2012 season

Above: Billy Stud Youngsters

Breeding involves investing time, money and commitment and every breeder, however large or small, wants to produce sound and healthy young horses with a bright future ahead of them.

Developmental orthopaedic disease (DOD) is a term used to describe various bone and joint disorders of young horses and includes epiphysitis, angular limb deformities, contracted tendons, osteochondrosis dessicans, bone cysts and wobblers syndrome.

The bones of the unborn foal are formed from cartilage which is slowly changed into bone, this process is known as endochondral ossification. By the time the foal is born most of the cartilage will have been converted to bone, however, in the growth plates of the long bones of the limb, cartilage growth continues for approximately 18 months. When the blood supply to the cartilage is disturbed bone growth is disrupted and DOD can occur.

Several factors are involved in the incidence of DOD, including genetic predisposition, rapid growth, exercise, trauma and nutrition, however, often it is a combination of factors that leads to DOD.

Genetics

Research has identified that some stallions are producing offspring with a higher incidence of DOD than would be expected, even though the stallion himself may not be affected. Conformational defects can also place uneven stress on bones and joints. Rapidly growing and maturing breeds such as Warmbloods and Thoroughbreds are at greater risk of developing DOD, and it is thought that the foal’s muscle mass is too great for the immature skeleton to support. The same problem can also occur if foals are allowed to become overweight.

Exercise

Excessive exercise, or a lack of exercise have both been implicated as risk factors for the development of DOD. Appropriate exercise is vital for developing a strong skeleton, however, concussive trauma caused by hard ground or forced exercise such as lunging can place excessive strain on bones and joints. On the other hand, restricted exercise, such as box rest, reduces the stress placed on bones causing them to weaken, which may lead to DOD problems when the foal is turned back out again and normal exercise is resumed. Unless it is absolutely necessary, box rest should be avoided and when turn out is reintroduced this should always be done gradually.

Nutrition

Research has shown that feeds high in soluble carbohydrates (starches and sugars) are associated with the incidence of DOD. Such feeds tend to produce a high glucose and insulin response and as they are generally fed in relatively large quantities once or twice a day, this can lead to a feeding-fasting cycle which is very different to the way in which horses have evolved to eat. It is thought that the high blood glucose and insulin levels may affect cartilage growth and maturation by influencing the growth hormones. Feeds based on fibre and oil do not elicit the same glycaemic response and can still provide adequate energy and protein.

While on the subject of protein, it has long been blamed as the cause of DOD, however, numerous investigations have not found a direct link between high or low intakes of protein and DOD. Protein is required for growth and development of tissue, however, it is the quality, not quantity of the protein that is important. Essential amino acids that the horse cannot manufacture itself must be supplied by the diet. Lysine is the first limiting amino acid, and if it is not present in sufficient quantities it will affect the synthesis of other amino acids. Good quality protein sources such as soya have an amino acid profile that is easily available to the horse.

Mineral excesses and deficiencies have been cited as possible causes of DOD. Copper is involved in the synthesis of cartilage and a copper deficiency may result in weakened cartilage. Research has shown that mares supplemented with copper in late pregnancy produced significantly fewer foals with DOD. Interestingly copper supplementation of mares and foals after birth did not reduce the incidence of DOD. Supplementation of the mare during late pregnancy increases the liver copper stores of the foal ensuring that adequate levels are available to the foal during the rapid growth phase after birth. High levels of zinc can interfere with copper uptake, so it is important to ensure that the feed or supplement you are using is correctly balanced.

Calcium and phosphorous are vital for correct bone formation and high levels of phosphorous have been implicated as a possible cause of DOD. However, it is the ratio between the two that is most important, and again it is worth checking that the ratio of the product you are using is ideally 1.5:1 to 2:1 calcium:phosphorous.

DOD is a multi-faceted problem and while some aspects such as genetics may be out of the hands of the owner, nutrition is one area that it is much easier to exert control over. A well balanced diet that is low in starch and sugar and with a correct balance of nutrients will provide the young horse with the best start in life for healthy growth.

Above: A Billy Stud mare and foal