Page 244 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.5 The hindlimb 219

VetBooks.ir can also occur in older animals. Although selenium Diagnosis
Commonly, the only way to diagnose and correct
and vitamin E appear to have a synergistic effect in
preventing this condition, it appears that selenium
deficiency has a more important role. nutritional deficiencies is to evaluate the ration and
water ingested. If a problem develops in a nursing
It is suggested that inadequate levels of protein in foal, it is recommended to ascertain that the mare
a mare’s diet can cause hypothyroidism in the fetus, is producing enough milk and that the composi-
which may persist postnatally and affect normal tion of the milk, especially with regard to miner-
development. This deficiency may lead to incom- als, is correct. In horses with nutritional secondary
plete ossification of the carpal/tarsal cuboidal bones, hyperparathyroidism, clinical laboratory findings
thus causing angular limb deformities (ALDs). may include mild hypocalcaemia and hyperphos-
phataemia; however, these values may be within the
Clinical presentation reference intervals. Fractional urinary clearance of
Clinical signs vary with the condition. Foals and calcium may be normal or low and that of phos-
young horses with DODs may be lame and have phorus may be normal or high. Serum PTH level
synovial effusion, swelling at the level of the phy- is increased. With an acute severe electrolyte defi-
seal growth plates or limb deformities. ALDs may ciency (e.g. after an endurance exercise), serum levels
be present at birth, but commonly occur within the of electrolytes may be below normal ranges; how-
first few weeks. Horses affected by nutritional sec- ever, in chronic deficiencies, serum concentrations
ondary hyperparathyroidism may show symmetrical may not reflect total body electrolyte imbalances.
enlargement of facial bones, upper respiratory noise In these cases, renal fractional excretion should be
and lameness, and young horses may develop physi- determined by sampling urine and blood concur-
tis and limb deformities. Bone resorption around the rently to determine creatinine and electrolyte con-
lamina dura of the molars and premolars may result centrations. Measuring of muscle enzyme levels in
in pain and masticatory problems, and in severe cases the serum of horses with exertional rhabdomyoly-
teeth may become loosened. Exertional rhabdomyol- sis is useful; however, the degree of elevation does
ysis results in a stiff and stilted gait in affected horses not necessarily reflect the severity of clinical signs.
and occasionally these animals are unable to walk. Horses suspected of having the chronic form of
The hindquarters and back muscles may be firm and exertional rhabdomyolysis can be subjected to a sub-
painful on palpation and the horse may sweat exces- maximal exercise test and muscle biopsy.
sively and have a high respiratory rate due to the
pain. The skeletal muscle form of white muscle dis- Management
ease is mainly characterised by muscular weakness There is some evidence that supplementing the
and stiffness and affected animals may be unable to mare’s diet during the last trimester with copper may
stand. Limb muscles are swollen and may be firm result in significantly fewer cases of OCD. However,
and painful on palpation. Muscle fasciculations and although supplementing the mare’s diet to improve
a stiff and stilted gait can occur in horses with hypo- milk composition may succeed, if correct balance of
calcaemia and/or hypomagnesaemia, both of which mineral is not achieved, weaning of the foal is rec-
are very uncommon. Hypothyroidism in the fetus ommended. Food analysis may prove valid as part of
may cause delayed prenatal and post-natal devel- the management of impaired endochondral ossifi-
opment, resulting in permanent stunting. Delayed cation. Treatment for nutritional secondary hyper-
ossification of the cuboidal bones of the carpus and parathyroidism requires correction of the ration by
hock is also suggested to be related to this condition. increasing calcium and reducing phosphorus intake
to the level required, and restricting access to plants
Differential diagnosis containing oxalates. Unless fractures are present,
Septic polyarthritis; neuromuscular disease; poly- lameness usually disappears within 6 weeks. The
saccharide storage myopathy; aortoiliac thrombosis; objective of treating horses with the acute form of
colic. exertional rhabdomyolysis is to reduce anxiety and