PG . 40
AQHA HORSE HEALTH
is an indication of growth , it is not sensitive enough to reveal the effects of lowered amino acid absorption on skeletal or muscle development and gives no indication of body composition . Height is more indicative .
Recently a connection has been found between OCD and insulin levels after feeding . Diets high in energy and containing sweet feed or other high sugar concentrate increase the incidence of DOD . These diets can cause high blood glucose , insulin and acid levels for up to 4 hours after feeding . Foals of mares fed high starch / sugar feeds have been found to be relatively insulin resistant / glucose intolerant between 3 and 12 months of age – the most common age for OCD lesions to develop . At risk foals should be fed diets based on fibre and oil plus a low starch , nutrient-dense balancer to reduce the risk of lesions developing . A recent study of 300 Thoroughbreds , Quarter Horses , Warmbloods and mixed-breeds found over 22 % of even normal , healthy horses are unable to regulate their blood glucose and insulin levels .
However , dietary changes have not totally eliminated DOD . Many cases of OCD are likely the result of excessive biomechanical force on the developing cartilage . These forces disrupt the blood supply to the cartilage and prevent its conversion to bone . Possible reasons why the cartilage does not withstand these forces include :
• specific joints have ‘ windows of vulnerability ’, for example , hocks are most vulnerable from birth to 3 months of age , stifles from 5 to 8 months – even though in both cases lameness and swelling may not be seen
• foals with a genetic predisposition for rapid skeletal and muscle development may develop greater muscle mass than the rapidly growing bone can support – genetics is thought to contribute 25 % of the risk for DOD , management 75 % ie genetics ‘ loads the gun ’ and the environment ‘ pulls the trigger ’
• foals can quickly become fat if overfed and this can overload the joints
• conformation defects can lead to uneven and abnormal loading of the joint surface .
• foals that have their exercise-restricted due to illness have reduced bone density and when returned to pasture the bone is not strong enough to support a normal amount of exercise and the joint cartilage collapses .
• sudden changes in exercise patterns can lead to fatigue and joint overload .
• for each joint , there are windows of susceptibility and risk during which dietary factors and growth rates ( weight and height ) may play key roles . Lesions of osteochondrosis are formed in a very limited window of time , namely the period when the epiphyseal cartilage is supplied by vulnerable blood vessels . Prophylactic measures , therefore , should be focussed on the times of joint vulnerability .
SUMMARY OF RISKS FOR HOCK AND STIFLE LESIONS HOCK • Higher birth weight
• Higher daily weight gain
• High daily weight gain in the 4 weeks before lesons found
• 5kg heavier at 25 days
• 14kg heavier at 6 months old
• Intermittently upright ( contracted tendons )
STIFLE • Taller at birth
• 5.5kg heavier at 25 days
• 17kg heavier at 4 months
• Rapid height increase between 3 and 5 months old
• Heavier at 3 and 5 months old
Foals needing micromanagement include : ( 1 ) higher birth weight and / or height ( 2 ) fast average daily and monthly gains in height and weight ( 3 ) colts ( 4 ) foals out of / by a mare / stallion that have previously had a Wobbler foal ( 5 ) foals by a stallion that had sired a Wobbler ( 6 ) larger , heavier or more heavily muscled than average foals ( 7 ) very valuable foals
Recent international research has found a link between OCD and magnesium deficiency in growing horses . Supplementing foals with magnesium from birth to 12 months of age resulted in a 50 % reduction in OCD of the hock and fetlock at 5 months of age and a 14 % reduction in stifle OCD at 12 months of age .
A balanced diet providing the correct amount and ratio of minerals , essential amino acids and energy will assist in preventing lesions that result from defective cartilage formation . The incidence of DOD is much higher in horses fed unbalanced diets . Correct dietary management will assist in regulating growth and preventing excess condition – especially for biomechanical-induced forms of DOD and in foals with a genetic potential for rapid growth .
The number one rule ( unless veterinary advice indicates otherwise ) is not to let the foal eat the mares feed or provide the foal with feed until it is 2-3 months old . Foals growing well on the mare don ’ t need additional feed till 2 - 3 months of age , so it is important to place mares feed bins out of reach of foals or use a nosebag for the mare ’ s feed .
From the very first steps taken by each new foal , skeletal injuries and issues can affect their future soundness . Careful management of nutrition and growth rate can pay big dividends in future soundness and longevity .
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