Milk Replacer Project 2020:

Some FAQs as Wild Mammal Baby Season Approaches


Many rehabilitators are ramping up preparations for upcoming wildlife busy seasons. There are many different tasks on their ‘to do lists.’  Some mammal rehabilitators are already ordering milk replacer powder, since wild mammal babies may be born in the winter or spring, depending their location, species and more. They are debating with which milk replacer powder to order this year, especially after reports of so many health problems in wild mammal babies in 2019. They are asking, “What do I order?” and “What recipe do I use?”


Those are great questions that sound simple. However, the answers are not short or easy. As much as we appreciate that rehabilitators want fast answers and to place orders quickly, there are still some uncertainties as rehabilitators consider their decisions. Knowing that, here are some frequently asked questions (FAQs) posed to WildAgain during our ongoing research – and some ‘early’ responses. More thorough information will be available asap on products, preparation methods, factors that may have caused previous concerns, and possible ways to prevent them.



1. What caused the nutritional problems in wild mammal babies in 2019?


2. I need milk powder now. What powdered milk replacer should I order?


3. How can I know I’m feeding the ‘right’ product(s) and formula recipe?


4. How can I learn more about the mother’s milk of the mammals I rehab?


5. What is ‘good health’ in animals?


6. How do I know if I’m seeing appropriate growth and development rates?


7. How can I recognize early signs of nutritional problems?


8. Back to products: how do I select the right one?


9. Is it okay to blend multiple powders together? What about adding other ingredients?


10. How can I create formula recipes for the mammal babies?


11. Now, can I finally just mix the formula ingredients and feed?


12. PetAg® wrote they were going to change Esbilac® in fall, 2019. Did they change it? Is it effective and safe? What about Goats Milk Esbilac® as a substitute?


13. Wrap-up


1. What caused the nutritional problems in wild mammal babies in 2019?


First, while health problems developed in some wild mammal babies in 2019 that appeared to be directly related to nutrition, others did not develop similar problems. Second, there are many possible factors that have to be considered – including species, age of animals, health conditions, recipes and mixing methods, feeding practices, and, yes, milk powders! Rehabilitators and others are working diligently on this urgent situation and the research is progressing. Early data collection and analysis strongly suggests likely contributing factors, and more information is expected soon. Meanwhile, WildAgain does not believe it is appropriate to suggest there is a single cause or solution, nor will we recommend a specific product or formula recipe.


2. I need milk powder now. What powdered milk replacer should I order?


If it is necessary to order milk replacer powder immediately, consider placing just a small initial order. Choose milk powders that experienced/trusted rehabilitators reported having no or only minor problems with in 2019. Some rehabilitators plan to order milk powders throughout the year, rather than in bulk.  Buying products produced at different times may reduce problems should any be reported later about a particular product or lot number. Other rehabilitators are purchasing products from two different manufacturers so they can (1) blend products to mitigate possible problems from a single product and (2) have a back-up formula to switch to if problems develop.


3. How can I know if I’m feeding the ‘right’ product(s) and formula recipe?


Rehabilitators are well aware that young mammals nursing from their mothers get the most appropriate milk. So when wild mammal babies are brought into rehabilitation, the best thing is to try to provide a milk replacer that closely matches the milk composition for the species. Clearly, there are no commercial sources of milk by mother squirrels, opossums, rabbits, raccoons, and other wild mammals (nope, no dairy farms milking those species). Since one cannot purchase milk produced by these wild species, rehabilitators use available products to try to create a formula that meets the species needs and results in an acceptable level of growth, health and development.  However, we are mindful that manufactured milk replacers are not going to have exactly the same composition, nutrition, or digestibility as the mother’s milk.


As to feeding the ‘right product?’ There are several parts to that question. (1) Is the milk powder one that can be used in a way to match the milk composition of the mother? Historically, people buying milk powders have used the Guaranteed Nutrition Analysis (GNA) on the label to make that decision. [NOTE: Tests by an independent lab have revealed variations in some of the products that are different from the GNA on the labels.]

(2) Have rehabilitators reported ‘good health, growth and development’ with animals when that milk powder was a major ingredient? Or have recent problems been reported? (3) What is the product history (e.g., quality, effectiveness, reliability, transparency, and lack of problems)? In addition to being able to learn about those things from rehabilitators, recent research provides some information on this, including on


As to ‘right recipe’, that goes back to looking at the milk composition studies for the species, and developing a recipe that is a close match to mom’s milk.  But other important factors to consider include: how it is prepared, feeding amounts/frequency, digestibility, as well as its effectiveness with the animal.


4. How can I learn more about mother’s milk of the mammals I rehab?


Information on cow, goat and sheep milk is vast. However, published research on wildlife species milk composition analyses, while limited, can be found in scientific publications ( offers resources). Similar information has been referenced in some rehabilitation publications, such as the NWRA Principles of Wildlife Rehabilitation, 2nd ed.  Milk composition analyses for common mammal species rehabilitated in North American also are available in the downloadable nutrition calculator at, and other milk composition species and studies can be added.


5. What is ‘good health’ in animals?


This depends on what a rehabilitator means when using the word ‘healthy.’  Does it mean steady weight gain in young animals?  Does it mean lack of gastrointestinal problems – or just minor problems? Or something else? The definition of good health may be on a continuum, ranging from ‘health like it would have with its mother in the wild’ – ‘ongoing health problems with tenuous survival’ – to ‘unable to survive in the wild’ – to ‘death.’


Since these definitions and measures of ‘good health’ can vary by person, rehab facility, or veterinarian, it may be beneficial for rehabilitators to establish a more mutually understood definition of ‘healthy’ for use when referring to conditions or causes, including nutritional factors.  Identifying the causes of health problems in young mammals while on formula in 2019 was especially challenging, due in part to variable definitions of what rehabilitators considered normal and healthy. In some cases, the reported health problems could have been a result of multiple contributing factors (rehab practices, specific products or recipes, etc.).


6. How do I know if I’m seeing appropriate growth and development rates?


Rehabilitators know that diet directly influences growth and development. Familiarity with the natural history of the species, knowing how the young animals appear when they first arrive at rehab after feeding by their mothers’, and normal weight ranges are all vitally important.

Also critically important is experience by rehabilitators. Rehabilitators regularly monitor weight gain to determine if the animal is growing and whether they are within a normal range.  If the animal is not gaining weight at the expected rate (e.g., slow, too fast, or inconsistent), various factors are considered. Some rehabilitators mention that while an animal’s rate of weight gain may be a little ‘slow’ on some diets or they seem very hungry, they consider that acceptable as long as the animal does not show other health problems, such as diarrhea. They try to identify reasons for slow weight gain (e.g., formula products, recipes, feeding amounts and frequency) and adjust.  On the other hand, if the animal is gaining more weight than normal and looking substantially ‘chunkier’ than when fed by its mother, reasons for that are considered as well (e.g., such as excess fat or kcals in the diet or overfeeding).


Rehabilitators know that development is more than just weight gain. It involves physical and behavioral changes, such as coat/fur development, the opening of eyes and ears, ability to thermoregulate, adept mobility, alertness, and even play. They also consider activity level, strength/muscle tone, body mass, and speed.  Monitoring development means noting how the animals compare to the young animals raised by their mothers.


7. How can I recognize early signs of nutritional problems?


Again, this is a very complex topic – and it builds on the topics of health, growth, and development. It means considering what is ‘normal’ and ‘healthy’ for the specific species, age, and developmental stage - and constantly monitoring those details. It involves noting factors like weight gain, gastrointestinal health (e.g., bloat, diarrhea, constipation), coat development and quality, and musculoskeletal development.  It’s also looking at the more subtle signs, like interest in food, sleep amount and speed of waking, comfort moving, social interaction with litter/cage mates, and so forth.  It is helpful to document things you notice, even the minor things – and detecting changes. Rehabilitators may have noticed some of these subtleties with some of the recent cases and attributed them to other causes. They may not have been viewed as indicators of possible nutritional disorders, until patterns showed up with multiple animals and more obvious problems appeared.


The difficulties increase when animals are tiny and subtle symptoms can be challenging to notice or describe. A demanding workload and other responsibilities can add to the challenges -- as well as likely being tired, stressed, and short on time for a single caregiver. Many of these subtleties or changes may even be easily missed with multiple caregivers working infrequent shift schedules.  It is important to remember that many different factors can affect weight, growth and health and that there can be multiple possible causes of the problems.


8. Back to products: how do I select the right one?


There is no easy answer on this question either. Many mammal rehabilitators use manufactured milk powders as the primary ingredient of the formula they feed the young mammals. Commercial milk replacers may be described by the protein/fat percentages, such as 33/40, 32/40, 40/25, 20/50, etc. Some of the manufacturers use a product name (e.g., Esbilac®  or KMR®), while others refer may to it by the species it might be used to feed: opossum, squirrel, raccoon, or deer formula. Milk powders can more accurately be referred to by their primary components, which are proteins/fats. This allows for easier consideration of how they may be used as ingredients to create a formula that more closely meets the milk composition analysis for the species.


Milk replacer product labels include information on percentage of protein (the first number) and fat (the second number), such as Fox Valley 32/40 (32% protein, 40% fat). Rehabilitators know that young mammals need both proteins (essential for growth) and fats (necessary for growth and physical activity) – as well as other key nutrients, such as calcium, phosphorus, manganese, copper and iron. While those considerations can be used when selecting products, rehabilitators should also consider the other factors mentioned – like comparison to the mother’s milk; the animal’s health, growth, and development; product quality and digestibility; and more. There are also considerations of availability, cost, budget, etc. The person selecting the milk replacer products, recipes, and so forth will be considering a wide variety of factors.


9. Is it okay to blend multiple powders together? What about adding other ingredients?


Rehabilitators and others reviewing the milk powder compositions have noted that mixing a single milk replacer powder with water results in formulas that are unlikely to be a close match for the milk composition for wild species. Whereas, combining milk powder products, and possibly other ingredients, may achieve a closer match for the milk composition for the species.  For example, rehabilitators have added small amounts of extra fat to the recipe for species needing more fat. For species needing higher protein levels in their milk, some rehabilitators select a milk replacer higher in protein, blend milk replacers to achieve that level, or add another protein source. Others might increase the amount of water to dilute the formula, such as for earlier stages of lactation for neonate opossums, according to natural history and research (Bergman and Housley). That said, it is essential to understand the reasons, possible affects, potential benefits and problems from combining different milk powders and other ingredients, or changing ingredient amounts (including water).


Others asked about possibly adding a mineral supplement. While possible, one needs to know exactly what minerals the animal needs (species, age), the interaction with other minerals and components, amounts of minerals in the rest of the food (current tests, not just on labels), the digestibility of the minerals, and much more. Adjusting mineral levels is extremely complicated and can have unintended consequences. As rehabilitators know very well, mixing ingredients or recipes that look like milk and that a mammal baby will eat does not guarantee that it is nutritious or can be utilized by a not yet fully developed digestive tract.


Another key consideration is how, when, and with what methods the different formula components are combined. The type, blend and amount of ingredients as well as different preparation methods are major considerations – and again require much further attention. (A paper on this is expected to be posted soon on


10. How can I create formula recipes for the mammal babies?


As mentioned, scientific publications provide equations on nutrition. The NWRA Principles of Wildlife Rehabilitation, 2nd Ed, provides information on this as well. Some rehabilitators choose to simplify and accelerate the recipe creation process by using the nutrition calculator prepared for rehabilitator use at That calculator includes the current and longitudinal nutritional profiles of milk powders from several manufacturers, various products, and multiple lot numbers conducted by an independent laboratory, as well as other tests. Using current information from the independent lab tests can help since the product labels may be out-of-date or even inaccurate at times.


The nutrition calculator starts with selecting the species of “mom’s milk” that the person wants to match. These values are based on nutritional analyses from various studies done on the milk of each species. Next, the person selects the ingredients considered in the recipe (this includes milk replacers as well as other additions, e.g., cream). Then the amounts are indicated, either by parts – like one part powder, 2 parts water- or by weight. The results will then show how closely that “recipe” matches mom’s milk - including solids, protein, fat, carbs, kcals, calcium, phosphorus, and even the Ca:P ratio. While the calculator can do the math, a perfect 100% match to mom’s milk is highly unlikely (more specifics are provided on


Comparing formula recipes to the mother’s milk composition for the species allows the rehabilitator to try to more closely match the mother’s milk. That said, even if a ‘recipe’ looks like a reasonable match to mother’s milk by the numbers, it is still essential to assess how well the formula actually works when fed (digestibility, growth rate, etc.) and adjust as needed. On the flip side, if products and recipes do not reasonably match the nutritional profile needs of the species, that may result in problems either immediately (e.g., gastrointestinal disorders, hunger, slow weight gain) or later (e.g., malnutrition, malformations, fractures).


11. Now, can I finally just mix the formula ingredients and feed?


Once the products and recipes are selected, many assume the formula is ready to make and feed. Research from 2010 conducted by WildAgain, as well as again and expanded in 2020, shows that there is more to preparing the milk powders than just combining the powders and water and feeding immediately.


Many rehabilitators have followed instructions on the milk powder labels saying to scoop a ‘part’ of powder and mix with two ‘parts’ water. However, extensive tests weighing milk replacer powders shows substantial variability in the weights of different lots of the same products – as well as weight changes documented over 15 years. This means that there can be significant variation in the concentration of the formulas – which then affect nutrition, growth and development. Further, such variations can cause under- or overfeeding, gastrointestinal disorders, hunger, and more.


While it is fairly easy to weigh the ingredients, one must remember that one does not just weigh the milk powder and double that amount to get the weight for the water. Water weighs about 15 grams per tablespoon, whereas the milk replacer powders weigh about 6.5 grams per tablespoon. So if you weigh 30 grams of milk powder, you cannot just double that weight in water. If you want to confirm the weights planned for a formula recipe, the nutrition calculator offers a feature that converts recipe ingredient values measured in parts to corresponding weights (grams). Changing from the scooping measurement method to weighing takes some adjustment, but is more accurate.

Some milk powder directions say to mix with warm water (≈100°F), others don’t. Some manufacturers say the formula can be fed immediately after mixing, others do not specify a time frame. Esbilac® powder that was manufactured before 2009 used a multi-step drying method. That Esbilac® (pre-2009) was more quickly rehydrated and reconstituted than that made with the single step spray dry method (Casey, 2012). In those tests, when the Esbilac® powder made with the single step spray dry method (after 2008) was prepared with hotter water (about 175°F) and allowed time to ‘rest’ in the refrigerator for a minimum of 4 hours before feeding, it showed improved solubility.  Since 2010, preparing Esbilac® with hotter water and allowing ‘rest’ time in the refrigerator before feeding seemed to improve the solubility. A formula with better solubility is easier to digest, which then can improve the amount of nutrition the animal receives, improving growth and health.


However, recent and expanded research is investigating how Esbilac® and other milk replacer powders rehydrate and dissolve at different temperatures and ‘resting’ times. So far, the results are somewhat mixed, which could be a result of a change in both the manufacturing process or product formulation over the last 10 years by one or more of the manufacturers. Those tests and analysis are expected to be available shortly on


Early research of dog milk composition showed about 34% protein and 40% fat. Manufacturers produced milk replacers for the relevant protein/fat level, and other nutrients considered for growth and health. Milk replacer powders, such as Esbilac®, have been manufactured to be made into formula and fed to puppies since the 1960’s. Currently manufactured by PetAg®, Esbilac® continues to be produced and marketed as a supplemental food for puppies. In 2014, a veterinary nutrition team conducted research on dog milk composition and conducted extensive studies comparing puppy milk replacers. That paper clearly explained the milk powders produced for puppies still have a long way to go to meet nutritional needs of the animals. Plus, the study explained that the product labels also need improvements. The paper is at

12.  PetAg® wrote they were going to change Esbilac® in fall, 2019. Did they change it? Is it effective and safe? What about Goats Milk Esbilac® as a substitute?


In September 2019, PetAg® sent an email ‘alert’ and a follow up set of FAQ’s to rehabilitators who had contacted them with concerns about Esbilac®. They explained that the health problems rehabilitators had been reporting were likely related to the particle size of Dicalcium phosphate (DCP) in Esbilac®, which had been changed by the supplier approximately two years prior. They indicated that the larger particle size of the DCP would be difficult to be broken down and absorbed by small wildlife, even though it was still ‘satisfactory’ for use with puppies. In a follow up statement, they verified that they were able to secure a source for more finely milled, micronized DCP and that the modified Esbilac® product would be available in 30-60 days. It was later learned specifically that Esbilac® manufactured after September 30, 2019 would be produced with the new micronized DCP.


WildAgain recently obtained the Esbilac® manufactured in October 2019. A sample was tested at the lab and the results (lot # 2889E-2969 #03) are posted in the Esbilac® Lab Test Data Spreadsheet (click here). While the test results show how the milk powders change in terms of primary components (percentage content of protein, fat, primary minerals and trace elements), the tests do not measure content (or particle size) of specific supplemental ingredients such as DCP, or comment about digestibility, effectiveness, or safety. For this reason, WildAgain is unable to confirm whether the DCP has been changed to a form that is more readily absorbed by the wild mammal young.


While Pet Ag was in the process of producing Esbilac® with the new source of DCP, they suggested using Goats Milk Esbilac® (GME) as an alternative.  They explained that GME is made with an anhydrous DCP that is easier to digest. Information on the GME nutrition profile from the lab tests is available (click here).


WildAgain continues to conduct research on the milk replacer powders. The independent lab tests on nutrient profiles, and information from other WildAgain tests (e.g., weights, rehydration), are being posted on in the nutrition calculator, spreadsheets, measurement paper, etc. Those tests do not assess the digestibility, safety or ultimate effectiveness of any of the milk powders. WildAgain cannot assess these aspects of the products, since manufacturers may change the products (formulations, ingredients, suppliers, manufacturing methods, etc.) at any time without notice. Plus, factors like recipes, product preparation, and so forth may affect the results from using the powders. Rather, WildAgain will provide information to support rehabilitators as they consider such decisions – including the information in the responses to these FAQ’s.


13. Wrap-up


WildAgain is very aware that there are many more questions about the milk replacer products and formulas. We also know the responses are incomplete, as the research is ongoing. More information is expected shortly. Information will be posted on as it is available.


Thanks for your interest in the topic – and commitment to wildlife.




Allan and Shirley Casey, co-founders of WildAgain Wildlife Rehabilitation, Inc. in Colorado, have been licensed rehabilitators since 1986. They conduct research on a variety of rehabilitation related subjects, including nutrition, wildlife health, rehabilitation regulations, and trends. They have written 120+ articles for rehabilitation and veterinary publications, as well as the Squirrel Rehabilitation Handbook. The Caseys have no affiliation with any milk replacer company.


© 2020 WildAgain Wildlife Rehabilitation, Inc. Colorado. Reprints for personal use only.





Bergman and Housley. 1967. Chemical Analyses of American Opossum  (Didelphys Virginiana) Milk. Comparative Biochemical Physiology. Vol. 25, pp. 213-218.


Casey, Allan and Shirley Casey. 2012. Solubility Issues with Milk Replacer Powders – An Easy Fix. Wildlife Rehabilitation Bulletin. National Wildlife Rehabilitators Association. Vol. 30, n 1, pp 36-40.


Casey, Allan.  2002. Mammal Nutrition: How Cookbooks Can Be Harmful. Wildlife Rehabilitation: Selected Papers from NWRA Symposium, 2001, pp. 101-109.


Casey, Shirley. 2012. Utilizing Squirrel Natural History to Make Rehabilitation Decisions. Wildlife Rehabilitation Davis, Lessie, ed. Wildlife Rehabilitation Resources: Squirrels. National Wildlife Rehabilitators Association. St. Cloud, MN.


Casey, Allan. 2020. WildAgain’s Nutrition Calculator.


Gage, Laurie. 2010. Hand-Rearing Wild And Domestic Mammals. Wiley-Blackwell. NJ.


Green, Brian, William J. Krause, Keith Newgrain. 1996. The Milk Composition Analysis of North American Opossum (Didelphis virginiana).Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology. Vol. 113, Issue 3, pp. 619-623.


Heinze, C., et al. 2014. Comparison of the nutrient composition of commercial dog milk replacers with that of dog milk. Journal of the American Veterinary Association. Jun 15; 244(12), pp. 1413-22.


Krause, William and Winifred Krause. 2006. The Opossum: It’s Amazing Story. University of Missouri.


McRuer, David and Kenneth Jones. 2009. Behavior and Nutrition of the Opossum (Didelphis virginiana). Veterinary Clinics of North America: Exotic Animal Practice. Vol.12, n. 2. Pp217-236.


Moore, Adele and Sally Josten. 2002. NWRA Principles of Wildlife Rehabilitation, 2nd edition. National Wildlife Rehabilitators Association, St. Cloud, MN.


Nixon, Charles and W. J. Harper. 1972. The Composition of Gray Squirrel Milk. The Ohio Journal of Science. Vol. 72, n. 3. Pp 3-6.


Oftendal, Olav. 1984. Lactation in the Dog: Milk Composition and Intake by Puppies.   The Journal of Nutrition.  Vol. 114. Issue 5, May, pp. 803-812.





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