Dry Matter Versus Wet Matter Basis – What’s The Difference?
This website provides considerable quantitative data about various milk replacer products and other substitute milk formula ingredients – both in dry form and wet form. The DRY form is a powder, prior to mixing with water. The WET form is either 1) a product purchased already in a liquid form, or 2) a dry powder after mixing it with water. The component percentage values for solids, moisture and ME kcals are significantly different, depending on whether the product is in the dry or wet form.
Questions and misconceptions regularly arise because of this difference between wet and dry forms, and at times, due to ambiguous disclosures on the product labeling.
Here are a couple of recent social media posts. You decide, as a rehabilitator, if what is said is accurate.
Post #1. Removing names and species, here is a paraphrase of the first post:
“…a can of liquid Esbilac says it contains >4.5% protein, while the bag of powdered Esbilac is greatly different at >33% protein. I’m using the powder for sure as it has 7 times more protein and so should you!”
Do you think this is correct? _____ Yes _____ No (see complete answer below)
Hint: Since these two products are both Esbilac, do you think one would have 7 times the protein as the other?
Post #2. Removing names, here is a paraphrase from another post:
“…in comparing calories between Goats Milk Esbilac and FoxValley 32/40, the GME has 900 calories and FV 32/40 has 5480 calories. That's why the animals are gaining weight so much better on FV and why everyone should use it. The GME label says 900 kcals/kg. And since FV reports it per 100 grams (548 kcals per 100 g powder), you need to multiply it by 10 to make it per kg, therefore 5480.”
Do you think this is correct? _____ Yes _____ No (see complete answer below)
Hint: Since these two products are 32/40 & 33/40 formulations and have almost identical protein and fat content, and they weigh nearly the same in grams, do you think one has 6 times more kcals as the other?
Answer to Post #1 - Esbilac®.
The answer is no - one form of Esbilac® does not have 7 times more protein than the other. The percentage values for Esbilac® are indeed correct, but one is for dry powder while the other is for wet liquid. The discussion presented below shows how to adjust dry to wet values, or wet values to dry, in this case, for the same product. And yes, it involves a little bit of math.
Consider columns B and C in the table below. Column B shows the values for liquid Esbilac® with solids at around 15%. That means that most of the can is water. Column C shows the values for powdered Esbilac® with solids around 95%. Most of the package is dry powder, with very little moisture or water content. Whether in a wet form or a dry form, the more total solids a product contains, the more nutrients such as protein, fat, carbohydrates, minerals, etc. it contains. Therefore, it contains less water.
Understanding the dry matter values is beneficial in two ways. First, it provides a basis when comparing values of other products, making sure they are comparable on a dry to dry basis, such as shown on the Lab Test Data Spreadsheet displaying values from the proximate analysis (proteins, fats, etc.). Second, it provides the user with a starting point to estimate what the wet values will be when mixed with water.
[Note: In deference to technical accuracy, the term ‘dry matter basis’ refers to a substance where all of the moisture (water) has been removed, which makes analysis of wet and dry foods most easily comparable on a 100% dry basis. To make this discussion more straightforward, and to avoid considerable math and conversions, the term ‘dry’ used herein means “powder as purchased and prior to mixing with water,” recognizing that the milk replacer products contain 4-6% moisture (water).]
The table below and the accompanying explanations provide a more thorough overview of the difference between wet and dry matter values. It uses the mother's milk composition of the Eastern gray squirrel as an example, comparing the values of the mother’s milk to a formula based on using powdered Esbilac®. Similar comparisons may be easily developed for other species by using the Wildlife Formula Calculator.
Column A. This column shows the values for the Eastern gray squirrel mother’s milk, based on an average of the proximate analysis values reported in the studies conducted by Shaul (1962) and Nixon and Harper (1972). Values shown are for the percent of total solids, protein and fat as contained in the milk. The kcals (calorie or energy) value for 1gram (or 1cc) of milk is also shown, using the standard Atwater system calculation. These values are generally used as a starting reference point when designing any formula recipe, based on using one or more of the powdered milk replacer products. This column is on an as-fed or wet matter basis.
Column B. This column shows the values for Esbilac® sold as liquid in a can. Most rehabilitators do not purchase this form of milk replacer, as they are more expensive, require more storage space than powdered products, must be used quickly after opening, and are not as close a match to wild mammal milks. This column is on a ready-to-use, as-fed or wet matter basis.
Column C. This column shows the nutritional values for Esbilac® powder. This is the form of milk replacers preferred by most rehabilitators due to lower cost and easier storage. These values are listed on the labeling for the product and indicate either minimums or maximums, commonly referred to as the Guaranteed Analysis. Note: The value for kcals is not provided on a dry basis on the label but is only reported on a wet basis for a formula reconstituted at 1 part powder mixed with 2 parts water ("as reconstituted 2:1"). The label introduces confusion in two ways. First, in describing the product, it displays different numbers on a different basis. It states dry form for nutritional components and wet form for kcals. Second, while a value for ME (kcals) is provided, it lacks an accompanying descriptor indicating the calculation convention used - whether standard Atwater, or the lesser value modified Atwater adopted by the Association of American Feed Control Officials (AAFCO). Unfortunately, this column mixes apples and oranges as to a common matter basis.
Column D. The values in this column are the results of independent laboratory testing for 13 lots of Esbilac® produced in 2019. A proximate analysis was performed, as well as a mineral analysis. These are all dry matter values, and are much more precise and reliable than the Guaranteed Analysis values shown in column C. These values are accurate to within the +/- 5-7% which is the generally accepted analytical measurement error. This column is on a dry matter basis (again defined as the powder in the package).
Columns E and F. The values in column E are for a wet formula that was prepared using one part of powder and two parts water, as directed on the Esbilac® label. The percentage values for solids, protein and fat are much lower than the values in Column C, since the full-strength powder has been diluted by mixing it with water. Column F shows that this formula falls below the values for the mother’s milk (Column A) by 50-60%.
Columns G and H. The values in column G are for a wet formula that was prepared using one part powder, 2 parts water, and 1/3 part heavy whipping cream. Again, the percentage values for solids, protein and fat are much lower than the values in Column C, since the powder was diluted by mixing with the water and cream. But as shown in Column F, this formula recipe more closely matches the values for the mother’s milk (Column A), within about 60-80%. To prepare a formula that approaches 100% to mother’s milk would require a level of solid matter that is not well tolerated by very young squirrels and can cause health problems. Mother’s milk admittedly contains more solids, as it is precisely tailored to be digestible by the squirrel’s developing digestive system – certainly more so than a commercial milk replacer powder.
A take-home message of this discussion can be illustrated by the following thought and example. In the past, some rehabilitators have refused to consider using liquid Esbilac® in the can because it is so dissimilar to the powdered version in terms of nutrient content, with some referring to it as ‘Esbilac® Light.’ Given the discussion of wet vs dry above, let’s see if this is actually a true characterization…
The table to the right excerpts from the larger table in the discussion above, focusing just on columns B and E. Since these columns are both on a wet matter basis (B showing liquid can values and E showing the powder reconstituted 1 part powder to 2 parts water), they can now be compared on an “apples to apples” basis. As shown, the nutrient values and kcals are so very similar, such that the label of a ‘Light’ product is most likely unwarranted.
Answer to Post #2 - GME versus FoxValley 32/40.
The answer is no - as the two products are very similar in kcal content. This comparison is a bit more difficult in that the post is evaluating the two different products on an inconsistent basis. One is quoted in dry powder form and the other in wet liquid form. This is apples to oranges, and illustrates a very common confusion, as evidenced in this post, between comparing substitute milk replacer products on a dry versus wet matter basis. The example below compares the products on a dry-to-dry matter basis, and then compares them on a reconstituted wet-to-wet matter basis. As you will see, they are almost identical in kcal content.
Comparing on a dry to dry matter basis
The FV 32/40 website indicates 548kcals/100 grams of dry powder. So to get a gram equivalent, you need to divide both sides by 100 to get 5.48 kcals/ 1 gram of powder. A way to verify this is to use the Standard Atwater factors as shown in the blue shaded box below. The factors are applied to the nutritional components of percent of protein, fat and carbs. The math yields 5.48 kcals/gram.
Apply the same procedure and math to the GME in the yellow shaded box and it yields 5.52 kcals/gram. Very slightly higher than the FV 32/40 due to containing one percentage point higher protein content. As shown, the two products contain almost identical kcal values.
Comparing on a wet to wet matter basis
This comparison is a little more difficult but can be done easily with the right data. For each product you need the weight (in grams) of one tablespoon of the dry powder and the kcals/gram of the dry powder as just calculated above.
The calculations for both products are shown below. You first calculate the weight of a reconstituted wet formula. Then, you take the proportion of that liquid formula that constitutes the now reconstituted powder (as shown, 19-20% in this case) and multiply that value by the kcals/gram of the dry powder calculated previously above.
The result is the GME wet formula contains 1.117 kcals/gram and the FV 32/40 contains 1.037 kcals/gram.
So the GME is only slightly higher in kcals (around 8% higher) than the FV 32/40. That is driven by the fact that lab tests indicate that GME weighs about 8% more in the dry matter form.
WildAgain's Wildlife Formula Calculator mentioned above takes care of all of the required math and conversions from dry to wet matter basis, even when combining dry ingredients (milk replacers) with wet ingredients (water, cream etc.). If you see a posting on social media and want to check it for accuracy regardless of species, you can do the math yourself. Or use the Calculator and allow it to do that work for you!
If you glance at a product package label that seems confusing, because it seems to imply that wet and dry matters are somehow interchangeable, just know they are NOT. It is confusing as there is no standardization between how the manufacturers disclose kcal value contents of the product. Only after you understand the differences in how they are presented and calculated, can you then realize they must be normalized to some comparable basis, generally a dry matter basis. Then they are comparable!