Milk fever is a low blood calcium disorder that occurs just before, during, immediately after, or up to 10 days after calving. With the onset of lactation, there is a relatively large drain in blood Ca going into milk. In order to maintain homeostatic control of blood serum Ca, a normal cow will mobilize Ca from other sources primarily bone and absorption of dietary calcium from the intestine. If exchangeable calcium from the bone is too low, blood serum Ca cannot be maintained and drops rapidly resulting in milk fever.
Recommendations for the prevention of milk fever have traditionally included the proper feeding of calcium and phosphorus especially during the late lactation and dry period. More recently, dietary acidity and alkalinity have been associated with controlling the incidence of milk fever and this is where potassium concentration in forage plays an important role. Acidic diets fed to dry cows have shown significant decreases in the incidence of milk fever. Apparently, the acidic condition increases exchangeable bone Ca and increases the absorption of Ca in the intestine. An index called the dietary cation-anion difference (DCAD) has been used to determine acidity and includes potassium, sodium (Na), chloride (Cl) and sulfur (S). DCAD is calculated on a milliequivilant per kilogram of dry matter basis with the formula,
DACD (mEq/kg D.M.) = (%Na*434.9 + %K*255.74) - (%Cl*282.06 + %S*623.75).
High concentrations of K in forages fed to dry cows can easily tip the balance of cations to anions creating an alkaline diet, thus, increasing the incidence of milk fever.
Back to "Managing High K Forages for the Dry Cow"
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