Metabolic Disease With Neuro Signs Flashcards
What is the aetiology of hypomagnesaemia?
- Multifactorial, related to Mg in diet and presence of competing cations (K, Na)
- No feed back mechanism to control Mg concentration, Mg excess excreted in urine
- Main absorption in forestomachs, increases with Na:K ration >5:1
- Alteration in CNS and peripheral nerve function
- There are reserves in bone but there is poor short term mobilisation
- Chronic hypomagnesaemia increases chances of hypocalcaemia
- Sheep; similar, but not as common
- Calves; similar not as common
- Morbidity 2-12%
- Mortality approx. 30%, higher in beef (due to short course of disease, 5-10 hours)
- Important disease for beef and dairy farmers
Name risk factors of hyppomagnesaemia
- lush pastures which have received large applications of fertilizers containing high levels of nitrogen and potassium, ammonia in rumen impairs Mg absorption
- Bucket fed calves (milk is low in Mg)
- (Silage from) Pastures low in Mg, generally poor quality pasture
- Pasture species, season, soil type, climate, DMI etc
- Risk period: peak lactation/late pregnancy
- Most common is a combination of factors: inadequate energy intake, low Mg content, cold, wet ,windy weather
Name clinical signs of hypomagnesaemia
- Tetanic muscle spasms
- Whole body tremor
- Bellowing
- Aggressive
- Blindness
- Elevated pounding heart rate
- Hypertonicity and seizures (vs flaccid muscles and recumbency in hypo Ca)
- Hyper alertness, hyper responsiveness, hyperesthesia
- Eventually animals fall on their side in convulsions
- Sudden death after excitement / therapy
- Frothing at the mouth
- Retraction of eyelids
- Pricking of the ears
- Nystagmus
- Opisthotonus
- Elevated heart rate and strong
Name 3 differentials for hypomagnesaemia (4)
- Acute lead poisoning
- Rabies
- Nervous ketosis
- BSE
How can we diagnose hypomagnesaemia?
- Clinical signs and history
- Serum Mg reference range 1.7-3 mg/dL (tetany average 0.5 mg/dL)
- Response to Tx
- Sometimes concurrent hypocalcaemia
- Aqueous humour or cerebrospinal fluid magnesium concentration, even up to 12h post mortem
- Non-specific necropsy findings
How can we treat hypomagnesaemia?
- Safest general recommendation: 400ml Ca-Mg bottle, 50 ml for sheep
- Combined with SC concentrated solution of Mg salt
- IV magnesium salts can be dangerous: cardiac dysrhytmias, medullary depression, respiratory failure
How can we prevent hypomagnesaemia?
- Prophylactic oral therapy (biological availability for Mg carbonate, Mg oxide, Mg sulfate is 44%, 51% and 58% respectively)
- Top dressing pasture, daily drenching, dusting, spraying, provision in drink water, magnesium buckets
- Intraruminal Mg bolus
What is staggers?
Hypomagnesaemia
What does chronic hypomagnesaemia increase the chance of?
Hypocalcaemia
What causes the signs of hypocalcaemia?
•Decreased calcium ions at the axonal membrane initially result in tetany, ultimately there is enough of a loss of calcium at the neuromuscular synaptic membranes so as to reduce acetylcholine release causing degrees of paralysis. Cattle appear to be more susceptible the neuromuscular blockade, that masks the tetany seen only very early in the course of disease.
A) What is the effect of hypocalcaemia on the heart?
B) What causes the effect on heart rate?
A) Tachycardia and weak heart rate
B) Low calcium and the heart muscle doesn’t function as well and the contraction isn’t as good. So the heart rate increases to keep the pressure up.
What is nervous ketosis?
Hypogylcaemia
What is the aetiology of hypoglycaemia?
- Multifactorial
- Disease in cattle and sheep occur in different parts of pregnancy-lactation cycle
- Energy balance; inadequate nutrition
- Cattle respond readily to treatment, sheep highly fatal
- Excess ketone bodies (see lecture Yr 2 GI)
- Prolonged course (several days) results in evident brain lesions: cerebro-cortical neuronal necrosis
- Possible effects (hypo-glycaemic encephalopathy) on fetuses of affected ewes
- Neonatal large animals (starvation, cold exposure, other diseases)
Name clinical signs of hypoglycaemia
- Muscle weakness
- Tremor
- Head pressing
- Compulsive licking (self/objects)
- Ataxia
- Blindness
- Hyperesthesia
- Anorexia
- Drop in milk
- Opisthotonus / stargazing
Name 3 differentials of hypoglycaema in cattle (4)
- Rabies
- Hypomagnesaemia
- BSE
- Lead poisoning