Phosphorus is an essential mineral for calving cows. Ensuring your fodder beet crops are well maintained can help to “fortify” P, advises Dr Jim Gibbs. Anne Lee reports.

Phosphorus (P), like calcium (Ca) is in high demand at calving with cow requirements for the essential mineral climbing during the last two weeks of pregnancy so ensuring supplement is “fortified” with P if it’s low in the wintering diet is a must.

Lincoln University senior lecturer and veterinary scientist Dr Jim Gibbs says Ca and P are stored together in bones as hydroxyapatite, but the control of P in the blood is very different to that of Ca.

“The most important driver of P status of the cow is the % uptake from the diet – this can be very low (<20%) when P is in surplus, and high (>70%) when P is low.”

If blood P is low after calving, there are two tell-tale signs farmers may see:

  • Usually, more milk fever cases in general
  • In extreme deficiency cases, ‘creeper cows’ are seen – these are down cows after calving, but mentally brighter than milk fever cases and just can’t get up. They respond poorly to Ca.

If both of these are seen, it is likely that P intakes across winter have been low.

Jim says higher production herds are more likely to be at risk.

In fodder beet wintering, P is largely held only in the leaf, and only ‘green’ supplements have high P content.

“Therefore, in poor crops with low leaf, when the herd is fed hay/straw/cereal silages as a supplement, the diet P can fall below recommended levels (0.24% drymatter).

“In well managed crops with good leaf, and where grass silage or pasture makes up the supplement, P intakes are almost always above P requirements according to the internationally accepted feed reference standards.”

Where P content of the beet and supplement total diet is below requirement, the best supplement to supply P is DiCalcium Phosphate (DCP), an inexpensive and easily available mineral powder, he says.

The addition of 50g/cow/day supplies about 9g of P, and is easily spread across supplements to be fed every day.

More than 50g DCP/day is never required, he says.

For those poorer crops with low leaf or when low P supplements are being added DCP should be fed every day in winter, and then continued in the springer ration to calving.

Don’t rely on methods of supplementation of P that involve cows voluntarily accessing it.

Licks, blocks and crumbles are all voluntary supplements and it’s impossible to know if every cow has used them.

This can leave a significant % of the herd exposed to P deficiency – often 35%, he says.

You can’t rely on dosing cows via water either.

“In winter, beet crop fed cows are highly overhydrated because beet is a low DM% feed, and cows can be eating 100+L of water a day – so many will not drink at all.

“Relying on water soluble P sources is useless and dangerous,” he says.

In fodder beet crops where a high proportion of the bulb is in the ground the amount of P in daily intakes of cows feeding on well leafed crops is more unlikely to be below requirements.

A large-scale study currently underway looking at the proportions of bulb and leaf being eaten will shed more light on feed characteristics of cow intakes in New Zealand.