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The crude and true story of milk protein

Tom Wright and John Cant for Progressive Dairyman Published on 31 May 2019

The system for payment for milk protein changed in Canada in September 2018 from one based on crude protein (CP) to the new system based on the true protein content of milk.

The first thing most dairy farmers noticed after the change was: The reported milk protein levels for their milk shipments were lower than they were used to seeing.

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Adjustments to the prices used in component pricing ensured the change was designed to be revenue-neutral for producers.

The switch to using true protein was implemented for payments to producers and for billing processors. Other countries have previously adopted true protein as the standard, including Australia, France and the U.S.

Implementation of this change in the industry was seamless because the laboratory equipment used to measure CP and true protein is the same, and the calibration standards used to ensure accuracy are provided by the manufacturer of the equipment.

CP measures nitrogen-containing molecules, including the major milk proteins, casein and whey. But CP also includes non-protein nitrogen (NPN) compounds like urea, ammonia, creatinine and many others present in milk at very low levels.

These non-protein compounds have no economic value in the dairy industry. By switching to a system based on true protein (casein and whey), it excludes paying for the compounds in milk that have no value for further processing.

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The NPN compounds in milk represent between 4.5 and 5.7 percent of protein when the old CP system was used. The dominant compound in the NPN is milk urea nitrogen (MUN), which accounts for about 50 percent of the total.

The rule of thumb is to add 0.19 percentage units to the reported true protein result to get an approximation of what the CP result would have been.

As you might expect, the rule of thumb works for most herds most of the time, but there are some things that can influence the difference between measures of true protein and CP: Season (higher environmental temperatures will lower CP percent in milk); mastitis will lower milk casein but increase whey; days in milk (CP, casein and NPN drop after calving then start to increase after five to 10 weeks); lactation number (casein content drops as parity increases); and then there are also breed differences and genetic differences.

Feeding management also plays a role in the NPN content of milk. MUN is a breakdown product from the protein in a cow’s diet. Dairy farmers get information on the MUN levels in their shipments after every pickup.

Some producers routinely monitor MUN levels to verify that their feeding program keeps MUN within their target range and to ensure the ration is balanced for protein and energy.

Best practices for MUN monitoring are to use the weekly average for MUN values as opposed to making ration adjustments after every report because there is always some change in the value from each bulk tank analysis.

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MUN values above 12 to 14 milligrams per decilitre, or very erratic values, can signal there is room for improvement in the feeding program or ingredient consistency.

Recently, milk samples were collected twice weekly from a group of 28 cows at the University of Guelph fed the same diet and housed in the same pen during the fall of 2018.

Each of the 500 samples was analyzed for both CP and true protein, as shown in Figure 1.

Crude protein and true protein results from 28 cows fed the same diet sampled routinely during the fall of 2018

In each case, the value for true protein was lower than the value reported for CP, as expected. The difference between the two protein measurements is shown in Figure 2.

The difference (crude protein % - true protein %) between reported values for the milk samples averaged 0.196, which is close to the expected difference

The average difference between percent CP and percent true protein was 0.196, which is very close to the rule of thumb of 0.19.

The maximum difference was 0.27, and the smallest difference was 0.13, suggesting the rule of thumb works but there can be some variation at the individual cow level from day to day.

The take-home message on the switch from CP to true protein is: For most herds, you can estimate CP by adding 0.19 to the reported true protein value.

Monitoring MUN, which is the largest part of NPN compounds in milk, is an effective way to check that the feeding program is not wasting dietary protein being fed to milking cows.

If your MUN values are high, you can discuss that with your feed adviser to avoid wasting nutrients.  end mark

John Cant is a professor at the University of Guelph.

Tom Wright
  • Tom Wright

  • Dairy Specialist
  • OMAFRA

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