Cut feed P to save money

6 July 2001

Cut feed P to save money

Cost-effective solutions to

reduce pollution from

livestock farms were outlined

at a Frank Wright briefing,

Richard Allison reports

CUTTING feed costs by reducing phosphorus in dairy rations will not affect dairy cow fertility or milk production, according to Frank Wrights David Wilde.

"For many years, the phosphorus allowance for dairy cattle assumed 50% of that in the ration was available, but recent research shows it is nearer 70%. This means that excess phosphorous has been unwittingly fed, contributing to environmental pollution and wasting cash."

Most producers and advisers fear reducing dietary phosphorus will cause infertility. But dairy rations typically contain 0.5% phosphorus on a total ration dry matter basis – double the level shown to impair fertility, Mr Wilde told a recent Press briefing.

Confusion over the inclusion of low phosphorus exist because research has not separated the effects from insufficient energy and protein.

He advised formulating dairy rations to contain 0.4% phosphorus for cows yielding more than 25kg and 0.34% for cows yielding less. "This new level is based on extensive US research and includes a safety margin."

But speaking to farmers weekly, Gordon Hemingway of the Glasgow University Vet School, argued that phosphorus level should be nearer 0.45% for cows yielding more than 35kg. "Herds averaging 25kg a day will include a large range of yields and 0.4% could be marginal for some cows."

And David Beever, of Reading University, sees no major problem with cutting back on phosphorus, but highlights the need for more research. "We need to unravel the reasons why dairy cows excrete so much phosphorus.

"The cows gut appears to have a major role in phosphorus recycling, but little is known. With this knowledge, we may further reduce phosphorus excretion by dairy cows."

Mr Wilde added that to achieve this new lower level in rations, phosphorus content of parlour concentrates must be reduced to 0.5% in winter and 0.4% during summer. "The difference between winter and summer reflects the higher phosphorus content of grass compared with winter forages."

Most high protein rations contain enough phosphorus without adding any extra. "However, do not cut out trace elements, but change to a low phosphorous vitamin and mineral supplement."

Also consider calcium levels in the diet because excess calcium will reduce the efficiency of phosphorus use by dairy cows. Aim for a calcium to phosphorus ratio of 1.75:1 by replacing di-calcium phosphate with limestone. This will also reduce ration costs, said Mr Wilde.


&#8226 Fertility and milk yield unaffected.

&#8226 Lower ration cost.

&#8226 Reduces environmental pollution.

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