Medicine Lecture 5th Stage 11-12-2017 Dr.Osamah Muwafk
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HYPOMAGNESEMIC TETANY OF CALVES
Etiology:
1. Inadequate in the dietary intake of magnesium
Epidemiology:
1. The disease is not common
2. Cases may occur sporadically
3. a number of deaths may occur on one farm within a short period of
time
4. occurs in calves 2 to 4 months of age
5. It is most likely to occur in calves being fattened for veal
6. Milk has low concentrations of magnesium.
7. A milk diet provides adequate magnesium for the requirements of a
growing calf up to a body weight of approximately 50 kg
8. the efficiency of magnesium absorption in intestine decreases from
87% to approximately 30% at 3 months of age
9. diarrhea can decrease the efficiency of absorption
10. young calves can mobilize body stores of magnesium in skeleton
11. occur in calves on milk replacer because of chronic scours and the low
magnesium content of the replacer
12. A significant loss of magnesium in the feces also occurs in calves
allowed to chew fibrous material, such as bedding; the chewing
stimulates profuse salivation and creates greater loss of endogenous
magnesium
Pathogenesis:
1) On affected farms, calves are born with normal serum magnesium
concentrations of 2 to 2.5 mg/dL
2) the concentrations fall gradually in the succeeding 2 to 3 months,
often to below 0.8 mg/dL
3) Magnesium deficiency inhibits the release and action of parathyroid
hormone, and this is thought to be the genesis of the concurrent
hypocalcemia
Medicine Lecture 5th Stage 11-12-2017 Dr.Osamah Muwafk
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4) Tetanic convulsions occur
Clinical Findings:
a) the calves are apprehensive
b) show agitation and retraction of the eyelids when approached
c) hypersensitive to all external stimuli, but they show no tetany
d) fine muscle tremors appear, followed by kicking at the belly
e) frothing at the mouth, and spasticity of the limbs
f) Convulsions follow, beginning with stamping of the feet, head
retraction, chomping of the jaws, and falling
g) During the convulsions the following signs are present:
1) Jaws are clenched
2) Respiratory movements cease
3) There are tonic and clonic movements of the limbs
4) There is involuntary passage of urine and feces
5) There are cycles of protrusion and retraction of the eyeballs
h) The pulse rate rises to 200 to 250/min
i) the convulsions disappear terminally
j) The pulse becomes impalpable, and cyanosis appears before death
k) Older calves usually die within 20 to 30 minutes of the onset of
convulsions, but young calves may recover temporarily only to
succumb to subsequent attacks
Clinical Pathology:
1. Serum magnesium concentrations below 0.8 mg/dL (0.33 mmol/L)
indicate severe hypomagnesemia
2. Erythrocyte magnesium concentrations are also low, indicating a
chronic deficiency
3. Values below a ratio of 70 : 1 for calcium : magnesium may be
regarded as normal, and those above 90 : 1 are indicative of severe
magnesium depletion
4. An incidental change is the marked increase in serum creatinine
kinase activity in calves after an acute attack of hypomagnesemic
tetany
Medicine Lecture 5th Stage 11-12-2017 Dr.Osamah Muwafk
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Necropsy Findings:
1. calcification of the spleen and diaphragm
2. calcified plaques are present in the aorta and endocardium, together
with hyaline degeneration and musculature
DIFFERENTIAL DIAGNOSIS
1) Acute lead poisoning
2) Enterotoxemia caused by Clostridium perfringens type D
3) Polioencephalomalacia
4) Tetanus
5) Vitamin A deficiency
6) Meningitis
TREATMENT:
a) Response to magnesium injections (100 mL of a 10% solution of
magnesium sulfate) is only transitory because of the severe depletion
of bone reserves of magnesium.
b) This dose provides only a single day’s requirements.
c) A magnesium sulfate enema in warm water (containing 15 g of
magnesium sulfate) was associated with a rapid response in
hypomagnesemic 3-month-old calves
d) Follow-up supplementation of the diet with magnesium oxide or
carbonate
e) Chloral narcosis or tranquilization with an ataractic drug may be
essential to avoid death as a result of respiratory paralysis during
convulsions
Control:
1. The provision of hay that is high in magnesium, such as alfalfa, helps
to prevent the disease, as will well-formulated concentrates
2. If begun during the first 10 days of life, supplementary magnesium
feeding will prevent excessive drops in serum magnesium