The Role of Nutrition in Developmental Orthopedic Disease: Nutritional Management

Chapter 55The Role of Nutrition in Developmental Orthopedic Disease


Nutritional Management



Joe D. Pagan


Nutrition may play an important role in the pathogenesis of developmental orthopedic disease in horses. Deficiencies, excesses, and imbalances of nutrients may result in an increase in the incidence and severity of physitis, angular limb deformity, wobbler syndrome (wobbles), and osteochondrosis.



Nutritional Factors as a Cause of Developmental Orthopedic Disease



Mineral Deficiencies


A deficiency of minerals, including calcium, phosphorus, copper, and zinc, may lead to developmental orthopedic disease. Most commonly fed cereal grains and forages contain insufficient quantities of several minerals. A ration of grass hay and oats supplies only 40% and 70% of a weanling’s calcium and phosphorus requirements, respectively, and less than 40% of its requirements for copper and zinc (Table 55-1). The best method of diagnosing mineral deficiencies is through ration evaluation. Blood, hair, and hoof analysis is of limited usefulness.



TABLE 55-1 Mineral Requirements for Weanlings

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Mineral Excesses


Horses can tolerate fairly high levels of mineral intake, but excesses of calcium, phosphorus, zinc, iodine, fluoride, and heavy metals, such as lead and cadmium, may lead to developmental orthopedic disease (Table 55-21,2).


TABLE 55-2 Toxic Mineral Levels*











































MINERAL MINERAL LEVEL NEEDED BY YOUNG HORSE (PPM) TOXIC LEVEL (PPM)
Zinc 60-70 9000
Iodine 0.2-0.3 5
Fluoride — 50
Lead — 80
Selenium 0.2-0.3 5
Manganese 60-70 4000
Copper 20-30 300-500
Cobalt 0.1 400
Iron 125 5000

* Adapted from Cunha TJ: Horse feeding and nutrition, ed 2, Orlando, 2007, Academic Press1; and National Research Council: Nutrient requirements of horses, ed 6, Washington, DC, 2007, National Academies Press.2


Mineral excesses occur because of overfortification or environmental contamination. Massive oversupplementation of calcium (>300% of required amount) may lead to a secondary mineral deficiency by interfering with the absorption of other minerals such as phosphorus, zinc, and iodine. Excessive calcium intake may be compounded by using legume hays as the primary forage source. Iodine and selenium oversupplementation occurs if supplements are fed at inappropriate levels. A ration evaluation is the best way to identify this type of mineral imbalance.


Environmental contamination is a more likely cause of developmental orthopedic disease, because contamination may result in extremely high intakes of potentially toxic minerals. If a farm is experiencing an unusually high incidence of developmental orthopedic disease or if the location and severity of skeletal lesions are abnormal, environmental contamination should be investigated. Blood, feed, and water analysis should be performed. Chemical analysis of hoof and hair samples may reveal valuable information. Farms that are located near factories or smelters are most at risk, although osteochondrosis caused by zinc-induced copper deficiency has been reported on farms using fence paint containing zinc or galvanized water pipes.



Mineral Imbalances


The ratio of minerals may be as important as the actual amount of individual minerals in the ration. High levels of phosphorus inhibit the absorption of calcium and lead to a deficiency, even if the amount of calcium present is normally adequate. The calcium/phosphorus ratio in the rations of young horses should never be below 1 : 1 and ideally should be 1.5 : 1. Too much calcium may affect phosphorus status, particularly if the level of phosphorus is marginal. Calcium/phosphorus ratios greater than 2.5 : 1 should be avoided if possible. Forage diets with high calcium levels should be supplemented with phosphorus. The zinc/copper ratio should be 3 : 1 to 4 : 1.



Dietary Energy Excesses


In the Thoroughbred (TB) industry, large, well-grown yearlings are desirable when offered for sale at public auction because selling price is influenced by body size. Yearlings that sold higher than the median of the session in which they were sold were heavier and taller than yearlings that sold below the session median.3 In addition, TBs that were heavy and tall as yearlings had the most earnings, graded stakes wins, and grade-1 stakes wins.4 Because of the premium price paid for mass, young TBs are often grown rapidly to achieve maximal size. Excessive energy intake can lead to rapid growth and increased body fat, which may predispose young horses to developmental orthopedic disease. A Kentucky study showed that growth rate and body size might increase the incidence of certain types of developmental orthopedic diseases in TB foals.5 Yearlings that showed osteochondrosis of the hock and stifle were large at birth, grew rapidly from 3 to 8 months of age, and were heavier than the average population as weanlings.


The source of energy for young horses also may be important, because hyperglycemia and hyperinsulinemia have been implicated in the pathogenesis of osteochondrosis.6,7 Foals that experience an exaggerated and sustained increase in circulating glucose or insulin in response to a carbohydrate (grain) meal may be predisposed to develop osteochondrosis.8


In a large field trial, 218 TB weanlings (average age 300 ± 40 days, average body weight 300 ± 43 kg) were studied.8 A glycemic response test was conducted by feeding a meal that consisted of the weanling’s normal concentrate at a level of intake equal to 1.4 g of nonstructural carbohydrate per kilogram of body mass. A single blood sample was collected 120 minutes after feeding to determine glucose and insulin levels. A high glucose and insulin response to a concentrate meal was associated with an increased incidence of osteochondrosis. More research is needed to determine whether the incidence of osteochondrosis can be reduced through feeding foals concentrates that produce low glycemic responses.



Ration Evaluations


The best way to determine whether nutrition is a contributing factor to developmental orthopedic disease is to perform a ration evaluation, which compares the intake of several essential nutrients with the requirements of the horse. Gross deficiencies or excesses of key nutrients then can be identified and corrected. In the past, ration evaluations were time-consuming and cumbersome, because much of the mathematical calculation was done by hand. Fortunately computer programs are now available that make ration evaluations quick and easy to interpret. Kentucky Equine Research (Versailles, Kentucky, United States) has developed an equine ration evaluation program called MicroSteed (www.ker.com).



Types of Evaluations


Ration evaluations can be approached in two ways. One way is to add up what is being fed and compare it with the horse’s requirements. This may not be easy because most horse owners do not know exactly what their horses are eating. Alternatively, a new ration may be developed.



Protocol


Every nutrition evaluation should include a description of the horse, definition of nutrient requirements, determination of nutrients in feedstuffs, determination of intake of feedstuffs, calculation of nutrient intake, comparison of intake with requirements, and adjustment of the ration to correct deficiencies or excesses.



Describing the Horse


Different classes of horses have different nutrient requirements, and each class may eat different amounts of forage and grain. Within each class of horse, it is important to know the horse’s current body weight, its age and mature body weight if growing, and its rate of body weight gain or loss.



Defining Nutrient Requirements


Ration evaluations are intended to compare a horse’s daily nutrient intake with a set of requirements to determine how well the feeding program meets the horse’s nutritional needs. The National Research Council (NRC) publishes a set of requirements for horses, but NRC values generally represent minimum requirements for most nutrients. These are the levels of intake that are required to prevent the onset of clinical signs associated with frank deficiency. No allowances are included to account for factors that may increase the requirement of a nutrient. The bioavailability of nutrients may be different, and other substances within a ration may interfere with the digestibility or use of a nutrient.


MicroSteed includes two different sets of nutrient requirements—the NRC and Kentucky Equine Research requirements—based on a combination of NRC numbers, research conducted since publication of the most recent NRC recommendations, and experience in the field. The user has the option of selecting NRC or Kentucky Equine Research requirements or adding a custom set of requirements.


NRC values for digestible energy and protein fairly accurately describe the needs of most horses. These two requirements were primarily developed from direct measurements of growth response and energy balance. Other requirements, such as those for calcium and phosphorus, were developed using more theoretical calculations involving estimates of endogenous losses and digestibility. Still others were based on values developed for other species or from single experiments that were far from conclusive. Kentucky Equine Research requirements use values ranging from 1.25 to 3 times those recommended by the NRC for most vitamins and minerals. These nutrient requirements are not absolute, but it is assumed that they adequately reflect horses’ needs under a wide range of conditions.



Determining Nutrients in Feedstuffs

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Jun 4, 2016 | Posted by in EQUINE MEDICINE | Comments Off on The Role of Nutrition in Developmental Orthopedic Disease: Nutritional Management

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