DairyNZ is warning farmers to take care feeding palm kernel to pre-calving cows to avoid the risk of milk fever.

The high phosphorus content of palm kernel has been a problem in recent seasons, with a growing number of animals affected by the disease.

DairyNZ principal scientist Dr John Roche says once a cow is hit by milk fever, it can be a long, costly recovery process.

“It’s a disorder were a cow doesn’t have sufficient calcium in her blood to maintain milk production and the functioning of her smooth muscle, so if that drops too low basically her muscles don’t work and she can go down.”

But Dr Roche is stressing that overfeeding is the only danger, and farmers without a milk fever problem have no reason to worry.

“That’s one of misconceptions that we want to get away from. The original recommendation - people took it that they should avoid palm kernel entirely. That’s not the case. If a farmer doesn’t have a milk fever problem then they should ignore this recommendation”

RISKS FOR MILK FEVER AND PALM KERNEL (PKE):

• Genetics – for example, Jersey cows are five times more likely to get milk fever than Holstein-Friesians
• Cows that are too fat or too thin are more susceptible
• Anything that makes a cow sick (mastitis, uterine infections, ketosis) or reduces a cow’s dry matter intake (feed restriction in the colostrum mob) will all increase the risk of milk fever
• A difficult calving.

Milk fever after calving

“The most important way for preventing milk fever at any time is through supplementing cows with magnesium for the last two weeks before calving. Cows should receive 20g magnesium/cow/day,” says Dr Roche.

“This is equivalent to about 40g CausMag (magnesium oxide)/cow/day. If dusting on pasture or silage at least double this rate (80g CausMag/cow/ day),” he says.

“Supplementing cows with calcium (ground limestone) during the colostrum period will reduce the risk of post-calving milk fever.”

Milk fever before calving

Milk fever before calving is less typical and, therefore, far more difficult to deal with, says Dr Roche.

“Pre-calving magnesium is still the most important way of preventing milk fever,” he says.

“Springing cows should not graze effluent (or night) paddocks, because of the increased concentrations of potassium and phosphorus in the grass.

“Most people are acutely aware of the effect of potassium on milk fever and so effluent paddocks are avoided with springer cows. However, fewer people are aware of the effect of phosphorus.”

High dietary levels of phosphorus reduce the effectiveness of vitamin D in helping the cow absorb calcium.

Dr Roche says feeds that are high in phosphorus should be minimised pre-calving.

“This would include silage or hay made from paddocks that get a lot of effluent or by-products like Palm Kernel Extract (PKE), wheat middlings (Broll), and wheat or maize distillers’ grains (DDGs). Although these by-products are relatively good energy supplements and are useful carriers for minerals, where possible, feeding to springer cows should be less than 3 kgDM/cow/day.”