The Detrimental Effect of High Ash in Milk Replacers

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DSC_0214In recent years, a great deal of attention has been focused on the significance of ash in calf milk replacers (CMR). In order to understand the importance of ash in today’s CMR’s, 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 that best meets the calf’s needs.

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%.

A standard analysis of the ash in CMR shows that is comprised mostly of sodium, potassium, and chloride. These are salts that come from whey powder, which is a by-product of the cheese industry and commonly used as an energy source in the formulation of CMR’s. Depending on the type of cheese being manufactured, the whey may have ash levels in excess of 10%. If the lactose has been removed from the whey (de-lactose whey), the ash level may approach 20%.

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% ash on a dry matter basis. Therefore, we can assume that a CMR with an ash level of 6 – 7% (such as ANC’s IDEAL Milk Replacers) would be appropriate for the calf. In fact, the NRC considers an ash level of 7% to be the standard for CMR’s. 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 to the calf. Think of it this way, a CMR with an ash level of 12% has the equivalent of 2 ½ pounds of added salt in every 50 lb. bag when compared to a CMR with 7% ash. Furthermore, there is no caloric value in ash so a CMR with 12% ash has 4500 kCal lower metabolizable energy in every 50 lb. bag as well. Dairy nutritionists would immediately understand the disastrous impact that adding 5% salt to a TMR would have on cow health and performance, yet an additional 5% salt in milk replacers for calves is considered commonplace.  It should be equally apparent that high ash CMR’s are nutritionally deficient and financially counter-intuitive.

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% 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 delactosed whey, the ash level goes up and metabolizable energy (ME) goes down. The daily ME maintenance requirement for a 100 lb. calf is 1750 kCal. As you can see in the sample calculation below, the 7% ash CMR provides an additional 300 kCal above the maintenance requirement which is available to the calf for weight gain.  The 12% ash CMR provides only 209 kCal above the maintenance requirement of 1750 kCal. In other words, the 7% ash CMR provides nearly 50% more ME for growth than the 12% CMR!

Here are the sample calculations illustrating the energy difference between low and high ash CMR’s:

20% Protein + 20% Fat + 5% Moisture + 7% Ash + 48% Lactose = 100%   (2050 kCal ME/lb.)

If the CMR has an Ash Content as high as 12% then the calculation would be:

20% Protein + 20% Fat +5% Moisture + 12% Ash + 43% Lactose = 100%   (1959 kCal ME/lb.)

  • The metabolic energy (ME) of both lactose and protein is 4 kCal/gram, and the ME of fat is 9 kCal/gram.
  • Therefore, the ME of 1 pound dry matter of CMR would be:

At 7% Ash –                         2050 kCal ME/lb.

At 12% Ash –                       1959 kCal ME/lb.


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 farmer to have a discussion with their nutritionist or CMR representative to insure 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 QC department or third party laboratory.

Article originally written for Progressive Dairyman.

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