NUTRITION and OSTEOCHONDROSIS
CAN WE PREVENT OSTEOCHONDROSIS THROUGH NUTRITION?
Developmental orthopedic disease can rob a young horse of his future as a sound athlete. The consequences of diseases such as osteochondritis dissecans and angular deformities render many young horses structurally inadequate for the work for which they were intended. Over the last several years, researchers have found that appropriate nutrition of the gestating mare as well as her young offspring may decrease the risk of improper bone development, thus sidestepping developmental problems and possible unsoundness.
The nutritional requirements of a broodmare can be divided into three stages based on phase of production:
STAGE I (Early Pregnancy): The first stage begins at conception and lasts through approximately the first seven months of gestation. Barren mares and pregnant mares without sucklings by their sides also fit into this category.
STAGE II (Late Pregnancy): The second stage encompasses the last trimester of pregnancy, which is from around seven months of gestation through parturition (foaling).
STAGE III (Lactation): The final stage is lactation, a period that lasts four to six months after foaling.
The most common mistakes made in feeding broodmares are overfeeding during early pregnancy and underfeeding during lactation.
Proper feeding during pregnancy requires an understanding of fetal development during gestation.
Contrary to popular belief, the fetus does not grow at a consistent rate throughout the entire 11 months of gestation. The fetus is particularly small during the first five months of gestation and only reaches approximately 20% of its birthweight at the 7-month mark. Because this accounts for less than two percent of the mare's weight, the fetus's nutrition requirements are minuscule compared with that of the mare at this stage. Therefore, the mare can be fed essentially the same as if she were not pregnant.
Mare owners often increase feed intake after the mare is pronounced in foal, reasoning that she is now "eating for two". Increased feeding is unnecessary and may lead to obesity and foaling difficulties, especially if the mare has unlimited access to high quality pasture.
The fetus begins to develop rapidly after seven months of gestation. During this time the foal's demand for nutrition exceeds the mare's maintenance requirements. Therefore, adjustments should be made to the mare's diet during the 4 months prior to parturition (delivery).
Even though digestible energy requirements only increase about 15%, protein and mineral requirements increase dramatically during late pregnancy. This is because the fetal tissue being synthesized is high in protein, calcium, and phosphorus.
Trace mineral supplementation is critical during late pregnancy because the fetus stores these minerals (namely iron, zinc, copper, and manganese) in its liver for use post-parturition (after it's born). The fetus developed this nutritional strategy in response to a low content of these elements in mare's milk.
New Zealand researchers studied the effect of copper supplementation on the incidence of developmental orthopedic disease in Thoroughbred foals. Pregnant Thoroughbred mares were divided into two groups: copper-supplemented and control groups. Live foals born to each group of mares were further divided into similar copper-supplemented and control groups.
1) Copper supplementation of mares was associated with a significant reduction in the occurrence of developmental orthopedic problems in foals at 150 days of age. Foals from non-supplemented mares had significantly more incidence of orthopedic problems than foals out of supplemented mares.
2) Copper supplementation of the foals had NO significant effect on the incidence or severity of developmental orthopedic disease.
Mares in late pregnancy are often overfed energy in an attempt to supply adequate protein and minerals to the developing fetus. Excessive weight gain by the mare during late gestation warrants switching to a feed that is more concentrated in protein and minerals so that fewer calories are ingested on a daily basis. This will help to keep the mare at a healthier overall weight.
A mare's nutrition requirements increase significantly after parturition (foaling). During the first three months of lactation, mares produce milk at a daily rate equal to about 3% of their body weight. This milk is rich in energy, protein, calcium, phosphorus, and vitamins but contains low levels of other trace minerals (such as iron, zinc, copper, and manganese). For this reason it is tempting to supplement lactating mares with these trace minerals. However, research has shown that increasing the amount of these minerals in the lactating mare's diet does NOT significantly increase their content in the milk. Fortunately, the foal has developed the ability to store these minerals in its liver for post-parturitient use (as previously stated).
Calcium and phosphorus are not stored in high quantities in the foal's liver, however, and are instead obtained from ingesting mare's milk. It is important, therefore, to provide adequate supplementation of these minerals to the mare during lactation.
Mares in early lactation usually require from 10 to 14 pounds (4.5 to 6.5 kg) of grain per day (depending on the type and quality of forage they are consuming) to meet the sudden increase in demand. Grain intake should be increased gradually during the last few weeks of pregnancy so that the mare is consuming nearly the amount that she will require for milk production at the time of parturition. A rapid increase in grain intake should be avoided at foaling because this may lead to colic or laminitis. Milk production begins to decline after about three months of lactation, and grain intake can be reduced to keep the mare at a desirable body weight.
If the broodmare has been fed properly during late gestation, it is not necessary to provide mineral supplementation to the suckling until after it reaches 90 days of age. At this time, moderate amounts of feed can be introduced and gradually increased until the suckling is consuming around one pound (0.5 kg) per month of age. It is critical that the suckling be accustomed to eating grain prior to its weaning to avoid a dramatic decrease in growth rate. This sudden drop in growth rate is sometimes referred to as a "growth slump" or "weaning slump". When the weanling finally starts eating grain after its "slump", a compensatory growth spurt can occur that increases its predisposition to developing orthopedic disease.
THE MOST CRITICAL STAGE OF GROWTH FOR PREVENTING DEVELOPMENTAL ORTHOPEDIC DISEASE IS FROM WEANING TO 12 MONTHS OF AGE. This is the period of time when the skeleton is most vulnerable to disease and nutrient balance is most important.
Weanlings should grow at a moderate rate with adequate mineral supplementation. In temperate regions, the contribution of pasture is often underestimated, leading to excessive growth and increased risk of developmental orthopedic disease.
Once a horse reaches 12 months of age, it is much less likely to be affected by developmental diseases. Many of the lesions that clinically manifest in yearlings were formed at a younger age.
Nevertheless, proper nutrient balance remains important for the yearling. Since the skeleton is less vulnerable to developmental orthopedic disease as the yearling ages, it is best to delay increased energy intake in preparation for show conditioning or sales prepping as long as possible. No more than 90 days of increased energy intake is usually adequate prior to such an event to produce the desired effect.
Bone-related problems of the carpus (knee) are a major concern with yearlings that have been pushed for growth. To reduce the incidence of DOD in these horses, the level of trace mineral supplementation should remain high and a significant portion of the energy should come from fat and fermentable fiber instead of grain. Feed mixes for these horses can contain as much as 10% fat. Sources of fermentable fiber include beet pulp and soy hulls.