DETERMINING THE MINERAL REQUIREMENT OF DAIRY CATTLE

poisoning in horses and cattle is associated with lameness and loss of hair and hoof
malformations. Animals at pasture eventually die from starvation due to impaired mobility.
Se can be toxic at 8-10 mg/ kg diet.
Blind Staggers - cattle and horses
Certain plant species such as princesplume, woody aster and (Stanleya, Xylorrhiza,
and Astragalus species) found in pockets of the American upper great plains and deserts
are Se accumulators and can contain several hundred to a thousand mg Se / kg. They are
generally unpalatable but animals consuming these plants can develop Se toxicity. If
consumed in high amounts the animal can exhibit acute poisoning - blind staggers. More
commonly in periods of drought the animals on pasture may be hungry enough to
occasionally eat a few of these Se accumulator plants.
Alkali disease
The soil (usually alkaline soils) may have high enough Se that forage plants grown in
these areas provide more than 10 mg Se / kg pasture may and over time the animals
develop lameness and emaciation- alkali disease. Profitable ranching is nearly impossible
in these particular areas of the country.
Molybdenum
Molybdenum is a component of xanthine oxidase, sulfide oxidase, and aldehyde
oxidase; enzymes found in milk and many tissues. Milk and plasma molybdenum
concentration increase as dietary molybdenum increases.
Deficiency - From a practical standpoint this is not a concern
Toxicity
Dietary molybdenum becomes a practical concern because it antagonizes the
absorption of Cu (and to a lesser extent Phos). Molybdenum toxicosis signs are essentially
those associated with Cu deficiency. Molybdenum and sulfate interact within the digestive
tract to form a thiomolybbdate complex which has a high affinity for Cu. Cu bound to this
molybbdate is unavailable for absorption (see section on Cu). The toxicity of molybdenum
can be overcome by increased Cu supplementation and Cu toxicity can be reduced by
molybdenum supplementation. The critical ratio of dietary Cu: dietary molybdenum needed
to avoid Cu deficiency ranges from 2:1 in reports from Canada to 4:1 on pastures in
England with a high molybdenum content (20-100 mg molybdenum / kg forage DM). In the
United States molybdenum is a significant problem in the western states and around the
Everglades in Florida.
Iodine
Iodine is necessary for the synthesis of the thyroid hormones thyroxine and
triiodothyronine that regulate energy metabolism. Thyroid hormone production is also
increased during colder weather to stimulate an increase in basal metabolic rate as the
animal attempts to remain warm.
Most iodine sources are readily available and the iodides of Na, K and Ca are
commonly used. K iodide tends to be easily oxidized and volatilizes away before the
animal can ingest it. PentaCa orthoperiodate and ethylenediamine dihydroiodine (EDDI)
are more stable and less soluble and commonly used in mineral blocks and salt licks
exposed to the weather.
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