Hypocalcemia / Milk Fever

Hypocalcemia, commonly known as milk fever, is a critical metabolic disorder affecting cattle that occurs when blood calcium levels fall dangerously low, typically around the time of calving. Despite its common name, this condition does not involve fever or infection but rather represents a severe imbalance in calcium metabolism that can rapidly progress to complete muscular paralysis and death if left untreated. The condition develops because the sudden onset of lactation creates an enormous demand for calcium that exceeds the cow's ability to mobilize calcium from bones or absorb it from the digestive tract quickly enough.

Milk fever predominantly affects dairy cattle, with the highest incidence occurring in high-producing breeds such as Holsteins, Jerseys, and Brown Swiss. The condition is most common in mature cows during their third to seventh lactation, as older cows have reduced ability to mobilize calcium from their skeletal reserves. Statistics indicate that approximately 5-10% of dairy cows in typical herds experience clinical hypocalcemia, while subclinical hypocalcemia may affect up to 50% of multiparous cows in the periparturient period. Beef cattle can also develop milk fever, though the incidence is considerably lower due to their typically lower milk production.

The economic and welfare impact of hypocalcemia extends far beyond the immediate crisis of a down cow. Direct losses include veterinary treatment costs, potential cow mortality rates of 5-8% even with treatment, and reduced milk production in the subsequent lactation. Indirect costs are equally significant and include increased susceptibility to other periparturient diseases such as retained placenta, displaced abomasum, mastitis, and ketosis. Research has demonstrated that cows experiencing milk fever have a 3-4 times higher risk of developing these secondary conditions, creating a cascade of health problems that can affect the entire lactation.

The good news for producers is that hypocalcemia is highly treatable when recognized and addressed promptly. Intravenous calcium therapy typically produces dramatic improvement within minutes to hours, with most cows standing and resuming normal function within 24 hours of treatment. However, the key to successful outcomes lies in early recognition of clinical signs and immediate intervention. Prevention through proper dry cow nutrition and management has become increasingly sophisticated, with dietary cation-anion difference (DCAD) manipulation proving highly effective at reducing incidence rates. Understanding and implementing these preventive strategies is essential for dairy operations seeking to minimize losses from this common but preventable metabolic disorder.

The primary cause of hypocalcemia is the sudden and massive demand for calcium that occurs at the onset of lactation. A high-producing dairy cow may secrete 20-30 grams of calcium in colostrum on the first day of lactation, while her blood contains only about 8-9 grams of total calcium. This creates an immediate deficit that must be addressed through rapid mobilization of calcium from bone reserves and increased intestinal absorption. When these compensatory mechanisms cannot keep pace with demand, blood calcium levels plummet from the normal range of 8.5-10.5 mg/dL to critically low levels below 5.5 mg/dL, triggering the clinical signs of milk fever.

Genetic and breed predisposition play significant roles in susceptibility to hypocalcemia. Jersey cattle appear particularly vulnerable due to their high milk fat percentage (which requires more calcium for synthesis) and smaller body size relative to milk production. Holstein cows, while individually less susceptible than Jerseys, represent the majority of clinical cases simply because they dominate the dairy industry. Within breeds, heritability of milk fever susceptibility has been estimated at 10-15%, suggesting that selective breeding could reduce incidence over time. Some genetic lines demonstrate markedly better calcium homeostasis than others, likely related to differences in vitamin D receptor efficiency and parathyroid hormone responsiveness.

Environmental and management factors significantly influence milk fever risk. Dietary calcium levels during the dry period are critically important, with both excessive and severely deficient calcium intake increasing risk. Paradoxically, high calcium diets during the dry period suppress the calcium mobilization pathways, leaving cows poorly prepared for the calcium demands of lactation. The cation-anion balance of the diet is equally important, with high potassium forages creating an alkaline metabolic state that impairs calcium mobilization. Housing stress, inadequate dry period length, and body condition extremes also contribute to increased susceptibility.

Age and production stage represent the most significant risk factors for hypocalcemia. First-lactation heifers rarely develop clinical milk fever because their calcium mobilization systems are highly active and they produce less milk initially. Risk increases dramatically with each successive lactation, peaking around the fourth to sixth calving. This age-related increase occurs because bone responsiveness to parathyroid hormone decreases with age, and the total bone calcium reservoir diminishes over repeated lactations. Cows that have previously experienced milk fever are at significantly elevated risk for recurrence in subsequent lactations.

The pathophysiology of hypocalcemia centers on the failure of homeostatic mechanisms to maintain blood calcium levels. Normally, declining blood calcium triggers parathyroid hormone release, which activates bone resorption, increases renal calcium retention, and stimulates vitamin D conversion to its active form to enhance intestinal absorption. In susceptible cows, these pathways cannot respond quickly enough to the sudden calcium demand. The resulting hypocalcemia affects neuromuscular function throughout the body because calcium is essential for muscle contraction and nerve impulse transmission. As blood calcium falls, progressive muscle weakness develops, beginning with decreased gut motility and progressing to recumbency and eventual cardiovascular collapse if untreated.

Early warning signs of hypocalcemia often appear within hours of calving and may be subtle enough to escape notice without careful observation. Initial symptoms include decreased appetite, reduced rumen motility leading to bloat, and a general appearance of unease or anxiety. Affected cows may shift weight between their hind legs, exhibit muscle tremors particularly visible over the shoulders and flanks, and show reduced coordination when walking. Body temperature in these early stages is often slightly elevated due to muscular tremors, which can be misleading given the common name of milk fever. Alert producers who observe cows carefully during the immediate post-calving period can often identify these early signs and intervene before the condition progresses.

As hypocalcemia advances, symptoms become progressively more dramatic and easier to recognize. The classic presentation involves three distinct stages that can progress over a period of hours. Stage I hypocalcemia features excitement, hypersensitivity, muscle tremors, and stiff gait with the cow still able to stand. The cow may appear anxious, grind her teeth, and show exaggerated responses to stimuli. This stage is often brief and may be missed if cows are not observed frequently. Rectal temperature during Stage I is typically normal or slightly elevated, and the cow retains the ability to eat and drink, though with diminished enthusiasm.

Stage II represents the classic milk fever presentation that most producers and veterinarians recognize. The cow becomes recumbent but can maintain sternal position with her head often turned back toward her flank in a characteristic S-curve. Muscles are cold to the touch due to decreased peripheral circulation, and body temperature drops below normal, often to 96-99°F. The muzzle becomes dry, pupils dilate, and heart rate increases while heart sounds become progressively more difficult to detect due to decreased cardiac contractility. Rumen contractions cease entirely, leading to progressive bloat. The cow may still respond to stimuli and make attempts to rise but lacks the muscular strength to do so.

Physical signs in advanced hypocalcemia reflect the progressive failure of calcium-dependent processes throughout the body. The smooth muscle of the gastrointestinal tract loses function, resulting in complete rumen stasis and abomasal atony that can predispose to displaced abomasum even after calcium treatment. The bladder becomes distended as smooth muscle controlling urination fails. Cardiac output decreases, blood pressure falls, and extremities become cold. The characteristic cool ears and cold rectal temperature help differentiate milk fever from other causes of recumbency such as mastitis or metritis, which typically cause fever.

Symptom progression to Stage III occurs rapidly if treatment is not administered. The cow loses the ability to maintain sternal recumbency and lies flat on her side in lateral position. Severe bloat develops as rumen gas cannot be eructated. Heart sounds become almost inaudible, and pulse becomes weak and rapid. The cow becomes completely unresponsive to external stimuli, pupils become fixed and dilated, and death typically follows within hours from cardiovascular collapse and respiratory failure. Even with aggressive treatment, cows that have progressed to Stage III have a significantly poorer prognosis due to secondary muscle damage and potential aspiration pneumonia.

Emergency symptoms requiring immediate veterinary intervention include complete recumbency with inability to maintain sternal position, severe bloat, cold extremities with weak or absent pulse, loss of consciousness, and labored breathing. These signs indicate that calcium levels have fallen to critical levels and death is imminent without treatment. Additionally, any cow that fails to respond to initial calcium treatment within 30 minutes, or that relapses after initial improvement, requires emergency reassessment as this may indicate complicated hypocalcemia, concurrent conditions such as toxic mastitis, or musculoskeletal injury from prolonged recumbency. Producers should have calcium solutions and administration equipment available and should not delay treatment while waiting for veterinary arrival in cases of severe milk fever.

Clinical diagnosis of hypocalcemia is primarily based on the characteristic presentation and signalment of the affected animal. The combination of a recently calved multiparous dairy cow in sternal recumbency with cold ears, dry muzzle, subnormal temperature, and dilated pupils is virtually pathognomonic for milk fever. Veterinarians can often make a confident presumptive diagnosis within moments of examining the cow. The history of recent calving (typically within 24-72 hours), high milk production, and absence of fever help distinguish milk fever from infectious causes of recumbency. Response to calcium therapy serves as both treatment and diagnostic confirmation, with dramatic improvement typically occurring within 15-30 minutes of intravenous calcium administration.

Diagnostic testing, when performed, centers on blood calcium measurement to confirm the diagnosis and assess severity. Normal blood calcium in cattle ranges from 8.5-10.5 mg/dL, while clinical hypocalcemia typically involves levels below 5.5 mg/dL. Ionized calcium, which represents the biologically active fraction, provides more clinically relevant information than total calcium. Blood samples should ideally be collected before treatment for accurate baseline values, though in emergency situations treatment should never be delayed for diagnostic purposes. Additional blood chemistry may reveal concurrent abnormalities including hypophosphatemia and hypomagnesemia, which often accompany hypocalcemia and may require specific treatment. Blood glucose levels help rule out concurrent ketosis, which commonly occurs alongside milk fever.

Differential diagnosis is essential because numerous conditions can cause recumbency in periparturient cattle. Toxic mastitis can cause severe depression and recumbency but is typically accompanied by fever, abnormal milk, and a hot, swollen udder. Calving injuries including hip luxation, femoral nerve paralysis, and obturator nerve damage cause recumbency but without the metabolic signs of milk fever. Hypomagnesemia (grass tetany) causes similar muscular signs but typically features hyperexcitability and convulsions rather than the progressive depression of hypocalcemia. Severe metritis, ruptured uterus, and hemorrhage are additional considerations. In practice, mixed presentations are common, and cows may suffer from multiple concurrent conditions.

Herd-level diagnostics become important when milk fever incidence exceeds expected norms of 3-5% in well-managed herds. Monitoring blood calcium levels in a sample of fresh cows (within 24 hours of calving) can reveal the extent of subclinical hypocalcemia, which often affects 50% or more of multiparous cows. Evaluation of dry cow ration composition, particularly potassium content and cation-anion difference, helps identify dietary risk factors. Urine pH monitoring in prepartum cows provides practical assessment of DCAD diet effectiveness, with target pH values of 6.2-6.8 indicating adequate dietary acidification. Analysis of forage mineral content, body condition scoring, and dry period length assessment round out the herd-level diagnostic investigation.

Emergency treatment of clinical hypocalcemia requires immediate administration of intravenous calcium, which is the cornerstone of milk fever therapy. Calcium borogluconate is the most commonly used product, typically supplied as a 23% solution. The standard treatment dose is 500 mL of solution containing approximately 10-11 grams of elemental calcium, administered slowly intravenously over 10-20 minutes. Rapid administration can cause fatal cardiac arrhythmias, so careful monitoring during infusion is essential. The cow should be monitored for signs of calcium toxicity including muscle tremors, cardiac arrhythmia, and collapse, with immediate cessation of infusion if these occur. Most cows show dramatic improvement during or shortly after treatment, with decreased bloat, return of rumen motility, and attempts to stand.

Medical management following initial emergency treatment focuses on preventing relapse and addressing concurrent conditions. Approximately 25-30% of cows relapse within 24-48 hours of initial treatment, necessitating careful monitoring and often additional calcium supplementation. Subcutaneous calcium administration provides a slower-release supplement that can help prevent relapse, with 500 mL of calcium solution divided between two or more injection sites. Oral calcium supplements, including calcium chloride gels and propionate boluses, offer another option for supplementation in early stages or for relapse prevention. Because meat and milk withdrawal times for calcium products are generally short or nonexistent, food safety concerns are minimal with appropriate products.

Supportive care is crucial for successful outcomes, particularly for cows that do not stand promptly after calcium treatment. Recumbent cows must be maintained in sternal position to prevent bloat and aspiration pneumonia, using hay bales or other supports if necessary. Rolling the cow from side to side every 2-3 hours helps prevent pressure damage to muscles and nerves. Providing deep, dry bedding with good footing reduces muscle strain when the cow attempts to rise. Access to fresh water and palatable feed should be provided as soon as the cow shows interest. Cows that remain recumbent despite calcium treatment should be evaluated for secondary conditions including musculoskeletal injury, concurrent diseases, or severe nerve damage from prolonged pressure.

Additional medical considerations often accompany hypocalcemia treatment. Concurrent hypophosphatemia responds to phosphorus supplementation, available as injectable or oral preparations. Hypomagnesemia may require magnesium sulfate supplementation, which can be administered alongside calcium therapy. Anti-inflammatory medications may reduce uterine inflammation and help prevent retained placenta. Prophylactic antibiotic therapy is sometimes administered to prevent metritis, though this practice should be balanced against prudent antimicrobial use. Dextrose supplementation addresses hypoglycemia that often accompanies milk fever. Downer cow treatment protocols, including flotation tanks or hip lifters, may be necessary for cows that fail to rise after metabolic correction.

Herd treatment protocols should be established for operations with significant milk fever incidence. Having adequate calcium treatment supplies on hand allows immediate intervention without waiting for veterinary arrival. Training farm personnel in proper intravenous technique and signs of treatment complications enables faster response. Many veterinarians establish protocols allowing trained farm staff to administer initial calcium treatment for straightforward cases while seeking veterinary attention for complicated presentations. Prophylactic calcium supplementation for high-risk cows at calving can prevent clinical cases, with various protocols including subcutaneous calcium around calving and oral calcium supplementation.

Treatment decisions in farm animal medicine must consider economic realities alongside animal welfare. For most dairy operations, the value of a high-producing cow justifies aggressive treatment of milk fever, including repeated veterinary visits if necessary. However, cows that remain recumbent for extended periods (more than 24-48 hours) despite appropriate treatment face poor prognoses due to secondary muscle damage and nerve injury. The decision to continue treatment versus humane euthanasia should involve veterinary assessment of the likelihood of recovery and the cow's quality of life. Salvage slaughter may be an option for cows that fail to respond, provided appropriate withdrawal times have been observed and the cow can be transported humanely.

Recovery from uncomplicated hypocalcemia is typically rapid and dramatic following appropriate treatment. Most cows that receive timely intravenous calcium therapy show visible improvement within 15-30 minutes, with return of rumen motility, decreased bloat, and increased alertness. Many cows stand within 1-2 hours of treatment, though some may take up to 24 hours even with successful metabolic correction. Once standing, most cows quickly resume normal appetite and milk production. Complete metabolic recovery, as measured by normalized blood calcium levels, typically occurs within 24-48 hours, though subclinical hypocalcemia may persist for several days in some individuals.

Post-treatment care and monitoring are essential components of successful recovery management. Treated cows should be monitored closely for the first 48-72 hours, as relapse rates of 25-30% mean nearly one-third of initially successful treatments will require additional intervention. Signs of impending relapse include decreased appetite, reduced milk production, cold ears, and wobbly gait. Having oral or subcutaneous calcium available for supplementation at the first sign of relapse can prevent progression to complete recumbency. Fresh water and high-quality feed should be available continuously, and milk production should be monitored as an indicator of metabolic status. Some practitioners recommend reduced milking frequency in the first few days to limit calcium drain.

Prognosis depends heavily on the severity and duration of hypocalcemia before treatment. Cows treated in Stage I or early Stage II typically have excellent outcomes with greater than 95% survival and minimal long-term effects. Stage III cases or cows that have been recumbent for extended periods face significantly poorer outcomes due to secondary complications including muscle necrosis (downer cow syndrome), nerve damage, and aspiration pneumonia. Even with successful treatment of the hypocalcemia, these secondary injuries may prevent recovery. Cows that have experienced one episode of milk fever have an increased risk of recurrence in subsequent lactations, estimated at 2-3 times higher than cows that have never experienced the condition.

Return to production considerations include both short-term and long-term impacts on the affected cow. In the immediate aftermath, milk production often decreases for several days before returning to expected levels. Milk composition may be altered, with reduced fat percentage in some cases. Long-term, cows that have recovered from milk fever face increased risk of other periparturient conditions including displaced abomasum, ketosis, mastitis, and retained placenta. These secondary conditions may require their own treatment and can significantly impact lactation productivity. Despite these concerns, cows that recover uneventfully from single episodes of milk fever generally return to full production potential and remain productive herd members for multiple additional lactations.

Vaccination does not play a role in hypocalcemia prevention because the condition is metabolic rather than infectious. Instead, prevention focuses on nutritional management during the dry period to optimize calcium homeostatic mechanisms before the cow enters lactation. The dietary cation-anion difference (DCAD) approach has become the gold standard for milk fever prevention in dairy herds. By feeding a diet with a negative DCAD (more anions than cations), a mild metabolic acidosis is created that activates calcium mobilization pathways, preparing the cow to meet the calcium demands of lactation. Common anionic supplements include ammonium chloride, ammonium sulfate, calcium chloride, and commercial anionic products.

Biosecurity measures are not applicable to hypocalcemia prevention as this is not a transmissible condition. However, consistent management practices across the dry cow group are essential for effective prevention. All dry cows should receive the same carefully formulated ration, and forages should be analyzed for mineral content, particularly potassium. High-potassium forages (greater than 2% potassium on dry matter basis) are particularly problematic as they create an alkaline metabolic state that opposes calcium mobilization. Separating close-up cows (final 2-3 weeks of the dry period) for more intensive management and specific close-up rations has proven effective at reducing milk fever incidence.

Nutritional prevention strategies extend beyond DCAD manipulation to include optimization of other dietary components. Magnesium supplementation is essential because magnesium is required for parathyroid hormone function and calcium mobilization from bone. Vitamin D3 supplementation, particularly in the final days before calving, enhances intestinal calcium absorption. Limiting dietary calcium during the dry period to 100-150 grams per day helps maintain active calcium homeostatic pathways, though this approach is less effective than DCAD manipulation when forage potassium is high. Phosphorus levels should be maintained at appropriate levels as both deficiency and excess can increase milk fever risk.

Management practices that reduce milk fever risk include maintaining appropriate body condition at dry-off and through the dry period. Overconditioned cows (body condition score greater than 4.0) face higher risk due to decreased feed intake around calving and reduced calcium absorption. Adequate dry period length of 40-60 days allows proper mammary gland involution and preparation for the next lactation. Minimizing stress during the transition period through proper housing, grouping strategies, and heat abatement (in hot climates) supports normal metabolic function. Exercise during the dry period may improve calcium mobilization, and some studies suggest that cows housed on pasture have lower milk fever rates than those in confinement.

Quarantine and testing protocols for milk fever prevention focus on identifying high-risk individuals and monitoring program effectiveness. Urine pH testing in prepartum cows provides practical feedback on DCAD diet effectiveness, with target pH of 6.2-6.8 in Holstein cows (slightly lower in Jerseys) indicating adequate acidification. Blood calcium monitoring in a sample of fresh cows (within 24 hours of calving) reveals the prevalence of subclinical hypocalcemia and helps assess prevention program success. Individual cow history should be tracked, with cows that have previously experienced milk fever flagged for intensive monitoring and prophylactic treatment at subsequent calvings. Prophylactic subcutaneous or oral calcium administration around calving effectively reduces clinical cases in high-risk individuals.

Daily management and monitoring of periparturient cows is fundamental to preventing milk fever deaths and minimizing production losses from hypocalcemia. Close-up dry cows and recently fresh cows require observation at least twice daily, with more frequent checks for cows identified as high-risk based on age, breed, or previous history. Monitoring should focus on appetite, demeanor, rumen fill, and mobility, with any abnormalities prompting closer evaluation. Fresh cows should be assessed for milk production, udder health, and clinical signs of metabolic disease. Maintaining detailed calving records, including time of calving, calf delivery difficulty, and cow condition, helps identify patterns and risk factors within the herd.

Housing and environmental management significantly impact transition cow health and milk fever risk. Close-up dry cows and fresh cows should have access to comfortable, well-bedded resting areas that encourage adequate rest and rumination time. Stocking density should be managed to ensure all cows can access feed and water without competition, with recommendations of no more than 80% capacity in close-up pens. Heat stress dramatically increases milk fever risk, so providing shade, fans, and sprinklers during hot weather is essential in many climates. Fresh water should be available at all times, with particular attention to providing water near the calving area as dehydration increases metabolic disease risk.

Herd health programs for milk fever prevention integrate nutritional management, individual cow monitoring, and treatment protocols into a comprehensive approach. Working with a veterinarian and nutritionist to develop a transition cow program appropriate for the specific operation is essential. This program should include dry cow ration formulation with appropriate DCAD, close-up cow management, monitoring protocols for fresh cows, and treatment guidelines for clinical cases. Regular evaluation of program effectiveness through fresh cow examination, blood calcium testing, and milk fever incidence tracking allows continuous improvement. Many successful operations achieve clinical milk fever rates below 2% through comprehensive programs.

Record keeping and monitoring systems enable early problem detection and program evaluation. Individual cow records should track milk fever history, calving dates, body condition scores, and any metabolic disease occurrences. Herd-level tracking of milk fever incidence by season, parity group, and other factors helps identify risk patterns. Fresh cow health monitoring systems that track daily milk production, activity, and rumination time can identify subclinical problems before they become clinical emergencies. Integration of these records into herd management software facilitates analysis and decision-making.

Economic considerations drive much of the decision-making around milk fever prevention and management. The total cost of a clinical milk fever case has been estimated at $300-400 when accounting for treatment, decreased milk production, increased culling risk, and secondary disease occurrence. Subclinical hypocalcemia, though less dramatic, may actually cause greater total economic losses due to its higher prevalence and effects on production and reproduction. Investment in prevention through proper dry cow nutrition typically returns $5-10 for every dollar spent through reduced milk fever incidence and improved overall transition cow health. Producers should work with their veterinarians and nutritionists to evaluate the cost-effectiveness of various prevention strategies for their specific operations.

Among dairy breeds, Jersey cattle demonstrate the highest susceptibility to hypocalcemia, with some studies reporting incidence rates 2-3 times higher than Holsteins. This increased risk is attributed to the Jersey's smaller body size relative to milk production, higher milk fat percentage requiring more calcium for synthesis, and potentially less efficient calcium homeostatic mechanisms. Jersey cows produce colostrum with exceptionally high calcium content, creating a severe drain on blood calcium reserves at the onset of lactation. Guernsey and Brown Swiss cattle also show elevated milk fever risk compared to Holsteins, while Scandinavian breeds including Swedish Red and Norwegian Red appear to have somewhat lower susceptibility.

Production type significantly influences milk fever risk, with high-producing dairy cattle facing much greater susceptibility than beef cattle. Within dairy breeds, individual cows with higher genetic potential for milk production are at increased risk because their calcium demands at lactation onset are correspondingly higher. First-lactation heifers rarely develop clinical milk fever regardless of breed because their calcium homeostatic mechanisms are highly responsive and their milk production is lower. Risk increases with each successive lactation, with peak incidence typically occurring between the fourth and seventh calvings. This age effect reflects decreased bone responsiveness to calcium-mobilizing hormones and reduced total skeletal calcium reserves after multiple lactations.

Genetic selection offers opportunities to reduce milk fever susceptibility within breeds, though this approach remains underutilized in most breeding programs. Research has identified genetic markers associated with calcium homeostasis efficiency, and heritability estimates for milk fever susceptibility range from 10-15%. Some breeding values for disease resistance now include milk fever or metabolic disease complex traits. Selection for improved calcium homeostasis must be balanced against production traits, and the genetic correlation between high milk production and milk fever susceptibility presents a challenge. Testing of vitamin D receptor gene variants and other calcium metabolism genes may eventually allow more precise genetic selection. In the meantime, individual cow history remains the best predictor of future milk fever risk, and cows with previous milk fever episodes should be flagged for intensive monitoring and prevention at subsequent calvings.

Ketosis commonly co-occurs with hypocalcemia, as both conditions reflect metabolic stress during the transition period. Subclinical hypocalcemia reduces rumen motility and feed intake, which predisposes to negative energy balance and ketone body accumulation. Studies have shown that cows with subclinical hypocalcemia in the first 24 hours after calving are 3-4 times more likely to develop clinical ketosis. Treatment of milk fever should therefore include evaluation for concurrent ketosis, and prevention programs should address both conditions simultaneously. Displaced abomasum is another common sequela of hypocalcemia, as reduced smooth muscle function leads to abomasal atony and increased risk of displacement. The association is strong enough that some practitioners administer prophylactic calcium to cows with displaced abomasum.

Retained placenta shows a well-documented association with hypocalcemia, likely because calcium is essential for uterine contractions that expel fetal membranes. Cows with milk fever are 2-3 times more likely to retain their placenta compared to normocalcemic herd mates. Metritis risk increases correspondingly, as retained placenta provides an environment for bacterial growth. Mastitis incidence also increases in cows with periparturient hypocalcemia, possibly because reduced smooth muscle function impairs teat sphincter closure. This cluster of periparturient conditions has been termed the transition cow disease complex, recognizing the interconnections between metabolic, reproductive, and infectious disorders during this critical period.

Downer cow syndrome represents a severe complication of milk fever that occurs when recumbency persists despite correction of hypocalcemia. Prolonged pressure on muscles and nerves leads to ischemic damage, particularly affecting the muscles of the hind limbs and the major nerves serving the rear quarters. Obturator and sciatic nerve paralysis, tibial nerve damage, and muscle necrosis can all result from extended recumbency. Once developed, downer cow syndrome carries a guarded prognosis despite intensive nursing care. Hip luxation and tibial fractures can also complicate milk fever cases, particularly when cows attempt to rise on slippery surfaces or when hip lifters are used improperly. Prevention through prompt treatment and proper nursing care of recumbent cows is essential.