Oorsig/Review
The costly effects of low blood calcium
levels (hypocalcaemia) in freshly calved
dairy cows
Dr Barry Coates (BVSc)
‘Clinical’ milk fever and subclinical hypocalcaemia
are essentially the same thing – they are both low
available calcium levels in the blood. It’s only the
degree or severity that differentiates the two
conditions. It’s the subclinical hypocalcaemia
however, that is far more costly than clinical
milk fever for two simple, devastating reasons: It
affects a much higher percentage of animals, and
secondly, it goes largely unnoticed thus the term,
“subclinical”.
Milk Fever vs. Subclinical Hypocalcaemia
The start of each new lactation challenges a
dairy cow’s ability to maintain normal calcium
levels in her blood. Milk (especially colostrum)
is very rich in calcium and cows must quickly
shift their priorities to adjust for this sudden
calcium demand. Subclinical hypocalcaemia can
be defined as low blood calcium concentrations
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without any obvious, visible clinical signs.
Subclinical hypocalcaemia affects approx.
40-50% of 2nd lactation and older cows.
Hypocalcaemia has been linked to a variety of
damaging, secondary problems in cows soon
after calving. This happens because blood calcium
is essential for nerve, but especially muscle
function – and from a subclinical hypocalcaemia
point of view, particularly the smooth muscles of
gastrointestinal organs (rumen and intestines);
the uterus and teat sphincter are negatively
affected.
As you can see in Figure 1, the knock-on effects of
low blood calcium at, and soon after calving are
widespread and impactful – all without showing
any visible symptoms! Therefore clues like: lower
than expected milk production soon after calving;
abnormally high incidence of retained placentas
or displaced abomasums; higher than expected