Also referred to as parturient paresis or hypocalcemia, milk fever is a common nutritional disorder generally affecting older, high producing cattle.
The demand for calcium in the body of a cow increases at the beginning of lactation, as large amounts of calcium are lost through milk and hence the need to replenish it. This may lead to a decrease in blood calcium levels if the cow is unable to replace the lost calcium fast enough, consequently leading to a disease called milk fever.
Most milk fever cases occur within 48 to 72 hours of calving when demand for calcium for milk production exceeds the body’s ability to mobilize calcium reserves. Fever is a misnomer as body temperature is usually below normal. Low blood calcium interferes with muscle function throughout the body causing general weakness, loss of appetite and eventually heart failure.
Signs seen in cows with milk fever
At first, the cow experiences muscle tremors, lack of appetite and unsteadiness. Eventually, the cow is unable to rise, body temperature falls, and constipation occurs. Cows go down to a sitting position often with a kink in the neck. Death may occur if the cow is not treated promptly.
The beginning of milk production causes a decline in the animal’s blood calcium levels. If the cow is unable to replenish this calcium quickly enough, milk fever occurs.
Some high producing multiparous (those which have calved before) cows will develop clinical hypocalcemia just prior to signs of parturition. This occurs when there has been changes within the dry cow ration.
Older cows are more susceptible as they produce more milk and are unable to replenish calcium quickly enough.
Managing the diet can be a valuable aid in preventing milk fever. The key to prevention is managing a dry cow nearing parturition, which should be kept on a low calcium diet. Such a diet stimulates the calcium regulatory system to keep the blood levels normal by mobilizing the body stores from the bone. Lucerne, a feed high in calcium and potassium, should thus not be a major ingredient in close-up dry cow diets to avoid too high calcium levels before calving.
When the demand for calcium increases at calving, calcium can be mobilized much more rapidly thus preventing milk fever. In early lactation, high-yielding cows should receive as much calcium as possible. High-risk cows can be injected with vitamin D3 2–8 days before calving.
Diets providing less than 15 g of calcium per day per cow and fed for at least 10 days before calving will reduce the incidence of milk fever.