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Powdered Milk Replacer Lab Tests 2021 -
Changes, Trends and Possible Action Steps

WildAgain Wildlife Rehabilitation has been conducting research on milk replacer powders and posting the results for wildlife rehabilitators for years. In early 2021, wildlife rehabilitators contacted WildAgain Wildlife Rehabilitation, Inc. with questions about Fox Valley and PetAg milk replacer powders. As a result, WildAgain had 30 additional milk powder products/lots tested at a national certified independent laboratory. A summary of the test results follows, as well as possible action steps for rehabilitators.


Lab test results - summary.

- Moisture content exceeded specifications (Fox Valley).

- Protein levels may still exceed the amount stated on the label but are declining.

- Fat levels are increasing, though Fox Valley products still test low in fat.

- Carbohydrate levels are declining (15 to 50+%).

- Mineral (Ash) content levels are mostly constant.

- Ca; P; and Ca:P ratio values are all within range.

- Kcal content is increasing (due to higher fat levels).

- Fiber levels continue to decrease, but still exceed spec of 0%.

The following test results are based on a typical proximate analysis that quantifies percentage content of Moisture, ProteinFatAsh (minerals) and Crude Fiber. The results also discuss assays for Calcium and Phosphorus (other dietary macro and micro minerals are posted on the Lab Test Spreadsheet). The following chart is a summary overview of most of the 30 recent tests (lots from 2019-2021) and variances from the GA (for individual lot info and test results, click here for the Lab Test Data Spreadsheet). 

Milk Replacer Varaince from Guaranteed Analysis Summary.jpg

Suggested action steps.

Based on the recent test results and trends from prior years, the following action steps can help adjust formula recipes for newly tested milk powder content. 


1.)  The variances in protein, fat and other nutritional component content can affect formula recipes and nutrition in formula – and thus the animal’s well-being. The WildAgain Formula Calculator makes it easy to incorporate more current and precise independent lab-tested nutritional data for each product. 


Many of the milk replacer products are testing well above or below the (GA). Several of the products have been at these higher/lower levels for many years and are only recently trending differently. WildAgain’s Formula Calculator contains years of test data for many powdered milk products. The results of more recent lots of the products are being added regularly (i.e., 30 lots added in June 2021). This tool also helps rehabilitators create formula recipes that are a closer match to the composition of the species milk.  


2.)  Consider using multiple products to formulate a recipe. The old adage “don’t put all your eggs in one basket” applies. If only a single powdered milk product is used in the formula recipe, the formula is solely dependent on the content and quality of that single lot of that product. Mitigate this ‘single product’ risk by incorporating more than one milk replacer powder in the formula recipe, preferably from multiple manufacturers. This approach may also help create a recipe that more closely matches the mother’s milk nutritional profile.


3.)  Supplemental fats may still be needed in some recipes. Since the powders are currently testing higher than previous years, some rehabilitators may wonder if supplemental fats are still necessary for some formulas to better match the species milk composition. Others may be unsure of the effect on the recipe’s overall nutritional content from adding supplemental fat. WildAgain’s Formula Calculator provides a quick and easy way to determine if changes are needed in previously successful recipes are needed for continued supplementation to address fat deficiencies. 


4.) Dietary mineral supplementation seems unnecessary. The test results show that concentration levels for Calcium and Phosphorus consistently fall within an acceptable range, except for GME. The same is true for the Ca:P ratio. If a concern exists that one product has either too much or too little of any specific mineral, a blending approach easily evens out any high or low values and produces a more consistent substitute formula over time. Any mineral supplementation could easily risk exceeding an appropriate amount and inadvertently result in an unacceptable and problematic levels.


5.) Prepare formula carefully and reconstitute completely. Effective formula preparation is essential, yet it is often underestimated and overlooked as a vital and critical success factor in feeding practices. Performed correctly, this involves more steps than the label indicates. A formula mixing guide is available, both in a longer version that provides reasons for each step and a pdf that just lists the steps – regardless of formula recipe used.


Incomplete reconstitution (i.e., converting powder back to liquid form) can quickly compromise the effectiveness of an effective formula recipe for a species. A review of dairy industry and powdered milk research suggests a series of preparation steps that can help improve the chances of producing a more completely reconstituted liquid formula that provides the nutrients in a carefully constructed recipe. 


Some of the suggested steps from published research may be new to rehabilitators and vary from the overly brief instructions on the powdered milk labels. First, weighing ingredients prevents measurement error when using scooped volumes (which can introduce a +/- 10% error in the intended amount of an ingredient). Second, adding the powder to warm water (110° - 130° F) and allowing for some time for the powder to begin to ‘wet’ can improve reconstitution.  Third, since many of the milk replacers have poor wetting properties, much more mechanical mixing (stirring/whisking) is required well beyond a simple stir or shake. Fourth, each milk powder has its own relationship with water, so reconstituting each powder separately and then combining only when in final liquid form, and is beneficial in the appropriate recipe amounts. Fifth, and most importantly, allowing reconstituted milk replacers to rest in the refrigerator for at least 8 hours prior to use enables the milk powders to reconstitute much more completely. After reconstitution is complete, the milk replacer can be successfully combined with other liquid ingredients, such as heavy whipping cream or another fully reconstituted powdered milk replacer. These changes can make a substantial difference in the effectiveness of the formula – and the young animal’s well-being.


[Note: The level of proteins in more commonly used Fox Valley and Esbilac® powders continue to test much higher than the GA. Comprised mostly of casein milk proteins, rehydration requires a much more complete reconstitution process. Since casein is harder to digest and doesn’t reconstitute as readily, higher concentrations of casein could have caused or contributed to the digestive issues reported earlier this year. This could also explain some of the thicker, sludge-like results experienced when mixing a couple of the Fox Valley products.]


6.) Buy fresh and follow good storage practices. Purchase the powdered milk replacers to be used in formula as soon after the manufacture date as possible – do not rely on an expiration date. Ask the vender to provide lot numbers and dates to assess the age of the product. Then immediately and properly store in a cool, cold, or frozen condition, depending on timing of use. 

GME Rancidity Days Since Manufacture.jpg

All fat-rich milk replacer products have a risk of rancidity if not stored properly. This risk increases if milk powder containers are stored at room temperature, especially if opened. GME has been shown to be the most susceptible to oxidation and rancidity formation as early as 4 months from the manufacture date (see chart above). Click here for more info on detecting rancidity and mitigation steps.


The reconstitution properties of dried casein decrease over time as a function of any storage temperature (≈50% stored at room temp over 7-8 months). Colder storage slows this decrease in reconstitution efficiency. If the higher casein products have been stored improperly, even the best reconstitution techniques will be hindered and could result in the ‘sludge-like’ condition described earlier. 

7.) Return or discard products with off-odors or unusual/strange particles. Once a container is opened for the first time, start by checking and inspecting for features that seem unusual or previously unseen. An example is the image at right from a sample of Fox Valley 40/25, showing brownish particles that were seen by rehabilitators, and trapped in a 500µm sieve. Rehabilitators also reported suspect odors from Fox Valley 40/25 containers (i.e., described as banana in some and bubble gum in others) though the label did not indicate different ingredients or added flavorings.

Fox Valley 4025 Brown Specks.jpg

If milk replacer powders do not look or smell normal or ‘right,’ contact the vendor or manufacturer before using. They should have high interest if a product has been sold that fails to meet their internal quality control standards. Ask other rehabilitators if they have had a similar experience. Return the product and ask for a replacement or refund, or discard if concerned or if so instructed. If still unsatisfied, do not use the product and consider alternatives. 


This summary of the 2021 milk replacer testing builds on the prior 17 years of data compiled and analyzed by WildAgain. With that database to draw and build upon, trends become somewhat self-evident in the test results. The nutritional profiles of some products are fairly consistent over time, while others continue to show less consistency and sometimes significant variations between years. While the GA is intended to ‘guarantee’ a minimum or maximum nutrient content, certain products consistently fail to meet those thresholds. Some that have proven consistent over time are now showing troubling and concerning trends. All said, the GAs on product labels are proving to be much less reliable when put to the test through rigorous laboratory analysis. 


Looking beyond all of the charts and trendlines, this round of testing points to additional areas where attention is needed. A final level of quality control is always required on the part of the rehabilitator. As mentioned above, while products/lots may lab-test within expected values, reports of ‘brown specks’ are extremely concerning, and need to be investigated prior to using the product. Take action. Vigilance for the presence of rancidity is always required, even for products that may have never been of concern. Take action it smells odd. If previously unseen sludge appears when preparing formula, try the steps that should lead to a more complete reconstitution of the powdered milk, especially with the higher casein-rich products. If sludge is still present – take action (call the manufacturer, call other rehabilitators, blend with other products, discontinue use of the offending product) and think twice before feeding it to any animal.

For a more complete discussion of the test results, tables and charts, click here.

WildAgain does not have an affiliation with any manufacturer or vendor of powdered 

milk replacer products.

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