Wombaroo Rabbit Milk Replacer - Part 1. Product testing.
Wombaroo Rabbit Milk Replacer is one of many specialized substitute milk formulas produced by Wombarro Food Products located in South Australia, Australia and available online in North America. They make products for wildlife rehabilitators, aviculturists and animal breeders, as well as supplying specialty formulated milk products for animal studies to universities, hospitals and research institutions worldwide. Many of their products include the use of human-grade food ingredients, such as the Rabbit Milk Replacer.
This article (Part 1) discusses independent lab test results as well as WildAgain's in-house product performance testing on physical properties, measurement and reconstitution. Part 2 discusses and offers suggestions on the product to rehabilitators considering it's use for North American wildlife species (PDF).
A critical challenge facing mammal wildlife rehabilitators is providing a suitable substitute milk replacer to feed orphaned, nursing wildlife. The task involves understanding the composition of the mother's milk; then using one or more commercially available milk replacers (generally in powdered form) to construct a recipe that matches the mother's milk; and then preparing the formula to achieve a properly reconstituted formula. While rehabilitators have been generally limited to milk replacers commercially available for domestic animals (companion and livestock), other products have been brought to market in recent years that are formulated for other species - and may provide a closer match to certain wildlife species milk or used to blend a composition that is a closer match to a species. Wombaroo is a company that has a line of products that targets the market beyond puppies, kittens and livestock. Assuming that Wombaroo's Rabbit Milk Replacer is actually formulated for various domestic species of rabbits (European, California, NZ-White, etc.), its applicability for wild lagomorph species found in North America is worth considering.
Part 1. This analysis provides the chemical analysis of Wombaroo Rabbit Milk Replacer and some of its primary formula preparation performance characteristics such as measurement and reconstitution. It does not assess how the new product will perform when fed to orphaned wildlife in rehabilitation, though some of the information certainly can be used with decisions and use.
Part 2. An accompanying article discusses some of these test results and offers some suggestions that wildlife rehabilitators may consider when evaluating the product for use with wild rabbit species.
The following list highlights some of the key findings prior to a more detailed presentation of test results and analysis.
√ Ingredients. A primary differentiating characteristic of the product versus most of the other commercially available milk replacers is the use of human grade ingredients as was indicated in direct discussions with Wombarro. Proteins are sourced from a recombination of cow's milk fractions. Most of the fats originate from vegetable oil as well as some fish oil for the Omega-3 and Omega-6 fatty acids. The label also references "milk oil" fatty acids. The absence of added fermentation products or prebiotics is noted, as these supplements are becoming more routine with other US manufactured milk replacers (such as with PetAg®).
√ Proximate analysis. The product adheres to the Typical Analysis (TA) concentrations provided on the label as a 37% protein and 42% fat formulation, but does exceed the TA moisture content. Overall ash is about 15% below the TA value of 6%.
√ Ash. As for dietary minerals, calcium and phosphorus tested at .99% and .83% respectively. These concentrations are slightly lower than most cow's-milk based PetAg® products and noticeably lower than Fox Valley Nutrition products. However, the overall ash content at 5.12% seems very acceptable.
√ Fatty Acids. The relatively high concentrations of Caprylic (C:8) and Capric (C:10) acids are not surprising given the nutritional needs of young rabbits for these specific saturated fats. The product has one of the highest percentages of saturated fats of any of the other milk replacer tested by WidAgain. The corresponding and relatively low concentration of unsaturated fats should enhance shelf-stability.
√ Rancidity. Though not indicated on the labeling, other websites suggest that certain Wombaroo powder products have a shelf life of 18 months (if unopened and stored properly). Assuming an 18-month life, the sample tested was from a newly purchased, unopened container and was ≈450 days post-manufacturing (≈ around 80% in to its shelf life). The peroxide value tested at 2.3 which is well within established guidelines for edible oils of <10. Although just a single sample, this does suggest that the product has very good shelf-stability.
√ Physical characteristics. Powder is loose, fluffy and sticky. Measuring powder by volume or parts rather than weighing produced error rates of +6 to -12% from the calculated average 8.4 gram/Tbsp weight of the product.
√ Reconstitution (wetting and sinking). When correctly adding powder to warm water, the product showed very good wetting performance, with the test sample 90% wetted in <5 minutes. However, sinking performance was relatively poor with much of the wetted product still floating and unable to break the surface tension of the water to fully sink to the bottom of the mixing container.
√ Reconstitution (dispersal and dissolution). Hand stirring/whisking for 5 minutes was required to completely submerge the wetted powder and produce a smooth, milky liquid that appeared free of any remaining dry powder. The reconstitution tests showed that when prepared for an immediate use, 3.5% of the powder remained trapped by the three sieves. While this is relatively good performance when compared to other milk replacers, an 8-hour resting period from preparation (mixing) to final use (feeding) improved final reconstitution by 75% with only less than 1% of the powder not fully reconstituted. This is outstanding performance compared to the other milk replacer products, especially those that are cow-milk based.
Ingredients (as listed on the package label)
The following table indicates the product ingredients as listed on the package label. The Primary Ingredients listed indicate a cow-based formulation which recombines previously separated milk fractions. While not a widely known term, "milk oil" likely refers to the inclusion of the individual fatty acids found in milk. While vegetable oil is a very broad term, it may likely include palm kernel and/or coconut oil that provide higher concentrations of some of the medium chain triglycerides such as caprylic and capris fatty acids. Some of Wombaroo's educational literature indicates sourcing of the Omega-3 and Omega-6 fatty acids from fish oil.
The list of Secondary Ingredients shows many of the typical vitamins and minerals found in other commercial milk replacer products. The ingredients are listed using more common nomenclature, presumably influenced by Australian pet food labeling standards [See footnote - AS5812-2017] requiring a "...consumer friendly..." presentation. For example, the label uses terms such as Vitamin B1 and Calcium, rather than the US label presentation that typically references the actual chemical compound source, such as thiamine hydrochloride (a source for vitamin B1) or dicalcium phosphate or tricalcium phosphate (sources of calcium supplementation).
The label does not include the addition of supplemental pre- or probiotics that can now be commonly found in other milk replacers. Additionally, no preservatives are listed, which would be required under Australian labeling standards.
The following table shows the results of the proximate analysis performed by the lab as compared to the Typical Analysis which represents an average or 'typical' estimation as required by Australian labeling standards. The red shaded values indicate where the lab analysis determined that the component concentrations deviated from the typical values by 15% or more. The product does appear to adhere to the typical values for protein and fat.
Based on the tested values, the metabolizable energy content (ME Kcals) of the Wombaroo Rabbit Milk Replacer equals 5.63 per gram of dry powder. This is just slightly lower than the energy value disclosed on the label (converted from 24MJ/kg) likely due to the higher moisture content that exceeds the typical analysis. The values for this product are now included in the drop-down menu in the Wildlife Formula Calculator.
Ash - dietary minerals
The following table shows the results of the dietary mineral analysis performed by the lab. The product tested slightly lower in Calcium than some of the other cow's milk based milk replacers (generally >1.0%) and within range of Phosphorus in other products. The Ca:P appears to be within acceptable range at 1.19. The overall ash value (all minerals) at 5.12% also appears acceptable for a powdered milk replacer.
Fatty acid profile
The fatty acid profile of the product is shown below. The overall percent of fat in the product (Saturated - 65%; Monounsaturated - 27%; and Polyunsaturated - 8%) is very similar to the typical milk profile (Saturated - 65%; Monounsaturated - 32%; and Polyunsaturated - 3%). One of the primary differences is the higher concentrations of Caprylic and Capric fatty acids in the product at 3.3% and 6.9%, respectively, versus typical milk at only 1.5% and 1.7%, respectively.
These higher concentrations of C:8 and C:10 are well suited for wildlife formula recipes where MCT concentrations have found to be significantly higher, such as in rabbits and hares. See Part 2 of this article for a longer discussion of MCT values for rabbit milk.
Peroxide Value (PV) test results
Though not indicated on the labeling, other websites suggest that certain Wombaroo powder products have a shelf life of 18 - 24 months (if unopened and stored properly). Assuming an 18-month life for the Rabbit Milk Replacer, the sample tested was from a newly purchased, unopened container and was ≈450 days post-manufacturing (≈ around 80% in to its shelf life). The peroxide value tested at 2.3 which is well within established guidelines for edible oils of <10. Although just a single sample, this does suggest that the product has very good shelf-stability.
As with any milk replacer proper storage is critical especially for high fat content products. The label indicates to store the product in a cool, dry place. It also states that once opened, store in an air tight container. Though not specified, storage of the air tight container under refrigeration should be assumed to prevent the onset and progression of rancidity, especially a product with a 42% fat content.
Physical characteristics and measurement error [tests performed by WildAgain]
The product has a very loose, fluffy and sticky consistency - similar to spray-dried PetAg® powdered milk replacers. This physical property provides challenges when measuring a given amount of powder to include in a formula recipe. Mixing by parts using the provided scoop or some other volume measure results in measurement error ranging from +6% to -12% in the product. Weighing the powder eliminates this unnecessary user induced error, provides for a uniform formula at each mixing and preparation (Mixing Guide), and helps insure consistent nutrition in the formula.
Reconstitution tests - wetting and sinking [tests performed by WildAgain]
The following images show the results of the wetting and sinking performance of the product. As shown in the left image, when correctly adding powder to warm water, the product showed very good wetting performance, with the test sample 90% wetted in <5 minutes. However, as shown in the right image, sinking performance was relatively poor with much of the wetted product still floating and unable to break the surface tension of the water to fully sink to the bottom of the mixing container.
Reconstitution tests - dispersal [tests performed by WildAgain] and observed results
Hand stirring/whisking for 5 minutes was required to completely submerge the wetted powder and produce a smooth, milky liquid that appeared free of any remaining dry powder.
The reconstitution tests showed that when prepared for an immediate use, 3.5% of the powder remained trapped by the three sieves. While this is relatively good performance when compared to other milk replacers, an 8-hour resting period from preparation (mixing) to final use (feeding) improved final reconstitution by 75% with only less than 1% of the powder not fully reconstituted. This is outstanding performance compared to the other milk replacer products, especially those that are cow-milk based.
Following the chart below is a visual presentation of how Wombaroo Rabbit performed when poured through the stack of sieves. They are presented in order of the largest mesh sieve to the smallest.
"What's it all mean?"
Grummer, R.R. 1991. Effect of Feed on the Composition of Milk Fat. Journal of Dairy Sci 1991 Sep;74(9):3244-57. PMID: 1779073. DOI: 10.3168/jds.S0022-0302(91)78510-X
“…Typical milk fat from a dairy cow is approximately 5% Polyunsaturated FA; 70% Saturated FA; and 25% Monounsaturated FA…”
Soyeurt, H.; P. Dardenne; F. Dehareng; G. Lognay; D. Veselko; M. Marlier; C. Bertozzi; P. Mayeres; and N. Gengler. 2006. Estimating Fatty Acid Content in Cow Milk Using Mid-Infrared Spectrometry.
J. Dairy Sci. 89:3690–3695.
Pet Food Industry Association Australia. Understanding Pet Food Labels – Label Requirements Under AS5812. 2022. https://pfiaa.com.au/understanding-pet-food-labels/#1578353470732-c43fbb2c-6a71
The labelling guidance in AS 5812 [as revised 2017] has been developed to reflect and align with other existing global standards such as those in Europe and the US and help companies comply with Australian consumer law. The Australian Competition and Consumer Commission (ACCC) has a central role in promoting competition and ensuring fair trading.
[Excerpted ] “…The Standard advises that pet food labels list the ingredients (with the exception of water) in descending order (by weight) and states: “Ingredients will be presented in an informative and consumer friendly manner”…A further requirement is that the statement of ingredients shall list food additives, including advising if flavours, colours, preservatives, vitamins and minerals are added. The Standard specifically requires that where preservatives such as sulphur dioxide or sulphites are included these shall be identified on the label, by inclusion of their common, prescribed, proprietary name…”
Wombaroo Rabbit Milk Replacer is manufactured and sold for orphaned kits, large litters, or when mother's milk is limited. Wildlife rehabilitation is considered an on-label use.
Product assays performed by the independent lab adhere to the Official Methods of Analysis of AOAC INTERNATIONAL (Association of Official Analytical Chemists) and the Official Methods and Recommended Practices of the AOCS (American Oil Chemists Society).
The authors have no conflicts of interest with the independent lab, or any of the products or manufacturers discussed in this article.