An update on hypocalcaemia control
Abstract
Clinical milk fever (hypocalcaemia) is one of the most common metabolic diseases encountered in dairy cows. Subclinical hypocalcaemia in the first days post calving is very common but not often monitored on farm. If monitoring strategies are used the timing of sampling and the parity of animals is important in interpretation of results. Several studies show subclinical hypocalcaemia predisposes cows to an increased risk of diseases such as metritis and displaced abomasum as well as reduced reproductive performance and compromised milk yields. Targeted interventions with calcium supplementation can be effective in mitigating these risks. Preventative strategies normally focus on restricting dietary potassium in the lead up to calving and ensuring adequate magnesium status. Ca binding agents can also be very effective but it is a more expensive strategy.
The lactational demands on the dairy cow make it almost unique in its inability to maintain calcium (Ca) homeostasis at parturition. The incidence of clinical hypocalcaemia (milk fever) in the field generally ranges from 0 to 10%, but may exceed 25% of cows calving (Garis and Lean, 2008). Data from a UK retailer scheme showed that the recorded incidence decreased from 5.8 to 2.7% from 2009 to 2017 (Sainsburys plc., Press briefing, 2017) but up to date UK wide data are not available.
A clinical target incidence of less than 3% is realistic. It is easier to achieve these targets in larger herds where dedicated groups of cows with carefully controlled dietary macromineral concentrations are more feasible (seeBox 1).
Box 1.Dietary micromineral recommendations for control of hypocalcaemia
The use of Ca salt containing drenches around calving is popular and is reasonably effective at controlling clinical hypocalcaemia. The most soluble salts are the most effective; calcium chloride is the most soluble and carbonate is the least making it almost useless as a treatment/prevention in drenches and boluses. Calcium chloride drenches may be the most rapidly absorbed but can damage the oesophageal lining; mixtures with propylene gycol gels were formulated to mitigate this risk (Goff and Horst, 1994). Calcium propionate is more slowly absorbed but the duration of a serum blood Ca rise is slightly longer. However, it should be borne in mind that most proprietary salts and drenches contain between 40 and 50 g of Ca and these will only lead to a 2 hour rise in serum Ca. Higher quantities of calcium can give longer responses, Martinez (2016) observed a maximum of an 8 hour rise when using a Ca bolus containing 86 g of Ca.
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