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Golden Mantled Ground Squirrel with Youn

Wildlife Formula And Feeding

The majority of wild mammals presented for rehabilitation are juveniles still dependent on their mothers for food. Thus, formulas are essential their health, growth and long-term survival. Milk replacer manufacturers, rehabilitators, and others have developed and offered a variety of formula products and recipes for various species. Some formulas have been described as effective and others not when fed to the young mammals. The success of the formulas often has been attributed to the manufacturers’ products or a recipe. While the success of the formula with a wild mammal includes the milk replacer powder and recipe, other factors contribute as well. 


WildAgain believes that the more rehabilitators are familiar with the many critical aspects related to selecting, preparing and feeding appropriate formula for the species, greater likelihood that the wild mammal will be fed and able to use the nutrition it needs. Rather than suggest a particular recipe, this section provides a variety of resources to support the mammal rehabilitator making decisions regarding formula and feeding. It also shows that there are many factors that all contribute to a higher level of effectiveness of the formula – versus short term survival or development of obvious problems. The more a rehabilitator knows about these considerations, the greater chance of success. It is far beyond creating or adjusting a formula recipe to see if the avoids gastrointestinal problems, animal grows and survives in the short-term.

Part 1 - Mammalian milks - common purpose, different profiles


Mothers’ milks. Mammal milks have evolved to meet the particular needs of species over millions of years. While milks have some similarities (e.g., liquid; whitish color; primary components such as proteins, fats and carbohydrates), there are significant species specific differences. Understanding that species milks are different, rehabilitators strive to construct a formula that closely matches the components of a particular species’ milk. Understanding species milk is complex, with many aspects. This section provides information on various milk research studies.  Commercial milk replacer powder available to rehabilitators are not produced from wild mammals and do not completely match wild mammal milks. The products require careful adjustments and supplementations to meet the individual species needs. Understanding composition of wild mammal milks is essential when trying to construct a formula that matches the species - and improves the chance of it the young mammal's health, growth and survival.

Matching the mother's milk

Species milk studies (90+)

Fundamental components of milk. While some nutritional components are present in all milks, the percentages vary, at times widely. This section describes the functions of the primary nutritional components for young animals; sources of those components; concentrations present in some milk replacer powder products, product changes over time, and links to published resources and studies.




Kcals (energy)

Essential dietary minerals. Milks also contain inorganic elements that are essential to health and growth. This section briefly describes some common dietary minerals present in milks (e.g., calcium, phosphorus) and their beneficial dietary functions, sources and other considerations. It also describes some potential problems and solutions. Links to published resources are included.


Dietary minerals overview - macro minerals and micro nutrients


Part 2 - Ingredients to select from


Product testing. Wildlife rehabilitators have noticed changes in the commercial milk replacer powders over multiple years including this year. Some of the changes provided positive results. In other cases, problems developed in the young mammals that may have been related to changes in milk powders. As a result, a variety of tests were performed on the milk replacers to monitor nutritional composition content and trends since 2008 - providing data on concentrations of protein, fat, carbohydrate, solids, and minerals for the various products. This section describes the testing processes and provides the detailed independent lab test results. 


Product specific tests and analysis

Summary overview of 2023 product testing (PDF)

Esbilac® 2022: Test results (Part 1) and 7 key takeaways to consider (Part 2)

Goat's Milk Esbilac® GME® 2022: Test results (Part 1) and 8 key takeaways to consider (Part 2)

KMR® 2022: Test results (Part 1) and 8 key takeaways to consider (Part 2)

Goat's Milk KMR® 2022: Test results (Part 1) and key takeaways and comparisons (Part 2)

Wombaroo Rabbit Milk Replacer: Test results (Part 1) and key takeaways (Part 2)

Wombaroo Squirrel Milk Replacer: Test results (Part 1) and key takeaways (Part 2)

Tailspring Milk Replacers (goat milk based): Test results (Part 1) and key takeaways (Part 2)

MannaPro® Kid Goat Milk Replacer (cow milk based): Test results (Part 1) and key takeaways (Part 2)

Fox Valley 32/40 Milk Replacer (cow milk based): Test results (Part 1) and key takeaways (Part 2)

Fox Valley 40/25 Milk Replacer (cow milk based): Test results (Part 1) and key takeaways (Part 2)

Zoologic® 33/40 Milk Replacer: Test results (Part 1) and key takeaways (Part 2)

Zoologic® 42/25 Milk Replacer Test results (Part 1) and key takeaways (Part 2)

General considerations

Milk replacer update: Trends and analysis - Summer 2021 update

Product sample collection and lab test submissions

Detailed lab test data (Spreadsheet - 100+ product/lot sample results)

Dry matter basis vs wet matter basis - understanding the difference and how to compare

Powdered milk replacer - Storage time and temperature considerations


Fat supplements. The percentage of fats in species milks vary and is a critical component. The percentages of fats in milk replacer powders are often very different from the species to which is fed. As a result, rehabilitators may often add fat supplements to try to match the milk composition percentage of the species milks. Different types of fats have been used as supplements, including various types of fresh cream (e.g., heavy cream), plant based fats, and a few products specifically marketed for wild mammal formulas (e.g., UltraBoost, Multimilk). In addition to considering the amount, digestibility and effectiveness of the fat source, rehabilitators have considered the amount of lactose in the fat sources. This section compares the information on lactose in several supplemental fats commonly considered for use.

Heavy whipping cream

Supplemental and substitute fats

Cottontail _0770.jpg

Part 3 - Creating a recipe to match mom's milk


There are many factors that must be considered when comparing a formula recipe to the species milk: the milk composition for the species; ingredients; calories; and more. It can take considerable time, work, and resources to assess and compare each recipe. WildAgain offers a nutrition calculator that allows the user quickly and easily calculate and compare formula recipes for a species - and try to anticipate how the recipe may match the mother's milk and see how it performs before feeding it to a young mammal.


The user downloads the provided calculator (in Excel), selects milk composition studies for common species (or add other species of interest), enters ingredients and amounts, and compares the resulting formula to the species milk. Other features calculate the weights needed for the ingredients to facilitate measurement for various quantities. The calculator also offers typical nutrition analyses of some milk replacer powders commonly used with wildlife by year and specific lots, equations to independently calculate the nutrition without the calculator, a kcal calculator, and more.

Wildlife Formula Calculator


Part 4 - Preparing formula


Measuring ingredients. The labels of the milk powders usually direct the user to measure by using volumes, thus scooping the powder and water. Yet research on the ingredients show that it is far more accurate and produces more consistent results to weigh the ingredients rather than use volumes. This section describes the research, methodology, and test results. While it may means changing established preparation methods for many rehabilitators, weighing the ingredients makes a big difference for the animals fed formula.

Measuring Powdered Milk Replacers

Texture introduces error

Weighing versus using 'parts'

Reconstitution and solubility. Combining the milk replacer powders and waters certainly results in a whitish liquid. However, just mixing them together does not mean the powder is fully dissolved, nor is it immediately reconstituted into an easily digestible form for these young wild mammals. This section explains this process in some detail, including with illustrations and lab results. It shows photos the dispersal of different milk powders at different times and with different temperature water. It also describes how ingredients and age of milk powders can affect the reconstitution time. The tests and photos show that it makes a significant difference to mix the formula and let it rest in the refrigerator for at least 8 hours before feeding it. Many rehabilitators report making formula and then allowing it to ‘rest’ before feeding makes the formula more dissolved and smoother. 

The first link below provides a quick summary of the test results and suggestions to improve reconstitution of powdered milk replacers. It is highly recommended to read the other links as they help to explain why and how the reconstitution process and those factors that either aid or impede an effective outcome.

READ FIRST - Summary of tests/conclusions and suggestions to improve reconstitution of powdered milk replacers


Milk Powders for Human Babies and Other Mammals Reconstitute Differently. (PDF)

Reconstitution introduction and overview

The science of reconstitution: Wetting, sinking, dispersion and dissolution

Milk particle size

Longer resting time makes a difference

Dispersal test methodology

Dispersal test results - 500u sieve

Dispersal test results - 250u sieve

Dispersal test results - 125u sieve

Solubility test methodology

Solubility test results

Mixing ingredients. Once weighed (or scooped), product label instructions provide minimal guidance on mixing the milk powders to create formula. They instruct to measure by scooping parts and adding water. However, the powder textures, density and weights vary by product, container and over the use of the container (bottom powder compacts when scooped). Plus, research shows that the reconstitution of the powder changes from when first mixed with water and later which can affect the young digestive tracts ability to digest and utilize nutrition in the formula. As a result, the way the formula is mixed can have a substantial effect on the animal’s ability to benefit from the formula.

Mixing Guide Why and How 

Using water versus hydration fluid (PDF)

Red Fox Nursing Kits .jpg

Part 5 - Feeding regimen

Estimating formula feedings per day. A common question facing wildlife rehabilitators is estimating how many feedings of a substitute milk formula per day will result in a healthy, growing and thriving animal. Sources ranging from scientific research papers and publications to more informal social media postings provide various suggestions. Unfortunately, many of these sources provide widely varying instruction, little consensus, and very sparse references, which prompts a questionable level of confidence in the information. This section describes calculating the kcals needed for wild mammals, equations and examples. (View the summary page and longer PDF)

Using a high quality rodent chow. Weaning and weaned wild rodents that are in captivity need a balanced and nutritious diet, just like the younger animals need a nutritious formula. When in the wild, those rodents select their own diet to meet their needs. While in captivity they are dependent on the foods given by the caregiver. It is very difficult for the human caregivers to meet their fully balanced nutritional needs of proteins, fats, carbohydrates and essential minerals – even when offering a variety of foods. Also, some have assumed that the rodents eat substantial amounts of nuts and seeds – even though nuts and seeds have higher  levels of phosphorus and can cause improper calcium phosphorus ration, resulting in MBD. This paper includes criteria for rodent chows, analysis of products, and strategies for feeding the rodent chows.

Selection criteria and analysis of 39 products

Feeding regimen

Part 6 - Troubleshooting and other considerations


Powdered milk replacers FAQ’s. There are many questions about milk replacers – some of which are repeated most years. This series of Frequently Asked Questions (and answers) were developed when rehabilitators asking common questions as well as some that seemed to be related to concerns regarding what were believed to be changes in milk powders. Many of the questions and answers continue to be relevant – with more detailed answers in the previous sections and papers. (View the FAQ's)


What went wrong with formulas in 2019? Many rehabilitators reported what they considered to be unusual health problems with juvenile mammals in 2019-20, even though they had followed their standard practices that they previously considered to be effective. This short paper revealed many causes – and was followed by more detailed research and papers, many of which are in the previous sections. (PDF)

Rancidity in powdered milk products. Users of milk replacer powders assume milk powders are fresh, especially when used prior to the expiration date – and most are. However, since milk powders contain fats that can spoil, it is possible for the fats to become rancid. While important for the milk powders to be stored correctly both prior to and after opening, it is still important to check them when opening the package. This section describes rancidity, testing, and results of eating any rancid foods, including formula. And yes, a few milk powders have been rancid. Learn how to check the milk powders and review lab test results.

Rancidity testing in milk replacers - Early 2024 update (PDF)

Rancidity overview

The sniff test

Wildlife eating rancid food


WildAgain does not have an affiliation with any manufacturer or vendor of substitute milk replacer products.

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