CC - Milk Fever

Milk Fever: Hypocalcemia

Presenter: Miranda Vega, DVM

Food Animal Resident

Background Information

  • Incidence: Milk fever occurs in 3-4% of dairy cows in the United States each year.

  • Timing: It typically occurs in the periparturient period (around the time of calving).

  • Calcium Dynamics:
      - Increased fetal bone calcification.
      - Increased calcium deposition in colostrum.
      - Increased calcium deposition in milk.

  • Normal Blood Calcium Concentration: The total blood calcium concentration in an adult cow is normally 9-10 mg/dL.

Parathyroid Gland and Hormone Regulation

  • Parathyroid Hormone (PTH): Hormone secreted by the parathyroid gland that is crucial for calcium regulation in the blood.
      - Effects on Blood Calcium:
        - Decreases blood calcium concentration.
        - Increases calcium reabsorption in the kidneys.
        - Mobilizes calcium from bone to increase blood calcium levels.

  • Role of Vitamin D:
      - Converts to 1,25-dihydroxyvitamin D3, which increases calcium absorption in the intestines.

Pathophysiology of Milk Fever

  • Factors Affecting Tissue Responsiveness to PTH:
      - Metabolic Alkalosis: Impairs mobilization of bone calcium.
      - Decreased Mobilization of Bone Calcium: Reduces available calcium.
      - Decreased Intestinal Absorption of Calcium: Leads to lower levels in blood.
      - Increased Albumin Binding of Serum Calcium: Results in decreased active (ionized) calcium.
      - Decreased Magnesium: Affects PTH secretion and tissue responsiveness.
      - Decreased PTH Secretion: Reduces overall calcium regulation.
      - Decreased Responsiveness of Tissues to PTH: Further complicates calcium balance.

Predisposing Factors for Milk Fever

  • Age: Older cows are more susceptible than heifers.

  • Bone Calcium Stores: Lower bone calcium stores increase risk.

  • Vitamin D Receptors and PTH Receptors: Aging decreases the number of these receptors, reducing calcium mobilization.

  • Intestinal Absorption of Calcium: Impairment leads to lower calcium availability.

  • Breed Specificity: Channel Island breeds show higher susceptibility compared to Holstein.
      - This is due to higher calcium concentration in milk and colostrum and decreased intestinal receptors for 1,25-dihydroxyvitamin D3.

Clinical Signs of Milk Fever

Stage 1 (Calcium: 5.5-7.5 mg/dL)

  • Standing posture.

  • Restlessness observed in the cow.

  • Hyperexcitability.

  • Mild ataxia is noted.

  • Muscle fasciculations occur.

  • Normal body temperature is typically maintained.

Stage 2 (Calcium: 3.5-6.5 mg/dL)

  • Sternal recumbency.

  • Dry muzzle present.

  • Low body temperature.

  • Cold extremities.

  • Muffled heart sounds detected.

  • Increased heart rate (80-100 beats per minute).

  • Decreased rumen motility noted.

  • ‘S’ curve neck or head turned back.

  • Sluggish pupillary light reflexes (PLRs).

Stage 3 (Calcium: 2.0-3.5 mg/dL)

  • Lateral recumbency observed.

  • Muscle flaccidity.

  • Significantly increased heart rate (100-120 bpm).

  • Bloat may occur.

  • Unresponsive to external stimuli.

Reasons for Clinical Signs Explained

Recumbency

  • Role of Calcium: Critical in skeletal muscle contraction.
      - Decrease in calcium leads to a decrease in skeletal muscle contraction, resulting in muscle weakness and subsequent flaccidity.

Bloat

  • Role of Calcium: Essential for smooth muscle contraction.
      - A decrease in calcium leads to reduced smooth muscle contraction which results in decreased gastrointestinal (GI) motility and GI stasis.

Tachycardia

  • Role of Calcium: Vital for cardiac muscle contraction.
      - Decrease in calcium results in a diminished capacity of cardiac muscle contraction which leads to increased heart rate (tachycardia).

Cardiac Output Equation:

extCO=extSVimesextHRext{CO} = ext{SV} imes ext{HR}

  • Where:
      - CO = Cardiac Output
      - SV = Stroke Volume
      - HR = Heart Rate

  • Other terms involved: Contractility, preload, and afterload.

Diagnosis of Milk Fever

  • Approach:
      - Comprehensive history and physical examination of the animal.

  • Response to Therapy: Observe improvements post-treatment.

  • Blood Gas Analysis: Measurements of ionized calcium less than 1.0 mmol/L indicate deficiency.

  • Chemistry Panel: Assess overall metabolic function and calcium levels.

Treatment

For Standing Cows

  • Oral Supplementation: Can be administered orally or via orogastric tube.

  • Considerations: Must ensure the cow is swallowing adequately to prevent aspiration pneumonia.

  • Calcium Sources:
      - Calcium Chloride: 40-50 g.
      - Calcium Propionate: 100 g.

For Recumbent Cows

  • Intravenous Supplementation: Required for more severe cases.

  • Dosage: 1 g of calcium for every 100 lbs body weight.

  • Administration:
      - 1 x 500 mL bottle of 23% Calcium Gluconate contains approximately 10 g of calcium.
      - Administer slowly over 10-15 minutes to prevent cardiac arrest.

  • Expected Results: Normal calcium levels typically maintained for 6-9 hours post-treatment.

Post-Treatment Considerations

  • Cows should be standing within 2 hours post-treatment.

  • If not standing, consider alternative causes for recumbency other than milk fever.

The 5 M’s of a Down Cow

  • Mastitis: Infection of the mammary gland.

  • Metritis: Infection of the uterus.

  • Massive Disease: Could include various severe conditions.

  • Musculoskeletal Disorders: Include fractures and luxations.

  • Metabolic Issues: Induced by endotoxemia, sepsis, dehydration, hemorrhage, peritonitis, hypocalcemia, hypomagnesemia, hypophosphatemia, hypoglycemia, hypokalemia, and ketosis.

Post-Treatment Challenges

  • Relapsing Milk Fever: Occurs in approximately 20% of treated cows, commonly within 24 hours after initial treatment.

  • Management: May require oral or subcutaneous calcium supplementation 12-24 hours post treatment.

Increased Risk for Other Diseases Post-Milk Fever

  • Mastitis: Increased susceptibility due to weakened immune response.

  • Retained Fetal Membranes: Complications during parturition.

  • Metritis: Higher likelihood of uterine infections post-calving.

  • Ketosis: Metabolic disorder due to energy deficiency.

  • Displaced Abomasum: Affects the stomach's position and function.

  • Uterine Prolapse: Uterus slips out of place, potentially due to lack of calcium.

Prevention Strategies

Dietary Cation-Anion Difference (DCAD)

  • Concept: Managing blood pH through diet.
      - Dietary cations (K+, Na+, Ca2+, Mg2+) raise blood pH.
      - Dietary anions (Cl-, SO4^2-, PO4^3-) lower blood pH.

  • Application: Feed specific forages in the last 3 weeks of gestation.
      - Ensure forages have low potassium (K+) and higher chloride (Cl-) content.
      - Include anionic salts to the diet to lower pH.

  • Monitoring: Ideal urine pH range should be 6.2-6.8, targeting compensated metabolic acidosis.

Calcium Deficient Diet

  • Strategy: Feeding a calcium-deficient diet 7-14 days before calving.
      - This leads to a minor decrease in blood calcium, stimulating PTH secretion.
      - Prolonged exposure to PTH may overcome resistance caused by metabolic alkalosis, helping to prime calcium homeostatic mechanisms.

  • Challenges: Must restrict calcium intake to less than 20 g/day, can optionally use calcium binders but at increased costs and specificity concerns.

Oral Calcium Supplementation

  • Composition: Prepare a mixture containing calcium chloride for rapid absorption and calcium sulfate for slower absorption, combined with a fat coating for delivery.

  • Dosage: Administer one bolus at calving and a second bolus 12-24 hours post calving.

Questions?

  • Contact: Miranda Vega, DVM, Food Animal Resident