Molybdenum & Zinc

Question 1

What are the sources of Molybenum?

Answer 1

• prominent in acidic, wet, poorly drained soils
  
  • Regional - FL, OR, CA, NV
• Plants absorb water soluble Mo
• Industrial sources - brick and tile manufacturing, aluminum and steel mills, fertilizer plants

Question 2

Why is molybdenum necessary?

Answer 2

• Essential trace element
• Component of xanthine oxidase for purine metabolism

Question 3

What is the mechanism behind molybdenum toxicity?

Answer 3

• Mo is a Cu antagonist
• Mo promotes Cu excretion via formation of Cu-Mo complexes
  
  • antagonizes accumulation of Cu
• Mo-Cu-S complexes - thiomolybdates
  
  • Antagonize Cu most eficienty
  • Complex too big to be absorbed

Question 4

How does a Mo toxicity manifest?

Answer 4

• As Cu deficiency - enhanced by dietary sulfate
  
  • Reduced stability and strength of collagen
  • Reduced melanin synthesis
  • Compromised integrity of erythrocyte membranes
• May compete with P for mineralization of bone

Question 5

What are the clinical signs of Mo toxicosis?

Answer 5

• Greenish bubbly diarrhea after 1-2 weeks of exposure
• Decreased milk production or slowed growth
• Reduced libido on bulls and infertility in cattle
• Achromotrichia due to Cu deficiency and reduced melanin production
• Joint pain, lameness, spontaneous fractures, anemia, pica

Question 6

How is Molybdenum toxicity diagnosed?

Answer 6

• Lesions:
  
  • Anemia
  • Enteritis
  • Osteoporosis
  • Hemosiderosis
• Dx - Molybdenum Levels
  
  • >5 ppm in the liver
  • >0.1 ppm in the blood
  • Cu levels < 10 ppm in liver
    
    • <0.6 ppm in blood

Question 7

How is Molybdenum toxicosis treated?

Answer 7

• Cu injection
  
  • 60 mg SC for Calves
  • 120 mg SC for adults
• Dietary Cu to provide 1 gm daily per adult cow
  
  • 0.5 kg in 50 kg salt
  • 10 kg Cu/ton of grain - fed at 0.1 kg/co/day

Question 8

What are sources of Zinc?

Answer 8

• US pennies after 1983 - 98% Zn 2% Cu
  
  • NOT Canadian pennies
• Zn hardware on transport/kennel cages
• Galvanized wire or hardware
• Zn game pieces from board games
• Zn feed supplements (LA)
• Electrical pastes. fumes, paints, dust
• Anti dandruff shampoo (Zn pyrithione)

Question 9

How is Zinc processed by the body?

Answer 9

• Excreted primarily via bile and pancreas

Question 10

What is Zinc’s mechanisms for toxicosis?

Answer 10

• Interferes with absorption and utilization and Fe and Cu
• Absorption inhibited by Ca, Cd, Cu, and phytic acid
• Mucosal irritation from irritation from ingestion of some Zn salts (Zn oxide)
• Approximately ⅔ of Zn is loosely bound to protein in serum or plasma
  
  • Remainder is tightly bound

Question 11

What are the differential diagnoses for Zinc toxicosis?

Answer 11

• Autoimmune hemolytic anemia
• Onion & garlic poisoning
• Mothballs (naphthalene)

Question 12

What is the clinical pathology of zinc toxicosis in dogs?

Answer 12

• Severe hemolytic anemia
• High nucleated RBC - basophilic stippling
• Polychromasia
• Later, regenerative anemia
• Increased serum Alk Phos, bilirubin
• Hemoglobinuria, hematuria
• Other: Acute renal failure

Question 13

How does zinc toxicosis manifest clinically in dogs?

Answer 13

• 2 stages:
  
  • early - vomiting, anorexia
  • later - depression, diarrhea, weakness
• Advanced cases - hemolytic anemia leads to pale mucous membranes, icterus

Question 14

How is Zinc toxicosis diagnosed in dogs?

Answer 14

• Lesions
  
  • Hemorrhagic gastritis
  • Proximal renal tubular necrosis
  • centrilobular hepatocyte vacuolization, necrosis
• Abdominal radiograph to visualize coins or metal objects in stomach or intestine

Question 15

What is the Treatment to zinc toxicosis?

Answer 15

• Remove the Zn Foreign bodies
• Symptomatic - supportive, fluids for renal failure
• H₂ receptor blockers (Cimetidine, ranitidine)
• Chelation
  
  • D-penicillamine 110 mg/kg PO divided 6-8 h for 5-14 days
  • CaEDTA - 100 mg/kg divided 4x/day
• Often good recovery without chelation after removal of Zn foreign body