HYPOMAGNESEMIC
TETANY
(LACTATION TETANY,
GRASS
TETANY, GRASS
STAGGERS,
WHEAT PASTURE
POISONING)
Tetany associated with depression of serum
magnesium levels is a common occurrence in
ruminants and divided into 2 type:
1-LACTATION TETANY((Grass Tetany))in which
there may be a partial dietary deficiency of Mg
,but nutritional or metabolic factors reduce
the availability of increase body loss of Mg.
2-HYPOMAGNESEMIC TETANY OF CALVES : In
which there is a deficiency of Mg in the diet.
LACTATION TETANY
((Grass Tetany))
It is highly fatal disease of all
classes of ruminant, and reaches
it is highest incidence in lactating
cows characterized by
Hypomagnesaemia
Hypocalcaemia
Tonic –clonic muscular spasms
Convulsions and death due to
Respiratory failure .
Etiology
1-Short period of Starvation.
2-High level of K + in green cereal crops.
3- Young Green Grass has lower Mg content.
4-Heavy application of fertilizers rich in potassium and
Nitrogen .
5-Pasture containing less than 0.4 Mg of the dry matter
is likely to cause Hypomagnesaemia.
6-Diarrhea (decrease absorption).
7-There is a close association bet. Climatic condition
and serum Mg levels in animals exposed to cold wet
windy weather (cold increase urinary excretion of
Mg).also there is a possible role of hyperthyroidism in
the production of seasonal hypomagnesaemia.
Epidemiology
Occur mostly in cattle grazing on lush grass in
spring and animal grazing on wheat pasture
.the incidence of the disease varies from year
to year depending largely on climatic
condition and management , the morbidity
rate 12% in individual herds and up to 2% in a
particular area,
The mortality is high because of the short
course and may reach 20%.
PATHOGENESIS
Most clinical cases of the disease have serum magnesium
levels below 1 mg/dL compared with the normal levels in
cattle of 1.7-3 mg/dL seasonal hypomagnesemia
Magnesium has many influences on Impulse transmission
at the neuromuscular system, including effects on the
release of acetylcholine, on the sensitivity of the motor end
plate, on the threshold of the muscle membrane and on
activation of the cholinesterase system.
the increase excissive muscular contraction are duo to
facilitation of transmission of impulses through the
neuromuscular system the Mg levels in CSF are greatly
decreased and suggested centeral effect on the brain.
Clinical Signs
Acute lactation tetany
Sub acute lactation tetany
chronic lactation tetany
Acute lactation tetany
The animal may be grazing at the time and
suddenly cease to graze, adopt a posture of
unusual alertness and appear uncomfortable;
twitching of the muscles and ears is also evident.
There is severe hyperesthesia and slight
disturbances precipitate attacks of continuous
bellowing, frenzied galloping, and occasionally
aggression.
The gait becomes staggering and the animal falls
with obvious tetany of the limbs, which is rapidly
followed by clonic convulsions lasting for about a
minute.
During the convulsive episodes there is:
a- Opisthotonos
b- Nystagmus
c- Champing of the jaws
d- Frothing at the mouth
e- Pricking of the ears
f- Retraction of the eyelids.
The temperature rises to 40-40.5°C after severe
muscle exertion; the pulse and respiratory rates are also
high.
Death usually occurs within 5-1 h and the mortality rate
is high because many die before treatment can be
provided. The response to treatment is generally good if
the animal is treated early.
Subacute lactation tetany
the onset is more gradual ,Over a period of 3-4 days, there
is slight inappetence, exaggerated limb movements.
The cow often resists being driven and throws her head
about as though expecting a blow. Spasmodic urination and
frequent defecation are characteristic.
The appetite and milk yield are diminished and ruminal
movements decrease. Muscle tremor and mild tetany of the
hindlegs , straddling gait and trismus.
Animals with this form of the disease may recover
spontaneously within a few days or progress to a stage of
recumbency with a similar but rather milder syndrome than
in the acute form. Treatment is usually effective but there is
a marked tendency to relapse .
chronic lactation tetany
Many animals in affected herds have
low serum magnesium levels but do
not show clinical signs.
A few animals do evidence a rather
vague syndrome including dullness,
unthriftiness and indifferent appetite
and may subsequently develop one
of the more obvious syndromes.
Parturient paresis with hypomagnesemia
This syndrome is described under parturient
paresis and consists of paresis and circulatory
collapse in an adult cow which has calved
within the preceding 48 h but in which dullness
and flaccidity are replaced by hyperesthesia
and tetany.
CLINICAL PATHOLOGY
Normal serum magnesium concentrations are 1.7-3 mg/dL
These levels in cattle are often reduced in seasonal subclinical
hypomagnesemia to between 1 and 2 mg/dL but risk for tetany
is not present until the level falls to below 1.2 mg / dL.
Total serum calcium levels are often reduced to 5-8 mg/dL and
this may have an important bearing on the development of
clinical signs.
Serum inorganic phosphate levels may or may not be low.
Estemation of Mg level in serum , urine , CSF,and also
estimation of serum Ca level.
Differential Diagnosis
.
Cattle
• Acute lead poisoning
• Rabies
• Nervous ketosis
• Bovine spongiform encephalopathy.
Sheep
• Hypocalcemia
• Phalaris poisoning
• 'Stagger' syndromes.
TREATMENT
1-lV administration of preparations containing
magnesium or magnesium and calcium are
used.
2- . lV chloral hydrate may be administered to
reduce the severity of Convulsions during
treatment with magnesium. (e.g. 500 mL of a
solution containing 25% calcium
borogluconate and5%magnesium
hypophosphite for cattle,50 mL for sheep) lV
3-followed by a S/C injection of a
concentrated solution of a magnesium salt
50% (200 ml for Cattle and 20ml for sheep).
CONTROL
1-Daily Feeding of magnesium supplements
120 g is safe and effective but 180 g daily
may cause diarrhea. The dose for sheep is 7 g
daily or 14 g every second day.
2-The objective is to place a heavy 'bullet' of
magnesium in the reticulum from which site it
constantly liberates small amounts of
magnesium - about 1 g/d.
3-Top dressing of pasture and Foliar dusting
and spraying
4-Provision of shelter.