Macrominerals Flashcards
What conditions can magnesium deficiency lead to?
Staggers
Grass tetany
When does Mg deficiency arise?
Why is it more likely?
When high demand is combined with decreased intake
Little homeostatic regulation of magnesium in ruminants
What management factors can result in low Mg?
Low Mg in the diet (e.g. fed on fresh grass)
Poor feed intakes (when raining)
Poor absorption of the Mg due to:
- increased intake of positive ions - K (DCAB) or N
- Increased passage rate through gut (e.g lush pasture, low fibre)
What clinical signs are associated with acute magnesium deficiency?
Hyperaesthesia Ears twitching Sensitive to sound / hand clap Staggers and collapses Champing of jaws Sudden death Increased heart rate
What is meant by the term hyperesthesia?
Increased sensitivity to stimuli
What clinical signs are associated with subacute magnesium deficiency?
Slow onset Spasmodic urination and defaecation Muscle tremor Staggering gait Increased heart rate
Could be more vocal than normal
What clinical signs are associated with chronic magnesium deficiency?
Few signs
Poor appetite
Depressed milk yield
Increased heart rate
How can magnesium deficiency be treated?
URGENT
IV Ca borogluconate with magnesium hypophosphate - SLOWLY
- typically into mammary vein
Magnesium sulphate 25% SC ONLY
How can Magnesium deficiency be prevented?
Mg NOT PALATABLE
MgO in concentrates, mix w/ molasses
Mg oral bolus
Mg tablets/flakes added to drinking water
Avoid K fertiliser (or pig manure) if hypomag known problem
What are some other names for hypocalcaemia?
Milk fever
Acute flaccid paralysis
Bovine Parturient Paresis
What is the relationship between Ca and Mg?
Mg required as a cofactor at several stages of Ca homeostasis
- D3 and parathyroid hormone release
What is the biggest store of calcium in cows?
Where else is it absorbed?
Bone
GIT
Kidney
What are the homeostatic regulators of Calcium?
PTH - increases Ca2+ resorption in kidney, increases D2 to D3 conversion for increased absorption in SI, increased Ca2+ from bone
Vitamin D3 (converted in kidney) - increases absorption from GIT
Calcitonin - UNCERTAIN ACTION - normally reduces blood Ca2+, rare that it is too high in a cow.
What might you observe in a cow with subclinical hypocalcaemia?
Able to stand Hypersensitivity Excitable Tremors Ear twitching Ataxia Bloat
Why is hypocalcaemia associated with bloat?
How can this progress?
Smooth muscle responds faster to decreased calcium concentrations
There is stasis in the gut
Therefore eats less, less calcium taken in, CLINICAL HYPOCALCAEMIA
How can the transition from dry to milking affect the calcium levels of cows?
Dry cows don’t need as much Ca2+ therefore there is a low rate of absorption
When she starts producing colostrum, she will quickly start draining calcium and it takes time for the rate of absorption to catch up
This leads to a NEGATIVE CA2+ BALANCE
How might a cow with clinical hypocalcaemia present?
Recumbent - sternal recumbency S shaped neck Depressed Dry muzzle Cold extremities Bloat No Defaecation Delayed / Absent PLR
Why might hypocalcaemic cows be slightly cold to touch ?
Not moving (as much) therefore don’t generate as much heat
How would a cow with severe hypocalcaemia present?
Reduced consciousness Lateral recumbancy Unresponsive to stimuli Muscle flaccidity Reduced CO Bloat Death
How would you treat hypocalcaemia?
What do you need to be careful of?
20/40% Calcium Borogluconate
Maxacal
Mg, P, Glucose
IV - SLOW don’t want hypERcalcaemia, monitor heart rate
SC- deposit to prevent recurrence
(SIT ANIMAL UP)
What are some signs that a hypocalcaemic cow is recovering ?
Passes dung and eructation
Shows smooth muscle is starting to work.
Why might fat cows become hypocalcaemic?
Mobilising fats so eat less
Therefore less Ca2+ in
Why might old cows be more likely to get hypocalcaemia?
Lower reserves in bone
Why would you NOT drench hypocalcaemic cows?
Poor smooth muscle action
Don’t swallow properly
ASPIRATION OF DRENCH
How can you prevent hypocalcaemia in the herd?
Low Ca in dry cow ration, high Ca in milking ration
Magnesium,
DCAB
Drench at calving,
Bolus just before calving
What is a typical presentation for phosphorous deficiency?
‘Happy downer’
No response to Calcium injection
How would you treat a phosphorus deficiency?
Foston IV
What does DCAB stand for?
Dietary Cation Anion Balance
What cations and anions do DCAB balance?
Cations: Na+ and K+
Anions: Cl- and S2-
What is the goal of DCAB?
To provide excess anions over cations
(Na+K) - (Cl+2S) should = -100 to -200
Decreases pH of blood
PTH more effective
Which cows should DCAB be fed to?
DRY cows
How does DCAB work?
By feeding more negative ions, we create a metabolic ACIDOSIS as more H+ is produced to balance the charge.
Decreased pH causes a conformational change in PTH receptors making it more effective
Calcium homeostasis regulated more effectively so fewer problems around calving
How can a DCAB be implemented?
REDUCE K+ intake - found in young grass, leafy
ADD anions - MgCl MgS CaCl2 NH4Cl
How can neutral compounds effect the charge balance of the animal?
Cations stay behind in the GIT so only anions absorbed
What issues are there with feeding an ionic salts?
How might these be resolved?
NOT VERY PALATABLE
- could reduce DMI and cause negative energy balance, fatty liver etc
Can be dissolved in the water (MgCl2)
Reduce grass intake to make cows more thirsty
How could you assess the metabolic status of a cow being fed DCAB?
Monitor urine pH
What is the normal urine pH of cows? Why?
8-8.5
Alkaline due to K+ in grass
What Urine pH should you aim for with DCAB cows?
5.5-6.5
NOT ANY LOWER
What are the main clinical presentations of macro mineral imbalance?
Milk fever (hypocalcaemia)
Grass staggers (Hypomag)
