Controlling hypocalcaemia Flashcards
What is hypocalcaemia?
- Metabolic disorder
- Occurs due to net efflux of calcium from the extracellular fluid in greater quantities than the intestines or bones can replace
- Normal plasma Ca 2.1-2.8 mmol/l.
- Hypocalcaemic <2.0 mmol/l.
- Sets in usually 48-72h postpartum
How is calcium supply controlled?
- By the parathyroid gland
– mobilising calcium from the bone when blood calcium is low and mineralising or excreting it where supply is in excess. - PTH triggers calcitrol (active vit D) release from kidneys
– acts on intestines and kidneys to increase absorption.
What is calcium used for?
- muscle contraction
- immune function
- nerve impulse transmission
- bones and teeth
Effects of hypocalcaemia
- Reduce muscle contraction
- Increased neuromuscular irritability.
- Decreased smooth muscle contraction.
- Decreased skeletal muscle contraction.
- Affects posture & gait.
- Reduced cardiac muscle contractility.
- Affects function and circulation.
- Risk of mastitis is increased so sphincter muscles in teat are reduced, and she spends more time lying down, so risk of infection getting into the teat is higher.
Calcium requirements of the cow (maintenance, at calving, peak lactation, late pregnancy)
- maintenance: (650 kg cow, 20 Kg DMI), 25 g Ca/day
- at calving: 12 litres of colostrum, +30 g Ca/day, Total: 55 g Ca/day
- peak lactation: 40 litres of milk +73 g Ca/day, Total: 98 g Ca/day
- late pregnancy: Late pregnancy + 13.9 g Ca/day, Total: 38.9 g Ca/day
What hormones act to increase blood calcium?
- PTH
- Calcitrol
Risk factors
Around calving; Ca demand increases rapidly, endocrine control takes a few days to adjust.
- Resorption from the kidneys is the fastest repletion followed by increased intestinal absorption.
- Release of Ca from bone is the slowest.
Age of cow; Older cows have reduced calcium reserves and mechanisms respond slower.
Milk fever risk increases with parity as milk yield increases
- Peaking around 3-4
Other increased risk factors include;
- C-section, dystocia, BCS ≥4, hereditary.
Herd risk factors important too
- Eg, dairy crosses (Limousin x Holstein), channel island breeds, autumn calving cows.
Clinical signs of hypocalcaemia
- Skeletal muscle
- Weakness
- S-bend neck
- Smooth muscle
- Rumen atony
- GI stasis
- Poor uterine involution
- Cardiac muscle
- Poor contractility
- Slightly increased HR (c.f. “toxic” cow)
All associated with calciums role in muscle contraction.
- Tremors
– Early sign that is often missed
Treatment plan
400ml 40% calcium borogluconate slowly IV
- If given too fast inc. risk of hypercalcaemic relapse.
- Reverses physiological mechanisms.
- Halts PTH release and triggers calcitonin secretion due to surplus in blood.
- ~25%-40% relapse within 12 to 24 hours unless dose is managed.
Monitor heart rate and rhythm.
Consider blood sample in case no response.
Outcome of treatment:
- Eructation, defecation, urination & standing within ~20-30 mins
- If no response, consider alternatives and complications (e.g. “downer cow”)
Additional Ca options
Sub-cut
- Poor absorption
- Negative feedback
- Easy
- Relatively common
Oral
- Well absorbed
- Requires GI uptake
- Relatively easy
- Becoming more common
- Ensure she’s up before giving oral Ca
Additional treatment
NSAID
- 700 kg cow down
- Trauma common complication
- Why not?
Phosphorus
- P often low with milk fever
- Common preparation not active
- Should increase with Ca
Herd management: Ca restriction
- Effective nutritional management during the dry period and early lactation can decrease clinical cases to ~1%
- Restricting Ca intake during the late dry period can prevent hypoCa.
– Reduce dietary calcium to ~100g Ca/day. - Dry cows on high Ca diets reduce absorption from the diet and excrete excess.
– She cannot meet Ca demand as the mechanisms are already down-regulated. - Limiting Ca prior to calving, up-regulates PTH mechanisms
– Starts resorption from bone, increases dietary absorption etc, - Over 2-3 weeks cow is better prepared for increased demand.
- Must increase dietary Ca at calving.
- Difficult to keep Ca low enough.
- Can use Ca binder.
Herd management: Controlling DCAB
- Lowering blood pH can prevent hypocalcaemia.
- This is achieved through reducing DCAB in the dry period.
– Decrease Na+ and K+ (cations), increase Cl- and S- (anions). - Resulting slight acidosis increases binding of PTH and other effects.
- Improves the cow’s ability to mobilize calcium from the bones and to absorb dietary calcium from the small intestines.
- Must provide adequate Ca as increased mobilisation.
- Partial or full DCAB approach.
- Anionic salts can reduce palatability (↓DMI).
- Monitor for efficacy:
– urine pH using DCAB should be 6.0-6.5. - Grass can be high in K.
- Basically want to push her into slight acidosis
– By triggering this it will increase the binding of PTH
What is DCAB?
- Dietary cation-anion balance
