Page 243 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

218 CHAPTER 1

VetBooks.ir clinical signs, housing in an endemic area and rul- digested level of these nutrients important, but also
the relative amounts of any of these nutrients and the
ing out of other causes. ELISA titres and positive
Western blot testing are reported to be beneficial
may deliver an abnormal or impaired foal, and a
in some cases. A multiplex assay has been developed interrelations between them. A malnourished mare
by Cornell University that allows acute and chronic nursing foal may develop musculoskeletal abnormal-
infection to be distinguished. It also allows antibody ities following inadequate production of milk by the
titres from natural infection to be differentiated mare or production of milk with improper amounts
from those resulting from vaccination. of minerals or other nutrients.
DODs are thought to be caused in part by abnor-
Management mal cross-linkage of cartilage matrix and impaired
Treatment most commonly involves administration replacement of cartilage by bone as a result of copper
of tetracycline (6.6 mg/kg i/v q24 h) or doxycycline deficiency. Copper is an essential component of lysyl
(10 mg/kg p/o q12 h). Administration of ceftiofur oxidase, which is important in the cross- linking of
(2–4 mg/kg i/m q12 h) has been reported as well. collagen and elastin. Diets high in calcium and phos-
The duration of treatment may be as long as 30 days, phorus in young, growing foals have been shown to
but the rationale for this is empirical. Supportive interfere with copper and zinc absorption, adversely
treatment is occasionally indicated and may include affecting cartilage maturation, and experimental
chondroprotective agents and/or NSAIDs. Clinical zinc-responsive osteodystrophy has been reported;
signs in suspected cases have been reported to resolve however, the deficiency has not been confirmed
within 1 week of treatment. Aids in prevention of the in horses on natural feeds. Electrolyte depletion,
disease include daily grooming, application of tick mainly of sodium, potassium, magnesium and cal-
repellents containing permethrin and pasture man- cium, appears to predispose susceptible horses to
agement and care. An equine-approved vaccination exertional rhabdomyolysis, as these electrolytes play
is not yet commercially available. a key role in muscle fibre contraction. Depletion
occurs due to loss in sweat during over strenuous
MUSCULOSKELETAL exercise or as a result of dietary deficiency.
NUTRITIONAL DEFICIENCIES Horses that are fed on a diet high in phospho-
rus and/or low in calcium, with a phosphorus/cal-
Definition/overview cium ratio of 3:1 or more, may develop nutritional
Nutrition has a major role in the proper develop- secondary hyperparathyroidism. Feeding excessive
ment and function of the musculoskeletal system. amounts of wheat bran may be associated with the
Imbalanced nutrition affects horses of all ages and condition because of its high content of phospho-
disciplines, starting from the embryo, through rus. Grains with a high phosphorus/calcium ratio
the foal and growing horse stage, to the adult. may result in excessive absorption of phosphorus
Conditions that may occur as a result of these defi- and reduced absorption of calcium. Various pastures
ciencies include nutritional secondary hyperpara- contain high contents of oxalate, which binds cal-
thyroidism, OCD and/or any of the developmental cium and predisposes to the condition. This imbal-
orthopaedic diseases (DODs), exertional rhabdomy- ance leads to hyperphosphataemia, which stimulates
olysis, and white muscle disease. parathyroid hormone (PTH) secretion and inhibits
the synthesis of the active form of vitamin D in the
Aetiology/pathophysiology kidney. As a direct result of this osteoclastic activity
Nutrients suggested to affect the musculoskeletal is increased, resulting in excessive bone resorption
system when deficient include: electrolytes such as and bone loss.
sodium, potassium, calcium and magnesium; miner- Nutritional myodegeneration (white muscle dis-
als such as calcium and phosphorus; trace minerals ease) is due to inadequate selenium intake by a dam
(copper, zinc and selenium); vitamins (A, D and E); during pregnancy or lactation, hence this condition
protein; and digestible energy. Not only is the actual is most common in foals up to 60 days of age but