Clinically, rupture of the peroneus tertius is characterized by the ability to extend the hock while the stifle is flexed. This indicates a failure in the reciprocal apparatus. The rupture is usually palpable and occurs most commonly at the third of the muscle belly. There is no visible swelling associated with complete rupture unless there was a blow to the gaskin, in which case there may be swelling of the skin. If the rupture is complete the horse will exhibit no signs of pain and there will be no pain on palpation unless there is damage to the skin. Diagnosis is made through clinical signs and symptoms & ultrasonography. Treatment is stall rest for a minimum of three months with physiotherapy and a controlled exercise program to follow. Massage therapy, extracorporeal shockwave therapy, therapeutic ultrasound and laser therapy may be implemented during the convalescence period to reduce the formation of adhesions. Hypocalcemia Hypocalcemia related myopathy is commonly called or “milk fever”. The primary disorder is hypocalcemia, which is defined as a reduction in the amount of calcium ion in the bloodstream.
Causes of milk fever include decreased absorption of calcium in the GIT, decreased vitamin D absorption, lactation, stress, decrease dietary intake of Ca++ and possibly worms.
Calcium ion is essential for many body functions including the release of neurotransmitter, the contraction of skeletal muscles and cardiac muscle and the function of conductive fibres in the sinoatrial node of the heart. Myopathy associated with hypocalcemia stems primarily from the unavailability of calcium ion to trigger the release of inhibitory neurotransmitters into the neuromuscular junction. Without inhibitory signals, the skeletal muscles experience contraction similar to that seen with tetanus. If hypocalcemia progressively worsens there would be insufficient amounts of calcium to bind to the calcium binding site on the thin fibres of the contractile unit, preventing cross-bridge formation, and therefore preventing muscular contraction. Decreased ability of cardiac muscle to contract and the failure of the atria to contract simultaneously are also seen with severe or prolonged hypocalcemia. This leads to decreased blood flow, and a subsequent decrease in nutrient and oxygen delivery to the tissues. mares are more at risk of developing hypocalcemia, however hypocalcemia is considered rare in horses. Hypocalcemia may be seen with severe and prolonged malnutrition; however, the individual may die of starvation before the body has used up the calcium reserves found in bone. Clinically, hypocalcemia is seen initially as hypertonia and tetany of skeletal muscles and fasciculation of skeletal muscles, especially the masseter, temporalis and triceps muscles. Symptoms progress to include paresthesia and ataxia, cardiac arrhythmia, laryngospasm,
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