14 January 2000

Risk of milk fever if minerals cut back

By Jessica Buss

MISCONCEPTIONS about minerals and cutbacks on use last year could lead to a rise in milk fever in spring calving cows this year.

Mole Valley Farmers feed adviser Luppo Diepenbroek is concerned about recent reports from producers that cows are going down after calving or in the first weeks of lactation because they are phosphorus deficient. This is leading to requests for high-phosphorus dry cow minerals.

"Taking a blood sample from a cow once she is down and has not been eating will show she is short of phosphorus. But in reality the problem is an imbalance of calcium and phosphorus."

Phosphorus is expensive and feeding it to dry cows will have little benefit, he says. "It is too late to give a phosphorus supplement then because it is a long-term element stored in the body."

When cows are short of phosphorus it may have been caused by a shortage of minerals in mid-lactation.

"There is a tendency to cut back minerals when cows are in calf, which is unwise when feeding a high cereal diet because it upsets the cows calcium level." Unlike phosphorus, calcium is cheap, so intakes of it should be maintained, adds Mr Diepenbroek.

Another misconception means high-phosphorus minerals are commonly fed unnecessarily, especially with maize or whole-crop silages. But they may be essential with grass and grass silage-based rations.

"Minerals high in phosphorus used to be sold to increase fertility because it is involved in the energy cycle. But it does not help a cow make better use of energy and once in excess it depletes a cows calcium reserves, especially when feeding silages because they are acidic."

But a mineral supplement with 12% phosphorus costs £60/t more than one with 6% phosphorus.

Not only does it cost more, it can increase risk of milk fever, says Mr Diepenbroek. "A spring calving cow fed maize last summer to balance out grass, with a high phos mineral, is at high risk of milk fever at calving." This is because she has depleted her bones of calcium and phosphorus reserves, he says. &#42

HIGH PHOS MINERALS

&#8226 Often not needed.

&#8226 No benefit to fertility.

&#8226 Can increase milk fever.