growth centers on the water-soluble vitamin biotin. Certainly there is more data in the literature on the effect of biotin on hoof wall structural integrity than for all of the other nutrients combined. It is thought that the normal horse has a biotin requirement of 2-3 mg per day. Horses with bad feet generally do not have a significantly different plasma biotin concentration from their good-footed contemporaries. Normal plasma biotin concentration is from 200-300 mg/l. There have been numerous reports in the literature which have attributed improvement in hoof wall histological properties to supplemental biotin. In these studies, supplemental biotin levels of 15-20 mg per day have had positive effects on histological characteristics of the hoof wall tissue. Additionally, some have reported an increase in the tensile strength of hoof wall samples and have reported improvements in "hoof score." Generally, I feel that if you have a horse with bad feet, it is worth a try to supplement with biotin. My personal experience has been that some horses appear, subjectively, to respond to biotin supplementation while others, I'm convinced, would not respond if I fed ten pounds of the stuff per day.
There is every reason to believe that diets adequate in vitamin A may be superior to diets deficient in this vitamin in terms of promoting normal hoof wall growth. Vitamin A is involved in maintaining epithelial integrity (epithelium - cellular covering of internal and external body surfaces) and may have an important role in cell maturation and differentiation in the foot.
In addition to the vitamins specifically mentioned, other fat-soluble vitamins should be adequate in the diet and supplementation with the remainder of the B vitamin complex is beneficial. This is especially true when horses are stressed, growing rapidly, or in intense training. The primary functions of many of the B vitamins are carbohydrate and energy metabolism and formation of red blood cells. Therefore, when horses are being fed heavily or are being worked, it makes sense to think that their B vitamin requirements are higher than during maintenance.
Feeding for Different Foot Problems
The Foundered Horse
Feeding the foundered horse needs to be addressed in two distinct phases. 1) During the acute phase and 2) during the recovery phase. As I view the way in which foundered horses are nutritionally handled, I would generally agree with the nutritional management of the acute-phase horse and disagree with the manner in which horses are fed after the initial insult.
During the time immediately after the horse has foundered, it is wise to limit the amount of soluble carbohydrate in the diet. The main reason is that the gut is compromised, fermentation in the cecum is disrupted, rate of passage is not normal and the cecal epithelium is damaged. All of these factors point to the logic of feeding a diet high in soluble fiber and low in starch. In selecting dietary constituents for this horse, it should be stressed that the very things that make high-starch diets a bad idea are also going to limit the effectiveness of fiber digestion. Therefore, fiber sources that are fairly readily fermentable should be used. Feeding a horse such as this a very mature timothy hay is somewhat akin to feeding him nothing. Hay for these horses should be cut at early stages of maturity, have a low lignin (an organic substance that, with cellulose, forms the chief part of woody tissue) content, and a high leaf/stem ratio. There is no valid reason to assume that alfalfa or other legume-mixed hay are contraindicated. In comparing grasses and legumes, legumes are higher in digestible energy, minerals, vitamins and protein. All of these nutrients are important if the horse is going to recover mentally as well as physiologically. In most acutely foundered horses, anorexia or loss of appetite accompanies the disease, so nutrient density (while avoiding excess soluble sugar intake) is a goal.
After the horse is metabolically stable, another approach needs to be taken in nutritional management. I have seen countless foundered horses that appear literally to be starving to death. In other words, these horses are in a severe negative energy balance. These horses should be fed a diet that is at least adequate to meet their maintenance requirements for all nutrients. It seems that some kind of fat supplementation for the foundered horse provides an advantage. Fat is 2.25 times as high in digestible energy as an equivalent amount of carbohydrate, is digested primarily in the small intestine, and has a true digestibility of about 90%, depending on the source of the fat. By using some fat in the diet, one can increase the energy density of the diet while avoiding questionable intakes of soluble carbohydrate. Besides fat, readily fermentable fiber sources include beet pulp and soybean hulls. Some high-fiber, all-in-one rations are also good choices for feeding the foundered horse. Do not buy into the myth that all of these horses should get is poor-quality grass hay and not a lot of it. Remember that if regrowth of the hoof is a primary goal, it is essential that the protein/amino acid requirements of the horse be met.
In addition to the basal diet, it is probably well to supplement with a good hoof supplement. The recommendations I generally make in this regard are to get 50-100 mg of biotin, 9 grams of methionine and 400-600 mg of chelated zinc into these horses. This means that four times the normal dose of some of the well-conceived supplements would be required.
Feeding to Promote Hoof Wall Growth
Even though it is my opinion that more bad feet result from genetics and bad mechanics, there is a piece of the riddle that can be solved with good nutrition. I usually tell people to try to find a reputable feed manufacturer, identify the feed that is designed for the class of horse that they are feeding, open the bag and feed enough of it to get the body condition that they desire. Look for feeds that are balanced for macro and micro minerals, have supplemental fat- and water-soluble vitamins, which also contain high-quality supplemental protein sources such as soybean meal. Commercial feeds should not be cut with oats, as this wrecks the nutrient balance that the nutritionist has attempted to achieve. In addition to a good concentrate, emphasis should be placed on high-quality hay. My favorite hay is a mixture of about 60% alfalfa and 40% orchard grass. A lot of people say that kind of hay has too much protein (the hay described above runs from 14-17% protein). Interestingly, cool-season grass pastures during the growth phase have from 20-26% protein and people never say that pasture is "too high in protein." If energy is to be restricted to cause weight loss or to slow growth, the requirements for the other nutrients still need to be met.
For those who have performance horses and may have the attitude, "Don't confuse me with facts, I've made up my mind: horses must have oats," I have seen dramatic differences in hoof wall growth if I can at least get them to add two pounds per day of a supplement pellet (such as Allphase, Vi-Pro-Min, Stamm, Pacesetter, Pacemaker, Spur, Gro-N-Win) to the basal oat diet.
Finally, I think that if everything else is being done from a nutrition, shoeing/trimming point of view, it is worth a shot to use supplemental biotin, methionine and zinc. Unfortunately, powdered bat wings and foo-foo dust do not take the place of good nutrition. There is no quick fix, and maintaining a good foot on a horse is a combined result of good farriery, good nutrition, good health care and selecting for horses that genetically have a great foot. It is much easier to concentrate on making sure the basal ration is right than to look for quick fixes in the form of supplements, paints and oils!
Dr. Jackson can be reached at Kentucky Equine Research, 3910 Delaneys Ferry Road, Versailles, KY 40383.
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