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Powdered Milk Replacer Analysis - Summer 2021 Update



During the first half of 2021, several wildlife rehabilitators contacted WildAgain Wildlife Rehabilitation, Inc. with questions and concerns about milk replacer powders. They had purchased these in advance of the upcoming season and had just begun feeding to young wild mammals. As a result of these questions, and to continue WildAgain’s ongoing product research, a total of 30 milk powder products/lots were tested at a national certified independent laboratory. In-depth follow-up interviews were conducted with rehabilitators using the products. This paper summarizes and highlights test lab results for the products tested (lots manufactured in 2019-2021), examines critical trends, and suggests some simple strategies to address certain issues. Lastly, it poses some remaining questions that may warrant discussion and examination.


Here are the primary questions to be addressed:


1) What were rehabilitators’ concerns/questions about the milk powders in 2021?

2) What were the results of the 30 recent lab tests on the milk replacer powders made in 2019-2021? (In summary, what do the results mean in terms of trends and implications?)

3) What do the test results reinforce and/or confirm – and what do we still not know?

4) What action steps we should consider taking? 

Note: As in the past, WildAgain continues to provide information regarding substitute powdered milk replacers powders such as lab test results, trends, limitations of preparing and using certain products, and suggested strategies for optimizing the performance of the products for use in wild mammal substitute milk formulas. As always, it remains the responsibility of the individual rehabilitator to decide which products to incorporate into their feeding practices. While WildAgain may offer observations and suggestions, we are not advising on the preferred use of one or more specific brands, products, or formula recipes.

1) What concerns/questions did rehabilitators express about the milk powders?


Some containers of Fox Valley 40/25 with recent lot numbers (made in 2020-21) were found to have unexpected odors described as “bubble gum” or “banana”. In conversations with rehabilitators, Fox Valley management acknowledged this as ‘new’ intentionally added product flavorings (different from the previous vanilla-like scent). Fox Valley mentioned the option to request a particular ‘flavor.’ While the list of ingredients on the Fox Valley 40/25 label concludes with an obscure “…natural and artificial flavorings,” this provides no guidance to the user as to which flavor is included; when such flavorings are changed or substituted; or whether the product could be purchased ‘unflavored’.


Some rehabilitators reported that a few lots of Fox Valley 40/25 contained unidentified brown particles in the powder, which had not been noticed in previous years, and wondered could the brown specks have resulted from new flavoring ingredients, contaminants, or burnt particles. They also expressed concern over whether this could have contributed to animals developing a variety of nutritional and health problems after being fed that particular milk powder.

Fox Valley 4025 Brown Specks.jpg

FV 40/25 sample as sent to WildAgain. Visible brown particles observed.              Material trapped with 500µm sieve. (500µm = 1/2mm)

Some rehabilitators reported that Fox Valley 32/40 and 40/25 developed a thick ‘sludge’ on the bottom of mixing containers when preparing the formula using their previously successful mixing procedures. It clogged feeding syringes, gavage tubes and bottles, and affected feedings. Additionally, it prompted immediate concerns about the palatability and digestibility of such ‘sludge.’


A few rehabilitators who were using the Fox Valley 38/47 product in a formula recipe for rabbits questioned how the lab analysis results compares to the Guaranteed Nutritional Analysis on the label. Since it was a less familiar product, they knew other milk powders had varied from the label, and we had not previously tested it, they wanted to see if lab tests confirmed label values.


An unopened (6 month from manufacture date) can of Goats Milk Esbilac® (GME) powder stored at a cool temperature and then opened (12 months prior to the expiration date) was tested to confirm that it was still fresh and that the very mild detectable ‘goat’ odor was not indicative of rancidity. Concurrently, a can of Meyenberg Whole Goat Milk Powder (human grade) was also submitted for rancidity testing, as well as a proximate analysis with minerals.

2) What were the results of the lab tests on the milk replacer powders from 2019-2021? (What do the results mean in terms of trends and implications?) 

Proximate analysis and dietary minerals


The following test results are based on a typical proximate analysis that quantifies percentage content of Moisture, Protein, Fat, Ash (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). The results for the individual nutritional components are discussed in more detail below:

Milk Replacer Varaince from Guaranteed A

“Expected Value” versus the “Guaranteed Analysis” – a different perspective. As shown in the preceding chart, some trends quickly emerge. For example, for the Fox Valley products, the trends that Proteins are running consistently higher than the GA and Total Solids are running consistently lower than the GA. With that being the case, is there a more reliable metric to use to predict the product content? We believe there is. But first, here is a brief perspective on the term “Guaranteed Analysis.”


In conjunction with the FDA, many states have utilized recommended pet food labeling regulations associated with the Association of American Feed Control Officials (AAFCO - a voluntary membership association of local, state and federal agencies that develops model regulations and industry standards). Most states have adopted the standard that all pet food labels require a Guaranteed Analysis (GA) on the label to advise the purchaser of the product’s nutrient content. Basically, label guarantees are required for minimum percentages of crude protein and crude fat, and maximum percentages of crude fiber and moisture. 


While these GA values for min/max content are helpful in communicating a required threshold or baseline, they may exceed the guarantee by a small or large margin. This excess is almost assured given that AAFCO suggests to a manufacturer when setting the GA to use a number that will most likely be satisfied 95% of the time. The GA values are not intended to establish an ‘expected’ value for the nutritional component. 


WildAgain’s years of tests results provide the foundation to formulate an “Expected Value” based upon actual test data and trends. For example, if a product has a GA for minimum protein at 33%, but the last 10 test results average a level of 36%, which is the better indicator? The reader can decide, but WildAgain believes “Expected Value” is a better indicator for the product’s actual content. We will consistently reference the GA in our analysis and begin to provide an accompanying “Expected Value” based on prior lab test results for a given nutritional component where meaningful.

Total solids – (aka everything that is not water)


Moisture (water) content (%) is reported as part of the proximate analysis. To calculate Total Solids, simply subtract the moisture content from 100%. Total solids are composed of Proteins, Fats, Carbohydrates, Ash (a term for dietary minerals) and Crude Fiber, if any. The Total Solids percent content in all of the powdered milk replacers tested have a Guaranteed Minimum (GMin) of 95%. More accurately stated, the label actually indicates a Guaranteed Maximum (GMax) of moisture (water) of no more than 5%. This is a required regulatory disclosure by each manufacturer for each product to meet this threshold. A very low moisture content in a dry, powdered product seems obvious and expected.


The following charts show Total Solids values for PetAg and Fox Valley products for 15+ years. For all of the products tested (sample size of 172 and including the recent thirty 2021 test results) the long-term average value is 95.2%, or just about the same as the GMin for Total Solids. That’s good news and reassuring. The trendline predicts this to continue with little variation in the future. However, the trendlines are different for the two manufacturers, with PetAg trending higher over time and Fox Valley trending lower over time (and at a faster rate, most notably influenced by the more recent testing of Fox Valley product lots manufactured in 2020 and 2021).

Total Solids All Milk Replacer Products.
Total Solids PetAg products.jpg
Total Solids Fox Valley Products.jpg

This recent decline in the Fox Valley results for Total Solids puts into perspective the notion of an “Expected Value” versus an over-reliance on the GA as a predictor of Total Solid content in the various products. Consider the following summary table. 

Total Solids Expected Values.jpg

In the case of the PetAg products, the pre-2021 testing helps to establish an “Expected Value” of 95.6% which exceeds the GMin% of 95%. The recent tests report an average value of 95.7 which is well within the range of an expected value. Conversely, the recent Fox Valley test results report an average value well below the “Expected Value” and is causing the long-term trend to decrease and fall below the GMin%. Here are two additional views of the Total Solids test results:

Total Solids PetAg 2019 2020.jpg
Total Solids Fox Valley 2019 2021.jpg

Takeaway thoughts. On average, the PetAg products appear to be within the GA spec and the expected value. However, ALL of the Fox Valley products yielded surprising, troubling and very consistent results with test values below the GA spec; below the expected value; and trending downward. This means the moisture content has increased from 4.6% on average to 6.7%, an astounding 45% increase in water. That increase in water means less Total Solids (which means less total protein, fat, carbs and ash). While the cause for this is unknown, it could result from significant change(s) such as Fox Valley’s product ingredients, formulation, manufacturing process, or an internal quality control issue. 



Proteins in whole cows’ milk are approximately 80% casein and 20% whey. The Guaranteed Minimum (GMin%) for total protein in powdered milk products will vary depending upon the ingredient formulation for that specific product, and can result in significant deviations from the 80/20 mix found in whole milk.


The following chart shows total Protein values for PetAg and Fox Valley products for 15+ years. The long-term average variance from the GA for all products is 8.2% for all of the product/lots tested (sample size of 168 and including the recent thirty 2021 test results). That’s good news and reassuring that on average the products are in-spec in terms of exceeding the GA. This variance is about 2.5 times greater for the Fox Valley products overall. The trendlines suggest that the PetAg products are trending lower and closer to the GA. While the variance of the Fox Valley products are leveling out from the GA, they show a remarkably larger spread of values above and below the GA than seen in the PetAg products.

Protein Contents Milk Replacers Trends.jpg

Here is a view of the “Expected Values” of Total Protein from prior testing as compared to the reported values for the 2021 testing:

Protein Expected Values.jpg

In the case of the PetAg products, the current test results show protein 30% below pre-2021 testing “Expected Values.” This also influences a decline in the long-term trendlines. The Fox Valley results are within expectation but accompanied by a wide spread of variances depending on the specific product. Here are two additional views of the Protein test results:

Protein Trends 2019 2021.jpg

Takeaway thoughts. With only a couple of exceptions, the Fox Valley products averaged above GA values for Protein. The Fox Valley products have averaged high values over the years at about 13% above GA, with the current round of testing averaging 9.4% above GA. WildAgain’s Wildlife Formula Calculator incorporates these variances for the use when constructing substitute milk formula recipes. PetAg’s overall average has decreased about 30% (from 5% to 3.4%) and is testing closer to the GA. It is critical to review and consider the test results from individual products. Variances from GA seem consistent in the most recent tests for individual products, with Esbilac® at 12% above; GME just slightly below; and the Zoologic products at or just above the GA. 



Fats in powdered milk replacers can be sourced from many ingredients that are plant (a variety), dairy (butterfat) or animal (lard) based. The Guaranteed Minimum (GMin%) for total fat will vary depending upon the ingredient formulation for that specific product. This can result in significant deviations from the mix of saturated and unsaturated fats found in mother’s milk and can affect digestibility in young animals. 


The following chart shows total Fat values for PetAg and Fox Valley products for the past 15+ years. For all of the products tested, the long-term average variance from the GA for all products is -3.5% (sample size of 168, including the recent thirty 2021 test results). That’s not good or reassuring news that, on average, the products are out of spec in terms of failing to meet the GA. This negative variance is about 3.5 times greater for the Fox Valley products overall. The trendlines do provide encouraging news suggesting that the PetAg and Fox Valley products are both trending higher and closer to the GA. 

Fat Trends Milk Replacers 2019 2021.jpg

Here is a view of the “Expected Values” of Total Fats from prior testing as compared to the reported values for the 2021 testing:

Fat Expected Values.jpg

The current test results show a welcomed improvement in fat levels in PetAg products, above pre-2021 testing “Expected Values” and on spec with the GA. The Fox Valley products also show a welcomed increase in fat levels, but further improvement would be needed to meet the GA spec. Here are two additional views of the Fat test results:

Fat Test Values 2019 2021.jpg

Takeaway thoughts. As highlighted in the red-shaded cells in box above, both PetAg and Fox Valley products have tested consistently below the GA for Fat, but much more so for Fox Valley. This trend seems to be improving in that PetAg, on average, seems to be testing more closely to the GA and above the previously expected value. Fox Valley, on average, shows an even higher level of improvement towards the GA, but continues to test below acceptable levels. These tests highlight the importance of knowing the composition of the individual powders and comparison to GA. 

Kcals/gram – (aka Metabolizable Energy values)


The energy content (measured in kcals/gram) is not specifically measured in the proximate analysis, but is determined by the other proximate analysis reported values. Additionally, no specific GA is required to be disclosed for kcals/gram. A ‘kcal GA’ can be imputed by using GA values for other nutritional components. The following two charts show how the test results compare to these values for metabolizable energy content:

Kcal trends in milk replacers.jpg

Takeaway thoughts. The calculated Kcal values consistently equal or exceed the imputed values (shown in the blue columns above), if calculated simply using the GA for each product.  The exceptions are the very highest fat content products for both Fox Valley and PetAg. Products that do not provide the requisite daily Kcals may result in inadequate diets and undernourished animals.



The carbohydrate portion of biological material is made up of nitrogen free extract and crude fiber. Nitrogen free extract is also known as soluble carbohydrates, which consist of water, soluble vitamins, monosaccharides (simple pentose or hexose sugars), oligosaccharides (compound sugars), and polysaccharides (starches). Insoluble carbohydrate (crude fiber) is mainly polysaccharides consisting of hemi-cellulose and cellulose.


While a value for crude fiber is provided with a proximate analysis, a value for total carbohydrates is not. Rather, carbohydrates are typically derived by the calculation of Total Solids minus the following: Protein, Fat, Crude Fiber and Ash. As such, carbohydrates are a ‘remainder’. This calculation is often labeled as Nitrogen-Free Extract, or NFE. It is possible for a lab to test for specific components of carbohydrates, such as by conducting a sugar panel for dietary sugars such as dextrose, sucrose, lactose, etc.


The carbohydrate value is not tested, not subject to a GA disclosure, and is a product of many other variables. Therefore, an analysis of carbohydrate values, changes and trends is best performed on individual products, and not on an overall view of all of a manufacturer’s products combined. The following charts show the carbohydrate values for the last four years of available test data for several products. In order to focus primarily on carbohydrates, the charts have combined protein, fat and ash for simplicity in presentation. Fiber values are displayed for later discussion.


Esbilac® and Fox Valley are very similar in formulation so it is not unexpected that the total protein, fat and ash would be similar at around 80%, with predictable variations from year to year. What is surprising and remarkable though, is the decrease in carbohydrates from 2019 to 2020 (Esbilac® dropping -26% and Fox Valley 32/40 declining double that at -53%). This is a result in both products of carbohydrates, as a ‘remainder,’ being squeezed due to an increase to total protein, fat and ash (Esbilac® +9% and FV 32/40 +4%) and a decrease in Total Solids (Esbilac® -2% and FV 32/40 -1%). 

Carbohydrates Fox Valley.jpg
Carbohydrates Esbilac.jpg

The next chart for Fox Valley 40/25 shows the same pattern of a steady increase in total protein, fat and ash and at the same time a steady decline in Total Solids. Carbohydrates again feel the squeeze and reflect a steady decline. That decline is also influenced by a steady increase in fiber content year after year.

Carbohydrates Fox Valley 4025 .jpg

Takeaway thoughts. The change between year 3 and year 4 (most recent lots tested) for the three products charted above could suggest a trend toward a Ketogenic diet – and forcing more calories to be sourced from protein and fat, and less from carbohydrates. A fuller complement of carbs is essential for early stages of development in growing animals. A watchful eye is needed to incorporate these recent test results in the recipe formulations that may have been successful in the past, in order to ensure expected growth rates and overall health.



Typically, powdered milk, like all foods derived from animals, does not contain fiber. Yet lab tests reveal varying amounts of fiber in Fox Valley and PetAg powdered milk replacers. A search of the USDA Food Database for human grade powdered whole milk and whole goat milk indicates zero fiber content. This seems to make sense, as fiber, both soluble and insoluble, comes from plants. The milk powders just described in the charts above have product labels guaranteeing a maximum fiber content of 0%. This begs the question: what is the source of the fiber that is appearing and why is it showing up greater than 0% in the proximate analysis for substitute powered milk replacers? Except for the oil included in the products, most of the ingredients are dairy based, either whole milk or isolated components of whole milk (casein, whey, cream, etc.). The fiber is not coming from those milk products. USDA indicates 0% fiber in vegetable oil (combined oils) or individual oils, such as from canola or soybean. The fiber is not originating these oils either. 

Depending on the product, labels do indicate in almost all cases the inclusion of dried corn syrup solids or Maltodextrins as less prominent ingredients, perhaps to boost carbohydrate concentrations. Since these ingredients are plant based, is it possible that the lab testing is detecting dietary fiber from those sources and ingredients? 

The chart that follows shows the value for Crude Fiber for the range of years that WildAgain has had tests performed. As indicated, some very high values (>6-8+%) were reported years ago. It appears that looking at a more recent time frame (2018-2021), these values are leveling off and averaging at a much smaller concentration (PetAg 1.2% and Fox Valley 1.3%). However, it remains unclear why ANY level of Crude Fiber is present. Assuming Crude Fiber should not be present, could it be an inadvertent cause of digestion issues?

Fiber in Milk Replacers.jpg

Takeaway thoughts. It is unclear and surprising as to why any Crude Fiber is present in a powdered milk replacer since the Guaranteed Maximum % is zero. The recent stabilization at relatively low levels of only between 1-2% of total product content is an improvement for both PetAg and Fox Valley products. Future test results will need to be monitored closely to watch for any sudden increase in the trend and any outlier product test values.

Dietary minerals (aka ‘ash’)


WildAgain always requests the concentration of the various macro and micro dietary minerals with the proximate analysis when submitting products for testing. This value is reported as ‘total ash.’ The term originates from the fact that ash is the inorganic residue remaining after the water and organic matter (protein, fat, carbs and crude fiber) have been incinerated at 1,000 – 1,100o F for 24 hours. This provides a measure of the total amount of minerals within a food. We also get specific concentration values for 9 individual minerals.


The following chart shows the trendlines for total ash content for the two manufacturers. PetAg offers no guaranteed maximum on its product labeling for total ash. Fox Valley guarantees a maximum ash content of 9% on most of its products and runs about 27% higher on average than PetAg.


Both manufacturers have a trendline that shows a slight increase in total ash concentrations across all of their product lines, with most minerals within expected levels, based on prior values. Fox Valley products continue to show a continuing absence or, at best, a very low concentration of dietary Copper. Analysis and trends of the mineral concentrations of Calcium, Phosphorus, and Calcium to Phosphorus ratio follow.

Ash Content in Milk Replacers.jpg

Takeaway thoughts. There has not been much new or unexpected data from the recent test results which confirm that the average overall ash levels have remained reasonably constant over the years for both PetAg and Fox Valley. Neither appears abnormally high or deficient – the manufacturers just take a different approach to dietary mineral supplementation. If the average ash levels appear to the user to be too high or too low, a recipe that incorporates two or more products could provide a more balanced level of minerals and mitigate the frequent absence of Copper in Fox Valley products. The Lab Test Spreadsheet lists all nine dietary minerals for all of the product/lot test results.

Calcium and Phosphorus Concentrations


The charts that follow show the data values and trends for both Calcium and Phosphorus concentrations. USDA reference values for whole, low-fat and fat-free milk are also shown. While there is divergence on appropriate dietary Calcium levels, much of the literature concludes the green-shaded areas shown for both minerals provide adequate concentrations.

Calcium Trends in Milk Replacers.jpg
Phosphorus trends in milk replacers.jpg

Takeaway thoughts. There is not much new or unexpected data from the recent test results. Calcium and Phosphorus concentrations in the recent round of testing confirm that the average overall mineral levels have remained reasonably constant over the years for both PetAg and Fox Valley. Both mineral concentrations appear to be within the acceptable reference range for both Calcium and Phosphorus (with the exception of GME).

Calcium to Phosphorus Ratio


The following chart shows the Calcium to Phosphorus Ratio plotted over time as well as predicted trendlines. Most of the literature suggests that a Ca:P Ratio of 1.5 to be optimum, but is certainly acceptable if it falls within the green-shaded area on the chart.

Ca P Ratio trends in milk replacers.jpg

Takeaway thoughts. With the absolute concentrations of Calcium and Phosphorus remaining consistent over the years, it is not unexpected that the ratio of the two would indicate much change. It does indicate that with a higher ratio than PetAg, the Fox Valley products do contain a higher relative concentration of calcium. 



Another test conducted on GME for rancidity confirmed a chronic and continuing issue of elevated Peroxide Value (PV) values which indicate the presence and progression of rancidity in the product. This particular can had just been purchased and newly opened to submit a sample for testing. It was also 253 days (8+ months) from the manufacture date and 16 months prior to expiration. This can, plotted below with 6 recent lots that were previously tested, shows a clear correlation between time of manufacture and PV levels. 


Interestingly, the sample of Meyenberg powdered whole goat milk (human-grade) tested at n.d. (i.e., non-detected) for any presence of rancidity. The sample was from a newly opened can manufactured 13.5 months prior. This suggests that goat milk can in fact be successfully made and stored for months without the product developing rancidity. That prompts questions as to the causes of GME rancidity levels. Could it be caused by the ingredients and/or the manufacturing process? Since seven out of seven samples tested with high PV levels, some level of rancidity may be present for GME if it is 4 months or longer past the manufacture date. 

Rancidity in GME.jpg

Takeaway thoughts. Simply stated, seven out of seven lab tests show that GME contained elevated levels of rancidity. Even though the product indicates a 24-month shelf life, the chart shows an elevated peroxide value that tracks with time since the date of manufacture. Unless a user is able to obtain a very fresh can of GME (less than 4 months old), the risk for rancidity increases quickly over a very short time. Numerous and serious health issues can develop from being fed and ingesting rancid oils in milk powders. It would seem reasonable to expect that if Meyenberg can manufacture a powered goat milk product that is free of rancidity after 13.5 months, then PetAg should be able to improve upon their product stability with an acceptable shelf life.

3) What do the test results reinforce and confirm what do we still not know?


Higher moisture content in Fox Valley products. With remarkably and consistently higher Moisture levels (and thus lower Total Solids levels) it remains unclear as to the cause and/or intent of such a marked change across all Fox Valley product lines in the recent round of tests.  


While considered unlikely, an increase in moisture in a milk powder could allow bacteria to grow more readily. WildAgain did not arrange for testing for bacteria since we did not anticipate an increase in moisture in the milk powders that exceeded the guarantee level to such a degree (>5%). Such tests could be conducted by the laboratory if future factors suggest possible bacterial contamination, concerns develop, and resources are available.


High levels of Protein. The level of proteins in Fox Valley and Esbilac® powders continue to test much higher than the GA. Milk proteins are composed of mostly casein and some whey which are separated when processed. Since most of the separated whey is preferred for human supplements, milk powders produced for animal consumption include more of the separated casein, including milk replacers for pets and wildlife. Casein is more difficult to reconstitute then whey. Might that have caused the sludge-like consistency that was reported? Rehydrating dried casein requires a more complete reconstitution process to make it easier to digest and utilize, especially for younger wild mammals with less developed GI systems. Since casein is harder to digest and doesn’t reconstitute as readily, could higher concentrations of casein cause or contribute to the reported digestive issues?


Unexpected results could occur when the protein in the formula exceeds the GA by an unexpected amount. The formula may appear thicker when mixed, especially if it is not fully reconstituted. Feeding a higher percentage of protein to an infant, than contained in the species milk, could strain the kidneys.  This also could add nitrogen in the liver, making it work harder to process waste and toxins, and more. A neonate animal could have difficulty digesting extra protein if a milk powder is inadequately reconstituted.  This could cause them to possibly develop GI disorders and have a slower growth rate if unable to adequately digest and use the protein. It must be noted that such health conditions may be caused by other factors as well. 


Increasing levels of Fat closer to the GA value (plus GME rancidity issues). With overall fat content increasing as discussed above, formula recipes may need some fine-tuning versus what was successful in the past, especially with Fox Valley products. This will certainly have to be examined at the individual product level. 


Rancidity is an ever-present concern with products that contain high fat levels. Those that contain vegetable oils that have high levels of polyunsaturated fatty acids are most prone to oxidation and development of rancidity, such as with soybean oil (61%). Since GME lists soybean oil as its third most predominant ingredient, that could be a contributing factor to the rapid onset of rancidity in that milk replacer. Most of the other products list ‘vegetable oil’ as the primary source for fats. Unfortunately, with such a non-descript and generic term to describe the source and relative mix of the oils, it is impossible for the user to determine which specific plant-based oil is contained in the product and if it may have a high susceptibility to oxidation and rancidity (USDA database indicates 41+% of polyunsaturated fatty acids in vegetable oil – NFS (not further specified). Proper storage practices are necessary to mitigate the onset of rancidity.


Carbohydrate levels are declining. Formula recipes need to be re-evaluated to insure appropriate carb intake due to the decline in relative carb concentrations (again, WildAgain’s Calculator incorporates these variations). Most of the mothers’ milk studies indicate a carbohydrate level of .5 to 5.0% in the form of lactose (a disaccharide made up of glucose and galactose). Glucose is the only form of energy used by the brain. An inadequate amount of glucose in the blood and carb stores (in muscles and the liver) can lead to muscle fatigue and lack of concentration. Carbs are important for hormonal regulation. Lastly, as the primary energy source for the body, a lack of adequate carbs in the diet may likely compromise or restrict muscle, tissue, and skeletal development in young, growing animals.


Fiber Content. It bears repeating that powdered milk, like all foods derived from animals, does not contain fiber. As shown in the charts above, the fiber content is now averaging just under 2% for all products tested, with about 40% less in the PetAg products. While its presence is still unclear (GA at 0%), it has dropped significantly from prior years and appears to be stabilizing at current levels.


Ash Content. There has been little change from prior years. If one or more of the products have been used in formula recipes in the past, there is little reason to believe that any digestive or growth issues are attributable to the quantity of minerals in the products. That said, quality issues have arisen lately, such as the dicalcium phosphate (DCP) issue in Esbilac®, which PetAg disclosed and corrected. If there is concern over the quality of the minerals, outreach to the manufacturer to provide feedback is warranted and advisable.


Calcium, Phosphorus and the Ca:P ratio. These primary dietary minerals and their ratio all appear to be within the accepted reference range, except for GME, which continues to test at low concentrations of both calcium and phosphorus. It also appears from recent testing that concentrations are increasing slightly in the long-term trend.


A few more product specifics.


- Fox Valley 38/47. Tested at 34/44. Lower than the GA on Protein (-9.4%) and Fat (-6.8) and higher on Moisture GA by 27%. 


- Fox Valley 40/25 ‘Brown Specks.’ Visible as shown above and appear to be larger particles relative to the rest of the product. Clearly gets trapped by a 500µm sieve. (500µm = 1/2mm). Composition, origin and effects of using are unknown.


- Fox Valley 40/25. The purpose of the new ‘bubble gum’ and ‘banana’ scented flavorings is unknown. Apparently, there is an option to order the product without these additives if there is concern with any possible negative effects of feeding it.


- Fox Valley 40/25 and 32/40. The sludge at the bottom of a mixing container has not been observed previously and cause is unknown. Perhaps this is caused by a change in the type of dried casein contained in the product, which is typically the ingredient that is most difficult to reconstitute. Otherwise, the origin is unknown. 



4) Are there action steps that we should consider?


√ Buy fresh and follow good storage practices. Before anything else, make sure that the powdered milk products to be used in formula recipes are purchased as soon after the manufacture date as possible. Ask the vender to provide lot numbers and dates to assess the date of manufacture. Then properly store in a cool, cold, or frozen condition, depending on timing of impending use. While GME has been shown to be the most susceptible to oxidation and rancidity formulation, all of the milk replacer products carry the small risk of rancidity if not stored properly. Storing unopened, and especially opened, milk powder containers at room temperature or higher increase that risk.


The reconstitution properties of dried casein decrease over time as a function of any storage temperature. 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. 


The higher moisture in the Fox Valley products could provide a nutrient-rich medium for bacteria growth. Though unlikely in unopened containers, such contamination could occur if containers are left open.  Consider switching to a different container of milk replacer and arranging for the powder to be tested if unexplained bacterial infections develop in multiple small wild mammals being fed the same product


√ Return or discard products with off-odors or unusual/strange particles. Start by checking for freshness/off-odors and inspect for things that are unusual or do not look normal. If something does not look or smell quite right, consider a quick call to the vendor or manufacturer prior to use. 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 instructed to do so. If still unsatisfied, consider discontinuance of that product and consider alternatives. 


√ Consider using the WildAgain Formula Calculator for more current and precise lab-tested nutritional data than the required minimum/maximum GA values found on the label. As shown above, many of the milk replacer products are testing well above/below what the GA would ordinarily suggest. Several of the products have been at these higher/lower levels for many years. While some are still technically within guaranteed levels, perhaps using an “Expected Value” would yield more accurate calculations of the true amount of nutrients in a substitute milk formula. WildAgain’s Formula Calculator contains years of test data for most of the commonly used powdered milk products. Therefore, it makes the adjustment to a more actual Expected Value, rather than reliance on a GA, which tests have proven to be less accurate as to the contents in the container. The results of more recent lots of the products are being added from time to time, as in the case of the 30 lots added in June 2021.


√ Consider using multiple products to formulate a recipe. The old adage of “don’t put all your eggs in one basket” applies here and provides some common wisdom. If only a single powdered milk product is used in the formula recipe, the formula is totally dependent on that one single lot of that product. What if… that lot is an outlier in terms of nutrient composition vs the GA or Expected Value? Or it has not been stored properly and developed rancidity? Or it is deficient in a dietary mineral, such as Copper in many Fox Valley products? Or it has incorporated a lower quality of dried casein that is more difficult to reconstitute? 


A very simple and effective way to mitigate this ‘single product’ risk is to incorporate more than one milk replacer in the formula recipe. This approach also may provide a recipe that more closely matches the mother’s milk nutritional profile. Since each milk powder has its own relationship with water, reconstitute each powder separately and then combine when in final liquid form, in the appropriate amounts. 


√ Supplemental fats are probably still needed in some recipes. Some rehabilitators may wonder if supplemental fats are no longer required for some formulas to better match the species milk composition since the powders are currently testing higher than previous years. Others may be unsure of the effect on the recipe’s overall nutritional content from adding a certain fat additive in a specific amount. WildAgain’s Formula Calculator incorporates current test results for these higher fat levels for products that have been lab tested. The Formula Calculator provides a quick and easy way to evaluate previously successful recipes to determine if any changes are needed for continued supplementation options (types and amounts) to address fat deficiencies. 


√ Dietary mineral supplementation (esp. Ca) is probably unnecessary. The test results and the charts above show that concentration levels for Calcium and Phosphorus consistently fall within the 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 one of the minerals, a blending approach easily evens out any high or low values and produces a more consistent product over time. 


Though some have discussed supplementing Calcium, these minerals are present in such minute amounts that it is very easy to inadvertently exceed an appropriate Calcium level. Additionally, it can very quickly result in an unacceptable Ca:P ratio. 


√ Reconstitute carefully and completely. Rehabilitators try to use the best products, construct a substitute milk formula recipe appropriate for the species, and follow an appropriate feeding protocol (e.g., amount per feeding, number of feedings per day). However, if the formula is not well prepared, the animal will not get the complete intended nutritional content or the full benefit of the formula. Effective formula preparation is essential, yet it is often underestimated and overlooked as a vital and key critical success factor in an animal’s diet. WildAgain offers a Formula Mixing Guide that incorporates a series of preparation steps that can help improve the chances of producing a well reconstituted formula that contains the nutrients in the carefully constructed recipe. Some of the suggested steps may be new to rehabilitators and differ from the instructions on the powdered milk labels. For example, the Guide incorporates weighing ingredients rather than measuring by volume (which can introduce a +/- 10% error in the intended amount of an ingredient). Additionally, it specifies adding the powder to warm water (110° F - 130° F) and allowing for some time for the powder to ‘wet.’ Next, since many of the milk replacers have poor wetting properties, more mechanical mixing is required well beyond a simple stir or shake. Most importantly, these powders reconstitute much more completely if allowed to rest in the refrigerator for at least 8 hours prior to use. Once reconstituted, a final combination of ingredients can successfully occur by adding other liquid ingredients, such as heavy whipping cream or another fully reconstituted powdered milk replacer, when included in a blended formula. 



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. The 18 years of compiled data affords us the ability to build a new metric we have termed an “Expected Value.” We are using this metric as a better predictor for the nutritional composition of the next lot manufactured for the more commonly used powdered milk replacers.


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.


Check back often for news and updates as we add more test results. The “What’s New” section of WildAgain’s website will always highlight newly added content. The “Contact Us” link at the bottom of every page invites comments and alerts us to emerging concerns in the rehab community.


If you have made it all the way to the end of this page, you deserve a rest and Gold Star. Thanks for your work for wildlife and best wishes in your wildlife rehabilitation activities.

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