Review/Oorsig Volume 22, Issue 02 - Page 26

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 26 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