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The detrimental effect of high ash in milk replacers

Dan O’Reilly for Progressive Dairyman Published on 24 May 2016
Excess salt in the calf's diet is a health risk

In recent years, a great deal of attention has been focused on the significance of ash in calf milk replacers (CMRs). In order to understand the importance of ash in today’s CMRs, we first need to define it.

Ash content is commonly expressed as a percentage of the total composition of the CMR. That percentage value represents the overall level of minerals in the product. Although manufacturers are not required to specify the level of ash in a CMR, it is a value that should be carefully considered when evaluating and choosing a CMR to best meet the calf’s needs.

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Measuring the ash content of a CMR is a fairly simple process. Under laboratory conditions, a known amount of CMR powder is exposed to extreme heat for a specific length of time, reduced to ash and then re-weighed.

That weight is then expressed as a percentage of the sampled CMR starting weight. So if we start with a CMR sample weight of 60 grams and end up with 4 grams of ash, that CMR would have an ash content of 6.7 percent.

A standard analysis of the ash in CMR shows it is comprised mostly of sodium, potassium and chloride. These are salts that come from whey powder, which is a byproduct of the cheese industry and commonly used as an energy source in the formulation of CMRs.

Depending on the type of cheese being manufactured, the whey may have ash levels in excess of 10 percent. If the lactose has been removed from the whey (de-lactose whey), the ash level may approach 20 percent.

What does this mean to the calf? Let’s use whole milk as a point of reference. According to the National Research Council (NRC), whole milk from cows contains roughly 6 percent ash on a dry matter basis. Therefore, we can assume a CMR with an ash level of 6 to 7 percent would be appropriate for the calf.

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In fact, the NRC considers an ash level of 7 percent to be the standard for CMRs. Anything above that should be avoided, as it poses specific health risks for the calf. These risks include cellular dehydration, reduced dry matter intake, diarrhea, abdominal pain and other gastrointestinal challenges.

Think of it this way; a CMR with an ash level of 12 percent has the equivalent of 2.5 pounds of added salt in every 50-pound bag when compared to a CMR with 7 percent ash. Furthermore, there is no caloric value in ash, so a CMR with 12 percent ash has 4,500 kCal less metabolizable energy in every 50-pound bag as well.

Dairy nutritionists would immediately understand the disastrous impact adding 5 percent salt to a TMR would have on cow health and performance, yet an additional 5 percent salt in milk replacers for calves is considered commonplace. It should be equally apparent that high-ash CMRs are nutritionally deficient and financially counterintuitive.

When evaluating a CMR, there are a few basic concepts to be considered. On the tag analysis of the CMR, the protein and fat levels are clearly stated. In addition to protein and fat, there is approximately 5 percent moisture.

Everything else is ash and lactose (the sugar found in milk). Therefore, if the level of lactose goes down, as in the case of de-lactosed whey, the ash level goes up and metabolizable energy goes down.

The daily metabolizable energy maintenance requirement for a 100-pound calf is 1,750 kCal. As you can see in the sample calculation in Figure 1, the 7 percent ash CMR provides an additional 300 kCal above the maintenance requirement, which is available to the calf for weight gain.

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The 12 percent ash CMR provides only 209 kCal above the maintenance requirement of 1,750 kCal. In other words, the 7 percent ash CMR provides nearly 50 percent more metabolizable energy for growth than the 12 percent CMR (Figure 1).

Sample calculations illustrating the energy difference between low and high ash CMR's

To summarize, this loss in energy alone is very significant, but when you factor in the detrimental health risks of excess salts in the calf’s diet, it should be apparent that high ash is bad for calves.

To complicate matters even more, many farmers have water softeners installed to treat hard water. This can result in elevated levels of sodium in their water supply, which compounds the negative effect of having high ash levels in their milk replacer.

Therefore, it would behoove the producer to have a discussion with their nutritionist or CMR representative to ensure that optimal nutrition is being provided to your animals by your CMR. If they don’t know that information, it should be available from their quality control department or third-party laboratory.  PD

PHOTO: When you factor in the detrimental health risks of excess salts in the calf’s diet, it should be apparent that high ash is bad for calves. To complicate matters even more, many farmers have water softeners installed to treat hard water. This can result in elevated levels of sodium in their water supply. Staff photo.

Dan O’Reilly
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