Milk fever: new approaches to treatment and control (Proceedings)
Periparturient hypocalcemia (milk fever) is a common condition of dairy cows with an annual incidence of 5 to 8%. Effective treatment and control programs for milk fever are therefore required for dairy cattle. When used for treatment, calcium should be administered by the intravenous, subcutaneous, or oral route, depending on the severity of the clinical signs.
Oral CaCl2 (calcium gels) have been used in Europe since 1962. These are commercially available and are preferred to calcium drenches, which are more likely to be aspirated. Most formulations contain 50-70 g calcium per dose. Retreat at 12-24 hours, and don't exceed 120 g in a 24-hour period. Oral calcium salts are effective at increasing plasma calcium concentration; orally administered calcium is absorbed by a dose-dependent passive diffusion process across ruminal epithelium and a dose-independent calcium-binding protein mechanism in the small intestine that is modulated by Vitamin D. Passive diffusion across the ruminal epithelium occurs when the ruminal calcium concentration >1.5 mmol/L but is substantial when the calcium concentration in rumen fluid is greater than 6 mmol/L, which is approximately 2-3 times the normal value in plasma (normal range 2.2-2.6 mmol/l). Rapid correction of hypocalcemia by oral calcium administration must utilize passive ruminal diffusion, as small intestinal absorption is too slow to be of clinical value.
Two calcium formulations are currently recommended for oral administration to ruminants; CaCl2 and calcium propionate, but most commercially available products contain 50 g of CaCl2. Calcium chloride has the advantage of low cost and low volume (because of its high solubility), but CaCl2 can severely damage the pharynx and esophagus in ruminants with reduced swallowing ability, can lead to necrosis of the forestomach and abomasum when administered in high doses, and can lead to aspiration pneumonia when administered as a drench. Calcium propionate has the advantages that it is less irritating while providing a gluconeogenic substrate (propionate), but the disadvantages of higher volumes and cost. The effectiveness of ororuminal administration of higher volume calcium propionate solutions has been evaluated. Oral calcium solutions should only be administered to cattle that have normal swallowing ability, precluding their administration to animals with advanced clinical signs of hypocalcemia. Higher plasma calcium concentrations are obtained more quickly when calcium solutions are drenched after administration of vasopressin to induce esophageal groove closure, or when the calcium solution is administered as a drench instead of ororuminal intubation.Intravenous calcium is an effective treatment at an approximate dose of 2.2 g calcium / 100 kg body weight, with cardiac monitoring during administration. Calcium gluconate and calcium borogluconate are the preferred forms for intravenous and subcutaneous administration because CaCl2 causes extensive necrosis and sloughs of tissue when administered perivascularly. Compared to calcium gluconate, calcium borogluconate has improved solubility and shelf life. Plasma ionized calcium concentrations are increased to a greater extent following CaCl2 treatment when high equimolar solutions of CaCl2 and calcium gluconate are administered, leading to more cardiac arrhythmias during CaCl2 administration. A typical treatment to an adult lactating dairy cow with periparturient hypocalcemia is 500 ml of 23% calcium borogluconate by slow intravenous injection with cardiac auscultation, this provides 10.7 g of calcium. Although the calculated calcium deficit in a recumbent periparturient dairy cow is 4 g calcium, we should provide additional calcium to overcome the continued loss of calcium in milk. A field study comparing the effectiveness of different doses of calcium for treating periparturient milk fever determined that 9 g of calcium was superior to 6 g. A good rule of thumb for administering 23% calcium borogluconate solutions (2.14 g calcium/100 ml) to cows with periparturent hypocalcemia is therefore to administer 1 ml/kg body weight.
Subcutaneous administration of calcium solutions has been practiced for many years. To facilitate absorption, it is preferable to administer no more than 125 ml at a site, although this supposition (and volume) do not appear to have been verified. A 14-gauge needle is placed subcutaneously over the lateral thorax, 125 ml is administered, the needle is redirected and another 125 ml administered. The process is then repeated on the other side of the cow. Calcium chloride is not recommended for subcutaneous administration because of extensive tissue damage; the addition of dextrose to the administered calcium is also not recommended because it increases the tonicity of the solution and propensity for bacterial infection and abscessation. Rectal calcium administration is not recommended because it causes severe mucosal injury and tenesmus but does not increase plasma concentrations of calcium.