Reduced phosphate excretion by dairy cattle by cutting at a later stage

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The phosphorus content in grass is lower if the grass is cut at a later stage. This also means that the phosphate excretion of a dairy herd is reduced and farms that use BEX benefit from cutting later. But the energy and protein content of the grass is also less. In order to keep milk production at the same level, approx. 250 kg more concentrates are required per cow. Cutting at a later stage also has consequences for farm management: grazing is more difficult as parcels for cutting have to be left to grow for longer. This is shown by research by Wageningen UR Livestock Research commissioned by the Dutch Dairy Board.

By cutting grass at a later stage than normal it is possible to reduce the phosphate excretion on a dairy farm. The phosphorus content of grass decreases as the grass gets older. But as energy (VEM) and raw protein also fall with ageing, more concentrates (with phosphorus) are required to maintain milk production. For rations composed of (approximately) more than 70% grass, there is still reduced phosphate excretion despite the higher consumption of concentrates. The greater the percentage of grass, the greater the reduction, as the P content of a larger part of the roughage is reduced. This can be beneficial if a farm uses  BEX (Excretion Indicator) and has to dispose of manure based on phosphate. It is also advantageous for farms that use the KringloopWijzer (Recycling Indicator) as the reduced excretion is not the result of a reduction in the total uptake of nutrients on grassland. At farms where the surface area of silage maize is approximately 20% and the cattle graze, cutting later has little to no effect on the phosphate excretion as the P content in the basic ration is already low.

mpact on farm management

Cutting at a later stage can also result in a financial advantage as there is less surface area to cut. The total dry matter production is also higher with grass, but it has a lower feeding value. However, cutting later does have consequences for farm management. The grass has to be left to grow for longer so there is less land for grazing. In the case of intensive grazing this may mean that there is a (temporary) shortage of grass for grazing in dry periods, for example, while in the indoor period grass silage is left over. It is true that there is more grass silage then, but it is of a lower quality. Approximately 250 kg more concentrates are required per cow to keep milk production at the same level.

Maximum reduction 6.6 kg phosphate per ha

With 100% grass silage in the rations and keeping cattle indoors completely, the maximum reduction in excretion is approximately 6.6 kg phosphate per ha, which corresponds to 4.4 m3 slurry, as calculated using the BedrijfsBegrotingsprogramma Rundveehouderij (BBPR) the budget model for dairy farms developed by Wageningen UR Livestock Research. 

Cutting at the normal stage gives approx. 3000 kg dm/ha until June, including first cut, with approx. 2500 kg dm/ha in July and with approx. 2000 kg dm/ha after July. Cutting at a later stage results in approx. 4500, 4000 and 3000 kg dm/ha, respectively.

The effects are the opposite for cutting at an earlier stage: phosphate excretion increases, (more) roughage must be supplied, the consumption of concentrates falls and fodder production costs increase. The reduction in the content in grass silage is approximately 0.03 g phosphorus per kilogramme dry matter per day that the grass continues to grow. This has been demonstrated in field trials. More results and background information can be found in the reportLagere fosfaatuitscheiding op melkveebedrijven door zwaardere maaisneden' (‘Reduced phosphate excretion on dairy farms by cutting at a later stage’). 

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