Nutrition for Sound Development and Growth

OUTLINE

  1. Definition of D.O.D.
  2. Syndromes
  3. Factors Affecting
  4. Nutritional Contributions
    • Minerals
      1. Calcium (Ca)/Phosphorous (P)
      2. Copper (Cu)
      3. Zinc Zn)
    • Protein
    • Energy
    • Nutrient Requirements
  5. Biological Causes
  6. Suggestion for Nutrition on the Breeding Farm
  7. Summary

1) Developmental Orthopedic Disease (“DOD”)
A broad term representing a number of clinical syndromes affecting the musculoskeletal system of the horse during growth and development.

  • Estimated incidence in the horse ~ 10 – 65% (Bertone, McIlwraith)
  • point of confusion between reports of clinical instances of DOD and radiographic surveys of horses not necessarily showing clinical signs.
  • Expectation of horse owners = 0%

2) Syndromes include

  • Physitis (“epiphysitis”)
  • Osteochondrosis
    • Osteochondritis dessicans (OCD)
    • Subchondral bone cysts (SBC)
  • Angular limb deformities
  • Flexural deformities (“contracted tendons”)
  • Cervical compressive myelopathy (CCM – “wobblers”)

3) DOD is Multi-factorial

  • Nutrition – pregnant/lactating mare and foal
  • Exercise
  • Hormonal
  • Trauma
  • Heredity
  • Combination of any or all

4) Nutrition

To determine the impact of the nutritional program on DOD, it is most appropriate to assess the composition of the diet, not blood levels of nutrients. This is because the horse’s body will try to maintain blood levels of most nutrients within a certain range by the process of “homeostasis”. Also, time of feeding prior to blood sampling can affect the levels of nutrients in the blood. They may be high soon after feeding or low after a long overnight fast.
Two major areas of nutrition tend to contribute to DOD:

  1. Excess energy intake (especially high starch/sugar and/or protein)
  2. Inadequate or imbalanced Calcium/Phosphorous and/or Copper/Zinc

Attempting to slow growth rate by limiting the intake of concentrate (to limit calorie intake) often results in reducing the intake of copper and zinc, which can aggravate the problem. It is recommended that the intake of amino acids, vitamins and minerals are maintained by the use of a low intake, low NSC, highly fortified product (often called “ration balancer”).

Excess energy intake, especially from starch and sugar, can come from many sources. Consumption of feeds high in cereal grains, most notably, corn, and molasses will results in the horse taking in high levels of starch and sugar, which will drive up blood insulin levels. High insulin levels have been shown to inhibit growth hormone, critical for the development of normal cartilage and bone, and will contribute to DOD. In addition, research has shown that foals with DOD are more likely to be insulin resistant than normal foals.

Intake of high levels of protein, as is common when horses are fed straight alfalfa hay, will also cause problems. Straight alfalfa hay can provide over 2-times the protein required by a growing horse. Such excess protein will be, in essence, turned in to sugar in the horse’s body I with the same results as if it had been fed molasses!! In addition, excess protein requires the body to rid itself of excess nitrogen, which is excreted in the urine, resulting in increased urine output, wetter stalls and the ammonia smell in the barn with which we are all familiar!!!!!

Too much time on lush pasture can also result in high intake of calories, starch and protein.

It is important to note that, while a foal is nursing on its Mother, the mare’s intake of energy will also affect the foal and the likelihood of developing DOD.

Another problem with high levels of alfalfa in the horse’s diet is the calcium (Ca) to phosphorous (P) ratio. The ideal Ca:P ratio for the growing horse is 1.5:1. Young horses can probably tolerate ratios slightly over 2:1. The Ca:P ratio in alfalfa hay can be as high as 6 or 7 to 1! The P content in grain will adjust this somewhat, but comes at the cost of hundreds of starch calories.

To correct the imbalance requires a well-designed concentrate, with more P than Ca to correct the Ca:P ratio in the entire diet.

Grass hay will have a Ca:P ratio closer to 1:1 and usually needs no adjustment. Hay that is part grass and part alfalfa (or other legume, like clover) will have a Ca:P ratio that correlates to the percent of each in the mix. When you get to a mix that is about half-grass and half-alfalfa, hay analysis is warranted to make sure the Ca:P ratio in the diet is acceptable. In fact, hay analysis is a good idea whenever it is fed to breeding animals.

Another important concern is the levels of copper (Cu) and zinc (Zn) in the growing horse’s diet. Both copper and zinc are involved in cartilage formation and subsequent ossification.

The current National Research Council’s recommendations (NRC, 2007) for Cu and Zn are 10 and 40 parts per million (ppm) in the total diet, respectively. Recent research suggests those levels should be more like 35-50 and 80-100 ppm, respectively. Some studies as well as field experience show feeding these higher levels of copper and zinc results in dramatic reductions in DOD on many breeding farms.

In addition, Cu and Zn are two minerals that have shown improved absorption when they are CHELATED. Chelated minerals are bound to a protein or polysaccharide (complex sugar), which prevents other substances in the diet from binding them before they can be absorbed by the horse. Don’t worry!!! The levels of polysaccharides used for chelating minerals are EXTREMELY low and will not cause the issues discussed above.

Thus, we must consider the Ca:P ratio and intake, as well as the Cu and Zn intake in the TOTAL diet, hay and concentrate combined. Consult an Equine Nutritionist for help.

Exercise
Another important factor in preventing DOD is avoiding excessive forced exercise (like lounging for long periods). Each horse is individual in what amount of exercise it can tolerate, but if the horse’s knees are shaking after he is worked, you probably worked him too hard, and will aggravate DOD.

Research has shown that voluntary exercise is critical for normal bone development. Restriction to a stall for most of the day will contribute to the development of DOD. Afford as much free-exercise as possible for the growing horse.

Hormonal
Hypothyroidism (low thyroid hormone levels) has been correlated to DOD. Though uncommon, having a veterinarian check the DOD foal’s thyroid level may be of benefit.

We discussed above the negative effect high insulin levels, caused by high starch/sugar diets, will have on Growth hormone.

The important message here is that just assessing calories does not tell the whole story – the hormonal impact of starch and sugar need to be evaluated.

Heredity
Conditions that are inherited will affect the propensity of a horse to develop DOD. Such conditions include:

  • Rapid growth (has the highest correlation to DOD)
  • Poor conformation (upright pasterns, toed-in or out, calf-kneed etc.)
  • Fine-boned legs
  • High body weight (muscle and/or fat)
No D.O.D. ALL DEVELOPMENTAL ORTHOPEDIC DISEASE
Horses that will never have D.O.D. Horses for which D.O.D. can be prevented with well-designed diet and excellent management Horses that will have D.O.D. no matter what

See discussion of genetic theory in separate article UNDERSTANDING THE GENETICS OF INHERITED CONDITIONS IN HORSES.

Trauma
Injury to the affected leg(s), lameness in opposing leg putting pressure on the affected leg, obesity in mares leading to fetal malpositioning (foals legs bent in the mare’s uterus) can all lead to DOD.

5) Underlying Causes of DOD Syndromes

The process of cartilage maturation and ossification (turning into bone) is defective, due to one or more of the factors previously discussed.

Blood supply to the long-bones generally comes from the middle of the bone and moves towards the end of the bone. Cartilage at the growth plate, near the end of long bones, thickens and prevents adequate blood supply to deeper tissues, like the cartilage in joints, causing further tissue abnormalities or death.

Physitis

  • Growth plate does not mineralize properly
  • Growth plate widens
  • Swelling and pain occur
  • Flexural deformities may follow due to pain

Osteochondrosis (OC)

  • Abnormality of the articular cartilage
  • Can affect development of bone below (subchondral):

Can lead to:

  • Osteochondritis Dessicans (OCD) – cartilage flaps or fragments
  • Subchondral Bone Cysts (SBC) – lesions in bone below articular cartilage

Angular Limb Deformity

Asymmetrical development of growth plate (physes) or collapse of knee or hock bones

  • Congenital – foal is born with deformity; due to malposition in uterus
  • Acquired – foal is born with straight legs; deformity develops over time

Flexural Deformity

Due to pain in the limb from other DOD syndromes. Tendons may appear “contracted” but they are not. Can also be Congenital or Acquired.

  • Contracted tendons – tendons are not actually contracted!.affects coffin joint in foals & weanlings; knees & hock in older horses
  • Club foot – raised heel; hoof turned in
  • Cervical Compressive Myelopathy (CCM) “Wobblers Syndrome”
    • Swelling of vertebral bone and joints causes narrowing of vertebral canal.
    • Pressure on spinal cord causes ataxia (incoordination), base-wide stance, spasticity.
    • Most common cause of Wobbler’s in horses < 4 years old
    • Other causes of neurological signs:
      • EDM (equine degenerative myeloencephalopathy
      • EPM (equine protozoal myelitis)

6) Suggestions for Nutrition on the Breeding Farm

PREGNANT MARE

Critical components of skeletal formation begin in the first trimester:

  • Day 40: Functional elbow and stifle joints
  • Day 50: Distinct skull, ribs, hocks & fetlocks
  • Day 60: All of above continue to develop and hooves are evident

Historically, many thought that the early pregnant mare could be fed like an open mare until the last 3-4 months of gestation. Research has shown that this practice may actually predispose the foal to Developmental Orthopedic Diseases (DOD). Trace nutrients, many of which are critical to normal bone development, are stored in the liver of the developing fetus. Mares not receiving adequate nutrition during gestation may not be able to shunt enough nutrients to support the developing foal during the last trimester - the most rapid growth phase.

Special attention must be given to the diet of the pregnant mare from conception to foaling, especially for essential amino acid balance and the levels of copper, zinc and possibly manganese. Current NRC (2007) recommendations for copper and zinc are 100-125 mg and 400 mg/day, respectively. Some research suggests copper levels of 350 mg and zinc levels near 800-1,000 mg/day may reduce the incidence of D.O.D. The current NRC (2007) only addresses a single amino acid, lysine. The lysine requirements have been increased somewhat from previous publications without a correlating change to the overall protein requirement, suggesting increased attention to protein “quality” or amino acid balance instead of protein “quantity”. Researchers will learn more about other essential amino acids as our knowledge base increases.

Many pregnant mares are able to obtain enough calories from good quality forage to maintain or even gain weight. No forage, neither grass or legume, hay or pasture, will supply all the nutrients needed by the broodmare for her own maintenance much less the trace minerals needed for sound fetal development. If the mare’s diet is deficient in specific nutrients, the fetus can pull many of the nutrients it needs from the dam’s body, up to a point. This is why we generally see a lower number of nutrition-related DOD’s in a mare’s first or second foal. If the mare’s depleted body reserves are not replenished, deficiencies can occur in their future foals and eventually will affect the reproductive performance and health of the mare herself.

As stated above, some mares maintain their body weight more easily than others. Traditional feeds, designed to be fed at ¾ to 1 pound/100 pound of body weight and high in cereal grains and molasses, will often result in those types of mares becoming too fat. To keep the calories in a mare’s diet at a minimum so that she does not become obese but still assure adequate nutrition, concentrates have been formulated which contain three to five times the amount of critical amino acids, major minerals, trace minerals and vitamins found in most inexpensive horse feeds. These feeds are often called ration balancers. Pregnant mares weighing 1,000 pounds can be fed a minimum of two (2) pounds per day of this type of product. This can supply the nutritional equivalent of six (6) to ten (10) pounds of typical horse feed without the extra calories. Well designed ration balancers will be based on the type of forage your horse is eating (i.e. grass, grass/legume mix, or legume).

Some interesting research has been conducted at Virginia Tech on a concept termed “fetal programming”. Basically, it is attempting to define the effect of the pregnant mare’s diet on the foal’s physiology. One as yet unpublished finding was that mares fed a high non-structural carbohydrate (NSC – sugar + starch) diet tended to have foals with increased insulin resistance. This condition may predispose foals to D.O.D.

The exact definition of “low NSC” or “low sugar/starch” has not been agreed upon, but may be in the area of 15-20% in the TOTAL DIET (hay and concentrate combined). This level of NSC is very difficult to achieve in diets high in cereal grains and molasses – typical inexpensive “sweet” feeds. Most concentrates that are low in NSC are pelleted, as they must be formulated with highly digestible fiber sources, like beet pulp, soybean hulls and dehydrated alfalfa meal, and fat, in the form of soybean, flaxseed and rice oils.

The chart below shows the percent increase over maintenance for critical nutrients for the pregnant mare. Maintenance level is the 100% line (orange) and the Digestible energy (D.E.) increase with pregnancy is represented by the blue dashed line.

We see that the increase in the demand for calories (D.E. = digestible energy) is similar or less than the increases in crude protein (C.P.), lysine, calcium and phosphorous. As previously discussed, the demand for copper and zinc (yellow arrows) may also increase more than the need for calories, though it is not reflected on this chart, as the chart is based on strict NRC 2007 requirements.

Interesting comment on nutrition in pregnant mares and NSC:

Fetal Programming
Unpublished data from Virginia Tech.
Mares fed a high non-structural carbohydrate (NSC – sugar + starch) diet tended to have foals with increased insulin resistance. This condition may predispose foals to D.O.D. “Low” NSC (low sugar + starch) diet ~ 15-20% TOTAL DIET is supported.

Lactating Mares
Lactation is the most nutritionally demanding state a mature horse can be in, outside of intense race training. There is a SIGNIFICANT increase in the requirement for ALL nutrients, including energy. This is one of the reasons we often see thin lactating mares – the correct diet adjustments have not been made. Feeding high quality forage will reduce the amount of concentrate you will need to be fed per day. Having the forages analyzed and balancing the total ration based on the information will assure all nutrient requirements are met and that you are providing optimal nutrition in the most economical way.

The quantity and quality of mare's milk is primarily genetic, but her nutrition can have an important impact. It is important to make sure the mare’s daily intake of nutrients is AT LEAST equal to the nutrients she is putting out in her milk. If we do not match this nutrient input-output requirement, we cause the mare to deplete her body stores of many nutrients. This negative nutrient balance will eventually reduce the nutrients in her milk and adversely affect the foal. If the mare is not getting enough calories, she will lose weight. If she is low in other critical nutrient, unfortunately, we may not realize it until the foal begins to show poor condition, excessive condition and/or signs of D.O.D.

The amount and composition of mare’s milk also changes with the stage of lactation. Milk production gradually increases from foaling to 6-8 weeks post-foaling - so will her need for increased nutrition. After 8 weeks or so, her milk quantity and quality will gradually decline, as will her nutritional requirements. During this entire time, the foal is growing, and may be growing rapidly, so we must provide the foal a well-designed diet to provide what the mare’s milk is not. Recognizing this allows us to match the mare’s nutrition to the natural changes in her milk as well as provide the proper nutrition above what the milk is supplying to the foal in the form of a “creep feed”. (discussed later).

The chart below shows the percent increase over maintenance for critical nutrients for the mare in early lactation, in similar fashion to the previous chart.

Important to note is that the increase in the demand for calories (D.E. = digestible energy) is proportionately LESS than the increases in crude protein (C.P.), lysine, calcium and phosphorous. As previously discussed, the demand for copper and zinc may also increase more than the need for calories, though it is not reflected on this chart, as the chart is based on strict NRC 2007 requirements.

What does this mean?? It means merely feeding more of a feed designed for “all horses” or non-breeding horses WILL NOT meet the requirements of the lactating mare. The lactating mare requires a diet significantly different than one designed for other types of horses. As you will see, the same is true for young, growing horses.

Suckling Foals
As discussed above, many factors affect the amount of milk a mare produces and the nutritional composition of that milk. As the milk is the primary source of nutrition for the foal, especially in the first few weeks, the milk the mare produces has a direct effect on the growth and health of the foal.

During the early stages of lactation, the average mare will produce about 3% of her body weight per day in milk. For example, a 1,000-pound mare will produce approximately 30 pounds, or 4 gallons, of milk per day. As the mare’s milk production decreases over time, hunger encourages the foal to begin eating dry feed. The design of the feed the foal consumes is critical to it realizing its genetic potential.

Foals often show interest in solid feed at one to two weeks of age. At this time it is recommended you provide a “creep feed” in a creep feeder or in some area separate from the mare, to prevent her from stealing the foal’s feed.

Ideally, the creep feed will designed complement the mare’s milk, not to complement forages as in adult horses, as forage is a minimal part of the young foal’s diet. In addition, early in life, foals cannot effectively utilize vegetable-source protein (i.e. soybean meal, linseed meal, alfalfa), so a milk-based concentrate is best. Allowing the foal to steal the mare’s feed is unavoidable and acceptable, but the foal cannot eat enough or efficiently utilize a feed designed for an adult horse to prevent issues. The creep feed must meet the foal’s increasing mineral requirements due to growth as the mineral density in the mare’s milk decreases. After about 3 months of age, the foal can be transitioned from the milk-based feed to a more traditional vegetable-protein-based concentrate, but it must be designed with special attention to amino acid balance and levels of critical minerals and vitamins, especially calcium, phosphorous, copper and zinc.

Essential amino acid balance determines the “protein quality” of a feed. Good protein quality is required to maintain optimal, sound growth in the horse. The only amino acid currently addressed by the NRC 2007 is lysine. Though it is a good indicator of protein quality, other essential amino acids, like threonine, methionine and cystine may help improve true growth in horses. Some data exists on what the levels for these other amino acids may be, but it is not sufficient for the NRC Horse Nutrition Committee to publish a requirement. We know from other species, the balance between these nutrients is critical.

The ideal calcium:phosphorous ratio in the diet of the young, growing horse is between 1:1 and 2:1, hay and concentrate combined. Legume forages, like alfalfa and clover, may have calcium:phosphorous ratios as high as 8:1. The only way to correct this imbalance is to have the concentrate contain more phosphorous than calcium. Very few products have this unique feature. It is unlikely with average to good quality forages that either calcium or phosphorous would be deficient – imbalance is the most likely issue.

We have addressed the issue of copper and zinc levels previously. There is evidence that copper levels 3-4 times higher and zinc levels 2-3 times higher than the current NRC 2007 recommendations may help alleviate the incidence of D.O.D in many situations, especially programs with faster-growing horses. Such levels can be beneficial and are far from maximum tolerable levels, which, according to NRC 1989, are 12 times the requirement for zinc and 80 times the requirement for copper.
Other advantages of creep feeding are:

  • Reduces milk-production stress on mare
  • Provides nutrients mare’s milk does not, especially after peak lactation (6-8 weeks post-foaling)
  • Helps reduce weaning stress and weight loss and possible DOD due to faster gain after resumption of eating well.

In the case of an under-producing mare or an orphan foal, the foal may be offered a mare’s milk replacer. Signs of an under-producing mare can be an unthrifty foal, one that is not growing as expected or one showing signs of D.O.D. Some milk replacers have to be bottle fed, while others can be offered in a bucket in the stall or paddock. The milk replacer can be used in combination with a well-designed creep feed.

If you see signs of D.O.D. (i.e., physitis (swelling of the growth plate near the ankle or near other joints) or “contracted tendons”), before the foal is 8 weeks old, it may indicate the diet of the pregnant mare is not sufficient. Her program must then be changed to prevent her next foal from having these same issues. If D.O.D. symptoms occur between 8 and 16 weeks of age, the feeding program of both the lactating mare and the foal should be analyzed.

NOTE: Hair analysis to determine the adequacy of the horse’s diet has not been proven to be accurate. Analysis of blood sample for nutrients is only valid for certain nutrients (Phosphorous, copper, zinc and selenium). Others, like calcium, are subject to “homeostatic” mechanisms which maintain certain blood levels even in the face of dietary insufficiency. Thus, analysis of the ENTIRE diet, forage and concentrate, is the best method to assess your feeding program.

Weanlings and Yearlings
There are many opinions on when to wean. A complete discussion of this topic is beyond the scope of this presentation. When the decision is made to wean a foal, it is important that the foal is eating sufficient solid food to sustain its genetic growth rate. Some individuals will slow down their growth rate at 6 to 12 months, while others continue to grow rapidly. It is important to feed the horse’s physiology (which determines the growth rate), not necessarily it’s chronological age. Many yearlings grow as fast as weanlings, and must be fed a diet to support such a growth rate in a sound manner.

A common belief is that high protein diets cause D.O.D. This is not true!! Current research suggests that diets excessively high in calories, especially from NSC, can contribute to D.O.D., especially if the balance of calories to the other critical nutrients in the diet is not correct.

An approach I call “ground-up” nutrition, starts by meeting the growing horse’s non-calorie nutrient requirements – amino acids, minerals and vitamins – then adding a calorie source as needed to maintain desired body condition. This can be accomplished by feeding a ration balancer designed for the forage being fed at recommended levels.

Then, if more calories are needed for body condition, we can add oats, or more appropriately, a fat supplement or complimentary low NSC (“low starch”) product. This approach might be slightly more expensive in cost per day, but can save many times the cost in veterinary bills and lost sales value due to D.O.D.

The chart below shows the percent increase over maintenance for critical nutrients for the 6 month old growing foal.

As in the lactating mare, we again see that the requirements for crude protein, lysine, calcium and phosphorous increase faster than the energy requirement (D.E.). Young, growing horses require a specially designed diet to meet their unique needs.

With many poorly designed feeds, horses may have to be fed more to meet the requirements of non-calorie nutrients, thereby developing excess body condition and taking in high amounts of NSC, which can aggravate D.O.D. Try to keep young, growing horses in moderate flesh, body score of 5-6. Then, monitor body weight with a scale or weight tape every 2-4 weeks, so adjustments can be made as growth rate increases or decreases.

7) Summary

A. Make sure the TOTAL DIET (forage and concentrate combined) is balanced for the horse in question.

B. The key horses in a breeding program for which nutrition is critical to maintaining the individual’s health and developing sound, healthy foals:

  1. Pregnant mare beginning at conception.
  2. Lactating mare, especially in early lactation (1st 3 months).
  3. Suckling foal – “creep” feeding can provide distinct benefits.
  4. Weanling/Yearling – monitor growth rate and keep young horses in moderate body condition (body score 5-6).

C. Most likely nutrients to be imbalanced or deficient:

  1. Essential amino acids (starting with lysine).
  2. Calcium:Phosphorous ratio (especially if using legumes).
  3. Copper and Zinc levels.

D. Consult a qualified EQUINE nutritionist to help balance diets and adjust to problem situations.

References
Kronfeld DS, Meachem TN, Donoghue S. Dietary aspects of developmental orthopedic disease in young horses. Vet Clin North Am Equine Pract 1990; 6:451-466.
Lewis, L.D., 1995. Equine Clinical Nutrition: Feeding and Care, Williams and Wilkins, Media, PA.
National Research Council, 1989. Nutrient Requirements of Horses. 5th edition. National Academy Press, Washington D.C.
Pass MA, Pollitt S, Pollitt CC. Decreased glucose metabolism causes separation of hoof lamellae in vitro: a trigger for laminitis? Equine Vet J 1998; 26:133-138.
Ralston SL. Hyperglycemia/hyperinsulinemia after feeding a meal of grain to young horses with osteochondritis dissecans (OCD) lesions. Pferdeheilkunde 1996; 12:320-322.
Thompson, K.N., 1997.Basic Equine Nutrition and Its Physiological Functions, American Association of Equine Practitioners.
Thompson, K.N., 1997. The Veterinarian’s Practical Reference to Equine Nutrition, American Association of Equine Practitioners.
Proceedings of the Illinois State Veterinary Medical Association Winter Equine Meeting 2011

D.J. Burke, Ph.D.