Molybdenum:

Sources:

• Molybdenum present in excess quantities in the soil may be taken up by plants in sufficient quantities to produce toxic effects in grazing animals.

• The toxic syndrome of chronic molybdenum poisoning is known as teart.
• The severity of the disease is related to water-soluble molybdenum content of the herbage.
• Hay made from teart pastures is harmless.

Factors affecting toxicity

• Non-ruminants are less susceptible.
• The susceptibility of ruminants depends on several factors.

o When the intake of copper decreases, tolerance to molybdenum toxicity decreases.  High dietary content of sulphate with low copper increases toxicity.

 o Water soluble form of molybdenum is more toxic.

 o Cattle are less tolerant than sheep.

 o Young animals are more susceptible than old.

 Absorption and fate :

• The inorganic sulphate content in the diet affects the retention or excretion of molybdenum.
• When sulphate content is low, very little molybdenum is excreted in urine.

Mechanism of action:

• The storage of copper in the liver of sheep and cattle is significantly reduced by an increase in molybdenum intake.
• There is competition between molybdenum and phosphorus.
• Molybdenum can displace phosphorus. This causes skeletal lesions.
• Molybdenum forms complexes with catechols and this leads to bacteriostatic activity causing static effect on gastrointestinal bacteria leading to passage of liquid faeces full of gas bubbles.
• Anaemia due to copper deficiency is another feature of molybdenum toxicity.

Clinical signs:

• Molybdenosis in cattle is characterized by persistent severe scouring with the passage of liquid faeces full of gas bubbles. This is known as peat scours or tearts or teart disease.
• Affected animals loose weight, develop harsh, staring coats and their condition slowly deteriorates.
• Affected animals show abnormal pacing gait and this is called as pacing disease.
• Depigmentation of the hair occurs and this is visible mainly around the eyes giving a spectacled appearance to the affected animal.
• In less severe cases there may be a general unthriftiness and stunted growth in young animals.
• Sheep and young animals show stiffness of the back and legs and reluctance to rise. This condition is known as enzootic ataxia in Australia and swayback disease in UK.

Treatment:

• Daily administration of copper sulpahte is found to be useful.