Milk fever, also known as parturient paresis or hypocalcemia, is a metabolic disorder that primarily impacts dairy cows shortly before or after calving. This condition arises when the cow’s blood calcium levels drop suddenly as the demand for calcium increases sharply for colostrum and milk production. The body’s regulatory systems cannot react quickly enough to mobilize calcium from bone and absorb it from the gut to meet this high demand. Milk fever is considered a medical emergency because the lack of calcium impairs nerve and muscle function, potentially leading to paralysis, coma, and death if not treated swiftly.
Recognizing the Stages of Milk Fever
Milk fever is typically divided into three progressive stages based on the severity of the calcium deficiency. Stage 1 is characterized by subtle signs of excitability and hypersensitivity while the cow is still able to stand. Symptoms may include restlessness, fine muscle tremors, particularly in the flanks and head, and an unsteady gait. This initial stage is often short-lived and can sometimes go unnoticed.
As the condition worsens, the cow progresses to Stage 2, defined by sternal recumbency, meaning the cow is down but resting on its chest. The cow cannot stand up on its own, its extremities, such as the ears and muzzle, feel cold, and the heart rate becomes elevated but weak. A distinctive posture, where the head is tucked into the flank or presented in an S-shape, is a common sign of this moderate stage.
Stage 3 represents a life-threatening emergency, where the cow moves from sternal to lateral recumbency, lying flat on her side. The cow is often severely depressed, unresponsive to stimuli, and may rapidly progress into a comatose state. Muscle flaccidity is pronounced, and secondary complications like severe bloat can quickly cause death if treatment is not administered immediately.
Immediate Emergency Treatment Protocol
The immediate treatment for a cow exhibiting clinical milk fever involves the intravenous administration of a calcium solution to quickly restore blood calcium levels. The preferred solution is calcium borogluconate, typically a 23% solution, which provides a highly soluble and bioavailable source of calcium. A standard treatment involves administering 500 milliliters of this solution.
It is important that the intravenous calcium is administered very slowly, typically over a period of four to eight minutes, while the cow’s heart is monitored. Rapid administration can lead to elevated plasma calcium concentrations that cause cardiac arrhythmias and potentially acute cardiac arrest. Warming the solution to body temperature before injection is also recommended to improve effectiveness and reduce the risk of shock.
For cows in early Stage 1, or those that are still standing, intravenous treatment is often unnecessary and can even be detrimental. In these milder cases, or as a follow-up to IV treatment, calcium solutions can be administered subcutaneously or orally. When using the subcutaneous route, the injection site should be clean, and no more than 125 milliliters should be administered in a single spot to facilitate absorption and prevent tissue damage.
Post-Treatment Monitoring and Recovery
Following the initial calcium infusion, the cow must be closely monitored for signs of recovery and relapse, which occurs in a significant percentage of cases. A successful treatment usually results in the cow showing signs of improved alertness, muscle tremors subsiding, and an attempt to stand within a few hours. If the cow fails to stand after the IV treatment, administering an oral calcium bolus is discouraged due to the risk of aspiration pneumonia.
To sustain the elevated blood calcium levels achieved by the intravenous treatment, which only lasts for about four hours, follow-up oral calcium supplementation is highly recommended. Oral calcium gels or boluses, often containing calcium chloride or similar readily absorbed salts, are typically administered immediately after the cow stands up and again 10 to 12 hours later. This supplementary oral calcium significantly reduces the risk of relapse and the need for a second intravenous treatment.
Managing secondary complications is also a significant part of the recovery process, especially for cows that were recumbent for an extended period. The cow should be positioned correctly, resting on its chest with its legs tucked underneath, to prevent nerve and muscle damage caused by prolonged pressure. Ensuring easy access to fresh water and palatable feed encourages the cow to start eating and drinking, which supports the body’s natural calcium regulation processes.
Prevention Through Nutritional Management
Preventing milk fever focuses on maximizing the cow’s ability to mobilize her own calcium reserves in the days leading up to calving. The most widely adopted nutritional strategy involves manipulating the Dietary Cation-Anion Difference (DCAD) in the diet during the close-up dry period. The DCAD is a measure of the balance between positively charged minerals (cations) and negatively charged minerals (anions).
By adding anionic salts, such as calcium chloride or ammonium sulfate, to the pre-calving diet, the DCAD value is lowered, creating a mild, controlled state of metabolic acidosis. This slight acidification of the cow’s system increases the responsiveness of the bones and kidneys to Parathyroid Hormone, the body’s calcium-regulating hormone. The result is an increased release of calcium from bone stores and enhanced absorption of dietary calcium, effectively priming the system to handle the sudden demand at calving.
The goal is to achieve a negative DCAD, often aiming for a value between -50 and -150 milliequivalents per kilogram of dry matter. The effectiveness of this anionic diet must be monitored by testing the urine pH of the dry cows, with a target range typically between 6.0 and 6.8. High potassium forages should be limited in the pre-calving diet because potassium is a cation that raises the DCAD, making the blood more alkaline and counteracting the preventative strategy.